Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

Embryogenesis and early larval development

of the fish Sorubim cuspicaudus (Siluriformes: Pimelodidae)

Edwin Herrera-Cruz1; https://orcid.org/0000-0002-5527-2375

Yanan Ortiz-Acevedo1; https://orcid.org/0000-0002-6322-2917

Roger Valderrama-Londoño1; https://orcid.org/0009-0003-3946-3766

Gersson Vásquez-Machado2; https://orcid.org/0000-0002-4737-7038

Ana Estrada-Posada3; https://orcid.org/0000-0003-3585-3719

Jonny Yepes-Blandón1*; https://orcid.org/0000-0001-6276-5488

1. Research Group on Native and Exotic Aquatic Organisms, Facultad de Ciencias Agrarias, Universidad de Antioquia,

Medellín, Colombia; edwinherreracruz@gmail.com, yanansamarao@gmail.com, roger.valderrama@udea.edu.co,

jonny.yepes@udea.edu.co (*Correspondence)

2. HISTOLAB, Bogotá, Cundinamarca, Colombia; gmvasquezm@unal.edu.co

3. ISAGEN S.A. E.S.P, Medellín, Antioquia, Colombia; aestrada@isagen.com.co

Received 16-II-2024. Corrected 07-XI-2025. Accepted 24-VI-2025.

ABSTRACT

Introduction: Sorubim cuspicaudus is a migratory catfish listed as a vulnerable fish. The study of its embryonic

and larval development allows the identification of morphological and chronological events necessary to estab-

lish adequate management practices.

Objective: To describe the main events of the embryonic development and early larval phase of the trans-Andean

shovelnose catfish, S. cuspicaudus, under controlled conditions of incubation and larviculture.

Methods: Final maturing fish were induced for reproduction with a dose of 10 µg of GnRH/kg of live weight.

The embryos were incubated at 28 ± 0.5 °C and were analyzed at early stages (zygote-gastrula) every 5 minutes

and late stages (cleavage-hatching) every 15 minutes.

Results: Animal pole differentiation occurred at 0.5 hours post-fertilization (HPF), first cleavage at 0.58 HPF, 4,

8, 16, 32, 64 cells at 0.75, 0.92, 1.08, 1.17, 1.33 HPF respectively, blastula 1.5 to 4.37 HPF, gastrula 4.7 at 6.87 HPF,

organogenesis 7.37 at 11.37 HPF, pharyngula 11.87 at 13.37 HPF, and hatching at 15.92 HPF. The opening of the

mouth happened at 32 hours after hatching (HPH), food consumption at 43 HPH at 26.6 °C, yolk sac depletion

70.5 HPH, barbels at 35.7 HPH, fins at 6 days post hatching (DPH), swim bladder at 10.2 DPH, stomach with

glands at 12 DPH, additionally with sensory and locomotion organs.

Conclusions: The fingerlings show complete development and escape instinct at 14 DPH. It is suggested that 14

DPH could be the minimum age to carry out restocking programs with this species.

Key words: histology; larvae; fingerling; growth; ontogeny; catfish.

RESUMEN

Embriogénesis y desarrollo larval temprano del pez Sorubim cuspicaudus (Siluriformes: Pimelodidae)

Introducción: Sorubim cuspicaudus es un bagre migratorio catalogado en grado de amenaza vulnerable. El cono-

cimiento del desarrollo embrionario y larval permite identificar eventos morfológicos y cronológicos necesarios

para establecer prácticas de manejo adecuadas.

https://doi.org/10.15517/t27vbs38

VERTEBRATE BIOLOGY

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

INTRODUCTION

The trans-Andean shovelnose catfish Soru-

bim cuspicaudus (Littmann et al., 2000), belongs

to the Siluriform order, Suborder Siluroidei,

and to the family Pimelodidae (Prieto et al.,

2015). It is a fish characterized by its elongated

body, capable of reaching lengths of up to one

meter. Its dorsal side is dark, while the ventral

side is entirely white. A distinctive feature is the

black stripe that extends along the midsection

of the body from the area around the eyes to

the tip of the rays in the lower lobe of the caudal

fin. The fish possesses a flat and broad head,

with the upper jaw exceeding the length of the

lower jaw. Its eyes are positioned laterally, and

the maxillary barbels maintain a length below

that of the dorsal fin. Furthermore, the adipose

fin is notably shorter in comparison to the anal

fin. This description is intended for poten-

tial inclusion in scientifically indexed journals

(Galvis et al., 1997; Prieto et al., 2015).

S. cuspicaudus inhabits the basin of Lake

Maracaibo in Venezuela and the basins and

tributaries of the Catatumbo, Sinú, Atrato and

Magdalena rivers in Colombia (Buendía-Lara

et al., 2006). The fish has a scale-free exterior,

absence of intramuscular bones, presents a

favorable lipid profile, and readily adapts to

captive conditions. Additionally, it displays a

favorable receptiveness to induced reproduc-

tion techniques. Nocturnal in nature, it exhibits

fast movements within moderately deep aquatic

environments. It’s a carnivorous fish, demons-

trating a pronounced piscivorous inclination.

Furthermore, the fish engages in reproductive

migrations termed as “subienda,” which involve

upriver migration (Buendía-Lara et al., 2006).

Therefore, it is considered a promising species

with potential for commercial fish farming and

food security for a growing human popula-

tion. Nonetheless, this fish is not produced in

enough production volumes due to techno-

logical constraints that hinder the steady and

uninterrupted generation of fingerlings in the

required quantities (Prieto et al., 2015).

In Colombia, there are approximately

150 000 artisanal fishermen in maritime and

inland waters, representing more than 400 000

people, who directly depend on artisanal

extractive fishing for income and food, reflec-

ting the importance of the sector as a way of life

(García-Benítez & Flores-Nava, 2016). In recent

decades, the Magdalena River has undergone

strong environmental transformations due to

mining, oil extraction, and agriculture, among

other anthropogenic activities (Lozano et al.,

2017). Resulting in habitat loss and water quali-

ty degradation, affecting native fish (Lozano et

al., 2017; Mojica et al., 2012). Due to the above,

it is necessary to explore ex situ conservation

strategies such as captive reproduction, with the

purpose of producing fingerlings for restocking

Objetivo: Describir los principales eventos del desarrollo embrionario y fase larval temprana de S. cuspicaudus,

bajo condiciones controladas de incubación y larvicultura.

Metodología: Peces en maduración final se indujeron para reproducción con una dosis de 10 µg de GnRH/kg

de peso. Los embriones se incubaron a 28 ± 0.5 °C y, se analizaron en etapas tempranas (cigoto-gástrula) cada 5

minutos y tardías (segmentación-eclosión) cada 15 minutos.

Resultados: La diferenciación del polo animal ocurrió 0.5 horas post-fertilización (HPF), primer clivaje 0.58 HPF,

4, 8, 16, 32, 64 células 0.75, 0.92, 1.08, 1.17, 1.33 HPF respectivamente, blástula 1.5 a 4.37 HPF, gástrula 4.7 a 6.87

HPF, organogénesis 7.37 a 11.37 HPF, faríngula 11.87 a 13.37 HPF, eclosión 15.92 (HPF). Apertura bucal ocurrió

32 horas después de la eclosión (HPH), consumo de alimento a 43 HPH a 26.6 °C, agotamiento del saco vitelino

a 70.5 HPH, barbicelos a 35.7 HPH, aletas a 6 días después de la eclosión (DPH), vejiga natatoria a 10.2 DPH,

estómago con glándulas a 12 DPH, además de órganos sensoriales y de locomoción.

Conclusiones: Los alevinos presentan desarrollo completo e instinto de huida a 14 DPH. Se sugiere que 14 DPH

podría ser la edad mínima para a llevar a cabo programas de repoblamiento con la especie.

Palabras clave: histología; larvas; alevinos; crecimiento; ontogenia; silúridos.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

programs, food security and promotion of the

fish activity of the species (Prieto et al., 2015).

In the production of fingerlings of a native

species, three stages are identified: broodstock

management, induced reproduction and larvi-

culture (Atencio-García et al., 2010). Significant

progress has been made in the trans-andean

shovelnose catfish regarding the first two pro-

duction phases (Prieto et al., 2015). However,

the greatest limitations are found in larvicultu-

re, particularly in the management of the first

feeding. In this phase, the highest mortalities

are recorded as a consequence of cannibalism

and due to the change from live prays to the

consumption of balanced diets (Atencio-García

et al., 2010).

In S. cuspicaudus, an examination of embr-

yonic development becomes imperative to

establish a chronological sequence of the mor-

phological and histological processes culmi-

nating in the genesis of a new organism. Such

insights facilitate the refinement of incubation

and larviculture methodologies tailored to the

species’ requirements (Valbuena-Villarreal et

al., 2012). While numerous studies have studied

the ontogenic development of fish, variations

in the timing of differentiation, development,

and functionality emerge across species during

the initial stages of ontogeny. This diversity

underscores the need for species-specific inves-

tigations and in-depth analyses to thoroughly

comprehend these processes (Solovyev et al.,

2016; Treviño et al., 2011; Valbuena-Villarreal

et al., 2012). These studies are a valuable tool

as a strategy to understand the physiology of

the larvae and can be useful to improve culture

(Gisbert et al., 2014; Lazo et al., 2011; Solovyev

et al., 2016). Consequently, the objective of the

present work was to describe the main events

of the embryonic development and early larval

phase of the trans-Andean shovelnose catfish,

Sorubim cuspicaudus, under controlled condi-

tions of incubation and larviculture.

MATERIALS AND METHODS

Location: The research was carried out at

the Piscícola San Silvestre S.A. (PSS) fishery,

located in the city of Barrancabermeja (Santan-

der), with geographic coordinates: (7°06’31’-

7°06’31’’ N & 73°51’23’’-73°51’23’’ W), at 75

masl, with an annual average temperature

of 28.4 °C.

Source of the fishes: Adult S. cuspicaudus

fish (n = 100, mean weight = 700 ± 300 g) were

collected from the middle Magdalena river

basin (including the San Silvestre and Llanito

swamps: 7°07’43” N & 73°54’57” W) through

traditional fishing practice with cast nets, with

the support of local fishermen in 2018 and 2019.

The river water temperature was 25 °C. The

broodstock were transported in plastic tanks

with a capacity of 800 liters of water to the PSS.

In the fish farm, the broodstock were subjected

to a bath with salt (20 ppm) for 15 seconds and

later they were transferred to rectangular pools

with aeration and constant change of water

(filtered from the Ciénega San Silvestre) where

they remained for 24 hours, after this process,

they were transferred to a pond of 1 200 m2

with 1 meter depth. The fish were provided

with juvenile red tilapia (Oreochromis sp.) as

prey, allowing them to capture it freely, and

were additionally supplied with commercial

balanced feed containing 34 % crude protein

(CP) at a daily rate of 1 % relative to the bio-

mass. This feeding regimen was sustained until

they reached the stage of full maturation.

Gamete collection and fertilization:

Using ovarian biopsy, a mature female weighing

2 210 g and two males in the spermiation phase

were selected for hormonal induction emplo-

ying a dosage of 10 µg of GnRH analogue per

kilogram of live weight. After 12 hours, gametes

(seminal material and oocytes) were extrac-

ted for subsequent dry fertilization. Following

fertilization and a one-hour hydration period,

the oocytes (382.5 grams, equivalent to 1 093

oocytes/g) were introduced into two 60 l incu-

bation tanks featuring an upward water flow

(4 to 5 l/minute). Upon hatching, the resulting

larvae were collected within a 200 l incuba-

tor before being transferred to circular tanks

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offering continuous aeration, with a density of

80 larvae per liter.

Histology of the embryonic stages: To

characterize the embryonic stages, 20 fertilized

eggs from each stage were fixed in 10 % buffe-

red formalin; they were embedded in paraffin

and sectioned at 5-6 μm with a Leica RM2125

RTS rotary microtome. Sections were stained

with hematoxylin and eosin (H&E) according

to standard procedures (Wijayanti et al., 2017).

Fertilized oocyte samples were deposited

in 9 cm Petri plates at a density of ~150 oocytes/

dish. Early-stage embryos (zygote, cleavage,

blastula, and gastrula) were observed at 5-minu-

te intervals and late stage (cleavage to hatch) at

15 and 30 minutes intervals. Developmental

stages were determined morphologically using

a microscope (Leica DM750, Germany) equip-

ped with a digital camera (Leica MC120 HD,

Germany). To objectively describe the embr-

yonic development of S. cuspicaudus, embr-

yogenesis was divided into seven stages using

well-known markers for freshwater fish, such as

Danio rerio (Kimmel et al., 1995) and Capoeta

trutta (Zadmajid et al., 2017). This included the

following stages: zygote, cleavage, blastula, gas-

trula, cleavage, and organogenesis, pharyngula,

and hatching.

Histology of larval development: To cha-

racterize larval organogenesis, fish were ran-

domly sampled daily, ten larvae per sample,

from three batches during the endogenous,

endoexogenous, and early exogenous feeding

period. The sampled larvae were anesthetized

with clove oil (40 ppm; Sigma-Aldrich, USA),

their length and weight were measured to

determine the specific growth rate (SGR) =

100x (Ln (final weight) - (Ln (initial weight))

/ t; where t is the culture time expressed in

days and Ln is the natural logarithm. The

materials were fixed in 10 % buffered formalin,

embedded in paraffin, and sectioned at 5-6

μm with a rotary microtome (Leica RM2125

RTS, Germany.) Sections were stained with

hematoxylin and eosin (H&E) according to

standard procedures and photographed under

a light microscope (Nikon, eclipse 600, Japan)

with a digital camera (Nikon, DXM120, Japan).

The histochemical technique of Periodic Acid

Schiff (PAS) staining was used through which

they were characterized as the goblet cells of the

esophagus, stomach, and intestine.

All procedures involving the handling of

animals were performed in accordance with the

standards for the use of laboratory animals out-

lined by the Committee on the Care and Use of

Laboratory Animal Resources of the National

Research Council (National Academies, USA).

National Research Council of the National

Academies Eighth Edition (Albus, 2012). Addi-

tionally, this research has the research permit

issued by the Colombian National Aquaculture

and Fisheries Authority-AUNAP (Resolution

0955 of May 27, 2020).

RESULTS

S. cuspicaudus has slightly opaque yellowish

oocytes; after one hour of hydration, they reach

a diameter of 4 mm. After fertilization and

hydration, they present a perivitelline space

that easily doubles the diameter of the deve-

loping embryo; they are also of the telolecitic

type, since the embryo is formed in the animal

pole that corresponds to only one end of the

cytoplasm and presents a large amount of yolk

in the plant pole. S. cuspicaudus exhibits a

partial or meroblastic division during the early

stages of development as in most fishes (Kim-

mel et al., 1995; Ninhaus-Silveira et al., 2006).

The embryonic development of S. cuspicaudus

occurred at 28 ± 0.5 °C, dissolved oxygen of 6 ±

0.5 ppm and pH of 7.5 ± 0.2.

Zygote period (one cell): In the fertili-

zed zygote, chorion initiates swelling, giving

rise to the perivitelline space. The oocyte is

spherical, characterized by dense cytoplasm

comprising vacuolated and translucent mate-

rials, corresponding to protoplasmic residues.

Approximately 0.5 hours post-fertilization

(HPF), cytoplasmic segregation commences

towards the periphery, leading to the initial

differentiation of the vegetal and animal poles.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

The latter is referred to as the blastodisc (1 cell),

situated in a marginal zone primarily compo-

sed of primordial germ cells surrounded by a

homogeneous vitelline envelope, where cellular

divisions will commence.

Cleavage stage (cleavage) 2-64 cells:

Two-cell stage (at 0.58 HPF): During

this phase, the cleavage stage can be observed,

characterized by the formation of a two-cell

arrangement in the blastodisc of the meroblas-

tic type. Two blastomeres of similar size and

dome-shaped structure are generated in the

animal pole region. The area between the yolk

and blastoderm curves smoothly without appa-

rent differentiation between them.

Histological Sections Stained with

Hematoxylin and Eosin (H&E): An eosino-

philic structure is observed around the zygote,

generating a translucent space corresponding

to the perivitelline space, which is enveloped

by the vitelline membrane. Within the yolk

sac, circular eosinophilic structures of varying

sizes are visible, separated by translucent eosi-

nophilic material. In the animal pole region,

blastomere division is evident. The blastomeres

are of uniform size, dome-shaped, and have

divided in the same plane. It can be noted that

the more caudal region of the blastodisc, in

contact with the yolk space, assumes a convex

shape. Cytoplasm segregation towards the ani-

mal pole continues.

Four-cell stage (at 0.75 HPF): In the

dorsal view of the animal pole, the division

from two to four blastomeres is distinguished

by a perpendicular cleavage plane relative to

the previous division. The blastomeres adopt

an ellipsoidal shape, exhibiting distinct diffe-

rentiation. Additionally, the region in contact

with the vitelline space maintains its convex

morphology.

Histologically, the division of blastomeres

is evident, signifying ongoing cellular activity.

Simultaneously, the segregation of cytoplasm

towards the animal pole persists, playing a role

in the dynamic process of cellular differentia-

tion and specialization.

Eight-cell stage (at 0.92 HPF): Horizontal

division of the 4 blastomeres is observed in a

cleavage of each one, forming 8 of these, which

are intensely basophilic in color and darker

than in their previous phase. In addition, the

divisions have increased the size of the animal

pole, the sac. yolk occupies approximately 75 %

of the surface, its content is a particulate eosi-

nophilic material of various sizes, among which

translucent material is observed.

16-cell stage (at 1.08 HPF): Southern-

shaped division, blastomeres with dome mor-

phology, similar to previous phases, the cells of

this stage have decreased in size, they are still

located in parallel planes, with growth being

along the two planes, producing a matrix com-

posed of 4 x 4 cells. Abundant yolk is observed

in the vegetal pole; cell activity can be observed.

Histologically, the blastomeres are seen

to be intimately associated with one another,

interconnected by translucent eosinophilic

material resembling the substance that envelops

the yolk sac.

32-cell stage (at 1.17 HPF): Blastome-

res form in parallel planes, some overlapping

near the animal pole. Two distinct planes are

evident, one of which is more elongated, resul-

ting in a loss of uniformity compared to the

previous stage. The division at this stage entails

an arrangement of 4x8 blastomeres, now orga-

nized into two layers. The cells are smaller, with

those closest to the yolk sac margin exhibiting

slight flattening. An increase in the number of

blastomeres and the height of the animal pole is

apparent, and the histological section displays

some overlapping cells.

Sixty-Four Cell Stage (at 1.33 HPF): The

blastomeres are smaller in size, in comparison

to the previous cycle; a second vertical growth

phase occurs, and numerous overlapping blas-

tomeres are observed. From a lateral view, a

notably higher cellularity arranged in layers is

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evident. The cells visible from the lateral layer

are referred to as the blastodisc enveloping layer

cells. Furthermore, histologically, while over-

lapping cells are observed, with eosinophilic

material between the blastomere cells, the cells

situated in the central region are smaller, better

defined, and do not come into close contact

with the cells at the same level.

Blastula period (1.5 a 4.37 HPF): Onset of

the Blastula Period. Many blastomeres overlap

with others, with some becoming indistinct,

causing the dome-like shape to begin to trans-

form into a semicircular form. Additionally,

regarding the height aspect, cells of the envelo-

ping layer can be observed in the lateral region

of the animal pole. Histologically, an increased

height at the animal pole is evident, with nume-

rous closely adjacent blastomeres; the embryo

begins to assume a spherical shape; the most

outer layer of the blastomeres exhibits a scale-

like appearance, and faint eosinophilic material

can be seen among the blastomeres.

This stage represents a pivotal transition

marked by changes in the embryo’s morpho-

logy and cellular organization. The shift from

a dome-like to a more semicircular form, cou-

pled with the emerging cellular layers and

the presence of distinct cell types, undersco-

res the dynamic nature of early embryonic

development.

In the lateral view a high layer can be

observed, with irregular cellularity, the cells

of the blastodisc envelope are considerably

thinner than the rest of the cells. In the phase

of 512 cells, an increase in the levels of blasto-

meres of the enveloping layer can be observed.

There is reduced distinction between the cells

of the enveloping layer and their connection

with the yolk, which is particularly noticeable

in the marginal zone adjacent to this region. In

the dorsal view, identifying deep cells becomes

challenging, with only enveloping cells being

clearly apparent. Histologically, an increase in

blastomere count is evident, where marginal

cells adopt a flattened morphology. A nuclear

eosinophilic structure is observed between the

blastomeres and the yolk sac, known as the yolk

syncytial layer. Additionally, it is noted that

some adjacent blastomeres with this structure

are more separated and lack connections with

other blastomeres.

The height of the animal pole has decrea-

sed considerably, and it has begun to segregate

along the perimeter of the yolk sac, taking on

an elongated morphology, giving shape to the

blastoderm.

The lateral view allows us to observe how

the blastoderm has formed, which is charac-

terized by being more uniform in terms of its

longest axis and occupies approximately 30 %

of the yolk. The front view allows us to show

a slight asymmetry as far as thickness is con-

cerned. Histologically it is observed that the

syncytial layer of the yolk sac leaves its straight

shape, begins to become curved and bends

towards the curvature of the animal pole, the

blastoderm has uniform thickness. The syn-

cytial yolk layer begins to become thin.

Gastrula period (at 4.7 a 6.87 HPF): At

50 % epibolism (5.03 HPF), an expansion of

the blastoderm becomes evident, encompas-

sing half of the yolk sac’s area. The edges of

the blastoderm extend toward the vegetal pole,

constituting what is referred to as the germinal

ring. From a histological perspective, the outer-

most region of the blastoderm is characterized

by flattened cells, corresponding to those on the

outermost layer. Additionally, due to the con-

densation and arrangement of the blastomeres,

the cells in proximity to the yolk sac are desig-

nated as the hypoblast, whereas those nearer to

the enveloping layer are labeled as epiblast.

The blastoderm’s growth continues, cove-

ring 75 % at 5.7 HPF and achieving 90 %

coverage at 6.2 hours post-fertilization. Both

extremities of the blastoderm experience a

slight thickening. Within the yolk sac, a minor

elevation forms at the vegetal pole; neverthe-

less, it disappears six hours after fertilization

once the blastoderm has fully enveloped the

entire yolk sac.

Segmentation period and organogenesis

(7.37 at 11.37 HPF): The thickening of the

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dorsal epiblast forms the neural layer in the

anterior portion, which in histology allows us to

observe the formation of a nerve primordium.

This presents cells with cylindrical morphology

and oval ends, compatible with somites. The

yolk plug disappears. At the posterior end of the

embryonic axis, a slight thickening of the tail is

observed. The stage in which these phenomena

occur is known as the “bud stage”. Between 4-6

somites become visible in the neural tube. In

addition, in the neural keel the appearance of

the optic primordium can be observed, in the

trunk, the neural plate remains present. At 10

hours, the appearance of the Kupffer vesicle is

observed near the tail base, the yolk sac begins

to retract and elongate caudally, near the tail.

The neural plate and auditory vesicle have

begun to show further development, as has the

nervous tissue. At 12 hours, it has advanced to

the point where distinguishable structures such

as the tail, the primitive eye and the auditory

vesicle begin to form, in addition the formation

of encephalic nervous tissue begins to become

visible, and the head continues to be attached

to the yolk sac.

Pharyngula period (11.87 a 13.37 HPF):

Bilateral and symmetrical distribution of somi-

tes, extending from head to tail. The elonga-

tion of the yolk sac towards the caudal area is

more evident. The notochord becomes visible,

histologically the formation of myotomes is

observed, which are arranged as somites with

eosinophilic muscle fibers located in the midd-

le of the blastoderm and the tail. In addition,

the notochord is distinguished by the presence

of cells with a vacuolated cytoplasm with a

nucleus towards the periphery. This structure,

however, has not fully extended and is found

in the blastoderm behind the yolk sac region,

11:00 to 1:00 in the region of the head the

appearance of retinal tissue is observed for the

first time, in the optic primordium.

Hatching period and early larval deve-

lopment - 15.92 hours post hatching (HPH):

The post hatching period allowed to demons-

trate the growth and primary development of

several organs. These grow slowly and their

appearance is mainly consistent with their rudi-

mentary function. In the region of the yolk sac,

the development of the primitive intestine was

observed, characteristic for having an epithe-

lium of simple cuboidal morphology, with

some mucus cells arranged as a tube. In addi-

tion, advanced development of brain nervous

tissue was observed; near it the growth of the

primordial eye was observed; notochord has

extended caudally but has not yet developed to

tail; the somites of the middle and tail region

of the blastoderm have developed myotomes,

which histologically are oval-shaped divisions

with muscle fibers inside. Fig. 1 shows the most

outstanding morphological events in the stages

of embryonic development with respect to

time. The first changes were very fast, but from

the blastula onwards it is evident that it takes

longer to observe noticeable changes.

Day 1 DPH (Days Post Hatching): Head

still attached to yolk sac, indicative of endoge-

nous feeding; pigmented primordial eye which

histologically shows closed retinal tissue; The

digestive tract was characterized mainly by the

presence of an oral cavity lined by a stratified

squamous epithelium followed by the esopha-

gus and later a tubular structure with a central

lumen corresponding to the primitive intesti-

ne lined with a simple cylindrical epithelium

supported by a thin layer of connective tissue.

called the lamina propria, more externally the

muscular tunic composed of smooth mus-

cle and the serous tunic. Between the cranial

region and the yolk sac, the heart was obser-

ved, made up of thin fibers with central nuclei,

divided into two chambers. At this stage of

development, the skeleton was made up mainly

of hyaline cartilage.

2 DPH: The cephalic region has undergone

advanced development, with notable progress

in the formation of the primordial eye and

pigmented retina. Pigments are now becoming

apparent in the pectoral and intestinal areas. An

elongation of the mouth is evident, and histolo-

gically, clear demarcation of the diencephalon,

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telencephalon, and mesencephalon are obser-

ved within the head region. This differentiation

is characterized by distinct gray and white mat-

ter separation, with the presence of neurons,

neuropil, and some axons. Further histological

analysis reveals differentiation of the granular

layer, along with the presence of Purkinje cells

and dendrites. Regarding the digestive tract, a

similarity to day 1 report is observed, yet there

is notable advancement in the development of

the primitive intestine. Here, the mucosa, lined

with simple columnar epithelium, exhibits a

thin layer of connective tissue, giving rise to

small folds projecting toward the lumen, for-

ming the lamina propria (LP). Externally to

the mucosa, a delicate layer of smooth muscle

(tunica muscularis) is present, followed by the

outermost layer, the tunica serosa.

While the skeletal structure remains car-

tilaginous, like to the prior stage, there is

heightened prominence of the gill arches. In the

caudal region, multiple myotomes are evident,

along with a short yet distinguishable caudal

fin. Notably, a significant portion of the larva

continues to be comprised of the yolk sac, cha-

racterized by numerous globular structures that

facilitate endogenous feeding. Observations

reveal that the mouth and anus of S. cuspicau-

dus became apparent at 32 hours post-hatching,

with the initiation of live food consumption

observed at 43 hours post-hatching under a

temperature of 26.6 °C.

3 DPH: A granular pigmentation pattern

is evident spanning from head to tail, attribu-

ted to the presence of cardinal venules. Short

barbicels extending from the mouth towards

the caudal region were identified. Histologica-

lly, ganglion cells and pigmentary tissue were

observed within the eye region. A connection

between the central nervous system, spanning

from the brain to the spinal cord, was evident.

The skull structure remains cartilaginous, fea-

turing the presence of gill arches and filaments.

Fig. 1. Fundamental morphological events in embryo development regarding hours from fertilization to hatching.

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Notably, there is an expanded mouth opening

compared to prior stages, accompanied by a

more developed esophagus. The mucosal tunic

of the esophagus is lined with stratified cuboi-

dal epithelium containing abundant goblet

cells. External to the epithelium, a layer of loose

connective tissue corresponds to the lamina

propria. The muscular tunic consists of stria-

ted skeletal muscle, followed by the adventitia.

Towards the esophagus’s termination, a tran-

sition to a sizable saccular structure lined by

simple columnar epithelium is observed. Below

this layer, a lamina propria of loose connective

tissue is visible, followed by a layer of smooth

muscle known as the tunica muscularis, and

finally, the tunica serosa, as depicted in (Fig. 2).

layer of smooth muscle (tunica muscularis),

and an outermost layer, the serosal layer. The

yolk sac has diminished in size compared to

the previous phase. This reduction, coupled

with the contents within the digestive tract,

signifies an endoexogenous diet. Both the liver

and pancreas are visibly distinct, with the for-

mer characterized by predominantly vacuo-

lated hepatocytes, while the latter contains

cells rich in birefringent eosinophilic granules

(zymogen granules). At this stage, scant tubu-

les, composed of a simple cuboidal epithelium

corresponding to renal tubules, are discernible.

The presence of the yolk sac was noted until

70.5 HPH.

4 DPH: Similar to the prior stage, notable

advancements in head development and the

differentiation of the fish’s pectoral area were

evident. It is remarkable the elongation of the

heavily pigmented barbicels, which serve as

sensory organs. The upper portion of the cau-

dal fin initiates its development. Histologically,

a cross-sectional view reveals the presence of

both the dorsal and ventral medial fins, as well

as the arrangement of the spinal cord in terms

of white and gray matter. The notochord is also

evident. The progression of the digestive tract

closely resembles that of the preceding stage.

However, more distinct intestinal folds and an

increased number of goblet cells were observed.

Notably, the yolk sac has nearly completely

regressed at this point, marking the conclusion

of the period of endoexogenous feeding.

5 DPH: At this stage the skull continues

to be made of cartilaginous tissue similar to

the previous stage. The gills, intestine and

other organs showed further development. It is

noteworthy that in some animals the appearan-

ce of a small crystalline lens in the eye begins to

be differentiated.

6 DPH: Development similar to the pre-

vious stage with neurocranium composed of

cartilage; well differentiated esophagus, bran-

chial arches and barbicels more developed than

in the previous phase. At this stage we can

Fig. 2. Microscopic photograph of the esophagus of

S. cuspicaudus, day 3 DPH, the mucosa is lined by a

stratified cuboidal epithelium (E). The basal lamina (BL)

on which the epithelium is supported can be seen, and

more externally, the tunica muscularis (MT), composed of

skeletal striated muscle. The lumen (LU) of the esophagus

and goblet cells (GC) that produce mucus to facilitate food

passage can also be identified.

This dilation of the digestive tract, mar-

ked by the presence of proteinaceous material

within the lumen, is apparent. Adjacent to

this structure, the more developed intestine

features well-defined folds. Under a simple

columnar epithelium, a lamina propria of loose

connective tissue is observed, followed by a

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highlight the organization of the hepatocytes in

rows or cords, with central rounded nuclei; the

pancreas attached to the liver with cells forming

acini, spherical nucleus, basophilic cytoplasm

and abundant intracytoplasmic eosinophilic

granules (exocrine pancreas). Additionally, it

is worth noting the greater development of

intestinal folds and the presence of exogenous

food in the intestinal lumen, (Fig. 3). A greater

development of the eye and barbicels is also

observed, the latter pigmented and with the

presence of taste corpuscles, (Fig. 4). It is also

more visible in this phase the kidney with its

organization in tubules and lymphocytes in

the interstitium.

7 DPH: The morphological findings are

similar to the previous stage, however, a greater

differentiation of the retinal layers is striking, as

well as a larger crystalline lens. Gill arches and

filaments are more developed. Larger intestine

with several segments and abundant folds. The

presence of zooplankton and various proteina-

ceous fragments apparently parts of (insects)

in the light becomes more visible. On dilation

caudal to the esophagus the muscular coat

thickens. Some melanomacrophages begin to

appear in the liver and pigments are also evi-

dent in the kidney. Brain shows optic and olfac-

tory lobe development.

8 DPH: complete formation of the dorsal

and caudal fin, it is possible to differentiate a

double layer of smooth muscle in the dilation

of the digestive tract posterior to the esopha-

gus. Formation of the foregut is observed, with

tall, simple cylindrical epithelial cells, with

nuclei towards the basal domain; some folds

in this region appear quite long to the point

that they come into contact with folds on the

Fig. 3. Microscopic photograph showing the mucosa

forming folds, lined by a simple cylindrical epithelium

with goblet cells (GC); posterior to the tunica mucosa we

find the tunica muscularis (MT) composed of smooth

muscle and more externally a thin layer corresponding to

the serosa (ST). The lamina propria (PL) can be observed

beneath the epithelium.

Fig. 4. Microscopic photograph of the eye of S. cuspicaudus, showing the cornea (CO), inner nuclear layer-nuclei of bipolar

cells (INL), inner plexiform layer (IPL), lens (L), ganglion cell layer (GL), outer nuclear layer-nuclei of rods and cones (ONL),

outer plexiform layer (OPL), and pigment epithelium (PE). The image displays the layered structure of the developing retina,

which is essential for vision development in this catfish species.

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front face. These folds also showed ripples

and ramifications.

9 DPH: The morphological findings are

similar to the previous stage. It is noteworthy

the greater development of gill filaments with

already distinguishable lamellae; the esophageal

muscular tunic presents a greater thickness,

being observed in some areas composed of 3

layers of striated skeletal muscle. Intestine is

more developed and differentiable between

segments with posterior segment cells with

abundant cytoplasmic vacuoles.

12 DPH: At this stage, a well-formed fin-

gerling is observed with well-developed gills,

filaments and well-distinguishable lamellae.

Eye well developed. In the digestive tract, it

is noteworthy that in the dilation posterior

to the esophagus, the mucosa has begun to

form crypts and glands can be seen in some

areas; The entire structure is covered by simple

columnar epithelium and the layer of connecti-

ve tissue between the glands (LP) and external

to this other layer of connective tissue corres-

ponding to the tunica submucosa is evident.

External to this, the muscular tunic was obser-

ved, made up of two layers of smooth muscle:

the circular layer, the longitudinal layer, and the

serous tunic. In this phase, for the first time, it

can already be defined that this dilation of the

digestive tube corresponds to the stomach. The

liver presented greater development than in the

previous stages and in the pancreas not only

acinar cells but also ducts can be observed. In

the gills, the chlorine cells, the pillar cells of the

lamellae and the marginal canal are distinguis-

hable. Intestinal folds appear long and wavy.

Abundant zooplankton fragments are evident

in the stomach and intestinal lumen.

14 and 15 DPH: fingerling with developed

digestive tract characterized by an oropharyn-

geal cavity lined by a stratified squamous

epithelium and posterior to this an esopha-

gus with a stratified cuboidal epithelium with

abundant goblet cells, lamina propria of con-

nective tissue, muscular tunic composed of

2 to 3 layers of striated skeletal muscle and

the tunica adventitia, (Fig. 5); posterior to

the esophagus, stomach, (Fig. 6); with simple

columnar epithelium, abundant glands, folds

in the mucosa, LP clearly visible; tunica sub-

mucosa, tunica muscularis, and more exter-

nally the tunica serosa. In the light, there are

Fig. 5. Microscopic photograph of the caudal part of the

esophagus, highlighting the presence of folds projected

cranially, a mucosa lined by cuboidal cells, and abundant

goblet cells (GC). A transition zone between the esophagus

and the stomach is observed. The lamina propria (PL)

and very thick muscular tunica (MT) are more developed.

The adventitial tunica (AT), the outermost layer of the

esophagus, can also be identified in this transition zone.

Fig. 6. Microscopic photograph of the stomach with the

presence of abundant gastric glands (GG) with a simple

columnar epithelium, goblet cells (GC); some of these cells

have glandular contents in their cytoplasm (oxyntic or

parietal cells). Connective tissue fibers corresponding to

the lamina propria (PL) are observed between the glands.

The submucosa (SUB), a layer of connective tissue beneath

the lamina propria, can also be identified in this histological

section.

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abundant remains of zooplanktonic organisms.

The liver is well developed with hepatocytes

forming cords and with vacuolated cytoplasm.

The pancreas is well-developed with abundant

exocrine cells and presence of ducts. The intes-

tine also presented a well-marked development

with abundant elongated folds and undulations;

covered by a simple columnar epithelium and

presence of connective tissue under the epithe-

lium corresponding to the lamina propria (LP).

Behind this is a layer of smooth muscle, the

tunica muscularis. In the light abundant rema-

ins of zooplanktonic organisms (Fig. 7). The

fins are observed with greater development

than in the previous stages with ossified parts

and the presence of spines on the pectoral fins.

Fig. 8 describes the main morpho-anato-

mical events that occurred over time, from the

moment of hatching to day seven.

Fig. 9 presents a summary of the critical

moments, such as mouth opening, first feeding

from 43 hours to day 5, and feeding with wild

plankton in land-based ponds from 5 days to 20

days post-hatch. when the study ended. Day 1

the eyes, central nervous system, and very bul-

ging yolk sac are observed. On day 2, the mouth

opening and the start of live food consumption

are observed. On day 3, a more developed intes-

tine is observed, with more defined folds and

the presence of intestinal content. On day 4, the

branchial arches, the more developed oral cavi-

ty, the more developed eyes, the gray and white

matter are observed. On day 5, the eye identi-

fies the pigment epithelium, the external plexi-

form layer, the external nuclear layer, cornea,

lens, internal nuclear layer, internal plexiform

Fig. 7. Microscopic photograph of the stomach with

plankton, well-developed stomach with a mucous tunic

lined by a simple cylindrical epithelium and a lamina

propria (PL) of lax connective tissue; abundant mucosal

folds (MF) forming the mucosa are observed. Additionally,

the presence of glands and the muscular tunic (MT)

composed of smooth muscle is also evident. The stomach

content (SC) consisting of plankton and other food

remnants can be seen in the gastric lumen.

Fig. 8. Main morpho-anatomical events during the ontogeny of the Trans-andean shovelnose catfish S. cuspicaudus. The

numbers in the lines and the black lines represent the event and and the competition time as follows: 1. yolk sac decrease, 2.

development of cephalic area, 3. development of eye and retinal pigmentation, 4. pectoral fins, 5. development of barbicels,

6. caudal fin, 7. filling of swim bladder, 8. gill arches, 9. body pigmentation, 10. elongation and position of the mouth, 11.

mouth and anal opening, 12. more developed dental plates and nasal passages (nostrils), 13. first curvatures of the digestive

system (separation of stomach and intestine), 14. ossification (rays) and caudal fin elongation.

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plate, ganglionic layer. Between days 6 and 7,

a well-differentiated esophagus is observed, as

well as elongation of the branchial arches. Day

8 you can differentiate the stomach and foregut.

Day 9 and following, greater development of

gill filaments with lamellae is observed. On day

14, the fingerling presents physical and phy-

siological characteristics similar to those of an

adult specimen.

DISCUSSION

Fish oocytes are classified as telolecitos,

because they present a large amount of yolk

(Zadmajid et al., 2018). S. cuspicaudus oocytes

conform to this classification, presenting mero-

blastic divisions, limited to the animal pole;

the average diameter of fully hydrated S. cus-

picaudus oocytes was 4 mm and the larvae

were 3.96 mm long at hatching, similar to that

reported for Pimelodus grosskopfii (Valbuena-

Villarreal et al., 2012). The diameter of the

oocytes influences the incubation period, with

larger ones having a longer incubation time

than small oocytes (Valbuena-Villarreal et al.,

2012), but greater than Zungaro jahu, 2.4 mm

in hydrated oocytes and 4.3 ± 0.2 mm TL at

hatching (Nogueira et al., 2012). Fish species

that generate larger oocytes have a longer incu-

bation period compared to species with small

oocytes (Valbuena-Villarreal et al., 2012). S.

cuspicaudus produced oocytes considered small

(0.91 mm) and presented a short incubation

period. Temperature is another element that

plays an important role in incubation. In the

temperature range of a species, at higher tempe-

ratures, the incubation time is shortened while

at lower temperatures, this time is increased

(Portella et al., 2014).

On the other hand, the presence of a wide

perivitelline space in S. cuspicaudus is related

to the incorporation of water (hydration); a

wide perivitelline space protects the embryo

against environmental attacks, contributing to

its survival and giving it buoyancy in the water

column, which allows it to obtain a greater

supply of oxygen, as well as greater dispersion

in the aquatic environment (Cerdà, 2002).

The zygote period lasted 0.5 hours, simi-

lar to that reported for Cyprinodon variegatus

Fig. 9. Main histological changes and growth curve of S. Cuspicaudus larvae and/or young fish, from hatching to day 14.

14 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

(Lencer & McCune, 2018), longer than the time

reported for P. grosskopfii; 0.3 hours at 27 ± 1 °C

(Valbuena-Villarreal et al., 2012); 0.15 hours for

Ompok bimaculatus at 27 ± 1 °C (Arambam et

al., 2020); but it was less than in Z. jahu, 0.75

hours at 27.3 ± 0.4 °C (Nogueira et al., 2012).

In this period, the cytoplasm moves towards

the animal pole to form the blastodisc, which is

where future cell divisions will take place (Zad-

majid et al., 2017).

The cleavage period in S. cuspicaudus was

identified from 0.58 hours post fertilization

(HPF) when more than 50 % of the oocytes

with two cells were observed, to 1.33 HPF

when blastomeres of 64 cells were observed;

which was longer in Z. jahu from 0.8 to 1.67

HPF (Nogueira et al., 2012). It is defined as the

period composed of six stages, from two to 64

cells (Zadmajid et al., 2017).

The blastula period, in which the embryo

changes from spherical to oblong in shape and

begins epibolism, in S. cuspicaudus occurred

from 1.5 to 4.37 HPF; slower than P. grosskopfii

from 1.4 to 3.3 HPF (Valbuena-Villarreal et al.,

2012), and Pseudoplatystoma fasciatum from

1.15 to 3 HPF at 27.3 ± 0.6 °C (Zapata-Berrue-

cos et al., 2007), but faster than in Eremophilus

mutisii, from 9 to 11-12 HPF (Moncaleano-

Gómez et al., 2018). At the animal pole, a ball

shape, called the blastula, becomes visible and

the embryo changes from spherical to oblong

in shape (Zadmajid et al., 2018).

The gastrula period in S. cuspicaudus ran-

ges from 4.7 to 6.87 HPF; similar to Z. jahu 4.67

to 7.5 (Nogueira et al., 2012) and, P. f a s c i a t u m ,

4 to 6 HPF (Zapata-Berruecos et al., 2007) time

longer than in P. grosskopfii, from 3.6 to 5.7 HPF

(Valbuena-Villarreal et al., 2012), and lower

than in E. mutisii, from 12 to 30 HPF (Mon-

caleano-Gómez et al., 2018). Cell migrations

are generated to ensure that each germ layer

(mesoderm, ectoderm) is in the right place, so

that the organs and body tissues can be formed

in the correct location, the embryonic shield is

formed marking the dorsal side of the embryo,

in addition the tail bud is formed indicating the

end of the epibolia (Zadmajid et al., 2018).

The segmentation and organogenesis

period in S. cuspicaudus goes from 7:35 to 11:37

HPF, “at 11 HPF the first voluntary movements

are observed”, similar to P. f a s c i at u m , 7-11

hours (Zapata-Berruecos et al., 2007) and to

P. grosskopfii, from 7 to 11 HPF when the first

autonomic movements and blood circulation

with increasingly strong heart movements are

observed. The development of the Kupffer

vesicle and the formation of the subdivisions

of the brain are observed, the straightening of

the hind trunk occurs, the bulges along the

dorsal neural tube are observed, indicating

the formation of the hindbrain rhombomeres;

divided segments of the neural tube within the

hindbrain (Zadmajid et al., 2018).

The pharyngeal period in S. cuspicaudus

begins at 11:87 and ends at 13:37 HPF; and

in D. rerio from 24 to 48 HPF (Kimmel et al.,

1995). Finally, hatching in S. cuspicaudus occurs

at 15.92 at 28 °C, which is faster than in other

catfishes; 20-23 h for Heterobranchus longifilis

at 29 °C (Nwosu & Holzlöhner, 2000), 24 to

36 h for Pangasius sutchi at 20 °C-30°C (Islam,

2005), 25.5 h for Rhamdia quelen at 26 °C (de

Amorim et al., 2009), 40 h for Clarias garie-

pinus at 24 °C (Osman et al., 2008), 23 ± 1 h

for O. bimaculatus at 27.0 ± 1.1 °C (Pradhan

et al., 2013), 18 HPF at 27 ± 1 °C (Arambam

et al., 2020), 4 to 6 days for Ictalurus punctatus

at 25-27 °C (Chapman, 2000), same 15-17 h to

Hemisorubim platyrhynchos at 29 °C (Faccioli

et al., 2016) and, slower than P. grosskopfii,

12 h at 27 ± 1 °C (Valbuena-Villarreal et al.,

2012). Hatching is triggered by environmental

signals such as low oxygen tension, light inten-

sity, release of hatching enzymes as a signal to

adjacent eggs at different times during embryo

development (Nogueira et al., 2012).

Limited biological and productive per-

formance data is available for S. cuspicaudus,

mainly in the first stages of development that

are critical for the species. Hence, we document

early development, from oocyte fertilization, up

to 20 DPH, when the fingerling exceeds 4 cm

TL. Morphological and histological reference

points were employed, which can be utilized

by researchers and the aquaculture industry

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in forthcoming studies. Detailed information

on embryogenesis and larval development is

essential for captive reproduction of the species,

taking into account that high mortalities occur

in these early stages (Prieto et al., 2015). In this

regard, relevant information on eye, mouth and

gut development will help optimize early hand-

ling and feeding protocols, which is essential

for survival during this critical period (Portella

et al., 2014; Zadmajid et al., 2018).

In S. cuspicaudus, the development of the

eye begins from the first DPH where a pigmen-

ted primordial eye is observed which histologi-

cally shows closed retinal tissue, at the second

DPH the pigmented retina is observed, at the

third DPH histologically in the region of the

eye ganglion cells were observed and pigment

tissue, the connection of the central nervous

system between brain and spinal cord was evi-

denced. At the fifth DPH the appearance of a

small lens in the eye begins to differentiate, at

the seventh DPH a greater differentiation of the

retinal layers is observed, as well as a larger lens,

12 DPH, a well differentiated retina is obser-

ved and the fully developed eye. In this sense,

(Papadakis et al., 2018) in Argyrosomus regius

they found that at the first DPH the differentia-

tion of the retina began in layers, at 3 DPH cone

cells and the differentiation of cells in each layer

of the central part of the retina was visible, at 6

DPH it was visible. They observed the rods and

increased their density up to 17 DPH.

The mouth and anal opening in S. cuspi-

caudus occurred 32 hours after hatching at 26.6

°C, in the catfishes Ompok bimaculatus and H.

platyrhynchos it occurs at 2 DPH (Faccioli et

al., 2016; Pradhan et al., 2013). In Cichlasoma

uruphthalmos, the mouth opening is detected

at 2 DPE and the larvae begin to feed exoge-

nously between 5 and 6 DPE 28.1 ± 1.1 °C

(Portella et al., 2014).

Mouth opening time varies between spe-

cies and is influenced by temperature (Faccioli

et al., 2016; Portella et al., 2014; Zadmajid et al.,

2018). In addition, the opening of the mouth

and the depletion of the yolk sac are events

considered to be markers of the beginning of

feeding in larvae of fish (Faccioli et al., 2016;

Kimmel et al., 1995). In the trans-Andean sho-

velnose catfish, S. cuspicaudus the yolk sac was

observed up to 70.5 HPH, which is a shorter

period than that of other catfish, such as H.

platyrhynchos at 4 DPH (Faccioli et al., 2016),

C. gariepinus (Osman et al., 2008), Silurus glanis

(Kozarić et al., 2008), R. quelen (de Amorim et

al., 2009) and O. bimaculatus whose yolk sacs

last up to 5 DPH (Pradhan et al., 2013). In this

sense, S. cuspicaudus has a short endotrophic

feeding period of approximately 27.5 hours.

The initiation of feeding and the transition

from endogenous to exogenous food is a cri-

tical period in the development of fish larvae,

because they need to generate the ability to

survive on exclusively exogenous food and has

been associated with mass mortalities (Faccioli

et al., 2016; Gisbert et al., 2018; Portella et al.,

2014; Prieto et al., 2015). At 4 DPH, a greater

number of goblet cells was observed in the

intestine; this characteristic was also observed

in H. platyrhynchos larvae during days 3-4 post

hatching (Faccioli et al., 2014).

Although goblet cells are observed in the

esophagus of S. cuspicaudus from day 3, this

organ is well differentiated at 6 DPE and, by

day 9, it is observed to be thicker and have three

layers of skeletal striated muscle in some areas,

which it allows the distension of the organ and

the apprehension of the prey; the oropharynx

and esophagus had a stratified epithelium with

goblet cells. According to (Galvão et al., 1997)

the appearance of goblet cells indicates that the

oropharynx and esophagus are ready to receive

exogenous nourishment as their secretions pro-

tect the epithelium from damage caused by the

passage of food.

According Prieto & Atencio-García

(2008), S. cuspicaudus larvae are considered

altricial with rapid yolk sac depletion. The

trans-Andean shovelnose catfish larvae began

their first feeding (newly hatched brine shrimp

nauplii, instar I) at 43 HPH, at an average tem-

perature of 26.6 °C, with a weight of 1.2 ± 0.1

mg, total length of 5.0 ± 0.3 mm. The body was

observed to be translucent, with the presence

of the formed digestive tract, without diffe-

rentiation of annexed glands, whitish barbels

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in formation and defined gill lamellae, mouth

in terminal position and fully pigmented eyes,

similar to that reported by (Prieto et al., 2015).

Also, at the beginning of feeding, the intes-

tine showed a wide lumen that formed in the

anterior region with a sac-like shape. Some

authors have reported larval extracellular pro-

teolytic digestion in the foregut, where the pH

is alkaline and trypsin-like enzymes promote

proteolytic activity (Faccioli et al., 2016; Por-

tella et al., 2014). At 6 DPH the organization

of the hepatocytes in rows is observed, with

central rounded nuclei, the exocrine pancreas

attached to the liver with cells forming acini,

spherical nuclei and at 12 DPH the liver presen-

ted greater development and, in the pancreas,

as well as acinar cells ducts are also seen. At 12

DPH gastric glands were found in the stomach

of S. cuspicaudus. According to (Yang et al.,

2010), gastric glands in catfish appear earlier

than in other orders. However, the appearance

of gastric glands in S. cuspicaudus can be consi-

dered late as it occurs after other catfish, inclu-

ding Pelteobagrus fulvidraco at 3 DPH (Yang et

al., 2010), O. bimaculatus in 8 DPH (Pradhan et

al., 2012) and P. s u t c h i in 9 DPH (Islam, 2005).

The appearance of these glands is an important

event in larviculture and, together with the

secretion of pepsin, indicates that the stomach

has become functional and marks the transition

from larvae to juveniles (Ma et al., 2014).

Tank color had a significant effect (p <

0.05) on the overall performance of C. gariepi-

nus fingerlings, (Okomoda et al., 2017) who

found that rearing in black tanks resulted in

higher daily feed intake and better growth per-

formance compared to other tank colors. In the

same study they found that the fat and protein

content of the carcass at 8 weeks revealed a

trend similar to that observed for growth; it is

probable that the culture techniques used in the

present study favor the growth conditions of the

species. In the same way, and as in other catfish,

it was observed that the tilefish has a preference

for darkness, similar to what was reported for

C. gariepinus, (Almazán-Rueda, 2004; Britz &

Pienaar, 1992).

Compared to temperate-water fish, tro-

pical fish develop faster due to the effect of

temperature on metabolic rate (Gillooly et al.,

2002). The larvae and fingerlings of S. cuspi-

caudus had a growth, with some variations to

those reported for Pseudoplatystoma punctifer

(Darias et al., 2015; Fernández-Méndez et al.,

2015; Gisbert et al., 2014). The specific growth

rate (SGR) was low (13.56) up to 6 DPH (7.16

± 0.7 mm TL) corresponding to the stage called

first feeding, when the larvae were fed with

brine shrimp and kept in circular pools with

artificial aeration at a temperature of the water

of 26.6 °C, followed by a medium growth (SGR

22.38) until 11 DPH at 27.8 °C coinciding with

the development of the stomach and its atta-

ched glands and, finally, a high growth (SGR

34.88) until 20 DPE at 27.8 °C moment where

the growth evaluation ended. In this sense, the

growth pattern of P. punctifer larvae and early

juveniles in terms of weight showed an initial

phase of slow growth (SGR 0.19 ± 0.00) up to 12

dpf (12.02 ± 0.18mm TL), corresponding to the

larval stage, followed by an exponential growth

rate (SGR 0.53 ± 0.10) from 12 DPH onwards,

coinciding with the start of the juvenile stage

(Castro-Ruiz et al., 2019). Similar growth pat-

terns have also been reported in tropical and

freshwater fish species, such as P. fulvidraco

(Yang et al., 2010), Mystus nemurus (Srichanun

et al., 2012), Centropomus undecimalis (Jime-

nez-Martinez et al., 2012), Petenia splendida

(Uscanga-Martínez et al., 2011) and Lutjanus

guttatus (Moguel-Hernández et al., 2014).

The low and medium growth rate observed

from hatching to 12 DPH in S. cuspicaudus can

be interpreted as an evolutionary strategy to

consume available energy from yolk sac and

prey reserves to promote larval physiologi-

cal changes (gastrointestinal and body system

development) rather than somatic growth, as

also reported in O. bimaculatu (Pradhan et al.,

2013), Pangasianodon hypophthalmus (Rangsin

et al., 2012) and Atractosteus tropicus (Frías-

Quintana et al., 2015).

In this study, three important physiological

events were evidenced that favored the growth

and development of S. cuspicaudus larvae as

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: et27vbs38, enero-diciembre 2025 (Publicado Jul. 29, 2025)

follows: 1. From hatching to 6 DPE (days post-

emergence), a marked development of organs

was observed, including digestive organs, pro-

bably due to the type of live food supplied,

Artemia salina, favors the development of aqua-

tic organisms. 2. From 7 to 11 DPE, a greater

development of gastric glands was observed,

which favored the digestion of nutrients and,

therefore, growth. 3. From 12 to 20 DPE, a hig-

her specific growth rate was observed, probably

due to the variety of live food (primary produc-

tivity), present in the ponds. It is known that

live food is important for larval development,

thanks to its contributions to fatty acids and

essential amino acids.

The changes in the digestive system during

the first days are sufficient to allow the inges-

tion and digestion of food through the forma-

tion of goblet cells in the esophagus (day 3),

development of the eye (day 6), development

of the stomach, foregut, liver, pancreas, and

gastric glands (day 12). The onset of exogenous

food consumption in S. cuspicaudus occurs at

43 HPH, but full development of the stomach

together with the gastric glands was only obser-

ved up to 14 HPH, at which time full develop-

ment of other organs was evidenced, including

sensory and locomotion organs.

Based on these findings, it is indicated that

a minimum of 14 days post-emergence (DPE)

is necessary to procure fingerlings of trans-

Andean shovelnose catfish exhibiting com-

mendable quality, resilience, and a morphology

akin to that of adult specimens. This includes

characteristics such as ossified fin rays and

the manifestation of innate behaviors like the

escape instinct. These attributes render these

fingerlings suitable for restocking initiatives.

Ethical approval: All applicable interna-

tional, national, and institutional guidelines

for the care and use of animals were strictly

followed. All animal sample collection proto-

cols complied with the current laws of Colom-

bia. All procedures involving the handling of

the animals were performed according to the

Guide for the Care and Use of Laboratory Ani-

mals (Albus, 2012). A permit was granted by

the National Aquaculture and Fisheries Autho-

rity—AUNAP of Colombia under Resolution

0955 (27 May 2020).

Ethical statement: The authors declare

that they all agree with this publication and

made significant contributions; that there is

no conflict of interest of any kind; and that we

followed all pertinent ethical and legal proce-

dures and requirements. All financial sources

are fully and clearly stated in the acknowled-

gments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

We thank the company ISAGEN S.A.

(Colombia), for financing the study, to the

company Piscícola San Silvestre S.A. (Barranca-

bermeja, Colombia) for the logistical support.

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