Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

Morphology and anatomy of larval development in black neon tetra fish

Hyphessobrycon herbertaxelrodi (Characiformes: Characidae)

Pınar Çelik1; https://orcid.org/0000-0002-4417-3574

İhsan Çelik1*; https://orcid.org/0000-0001-7831-9175

1. Çanakkale Onsekiz Mart University, Faculty of Marine Sciences and Technology, Department of Aquaculture,

Çanakkale, Türkiye; pinarakaslan@yahoo.com, ihsanceliktr@gmail.com (*Correspondence)

Received 21-X-2024. Corrected 18-IV-2025. Accepted 19-I-2026.

ABSTRACT

Introduction: The black neon tetra (Hyphessobrycon herbertaxelrodi) is a popular ornamental fish, and under-

standing its larval development is crucial for aquaculture practices.

Objective: To examine the developmental stages during the larval period of black neon tetra produced under

laboratory conditions.

Methods: Larvae were sampled daily fromhatching until reaching the juvenile stage. Each specimen was photo-

graphed and prepared for anatomical observations.

Results: Morphological observations indicated that the mean total length (TL) of the larvae was 2.77 ± 0.08

mm on the first day after hatching (DAH) and increased to 12.26 ± 0.96 mm by the 29th-30th DAH when they

reached the juvenile stage. Initially, the fins were in a primordial form, with the mouth and anus opening on the

4th and 6th DAH, respectively. The anal and dorsal fins began to differentiate on the 10th and 14th DAH, coincid-

ing with the completion of notochord flexion on the 12th-13th DAH. The second swim bladder developed on the

14th and 15th DAH, and caudal fin bifurcation was observed on the 18th day. Anatomical observations indicated

significant changes in the developmental process of black neon tetra larvae. On the 1 st DAH, the digestive system

of the yolk sac larva was in the shape of a flat long tube. By the early 3 rd day, the mouth had opened, and the

swim bladder had noticeably swollen, taking the form of a tube in the digestive canal. On the 5 th day, the yolk

sac had been depleted, and the stomach and intestine began to develop. By the 10 th day, the liver had replaced

the yolk sac, increasing the folds of the stomach and intestine. The juvenile stage commenced on the 29th-30th

DAH, marking the end of the larval process.

Conclusions: The findings provide essential insights into the morphological and developmental milestones of

black neon tetra larvae, which are vital for enhancing aquaculture techniques and breeding protocols.

Key words: Tetra fish; Characidae; larvae; growth; aquarium.

RESUMEN

Morfología y anatomía del desarrollo larvario del pez tetra neón negro

Hyphessobrycon herbertaxelrodi (Characiformes: Characidae)

Introducción: El tetra negro (Hyphessobrycon herbertaxelrodi) es un pez ornamental popular y entender su

desarrollo larval es crucial para las prácticas de acuicultura.

Objetivo: Examinar las etapas de desarrollo durante el período larval del tetra negro producido en condiciones

de laboratorio.

Métodos: Se tomaron muestras de larvas diariamente desde la eclosión hasta alcanzar la etapa juvenil. Cada

ejemplar fue fotografiado y preparado para observaciones anatómicas.

https://doi.org/10.15517/2q40h220

VERTEBRATE BIOLOGY

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

INTRODUCTION

The global aquarium fish trade has trans-

formed into a multi-billion-dollar industry and

continues to grow every year. According to

report published a few years ago, the global

aquarium fish market was valued at USD 4.5

billion in 2020 and is exğected to reach USD

6.3 billion by 2028 (Grand View Research,

2021). Tetra fish, with more than 150 spe-

cies, are among the important fish groups that

are commercially valuable and popular among

hobbyists (Çelik & Çelik, 2022). Most living

organisms in the business involve fish species

of fresh water. The most commercially domi-

nant are the species of Cyprinodontiformes,

Perciformes, Characiformes and Siluriformes

families (Evers et al., 2019). Black neon tetra

Hyphessobrycon herbertaxelrodi is the species

of ornamental fish included in Characiformes

family. The present study morphologically

examined stages of larval development in black

neon tetra fish produced under laboratory

conditions. Knowledge of early stages in a com-

mercial fish species is of great importance

for the research conducted in the fields of

ichthyology, fisheries biology, protection of

ichthyofauna and improvement of aquaculture

techniques (Reynalte-Tataje et al., 2020; Rizzo

& Godinho, 2003; Santos et al., 2020). More-

over, data on larval development defined by

morphological and biometrical parameters are

quite essential for fish breeders to develop pro-

tocols for production and larva culture. (Lima

et al., 2020; Perrotti et al., 2019; Portella et al.,

2014). Considering the assessment above, it is

assumed that information on early life stages of

a commercially precious fish species would be

of great use in scientific and commercial terms

(Souza da Silva et al., 2022).

Fish development is generally divided into

embryo, larva, juvenile, young and adult stages

(Urho, 2002). Development of early life stages

in fish usually follows the same models until

the larval formation (Falk-Peterson, 2005). The

larval period is considered one of the most

crucial stages in the fish life cycle (Nowosad

et al., 2021). The rapid morphological changes

and organ development that occur during this

phase significantly influence the subsequent

development of fish and their survival rates

(Song et al., 2019; Zadmajid et al., 2019).

Understanding embryology and larval devel-

opments in fish has a key role in creating the

very approach to their biology and taxonomy

(Reynalte-Tataje et al., 2004). Morphological

characteristics help obtain comprehensive data

of life cycles on one hand and pave the way for

valuable traces of human ability to produce and

breed fish under aquaculture circumstances

on the other (Martinez et al., 2000; Martinez-

Lagos & Gracia-Lopez, 2009; Silva, 2004). Data

Resultados: Las observaciones morfológicas indicaron que la longitud total media (LT) de las larvas era de 2.77

± 0.08 mm el primer día después de la eclosión (DAE) y aumentó a 12.26 ± 0.96 mm para los días 29-30º DAE,

cuando alcanzaron la etapa juvenil. Inicialmente, las aletas estaban en una forma primordial, con la boca y el ano

abriéndose en el 4to y 6to DAE, respectivamente. Las aletas anal y dorsal comenzaron a diferenciarse en el 10º y 14º

DAE, coincidiendo con la finalización de la flexión del notocordio en el 12-13º DAE. La segunda vejiga natatoria

se desarrolló en el 14º y 15º DAE, y la bifurcación de la aleta caudal se observó en el día 18. Las observaciones

anatómicas indicaron cambios significativos en el proceso de desarrollo de las larvas de tetra negro. En el 1er DAE,

el sistema digestivo de la larva del saco vitelino tenía la forma de un tubo largo y plano. A inicios del 3er día, la boca

se había abierto y la vejiga natatoria aumentó notablemente, tomando forma de tubo dentro del canal digestivo.

En el 5to día, el saco vitelino se había reabsorbido y comenzaron a desarrollarse el estómago y el intestino. Para el

10º día, el hígado reemplazó el saco vitelino, aumentando los pliegues del estómago y el intestino. La etapa juvenil

comenzó en los días 29-30º DAE, marcando el final del proceso larval.

Conclusiones: Los hallazgos proporcionan información esencial sobre los hitos morfológicos y desarrollo de las

larvas de tetra negro, que son vitales para mejorar las técnicas de acuicultura y los protocolos de cría.

Palabras clave: pez tetra; Characidae; larvas; crecimiento; acuario.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

concerning the morphological development of

larval stages in fish is crucial for establishing

management protocols in aquaculture, espe-

cially for creating larviculture protocols (Papa-

dakis et al., 2018; Kupren et al., 2019; Lv et al.,

2019; Pepe-Victoriano et al., 2021).

The aim of this study is to examine the

developmental stages of black neon tetra (H.

herbertaxelrodi) larvae produced under labo-

ratory conditions. The black neon tetra is a

popular ornamental fish, and understanding

larval development is critical for aquaculture

practices. In this context, a detailed examina-

tion of morphological and histological changes

during the larval period will contribute to

the development of fish farming techniques

and breeding protocols. This study aims to

provide the necessary information for the cul-

tivation and conservation of this species by

identifying the important stages of the larval

development process.

MATERIAL AND METHODS

The study examined the larval develop-

ment of black neon tetra H. herbertaxelrodi

used by adult individuals older than one year

as broodstocks. H. herbertaxelrodi is a tetra

species classified in the Characidae family from

the Amazon River in origin. The body of H.

herbertaxelrodi is flat with a slight depth in

shape (Fig. 1).

It is silvery grayish black in color. The body

has a bright white line from the gill towards

the tail along the lateral sites (Fig. 1), which

assumes an iridescent white line as if it were

a neon light. The species is therefore called

“Black Neon Tetra” (Tropical Fish Hobbyist

Magazine, 2007). The body of a male is thinner

and smaller that of the female in structure.

All broodstocks were fed three meals a day

with the same feed (Protein: 46 %, Oil: 12 %

Fiber: 3 %, Ash: 11 %, Moisture: 8 %; Tetra-

min Granulat, Tetra, Germany). Water quality

parameters and spawning tanks were preserved

stable in the ranges of 24 ± 0.5 ºC temperature,

6.0-6.5 pH and 100-200 µ in conductivity.

100-watt aquarium heaters were used to keep

the water temperature stable. Female and male

broodstocks were preserved in 40 l separate

glass aquaria (Broodstock aquarium dimen-

sions: length 40 × width 30 × height 35 cm,

water depth/height 32-33 cm). The broodstock

aquaria were exposed to photoperiod program

of 9 h lightness / 15 h darkness. The lights were

kept on from 07.00 until 18:00. 3 female / 3

male broodstocks were randomly selected from

the aquaria and brought into the 15 l glass tanks

for production where broodstocks were seen

to spawn by dawn the following day. The eggs

gathered around the bottom during the spawn-

ing were left there after which the broodstocks

were removed from the tanks. Preserved at

stable temperature within the range of 24 ± 0.5

ºC, the eggs were left to incubate in the tank for

production to follow larval development.

Larval samples were randomly taken

every day from the first day of the hatching

until their juvenile. Larvae were observed by

means of SZX7: Olympus™ zoom stereomi-

croscope (Tokyo, Japan), were photographed

by the attached video camera (Q Imaging,

Micropublisher 3.3 RTV, Canada) and were

morphometrically measured by the picture

analysis program (Q Capture Pro, version

5.1.1.14, Canada). The growth data of the lar-

vae were obtained by measuring the lengths of

the larvae photographed under the microscope.

Larvae were fed once a day with brine

shrimp nauplii ‘Artemia salina’ (INVE Aqua-

culture Inc., Dendermonde, Belgium) by the

end of the experiment on 28 DAH. The feeding

rate was 5-10 individuals/ml. Artemia cysts

were incubated in 1.5 l seawater in a liter scale

cylindrical-conical plastic container at 25-26 °C

Fig. 1. Morphological appearance of the adult individual of

the black neon tetra fish, Hyphessobrycon herbertaxelrodi

(Original drawing, Çelik, 2011).

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and 25-30 ppm salinity. Aeration was main-

tained by a small pipeline from an aquarium air

pump down the bottom of the hatching device.

Artemia cysts were hatched within 24-26 h

under these conditions. The newly hatched

nauplii were harvested and added to the larva

tanks by means of a pipette.

Larval stages of development were identi-

fied according to Kendall et al. (1983) and were

grouped into four periods I: Yolk-sac larva

from hatching until depletion the yolk sac,

II: Preflexion larva from the depletion of the

yolk sac by the beginning of flexion of noto-

chord end III: Flexion larva from the start of

notochord flexion until its complexion and IV:

Post-flexion larva from the completion of the

notochord end flexion by the time when larval

development was over and juvenile was about

to begin. Larvae finished their development to

completely reach the forms of adult individuals

following stage IV at which younglings were

defined as juveniles then the observations of

larval development were concluded.

Anatomical observations: For anatomi-

cal assessment, larvae were randomly collected

daily from hatching (1 day after hatching =

DAH) until juvenile stage. The specimens were

fixed in a Bouin’s solution and 70 % alcohol,

dehydrated through a series of alcohol con-

centrations and were cleared in xylene and

paraffin-waxed. Wax blocks were cut using a

microtome (Slee, Cut5062, Germany) at 5 μm.

Sagittal sections were stained by Gill’s hema-

toxylin / eosin (HE) procedures for general

histology. The blocks were observed under a

light microscope (BX50: Olympus™) to describe

the larval development and were photographed

using a color video camera.

RESULTS

Morphological observations, 1 DAH (TL:

2.77 ± 0.08 mm): The mouth and anus were

closed, and the digestive system did not differ-

entiate yet. The eyes did not have pigmentation

and star-shaped anophores seemed to be dis-

persed on the yolk sac and body. Primordial fin

developed well, and no other fins differentiated

yet. The yolk sac was oval measuring about 20

% of the total length. Since pigmentation did

not develop, the outlets could be easily seen

through the otic capsule where they were pres-

ent (Fig. 2a).

2 DAH (TL: 3.34 ± 0.04 mm): The mouth

was still closed. The digestive system was in the

form of a semitransparent and differentiated

flat tube with the yolk sac beginning to lessen.

Although pigmentation increases in eye and

head sections, other parts of the body seem

more transparent. Black melanophores are dis-

persed or irregularly present in and around

the head, flanks and back sections as well. The

bladder lies near the anus. The pectoral fin bud

was present, but anal and dorsal fins have not

formed yet (Fig. 2b).

3 DAH - 4 DAH (TL: 3.49 ± 0.07 mm):

The swim bladder began to inflate on the 3rd

day. The pigmentation was completed in the

eyes. On the 3rd day the mouth was still closed.

The digestive system assumed an entire tube.

The yolk sac was still present (Fig. 2c). On the

4th day, still existed remains of the yolk sac

that were not completely depleted. The mouth

opened on the 4th day. The swim bladder

extended towards the posterior. The swim blad-

der enlarged posteriorly. The development of

the eye was completed. The primordial fin was

present, and the other fins did not differentiate.

The larva began to feed exogenously on the 4th

day (Fig. 2d).

5 DAH - 8 DAH (TL: 3.70 ± 0.17 mm -

4.51 ± 0.28 mm): There was if little yolk sac

even on the 5th day. The bladder has been

clearly visible just next to the anus. Pigmenta-

tion was increasing (Fig. 2e). The yolk sac was

completely depleted on the 6th day. The swim

bladder continued to extend posteriorly. Pieces

of digested food (Artemia salina) in the stom-

ach could be seen (Fig. 2f). The swim bladder

continued to enlarge in size. On the 7th day,

notochord was not still in flexion but flat in

shape (Fig. 2g). Pigmentation continued to

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Fig. 2. Larval development stages of black neon tetra Hyphessobrycon herbertaxelrodi. 1–8 DAH, 24 ± 0.5 ºC. A. Post-hatching

yolk sac stage (1 DAH). B. Yolk sac stage (2 DAH). C. Yolk sac stage, the gas bladder was formed but not completely filled

(3 DAH). D. Opened-mouth stage (4 DAH). E. Preflexion larva, exogenous feeding (5 DAH). F.-H. Preflexion larva (6, 7, 8

DAH). Scale bars: 1 mm.

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increase. Differentiation of dorsal and anal fins

did not occur (Fig. 2h).

9 DAH - 10 DAH (TL: 4.96 ± 0.17 mm

- 5.39 ± 0.11 mm): Despite an increase in pig-

mentation, the body of the larva hardly colored

thus appearing semitransparent. The volume of

the swim bladder continued to increase (Fig.

3a). The primordial fin that had existed since

the early days was present and the anal fin did

not differentiate yet. The tail fin rays began to

form (Fig. 3b).

11 DAH - 13 DAH (TL: 5.71 ± 0.12 mm

- 6.48 ± 0.22 mm): Pigmentation continued to

increase all over the body (Fig. 3c). The trans-

parent appearance of the body on early days

gradually vanished as the time passed. On the

12th day emerged the flexion on notochord

end. The tail fin rays began to become promi-

nent. Differentiation of dorsal and anal fins

started (Fig. 3d). Pigmentation increased. The

swim bladder enlarged towards the posterior.

The tail fin rays increased, thus becoming evi-

dent (Fig. 3e).

14 DAH - 16 DAH (TL: 6.61 ± 0.49 mm -

7.68 ± 0.61 mm): On those days, differentiation

of the dorsal and anal fins became visible as

well. The first swim bladder appeared signifi-

cantly enlarged and lengthened (Fig. 3f) with

the second swim bladder gradually emerging.

Dorsal and anal fin rays began to be prominent

(Fig. 3g). The number of dorsal and anal fin

rays increased to finally become visible to the

naked eye. The swim bladders continued to

increase in size. Pigmentation went on increas-

ing more than on the previous days (Fig. 3h).

17 DAH - 21 DAH (TL: 7.96 ± 0.35 mm

- 9.86 ± 0.42 mm): As the coloration was more

intense in head and dorsal areas of the body,

they lost their transparent appearance. How-

ever, the pigmentation was less in the areas of

the abdomen and stomach, thus they inevitably

seemed partially translucent such that digested

pieces of food (Artemia salina) could be seen to

remain in the stomach. The dorsal, anal and tail

rays became more prominent than they were in

previous days. The volume of the swim blad-

der continued to grow (Fig. 4a). Pigmentation

continued to increase the bifurcation on the

tail fin was observed to begin (Fig. 4b). There

appeared the adipose fin formation between

the dorsal and tail fins (Fig. 4c). Pigmentation

continued to increase all over the body. Tail

bifurcation increased. The dorsal and anal fins

continued to develop (Fig. 4d).

23 DAH - 29 DAH (TL: 10.25 ± 0.57

mm - 12.26 ± 0.96 mm): The swim bladder

continued to grow, and the pigmentation was

increasing. The dorsal, anal and tail fins kept

on developing (Fig. 4e). Just beneath the lateral

line increased the pigmentation (Fig. 4f). On

the 29th-30th days, the larva completed its

morphological development (Fig. 4g), follow-

ing which it reached the juvenile phase. The

external appearance of the larva (39 DAH)

seemed like in the figure. (Fig. 4h). 10 days after

juvenile when body appearances of the young-

lings morphologically assumed the shapes of

mature individuals.

Growth: The growth formula of black

neon tetra calculated by the exponential rela-

tionship model during the early larval period

was as follows; y = 3. 0053e0. 0531x (R2 = 0.9694,

n = 112); where y is the total length (TL) and ×

DAH. Total length of the larvae was 2.77 ± 0.08

mm, 3.70 ± 0.17 mm, 5.39 ± 0.11 mm, 6.85 ±

0.38 mm, 9.86 ± 0.42 mm and 11.35 ± 0.8 mm

on the 1st, 5th, 10th, 15th, 21st and 27th days,

respectively. Accordingly, the mean total length

of the larva that reached juvenile phase on the

29-30th days was found to be 12.94 ± 1.03 mm

(Fig. 5). The size of the yolk sac was measured

as 790.26 ± 45.19 μm on the 1st day when it was

hatched, followed by 728.39 ± 73.25 μm on the

2nd, 664.52 ± 3rd, 33.15 μm and 562.20 ± 43.40

μm 4th day. The yolk sac measured to be 400.39

± 227.38 μm after the 5th day was seen to be

completely depleted (Fig. 6).

The swim bladder of black neon tetra

larva is composed of two sections. The initially

formed swim bladder as the main, it begins to

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

Fig. 3. Larval development stages of black neon tetra Hyphessobrycon herbertaxelrodi. 9-16 DAH, 24 ± 0.5 ºC. A.-C.

Preflexion larva (9, 10, 11 DAH). D. Flexion stage, notochord flexion started (12 DAH). E. Flexion stage, the notochord was

completely flexed (13 DAH). F.-G. Postflexion larva, second inflation of the swim bladder (14-15 DAH). F.-H. Postflexion

larva (14, 15, 16 DAH). Scale bars: 1 mm.

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Fig. 4. Larval development stages of black neon tetra Hyphessobrycon herbertaxelrodi. 17-39 DAH, 24 ± 0.5 ºC. A.-F.

Postflexion larva (17, 18, 19, 21, 23, 25 DAH). G. End of metamorphosis (29 DAH). H. Juvenile stage (30-39 DAH). Scale

bars: 1 mm.

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assume a two nodular sac in appearance fol-

lowing the 14-15th days. The observations on

the study showed that the main swim bladder

began to inflate on the 3rd day. Therefore,

the longest total length the more the length

of the swim bladder continued. The reason

why the swim bladder decreased in length on

the 14-15th days is because the second swim

bladder was inflated (Fig. 7). When the second

nodule was formed by the main swim bladder,

following which the second nodule as the swim

bladder continued to extend backwards to the

body on the next days until the juvenile phase

started (Fig. 8). The size of the swim bladder

increased proportionally to the total length

(TL) of the larva.

The present study determined that brood-

stocks of black neon tetra spawned at dawn

few hours before sunrise. Spawning lasts for a

few hours. Incubation period of eggs is quite

short. Eggs hatch several days after fertilization,

which means that the embryonic development

phase has been completed in 20.00-22.00th

hour. The main processes of metamorphosis

could be summarized as follows; One observed

that the initial swelling of the swim bladder

occurred on the 3rd day after hatching while

mouth and anus opening and free swimming

was on the 4-5th days (Fig. 9). The yolk sac

was depleted on 6 DAH. The appearance of

caudal fin rays and differentiation of the anal

and dorsal fins emerged in the 10th and 14th

Fig. 5. Total length-age relationship through the larval development stage of black neon tetra larvae.

Fig. 6. Yolk sac length of black neon tetra larvae from 1 DAH to 5 DAH (mm).

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days, respectively. Flexing of the notochord end

called. Flexion was observed on 12-13th days

(Fig. 9). Differentiated anal and dorsal fin rays

became prominent on the 15th day. The second

swim bladder caused by the second nodule

was seen on the 14-15th days (Fig. 9). On the

20-21st days, the adipose fin was determined

to be visible for the first time. The beginning of

the caudal fin bifurcation was recorded on the

18th day, following which juvenile phase was

observed to be reached on the 29-30th days

when larval stage was over (Fig. 9).

Anatomical observations: On the 1st day,

the digestive system of the yolk sac larva was

in the shape of a flat long tube (Fig. 10a). The

swim bladder dorsal to the yolk sac was about

to be in the process of development. Early on

the 3rd day, the mouth was open, and the swim

bladder swollen with the digestive canal obvi-

ously in the form of a tube (Fig. 10b). The yolk

sac was depleted on the 5th day, and the stom-

ach and intestine developed instead (Fig. 10c).

The larva can ingest and digest exogenous

food (live feed / Artemia). On the 10th day, the

liver replaced the yolk sac with stomach and

intestinal folds increasing (Fig. 11a). The first

swim bladder dorsal to the digestive system

extended to the posterior (Fig. 11a). On the

19-20th days, the development of the second

Fig. 7. Length data from the first inflation of the first swim bladder to the juvenile stage (mm).

Fig. 8. Length data from the first inflation of the second swim bladder to the juvenile stage (mm).

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

swim bladder was completed (Fig. 11b). The

swim bladder could be seen as in a double nod-

ular form by histological evidence (Fig. 11b).

The stomach and intestine of the larva were in

a form or a structure similar to those of juvenile

individuals in those days when powder could

be digested. Large food particles were observed

in the stomach and intestine (Fig. 11b, Fig. 11c).

The body depth increased. 29-30 DAH; Meta-

morphosis was completed and the larvae have

thoroughly grown into juveniles.

DISCUSSION

Numerous fish species have the capacity

to spawn once a year whereas tetra species can

spawn many times all the year round (Cole et

al., 1999). They are defined as egg laying species

in reproductive behavior and do not assume

parental care (Hill & Yanong, 2002). Eggs of

tetra species are classified as slightly slimy

sticky and sinking ones (Cole et al., 1999; Cole

& Haring, 1999). The present study observed

that larvae of black neon tetra hatched 20-22

hours after fertilization. Females of black neon

tetra are bigger than its males. Water-related

parameters essential for them to reproduce is

that water be in softness to intermediate hard-

ness of 100 ppm in general, temperature 22-27

°C and pH 7.5 (Çelik et al., 2012). Spawning

occurs at dawn just hours before sunrise as in

other tetra species, followed by fertilization,

then hatching of embryos within the 22-26

h period (Goslawski, 1981; Kornobis, 1990;

Romig, 1995).

The studies on Gymnocorymbus ternetzi

(Çelik et al., 2012) and serpae tetra Hyphes-

sobrycon eques (Çelik & Cirik, 2020) species,

both of which are from the same family as in

the black neon tetra showed that their embry-

onic phases of development were completed in

20-22 hours, which applies for black neon tetra

as well. On the other hand, metamorphosis

phenomena of larval development processes

can be said to occur in the three tetra species

at about the same periods of time. For example,

initial swelling of the swim bladder occurred in

serpae tetra and black neon tetra on the 3rd day

while it was seen in G. ternetzi, on the 2nd day

(Çelik et al., 2012; Çelik & Cirik, 2020). Open-

ing of mouth and anus and beginning of free

swimming in black tetra species ensued on the

3rd day and in serpae tetra and in black neon

tetra species on the 4th day (Çelik et al., 2012;

Çelik & Cirik, 2020). It is interesting to note

that depletion of yolk sac showed differences

in the three tetra species. It was observed that

black tetra larva depleted the yolk sac in 3 DAH

(Çelik et al., 2012), serpae tetra larva in 4 DAH

(Çelik & Cirik, 2020) and black neon tetra in 6

Fig. 9. The main events of larval development in black neon tetra (Hyphessobrycon herbertaxelrodi), 24 ± 0.5 ºC.

12 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

DAH (the present study). Developmental pro-

cesses of the three tetra species exhibited that

appearance of caudal fin rays and differentia-

tion in anal and dorsal fins occurred in black

tetra and serpae tetra on 11-12 DAH (Çelik et

al., 2012; Çelik & Cirik, 2020) but in black neon

tetra on 10-14 days (the present study). The

process of the notochord end flexing, briefly

called flexion occurred in black tetra (Çelik

et al., 2012) and black neon tetra (the present

study) in 10-12 days in and serpae tetra (Çelik

& Cirik, 2020) in the 13 days. Differentiated

Fig. 10. Sagittal sections of black neon tetra larvae. A.

1 DAH (BX51: Olympus™, 100×). B. 3 DAH (BX51:

Olympus™, 40×). C. 5 DAH (BX51: Olympus™, 40×). at

alimentary tract; e eye; g gill; ga gill arches; i intestine; l

liver; n notochord; oe, oesophagus; ph pharynx; s stomach;

sb swim bladder; t teeth; ys yolksac.

Fig. 11. Sagittal sections of black neon tetra larvae. A.

10 DAH (BX51: Olympus™, 40×), B. 19 DAH (BX51:

Olympus™, 40×). C. 24 DAH (BX51: Olympus™, 100×). gb

gall bladder; i intestine; l liver; oe oesophagus; ph pharynx;

s stomach; sb swim bladder.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

anal and dorsal fin rays in black neon tetra

formed 3 days later than the other two tetra

species on the 18th day and in black tetra and

serpae tetra on the 15th day. Development of

the second swim bladder related to the main

bladder occurred in the three tetra species

almost at the same time (15-17 DAH). The first

appearance of the adipose fin was observed in

black tetra in 22-23 days (Çelik et al., 2012) in

serpae tetra in 24th-25th days (Çelik & Cirik,

2020) and in black neon tetra in 20-21st days

(the present study). Bifurcation of caudal fin

was found to begin in black tetra and serpae

tetra in 19th day (Çelik et al., 2012; Çelik &

Cirik, 2020) in black neon tetra in 18th day (the

present study), following which the end of the

larval process followed by reaching the juvenile

phase were seen to be completed in serpae tetra,

black neon tetra and black tetra in the 28th,

29th and 29-30th day, respectively. According

to metamorphosis processes in larval develop-

ment phases in the three tetra species different

in morphological appearance, their develop-

ment phases can be cited to be quite similar to

each other. There were variations between the

periods of time when some morphological pro-

cesses occurred. However, a general assessment

of the larval development process can suggest

that these three species develop similarly to

each other, from which one can draw a general

conclusion on larval development processes of

all the other tetra species.

During the larval development of teleosts,

the digestive system ontogenesis (the onto-

genesis of the digestive system) was defined

in three ways such as agastric, precocial and

altricial (Rønnestad et al., 2013). Agastric fish

species (Cyprinidae, Gobiidae) depends on

alkaline and pancreatic proteases for hydrolysis

of protein in the entire life cycle of the fish. As

the larva grows, digestive function of the intes-

tine increases based on its length, therefore the

digestive capacity of the larva would increase as

well (Dabrowski & Poczyczyński, 1988). Larvae

of Precocial fish species (Salmonidae, Bagridae)

develop fully functional stomachs with acid

protease activity prior to exogenous feeding,

which implies that precocial species increase

their digestive capacity significantly more than

agastric fish before they are fed with micropar-

ticle feeds exogenously (Yang et al., 2010).

Finally, altricial species exhibit a gastric larvae

characteristic until the time when the stomach

differentiates and digestion begins with the

protease activity increasing due to alkaline pro-

tease process in their initial feeding (Sparidae,

Paralichthyidae) (Faulk & Holt, 2009; Santa-

maría et al., 2004). Successful transition from

live to microparticle feeds in the larva breeding

of altricial species is mostly based on the dif-

ferentiation of a functional stomach (Faulk &

Holt, 2009; Rønnestad et al., 2013; Thompson

et al., 2019). Therefore, awareness of when the

stomach differentiates in the process of larval

development is important.

Likewise, it is of great importance to know

the processes such as opening of mouth, deple-

tion of the yolk sac and development of the

digestive system in the larva breeding business.

Larva of black neon tetra examined in the pres-

ent study is also included in the class of altricial

larva. It has been similarly reported that the

larvae of some tetra species such as black skirt

tetra G. ternetzi (Çelik et al., 2012), serpae tetra

H. eques (Çelik & Cirik, 2020) and neon tetra

Paracheirodon innesi (Lipscomb et al., 2022)

are altricial. It is not appropriate to supply these

species exogenously with microparticle feed

until digestion in their stomachs has been com-

pletely functional by then they are supposed to

be fed with live feeds like rotifers and Artemia.

Larvae of neon tetra, P. i nnesi species com-

plete their stomach development between 12

and 20 days after the hatching finally become

functional in digestive sense (Lipscomb et al.,

2022). In the present study, larvae of black neon

tetra were observed to similarly complete their

stomach development between the 10 and 19th

days following the hatching, according to which

it is recommended that larvae of the tetra spe-

cies hereby cited should not be supplied with

microparticle feeds before 19–20th days in the

larva breeding process. Altricial species can be

said to develop faster and thus have higher sur-

vival rates than precocial species (Nakatani et

al., 2001; Santos et al., 2020). The consequences

14 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

of the present study are consistent with those

of the trials made on some characin species

such as neon tetra P. i nnesi (Lipscomb et al.,

2022), black skirt tetra G. ternetzi (Lipscomb

et al., 2020) and black prochilodus Prochilodus

nigricans (Souza da Silva et al., 2022) but nev-

ertheless, more comprehensive studies can be

conducted in this field anyway.

Mouth and anus opening with the pig-

mentation of eyes are those processes that

occur simultaneously in the phase of preflexion

(Cajado et al., 2021; Oliveira et al., 2021; Silva

et al., 2021), all of which are of course related

to the fact that larvae are fed exogenously.

Accordingly, larvae of black neon tetra began to

feed exogenously from the 4th day after mouth

and anus opening, when they were inevitably

supplied with Artemia since their digestive

system did not develop completely. Transi-

tion from endogenous to exogenous feeding is

of critical importance considering the success

of larviculture (Abdo et al., 2015), because

if larvae capable of surviving thanks to their

yolk sacs in earlier days after hatching were

not fed exogenously due to depletion of them,

they could encounter autophagy towards their

own tissues that we can described as self-

digestion (Souza da Silva et al., 2022) which

was thoroughly observed by Ferreira et al.

(2009) who studied larvae of Glossolepis incisus

(Melanotaeniidae, Atheriniformes).

Pigmentation in fish larvae is the basic tax-

onomic criterion used to identify them in their

natural habitats and under controlled breed-

ing conditions (Lima et al., 2020; Santos et al.,

2020). It would thus be useful to know pigmen-

tation processes which occur in larval develop-

ment phases of fish species. The pigmentation

process from the hatching of black neon tetra

until its juvenile was observed in the present

study therefore proving that larvae assumed an

appearance of typically mature individuals after

29-30 days, which was reported to be the same

in similar tetra species as well (Çelik et al., 2012;

Çelik & Cirik, 2020). However, color-related

anomalies could be widely seen in fish larvae,

which inevitably leads to losses of yield and

quality in fish breeding business. Anomalies

observed in pigmentation are the very problem

in almost all fish species in aquaculture (Cal

et al., 2018), which on the other hand proves

more problematic in the ornamental fish sec-

tor since ornamental fish are organisms bought

and sold just because of their beauty and physi-

cal forms. Therefore, coloration of ornamental

fish such as black neon tetra is supposed to be

closely monitored from the early periods of

time of the process.

Formation of fins during early ontogen-

esis depends on development of swimming

skills which is of vital importance in terms of

influences on larval behavior and growth (Por-

tella et al., 2014). Fins are the organs capable of

increasing likelihood of larval survival as well

as strengthening movement and distribution of

larvae in water (Silva et al., 2021). It is therefore

of great use to follow the development pro-

cesses of fins in the larval period. In the present

study, it was recorded that larvae of black neon

tetra had well developed primordial fins in the

early days when they hatched and all the other

fins, but the pelvic fin did not differentiate

yet. Dorsal and anal fins began to differentiate

in the 11-13th days when tail fin rays further

developed to be prominent. Dorsal anal and tail

fins continued to develop in the 23-28th days

as well. Fins completed their morphological

development after 29-30th days. The larval fin

development in the present study was observed

to be similar in some black tetra species such as

skirt tetra G. ternetzi (Çelik et al., 2012), serpae

tetra H. eques (Çelik & Cirik, 2020) and neon

tetra P. in n e s i (Lipscomb et al., 2022) as well.

In conclusion, the morphological process-

es recorded during the larval development

of black neon tetra (H. herbertaxelrodi) were

reported to exhibit resemblance to those found

in the studies on some characin species such

as G. ternetzi (Çelik et al., 2012), Astyanax

lacustris (Stevanato & Ostrensky, 2018; Santos

et al., 2020), Brycon amazonicus (Neumann et

al., 2018), H. eques (Çelik & Cirik, 2020) and

P. i nnesi (Lipscomb et al., 2022). Negligible

differences can appear between developmental

stages due to such factors as water tempera-

ture, medium conditions and feeding/nutrition

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

regime in which the species is bred. Moreover,

there can be variations in periods of time in

other morphological processes such as mouth

opening, yolk sac depletion and free swim-

ming. However, metamorphic events during

larval developments of these species are seen to

occur similarly. On the other hand, it should be

emphasized that larval development processes

of characin species used as ornamental fish

are different from those of Cichlidae family

species including Cichlasoma dimerus (Meijide

& Guerrero, 2000), Astronotus ocellatus (Paes

et al., 2011), Labidochromis caeruleus (Saemi-

Komsari et al., 2018), Iodotropheus sprengerae

(Çelik et al., 2022).

The histological and morphological find-

ings revealed during the larval development

stages of the black neon tetra may provide

insights for professional businesses engaged

in the commercial production of this species.

The increased success of larval production in

aquaculture is directly related to the economic

aspects of the business. In this way, several posi-

tive contributions can be made, such as increas-

ing larval survival rates, enhancing growth

rates, and reducing stress levels. Therefore, the

findings shared in this study may be significant

to commercial aquaculture operators.

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 fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

REFERENCES

Abdo, T. F., Perrotti, P. B., Meireles, W. A., & Bazzoli,

N. (2015). Initial development of Prochilodus har-

tii (Pisces: Prochilodontidae) submitted to induced

reproduction. Zygote, 24(3), 408–417. https://doi.

org/10.1017/S0967199415000337

Cajado, R. A., Silva-de-Oliveira, L., Souza-de-Silva, F. K.,

& Zacardi, D. M. (2021). Early development of the

neotropical fish known as long sardine Triportheus

auritus (Valenciennes 1850) (Characiformes, Tri-

portheidae). Journal of Applied Ichthyology, 37(5),

759–769. https://doi.org/10.1111/jai.14228

Cal, L., Suarez-Bregua, P., Moran, P., Cerdá-Reverter, J. M.,

& Rotllant, J. (2018). Fish pigmentation. A key issue

for the sustainable development of fish farming. In

M. Yúfera (Ed.), Emerging issues in fish larvae research

(pp. 229–252). Springer.

Çelik, I., Çelik, P., Cirik, Ş., Gürkan, M., & Hayretdağ,

S. (2012). Embryonic and larval development of

black skirt tetra (Gymnocorymbus ternetzi, Bou-

lenger, 1895) under laboratory conditions. Aqua-

culture Research, 43(9), 1260–1275. http://dx.doi.

org/10.1111/j.1365-2109.2011.02930.x

Çelik, İ., Çelik, P., & Yalçın, B. R. (2022). Larval develop-

ment of rusty cichlid fish (Iodotropheus sprengerae

Oliver & Loiselle, 1972): Morphological observations.

Acta Natura et Scientia, 3(2), 203–213. http://dx.doi.

org/10.29329/actanatsci.2022.352.11

Çelik, P. (2011). Characidae familyasına ait üç balık türünün

(Gymnocorymbus ternetzi, Hyphessobrycon herber-

taxelrodi, Hyphessobrycon serpae) embriyonik ve lar-

val gelişim safhalarının incelenmesi [Doctoral thesis].

Çanakkale Onsekiz Mart University.

Çelik, P., & Çelik, İ. (2022). Embryonic development

of black neon tetra Hyphessobrycon herbertaxelrodi

Géry, 1961. Israeli Journal of Aquaculture-Bamidgeh,

74, 1-10. https://doi.org/10.46989/001c.57301

Çelik, P., & Cirik, Ş. (2020). Embryonic and larval develo-

pment of serpae tetra Hyphessobrycon eques (Steinda-

chner, 1882). Aquaculture Research, 51(1), 292–306.

https://doi.org/10.1111/are.14375

Cole, B., & Haring, M. (1999). Spawning and production of

the serpae tetra, Hyphessobrycon serpae. Center for

Tropical and Subtropical Aquaculture. Publication

Number 138.

Cole, B. M. S., Kotol, P. M. S., & Harıng, M. B. S. (1999).

Spawning and production of the lemon tetra Hyphes-

sobrycon pulchripinnis. Center for Tropical and Sub-

tropical Aquaculture. Publication Number 142.

Dabrowski, K., & Poczyczyński, P. (1988). Comparative

experiments on starter diets for grass carp and com-

mon carp. Aquaculture, 69(3–4), 317–332. https://doi.

org/10.1016/0044-8486(88)90339-0

Evers, H. G., Pinnegar, J. K., & Taylor, M. I. (2019). Where

are they all from?-sources and sustainability in the

ornamental freshwater fish trade. Journal of Fish

Biology, 94(6), 909–916. http://dx.doi.org/10.1111/

jfb.13930

Falk-Petersen, I. B. (2005). Comparative organ differen-

tiation during early life stages of marine fish. Fish

& Shellfish Immunology, 19(5), 397–412. https://doi.

org/10.1016/j.fsi.2005.03.006

16 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

Faulk, C. K., & Holt, G. J. (2009). Early weaning of

southern flounder, Paralichthys lethostigma, larvae

and ontogeny of selected digestive enzymes. Aqua-

culture, 296(3–4), 213–218. https://doi.org/10.1016/j.

aquaculture.2009.08.013

Ferreira, A. V., Vidal-Jr, M. V., Andrade, D. R., Mendonça,

P. P., Yasui, G. S., & Mattos, D. C. (2009). Consumo

de vitelo durante o desenvolvimento embrionário de

Melanotênia-Maçã, Glossolepis incisus, Weber 1907

(Melanotaeniidae). Ciência Animal Brasileira, 10(3),

721–729.

Goslawski, K. (1981). Żałobniczka Gymnocorymbus ternetzi

(Boulanger, 1985). Akwarium, 3-4, 74–76.

Grand View Research. (2021). Ornamental fish market size,

share & trends analysis report by product (tropical fresh

water, temperate fresh water), by application (commer-

cial, household), by region, and segment forecasts, 2021

- 2028. Grand View Research.

Hill, J. E., & Yanong, R. P. E. (2002). Freshwater ornamen-

tal fish commonly cultured in Florida (Circular 54).

University of Florida Extension Institute of Food and

Agricultural Sciences

Kendall, A. W., Ahlstrom, E. H., & Moser, H. G. (1983).

Early life history stages of fishes and their characters.

In H. G. Moser, W. J. Richards, D. M. Cohen, M. P.

Fahay, A. W. Kendall, & S. L. Richardson (Eds.), Onto-

geny and systematics of fishes (pp. 11–22). Allen Press.

Kornobis, S. (1990). Słodkowodne ryby

akwariowe. Wydawnictwo Poznańskie.

https://akwariat.pl/ksiazki-na-slodko/

slodkowodne-ryby-akwariowe-stefan-kornobis/

Kupren, K., Palinska-Zarska, K., Krejszeff, S., & Zarski, D.

(2019). Early development and allometric growth in

hatchery-reared Eurasian perch, Perca fluviatilis L.

Aquaculture Research, 50(9), 2528–2536. https://doi.

org/10.1111/are.14208.

Lima, D. L. G., Cajado, R. A., da-Silva, L. V. F., Maia, J.

L. S., & Zacardi, D. M. (2020). Descrição morfo-

lógica do desenvolvimento inicial de Brycon ama-

zonicus (Characiformes, Bryconidae) do Baixo

Amazonas, Pará. Macapá, 11(1), 60–67. http://

dx.doi.org/10.18561/2179-5746/biotaamazonia.

v11n1p60-67

Lipscomb, T. N., Yanong, R. P., Ramee, S. W., & DiMa-

ggio, M. A. (2020). Histological, histochemi-

cal and biochemical characterization of larval

digestive system ontogeny in black tetra Gymnocorym-

bus ternetzi to inform aquaculture weaning pro-

tocols. Aquaculture, 520(2), 734957. http://dx.doi.

org/10.1016/j.aquaculture.2020.734957

Lipscomb, T. N., Yanong, R. P., Ramee, S. W., & DiMaggio,

M. A. (2022). Larval digestive system ontogeny and

early weaning in neon tetra Paracheirodon innesi.

Fish Physiology and Biochemistry, 49(6), 1241–1255.

https://doi.org/10.1007/s10695-023-01254-w

Lv, X., Xu, S., Liu, Q., Wang, X., Yang, J., Song, Z., &

Li, J. (2019). Osteological ontogeny and allometric

growth in larval and juvenile turbot (Scophthalmus

maximus). Aquaculture, 498, 351–363. http://dx.doi.

org/10.1016/j.aquaculture.2018.08.063

Martinez, G., Aguilera, C., & Mettifogo, L. (2000). Inte-

ractive effects of diet and temperature on repro-

ductive conditioning of Argopecten purpuratus

broodstock. Aquaculture, 183(1–2), 149–159. https://

doi.org/10.1016/S0044–8486(99)00291–4

Martinez-Lagos, R., & Gracia-Lopez, V. (2009). Morpholo-

gical development and growth patterns of the leopard

grouper Mycteroperca rosacea during larval develop-

ment. Aquaculture Research, 41(1), 120–128. http://

dx.doi.org/10.1111/j.1365-2109.2009.02313.x

Meijide, F. J., & Guerrero, G. A. (2000). Embryonic and

larval development of a substrate–brooding cichlid

Cichlasoma dimerus (Heckel, 1840) under labora-

tory conditions. Journal of Zoology, 252(4), 481–493.

http://dx.doi.org/10.1111/j.1469-7998.2000.tb01231.x

Nakatani, K., Agostinho, A. A., Baumgather, G., Bialetzki,

A., Sanches, P. V., Makrakis, M. C., & Pavanelli, C. S.

(2001). Ovos e larvas de peixes de água doce: desenvol-

vimento e manual de identificação. EDUEM.

Neumann, E., Paes, M. C. F., Mendes, J. M. R., Braga, F. M.

S., & Nakaghi, L. S. O. (2018). Larval development

of Brycon amazonicus (Teleostei, Bryconidae) with a

focus on locomotory, respiratory and feeding structu-

res. Journal of Fish Biology, 93(6), 1141–1150. https://

doi.org/10.1111/jfb.13832

Nowosad, J., Kupren, K., Biegaj, M., & Kucharczyk, D.

(2021). Allometric and ontogenetic larval develop-

ment of common barbel during rearing under opti-

mal conditions. Animal, 15(2), 100107. https://doi.

org/10.1016/j.animal.2020.100107

Oliveira, L. S., Cajado, R. A., Silva, F. K. S., Bialetzki, A., &

Zacardi, D. M. (2021). Larval development of the fres-

hwater croaker Pachypops fourcroi (La Cépède 1802)

(Perciformes: Sciaenidae). Journal of Fish Biology,

99(6), 2056–2059. https://doi.org/10.1111/jfb.14894

Paes, M. C. F., Makino, L. C., Vasquez, L. A., Kochen-

borger-Fernandes, J. B., & Nakaghi, L. S. O. (2011).

Early development of Astronotus ocellatus under ste-

reomicroscopy and scanning electron microscopy.

Zygote, 20(3), 269–276. http://dx.doi.org/10.1017/

S0967199411000116

Papadakis, I. E., Kentouri, M., Divanach, P., & Mylonas, C. C.

(2018). Ontogeny of the eye of meagre (Argyrosomus

regius) from hatching to juvenile and implications to

commercial larval rearing. Aquaculture, 484, 32–43.

https://doi.org/10.1016/j.aquaculture.2017.10.038

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 74: e20264330, enero-diciembre 2026 (Publicado Feb. 25, 2026)

Pepe-Victoriano, R., Miranda, L., Ortega, A., & Merino,

G. E. (2021). Descriptive morphology and allometric

growth of the larval development of Sarda chiliensis

chiliensis (Cuvier, 1832) in a hatchery in northern

Chile. Aquaculture Reports, 19, 100576. https://doi.

org/10.1016/j.aqrep.2020.100576

Perrotti, P. B., Abdo, T. F., Meireles, W. A., Marcon, L., &

Bazzoli, N. (2019). Ontogenesis and embryogenesis

of Megaleporinus elongatus larvae (Characiformes:

Anostomidae) from the Jequitinhonha River basin.

Journal of Applied Ichthyology, 35(2), 520–528. https://

doi.org/10.1111/jai.13837

Portella, M. C., Jomori, R. K., Leitão, N. J., Menossi, O. C.

C., Freitas, T. M., Kojima, J. T., Lopes, T. S., Clavijo-

Ayala, J. A., & Carneiro, D. J. (2014). Larval develop-

ment of indigenous South American freshwater fish

species, with particular reference to pacu (Piaractus

mesopotamicus): A review. Aquaculture, 432, 402–417.

https://doi.org/10.1016/j.aquaculture.2014.04.032

Reynalte-Tataje, D. A., Lopes, C. A., Massaro, M. V.,

Hartmann, P. B., Sulzbacher, R., dos-Santos, J. A.,

& Bialetzki, A. (2020). State of the art of identifica-

tion of eggs and larvae of freshwater fish in Brazil.

Acta Limnologica Brasiliensia, 32(1), e6. http://dx.doi.

org/10.1590/s2179-975x5319

Reynalte-Tataje, D., Zaniboni–Filho, E., & Esquivel, J.

R. (2004). Embryonic and larvae development of

piracanjuba, Brycon orbignyanus Valenciennes, 1849

(Pisces, Characidae). Acta Scientiarum. Biological

Sciences, 26(1), 67–71.

Rizzo, E., & Godinho, H. P. (2003). Superfície de ovos de

peixes Characiformes e Siluriformes. In H. P. Godin-

ho, & A. L. Godinho (Eds.), Águas, peixes e pescado-

res do São Francisco das Minas Gerais (pp. 115–132).

Pontificia Universidade Católica de Minas Gerais.

Romig, T. (1995). Ryby akwariowe. Multico.

Rønnestad, I., Yúfera, M., Ueberschär, B., Ribeiro, L., Sæle,

Ø., & Boglione, C. (2013). Feeding behaviour and

digestive physiology in larval fish: Current knowled-

ge, and gaps and bottlenecks in research. Reviews in

Aquaculture, 5(S1), S59–S98. https://doi.org/10.1111/

raq.12010

Saemi-Komsari, M., Mousavi-Sabet, H., Kratochwil, C. F.,

Sattari, M., Eagderi, S., & Meyer, A. (2018). Early

developmental and allometric patterns in the electric

yellow cichlid Labidochromis caeruleus. Journal of

Fish Biology, 92(6), 1888–1901.

Santamaria, C. A., de Mateo, M. M., Traveset, R., Sala,

R., Grau, A., Pastor, E., Sarasquete, C., & Crespo, S.

(2004). Larval organogenesis in common dentex Den-

tex dentex L. (Sparidae): Histological and histochemi-

cal aspects. Aquaculture, 237(1–4), 207–228. https://

doi.org/10.1016/j.aquaculture.2004.03.020

Santos, J. A., Soares, C. M., & Bialetzki, A. (2020). Early

ontogeny of yellowtail tetra fish Astyanax lacustris

(Characiformes: Characidae). Aquaculture Research,

51(10), 4030–4042. https://doi.org/10.1111/are.14746

Silva, F. K., Cajado, R. A., Oliveira, L. S., Ribeiro, F. R. V.,

& Zacardi, D. M. (2021). Early ontogeny of Pimelodus

blochii Valenciennes, 1840 (Siluriformes: Pimelodi-

dae): Neotropical catfish. Zootaxa, 4948(1), 83–98.

https://doi.org/10.11646/zootaxa.4948.1.4

Silva, L. V. F. (2004, August 1-5). Morphology and early

development of silver catfish, Rhamdia quelen, (Silu-

riforme, Pimelodidae) embryos and larvae. In D.

MacKinlay (Ed.), Physiology of fish eggs and larvae

symposium proceedings [Symposium]. International

Congress on the Biology of Fish.

Song, Y., Cheng, F., Zhao, S., & Xie, S. (2019). Ontogene-

tic development and otolith microstructure in the

larval and juvenile stages of mandarin fish Siniperca

chuatsi. Ichthyological Research, 66, 57–66. https://doi.

org/10.1007/s10228-018-0648-1

Souza da Silva, F. K., Cajado, R. A., Silva-de-Oliveira, L.,

dos Santos, Z., dos Santos, J. A., Silva, L., Garcez,

R., & Zacardi, D. M. (2022). Early development of

Prochilodus nigricans Spix & Agassiz 1829 (Cha-

raciformes: Prochilodontidae) in captivity. Aqua-

culture Research, 53(12), 4540–4555. http://dx.doi.

org/10.1111/are.15951

Stevanato, D. J., & Ostrensky, A. (2018). Ontogenetic deve-

lopment of tetra Astyanax lacustris (Characiformes:

Characidae). Neotropical Ichthyology, 16(2), e170073.

https://doi.org/10.1590/1982-0224-20170073

Thompson, K. L., Faulk, C. K., & Fuiman, L. A. (2019).

Applying the ontogeny of digestive enzyme activity

to guide early weaning of pigfish, Orthopristis chry-

soptera (L.). Aquaculture Research, 50(5), 1404–1410.

https://doi.org/10.1111/are.14015

Tropical Fish Hobbyist Magazine. (2007, December). Spe-

cies profiles: Hyphessobrycon herbertaxelrodi.

Urho, L. (2002). Characters of larvae - What are they? Folia

Zoologica, 51(2), 161–186.

Yang, R., Xie, C., Fan, Q., Gao, C., & Fang, L. (2010). Onto-

geny of the digestive tract in yellow catfish Pelteobagrus

fulvidraco larvae. Aquaculture, 302(1–2), 112–123.

https://doi.org/10.1016/j.aquaculture.2010.02.020

Zadmajid, V., Sørensen, S. R., & Butts, I. A. E. (2019).

Embryogenesis and early larval development in wild

caught Levantine scraper, Capoeta damascina (Valen-

ciennes, 1842). Journal of Morphology, 280, 133–148.

https://doi.org/10.1002/jmor.20926