Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

Age and growth assessment of the near-threatened fish Rita rita (Siluriformes:

Bagridae) in the Ganges basin

Ankita Ankita1; https://orcid.org/0000-0002-3455-3557

M. Afzal Khan1*; https://orcid.org/0000-0002-8197-4311

Salman Khan1,2; https://orcid.org/0000-0001-9651-2657

1. Fish Biology and Otolith Research Laboratory, Department of Zoology, Aligarh Muslim University, India;

khanmafzal@yahoo.com (*Correspondence); ankitaverma0405@gmail.com

2. School of Life Science and Technology, Department of Zoology, IIMT University, India; sksalman21@gmail.com

Received 11-VII-2022. Corrected 03-XI-2022. Accepted 01-II-2023.

ABSTRACT

Introduction: Rita rita is a freshwater catfish under threat of extinction, mainly from loss of breeding and nurs-

ing grounds. A reliable method for age and growth estimation is needed by fishery managers.

Objective: To identify the best body structure for age and growth estimation.

Methods: We assessed estimates precision based on Average Percent Error (APE), Coefficient Variation (CV),

and Percent Agreement (PA) between readers separately analyzed each calcified structure. We used 390 fish

samples from three rivers, Ganga, Yamuna and Ramganga, from September 2018 to August 2019.

Results: The three indicators favored the use of vertebrae for age estimation; the growth band seems to be annual

and formed from May to September. The growth equations were Lt = 90.19(1-e-0.145(t+0.51)) for Ganga; Lt = 91.19

(1-e-0.14(t+0.59)) for Yamuna and Lt = 89.63 (1-e-0.15(t+0.68)) for Ramganga.

Conclusion: This species reaches moderate growth in these rivers, where vertebrae are the recommended age

estimation structure, followed, in case of need, by sectioned otoliths, whole otoliths and opercular bones. Pectoral

spines should be avoided, especially in older fish.

Key words: vertebrae; otoliths; ageing precision; VBGF; Marginal Increment Analysis.

RESUMEN

Edad y crecimiento del pez casi amenazado Rita rita (Siluriformes: Bagridae) en la cuenca del Ganges

Introducción: Rita rita es un pez de agua dulce bajo amenaza de extinción, principalmente por la pérdida de

sitios de reproducción y crianza. Un método fiable para las estimaciones de edad y crecimiento es necesario para

los administradores de recursos pesqueros.

Objetivo: Identificar la mejor estructura corporal para estimaciones de edad y crecimiento.

Métodos: Evaluamos la precisión de las estimaciones mediante el Porcentaje de Error Promedio (APE),

Coeficiente de Variación (CV), y Porcentaje de Acuerdo (PA) entre lecturas para cada estructura calcificada.

Usamos 390 muestras de peces de tres ríos, Ganga, Yamuna y Ramganga, de setiembre 2018 hasta agosto 2019.

Resultados: Los tres indicadores favorecieron el uso de vértebras para la estimación de edad; la banda de

crecimiento parece ser anual y se forma entre mayo y setiembre. Las ecuaciones de crecimiento fueron

Lt = 90.19(1-e-0.145(t+0.51)) para Ganga; Lt = 91.19 (1-e-0.14(t+0.59)) para Yamuna y Lt = 89.63 (1-e-0.15(t+0.68))

para Ramganga.

https://doi.org/10.15517/rev.biol.trop..v71i1.51734

AQUATIC ECOLOGY

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

INTRODUCTION

Rita rita (Hamilton, 1822) belongs to the

family Bagridae, which is distributed in the

freshwaters of India as well as many other

countries in the Asian continent. The target fish

species has high market value on account of its

consumer preference, nutritional value, orna-

mental value and palatability (Gupta & Baner-

jee, 2014; Mohanty et al., 2015). There has been

only one report (Tamubi et al., 1990) on the

age and growth characteristics of this species,

wherein no consideration of precision of age

estimates was taken into account. Molur and

Walker (1998) categorised it as a threatened

fish of the Indian subcontinent and suggested

that it could face the risk of extinction mainly

due to overfishing and loss of breeding sites.

Bangladesh, The International Union for Con-

servation of Nature (IUCN) (2015) categorizes

fish as endangered in Bangladesh but globally

as Least Concern. Therefore, the population of

Rita rita should be scientifically managed and

protected by undertaking suitable measures.

Age estimation of fish is a necessary first

step in age-based fish population assessment

and successful resource management (Maceina

& Sammons, 2006). The ability to obtain precise

age estimates is critical for estimating dynamic

rate functions like mortality and recruitment

(Khan & Khan, 2020). A precision measure is

important for evaluating the relative simplicity

of determining the age of a given hard struc-

ture, examining the reliability of an individual’s

age estimations, and measuring the ager’s level

of skill relative to others (Campana, 2001). By

incorporating a validation method, errors in

estimating the age of fish can be minimized.

There is an alternative validation technique i.e.,

comparing the age estimates between differ-

ent hard anatomical structures that potentially

provide valuable insights into the accuracy and

inaccuracy of age-estimating structures (Sylves-

ter & Berry Jr, 2006).

Researchers have compared age enumer-

ated from different hard structures in fresh-

water fishes such as Channa punctata (Khan

et al., 2013), Labeo bata (Khan et al., 2015), C.

striata (Khan et al., 2017), Sperata aor (Nazir

& Khan, 2020), Leuciscus vorax (Rashid &

Basusta, 2021), Cycleptus elongatus (Radford

et al., 2021), Salvelinus namaycush (Osborne

et al., 2022) to quantify precision and detect

biasesrelated to each structure.

Amongst several methods available to vali-

date fish age interpretations (Campana, 2001),

Marginal Increment Analysis (MIA) is one of

the extensively utilized methods (Campana,

2001). This technique is based on the notion

that growth rings are produced annually, and

the width of the outer ring will depict an

annual sinusoidal cycle if plotted against the

month of capture. (Campana, 2001; Okamura

et al., 2013).

Age estimation in several fish species has

been validated using MIA for example, Merluc-

cius hubbsi (Costa et al., 2018); Brachyplatys-

toma rousseauxii (Hauser et al., 2018). Several

studies have successfully used the von Bertalanffy

Growth Function model (VBGF) to estimate

growth in a variety of fish species, such as Schizo-

pyge niger, S. curvifrons and Schizothorax esocinus

(Sabah & Khan, 2014), Channa punctata (Khan

et al., 2019), Gerres subfasciatus (Gray, 2019),

Catla catla (Brraich & Kaur, 2022). The basic

biological information required to devise sci-

entifically sound management policies for the

Rita rita population remains warranted, par-

ticularly those involving precise age estimation

and growth trends under changing conditions

across all of the fish’s primary habitats. Otoliths

have previously been used to investigate age

and growth studies in Rita rita (Tamubi et al.,

Conclusión: La especie alcanza un crecimiento moderado en estos ríos, dónde las vértebras son la estructura de

estimación etaria recomendada, seguido de, en caso de ser necesario, los otolitos segmentados, otolitos enteros y

huesos operculares. Debe evitarse el uso de espinas pectorales, especialmente en peces de mayor edad.

Palabras clave: vértebras; otolitos; precisión de la edad; VBGF; Análisis del Incremento Marginal.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

1990) however, there is no information avail-

able on the precision of its hard structure for

age estimation.

Therefore, this study was undertaken to

assess age estimates derived from various hard

(calcified) structures (vertebrae, sectioned

otoliths, whole otoliths, opercular bones and

pectoral spines) to identify the best structure

determining accurate age estimate in Rita rita;

the annulus formation was validated using

MIA, and the VBGF equation was developed

using length-at-age data from the structure giv-

ing precise age estimate.

MATERIALS AND METHODS

Sample collection: A total of 390 fish

samples of Rita rita were collected on a monthly

basis during the period September 2018 to

August 2019 from Narora site (28°19’68” N

& 78°38’14” E) of River Ganga, Mathura site

(27°49’24” N & 77°67’37” E) of River Yamuna

and Moradabad site (28°83’86” N & 78°77’33”

E) of River Ramganga (Fig. 1). Fish identifica-

tion was done according to Talwar and Jhingran

(1991). To the nearest centimeter, the total

length (TL) was measured. The total weight

(TW), which includes the gut and gonads, was

measured to the nearest gram. Otoliths, oper-

cular bones, vertebrae and pectoral spines were

extracted from the fish and prepared for age-

ing according to the protocols standardized by

Fish biology and Otolith Research Laboratory

(Khan & Khan, 2009; Khan et al., 2013; Khan

et al., 2017; Sabah & Khan, 2014). Otoliths

were sectioned according to Khan et al. (2016).

For sectioning, the other otolith of a pair

was embedded in silicon moulds consisting of

(Epothin TM Epoxy Resin and Epothin® Epoxy

Hardener in a 5:2 ratio) which were lightly

coated with release agent and allowed to solid-

ify overnight for the media to harden. Otoliths

Fig. 1. Map showing the collection sites of Rita rita from the River Ganga and its tributaries: River Yamuna and River

Ramganga.

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

were sectioned by using IsoMet® Low Speed

Saw (Buehler, 41 Waukegan Road, Lake Bluff,

Illinois-60044, USA) and after that each sec-

tion was polished using 1 200-grit CarbiMet®

2 Abrasive Discs on an otolith polisher, which

has been designed and developed in Fish biol-

ogy and Otolith Research Laboratory. A Nikon®

SMZ745T stereo zoom microscope was used to

analyze all the ageing structures. Two readers

separately analyzed each calcified structure. A

year’s growth was defined as an opaque and

translucent zone combined; age was defined by

the number of translucent zones.

Statistical analysis and calculations: The

average per cent error (APE), coefficient of

variation (CV), and per cent agreement (PA)

between the readers and the pair of ageing

structures were calculated to compare age esti-

mates from different hard anatomical struc-

tures. APE was calculated as per the formula

given by Beamish and Fournier (1981).

Where in xij represents the ith age estimation of

the jth fish, xj refers to the computed mean age

for the jth fish, and R denotes the frequency of

ageing for each fish.

The coefficient of variation was deter-

mined as the ratio of standard deviation over

the mean (Campana, 2001):

Where CVj is the coefficient of variation for the

jth fish.

Campana (2001) suggested APE and CV

to be reliable parameters for precise age esti-

mation in fish. While determining the most

suitable method for precise age estimation, PA

has been used as one of the precision param-

eters (Sabah & Khan, 2014). The percentage

of observations having similar age estimates

divided by the total number of observations

on age estimates is defined as percent agree-

ment. Percent agreement was calculated using

the template for ageing precision (Sutherland,

2006). A post- hoc test, Duncan’s Multiple Range

Test (Gomez & Gomez, 1984), was used to

determine variations in mean age readings from

different ageing structures (Khan & Khan, 2009).

Marginal Increment Analysis: Annulus

formation on vertebrae was validated by Mar-

ginal Increment Analysis using the equation:

R is the otolith radius, Rn is the last complete

growth ring radius, and Rn-1 is the previously

completed growth ring radius. Image analysis

software was used to take measurements from

the focus to the outer edge of each growth ring

(Rn). To demonstrate periodic trends in annu-

lus development, monthly mean MIR values

were plotted (Lessa et al., 2006).

Growth analysis: To evaluate variability

in growth, length-at-age data collected from

vertebrae (the most appropriate ageing struc-

ture in Rita rita) was used to develop the VBGF

equation (Ricker, 1975) by using non-linear

least-squares regression:

Where, Lt= total length (cm) of fish at age t; L∞

= asymptotic mean length; k = rate constant

that determines the rate at which Lt approaches

L∞; t = time or age of the fish; t0 = the hypotheti-

cal age at which the fish had zero length.

Comparison between observed and cal-

culated mean length-at-age was verified with

student’s t-test (Zar, 1996) for the selected fish

species. Growth parameters were estimated

using the non-linear regression method in a

Microsoft Excel-based application developed

by Cope and Punt (2007).

RESULTS

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

The sample size, minimum and maxi-

mum total length, used in the ageing precision

for the selected fish species are presented in

Table 1. The vertebrae in Rita rita provided a

precise age estimate. It exhibited the least APE

(1.54 %) and CV (3.17 %) values followed by

sectioned otoliths, whole otoliths, opercular

bones and sectioned pectoral spines (Table 2).

The vertebrae had the highest percentage of

reader agreement (Table 2). A comparison of

vertebrae age estimates was analyzed with those

from other structures (i.e., sectioned otoliths,

opercular bone, whole otoliths and sectioned

pectoral spines) suggested the least variation

between vertebrae vs sectioned otoliths age

estimates followed by vertebrae vs opercular

bone, vertebrae vs whole otoliths and vertebrae

vs sectioned pectoral spine (Table 2).

Mean age readings from vertebrae were

significantly (P < 0.05) different from pectoral

spines but similar (P > 0.05) to the age estimates

from sectioned otoliths, whole otoliths and

opercular bones. Thus, in the absence of the

most appropriate age estimate (vertebrae), we

may use age data from sectioned otoliths, whole

otoliths and opercular bones but the use of pec-

toral spines may be avoided to the maximum

possible extent (Table 3).

The von Bertalanffy growth model was fit

using the ages estimated from vertebrae. The von

Bertalanffy growth parameters of Rita rita from

the three rivers are presented in Table 4. Readabil-

ity scores presented in Table 5 showed that ver-

tebrae had the highest readability score (64.1)

followed by sectioned otoliths (56.41), whole

otoliths (41), opercular bones (14.36) and sec-

tioned pectoral spines (2.05). Fig. 2 shows the

number of specimens in each age group in all

the studied rivers. The age group 3 and 4 were

most dominant in the sampling from all three

rivers while a smaller number of samples were

found in age group 7. Ageing structures in

Rita rita vertebrae, sectioned otoliths, whole

otoliths, opercular bones, and sectioned pecto-

ral spines are shown in Fig. 3. Age bias graphs

between vertebral age estimations and each of the

other ageing structures are shown in Fig. 4.

Marginal Increment Analysis has been

used to validate age estimation in the target

fish species. The monthly mean of Marginal

Increment Ratio (MIR) declined from a high-

est of 1.02 in March to the lowest of 0.32 in

July (Fig. 5). The results of MIR revealed that

the annulus formation occurred from May to

September (Fig. 5). The proportion of opaque

Table 1

Estimated parameters of Rita rita collected from the

selected rivers.

Rivers Sample size TL Range (cm) Mean (cm)

Ganga 140 9.3 - 57.2 36.4

Yam u n a 120 10.2 - 56.1 33.6

Ramganga 130 9.8 - 54.4 34.2

TL: Total length.

Table 2

Measures of precision in Rita rita.

Ageing structures APE CV PA

Ver tebr ae 1.54 3.17 88.3

Sectioned otoliths 1.61 3.51 86.8

Whole otoliths 2.06 4.10 84.6

Opercular bones 3.38 6.12 80.2

Pectoral spines 5.40 8.44 76.3

Between structures

Vertebrae- sectioned otoliths 1.66 3.38 87.2

Vertebrae - whole otoliths 2.00 3.83 85.4

Vertebrae - opercular bones 3.53 5.65 81.9

Vertebrae–pectoral spines 5.93 7.52 79.0

PA: Percentage of Agreement, APE: Average Percentage

Error, and CV: Coefficient of Variation (CV).

Table 3

Comparison of mean values of age estimates from different

hard structures in Rita rita.

Ageing Structures Mean values of age estimates

Ver tebr ae 4.4223b

Sectioned otoliths 4.2896b

Whole otoliths 3.9918ab

Opercular bones 3.1854ab

Pectoral spines 2.876a

*Values having similar superscripts are insignificantly

different (P > 0.05) from each other.

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

bands on vertebrae increased regularly from

August to March and then decreased from

April to July. These results suggest that the

narrow translucent band formed during the

monsoon season (May to September) and the

wide opaque band formed during the rest of

the months.

The von Bertalanffy growth function equa-

tions derived using length at age data of verte-

brae of Rita rita were Lt = 90.19(1-e-0.145(t+0.51))

for River Ganga; Lt = 91.19 (1-e-0.14(t+0.59)) for

River Yamuna; Lt = 89.63 (1-e-0.15(t+0.68)) for

River Ramganga. There were no significant

variations between Rita rita’s calculated and

observed lengths of the River Ganga (R2 =

0.9781; d.f. = 6, P > 0.05), River Yamuna (R2 =

0.9686; d.f. = 6, P > 0.05) and River Ramganga

(R2 = 0.9731; d.f. = 6, P > 0.05) The von Berta-

lanffy growth curves of Rita rita from the three

rivers: River Ganga, River Yamuna and River

Ramganga showed significant differences (P <

0.05) with each other (Fig. 6).

DISCUSSION

In this study, the vertebrae of Rita rita

showed regularly formed annual rings, which

were clear to count, compared to other hard

anatomical structures (whole otoliths, sectioned

otoliths, opercular bones, pectoral spines). Our

Table 4

von Bertalanffy growth parameters in Rita rita collected from the Gangetic River System.

Species Selected rivers Sampling sites Ageing structures used L∞ (cm) k t 0Max. Age (years)

Rita rita Ganga Narora Vertebrae 90.19 0.145 0.51 7

Rita rita Yamu n a Mathura Vertebrae 91.19 0.14 0.59 7

Rita rita Ramganga Moradabad Vertebrae 89.63 0.15 0.61 7

Fig. 2. Number of individuals in each age group from the three rivers: Ganga, Yamuna and Ramganga.

Table 5

Distribution of readability scores for different hard structures in Rita rita.

Readability score 12345

Ver tebr ae 7.69 64.1 15.38 8.97 3.85

Sectioned otoliths 5.64 56.41 16.4 12.31 9.23

Whole otoliths 3.08 41 11.03 18.97 25.9

Opercular bones 1.79 14.36 4.62 30.77 48.46

Sectioned pectoral spines 2.05 6.15 40 51.79

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

results corroborate with the findings of Li and

Xie (2008) that in Siluriformes fishes, the best

ageing structure is vertebrae that were easy to

process and exhibited regularly formed clear

rings. Precise age estimation using vertebrae

has been reported in a variety of freshwater

fishes, such as Heteropneustes fossilis (Khan

et al., 2013), Schizothorax esocinus (Sabah &

Khan, 2014), Mastacembelus armatus, and

Ompok pabda (Khan et al., 2015), Capoeta

banarescui (Bostanci et al., 2015), S. aor (Nazir

& Khan, 2020).

Next to vertebrae, otoliths provided better

age estimates than other ageing structures. Sec-

tioned otoliths after polishing exhibited clearer

annuli as compared to whole otoliths and there-

by requiring less effort and time by the readers

to estimate age. Several studies reported sec-

tioned otoliths to provide precise age estimates

in Paralichthys dentatus (Sipe & Chittenden,

Fig. 3. Ageing structures in Rita rita A. vertebrae, B. sectioned otoliths, C. whole otoliths, D. opercular bones and E. sectioned

pectoral spines. Scale bar: 1 mm.

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

2001), C. striata (Khan et al., 2017). Because

of its distinctive attributes of being metaboli-

cally inert, otoliths are usually utilized as an

ageing structure, not showing reabsorption and

exhibiting acellular growth throughout fish life.

(Phelps et al., 2007).

Whole otoliths in Rita rita did not show

distinct annuli because whole otoliths are thick

at the center which reduces the clarity of growth

lines. As a result, the opaque rings on otoliths

could not be distinguished clearly. Since fish

growth shows declining trends with age, the

annuli come closer to each other near the edges

of the ageing structures and hence it becomes

difficult to distinguish annuli in small and thick

whole otoliths used in this study. Whole otoliths

underestimated the fish age compared to ver-

tebrae, opercular bones, and sectioned otoliths.

There are several findings in support of our study

that the use of whole otoliths rather than sec-

tioned otoliths can lead to an underestimation of

Fig. 4. Age bias graphs for Rita rita between two independent readers: A. vertebrae, B. sectioned otoliths, C. whole otoliths,

D. opercular bones and E. pectoral spines. Each error bar represents the 95 % confidence interval, and the solid line

indicates the theoretical 1:1 agreement line of age estimates between readers. Points above the line indicate ages that were

overestimated, whereas points below the line indicate ages that were underestimated.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

fish age (Abecasis et al., 2006; Khan et al., 2016;

Khan et al., 2017).

Khan et al. (2016) reported that the use of

the whole otolith in S. aor may underestimate

the age because growth rings in older individuals

were not clear enough to read because of curved

edges, and the zones across the edges became

dense and thus harder to distinguish the growth

rings. In the current study, opercular bones were

found to be inferior to other calcified struc-

tures (vertebrae, sectioned otoliths, and whole

otoliths) to age Rita rita. It was very difficult

to assess the age of the fish using opercular

bones because annual rings were poorly defined

and irreconcilable.

According to several studies, opercular

bones may overlook the fish age due to its thick-

ness at the base and this thickening continues

into spongy tissue, making the very first and/or

subsequent annuli less noticeable. (Ma et al.,

2011; Zhiming et al., 2018). Opercular bones

were found to be less accurate in a variety of

fish species when compared to other structures

such as scales and otoliths in Labeo rohita and C.

marulius (Khan & Khan, 2009), otoliths and ver-

tebrae in Schizothorax oconnori (Ma et al., 2011).

Fig. 5. Monthly mean marginal increment ratio for Rita rita vertebrae with 1-7 annuli.

Fig. 6. The von Bertalanffy growth curves for Rita rita population sampled from the Ramganga River, Yamuna River and

Ganga River showing significant differences (P < 0.05).

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

In this study, pectoral spines showed less

clarity to identify and read annuli as compared

to other ageing structures in Rita rita. They had

the minimum PA and maximum APE and CV

values among readers. Our results corroborated

with those of previous reports since the pectoral

spine continually overlooks the age of the fish

because of its nucleus that might be absorbed

and replaced by a hole (vascularization). As fish

age, its central lumen gets enlarged because of

the increased number of vascularized tissues and

its structure changes with age, thus eroding early

growth increments (McFarlane & King, 2001). If

initial growth rings were not identified correctly

then it leads to an underestimation of the age and

thereby causes an overestimation of growth and

natural mortality coefficients, which can have

serious consequences for fish stock management

and policy-making (Casey & Natanson, 1992).

Our results are in agreement with other studies

that have noted complications in the analyses

of annuli working with the pectoral spines in

fishes for example Ictalurus punctatus and Pylo-

dictis olivaris (Crumpton et al., 1987), and S. aor

(Nazir & Khan, 2020).

Validation of the age estimates in Rita

rita was done by MIA on vertebrae. There are

several causes of annuli formation in fish such

as water temperature, light exposure, metabo-

lism, endocrine, feeding, reproduction and the

environment (Morales-Nin & Panfili, 2005).

Spawning seems to be related to the formation

of growth checks on the vertebrae of Rita rita.

the mating season in Rita rita is from May to

September, with spawning maxima in June and

September in River Ganga which appears to

be coincident with the annulus formation as

shown in this study (Alam et al., 2016).

Slow-growing species had k values of

0.05-0.10/year, moderate-growing species had

0.10-0.20/year, and fast-growing species had

0.20-0.50/year, according to Branstetter (1987).

The value of k computed for Rita rita from the

three rivers was in the range of 0.12-0.15/year

indicating a modest growth rate. A high meta-

bolic rate is indicated by a high k value, and such

fish mature at a young age or a large size to their

asymptotic length (Qasim, 1973). Because there

were fewer large specimens in this study, the L∞

value of Rita rita was larger than the maximum

observed length. The growth coefficient (k) is a

valuable metric for measuring fish vulnerability

to depletion as well as comparing life history

methods (Musick, 1999). The absence of very

young or very old individuals has a significant

impact on growth model estimations (Ma et al.,

2010). The computed value of L∞ in Rita rita

was 90.19, 91.19 and 89.63 for the River Ganga,

River Yamuna and River Ramganga, respectively.

Sabah and Khan (2014) found a higher value of

L∞ than the recorded maximum length, which

was likely due to the small number of large speci-

mens (Karlou-Riga & Sinis, 1997). In the cur-

rent study, the estimate of t0 ranged from -0.96

to -1.18, which is an excellent predictor of the

accuracy of the estimated ages (Kerstan, 1985).

Sparre and Venema (1998) reported that growth

parameters varied from species to species, even

in the same species and also from different stocks

due to differing environmental conditions such

as temperature, water quality, food availability,

etc. Low temperatures can reduce the growth rate

of ectotherms (Angilletta Jr et al., 2004).

The age group 2, 3, and 4 were dominant

age classes, and these age classes were exploited

more by the fishermen. After these age groups,

exploitation decreased with the increase in the

age of fish. Net size and mesh size is an impor-

tant factor for the capture of fish. Generally,

fishermen use nets having small to moderate

mesh size. This form of fishing has an impact

on juvenile and brooder stocks. The number of

juvenile and brooder samples should be greater

than the number of middle age class samples for

healthy stock and heavy recruitment (Dwivedi

et al., 2017). Since the length at first maturity

of Rita rita is reported to be 29.5 cm (Saxena,

1972), the fish population in the present study

appears to be dominated by broodstocks. The

status of the age structure is an important indi-

cator of how fished populations are responding

to fishing pressures and stressors (Sarkar et al.,

2006). The findings of the present study may

be utilized for devising scientific and efficient

strategies for the management of Rita rita fish

species inhabiting the rivers, Ganga, Yamuna,

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71: e51734, enero-diciembre 2023 (Publicado Feb. 22, 2023)

and Ramganga. To ensure the species’ long-term

viability, suitable management measures must be

established.

Ethical statement: the authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict 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 acknowledgements sec-

tion. A signed document has been filed in the

journal archives.

ACKNOWLEDGMENTS

We thank the Chairman of the Department

of Zoology, Aligarh Muslim University, Aligarh,

India, for providing the necessary facilities for

the study. The first author is also thankful to the

University Grants Commission (UGC), New

Delhi for providing the financial support as a

UGC Non-Net fellowship.

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