Sexual Maturity and Relative Growth of the Critically Endangered Catfish Eutropiichthys vacha (Hamilton, 1822) (Siluriformes: Schilbeidae) in the Padma (Main tributary of the Ganges) River Northwestern Bangladesh

Posted on 11th Oct 2024 03:04:36 PM Fisheries


INTRODUCTION

Fisheries sector plays an important role in employment, nutrition, foreign exchange earnings and other aspects of the economy for Bangladesh (Alam and Thomson, 2001). Fish is a natural complement to rice in the national diet, giving rise to the adage Mache-Bhate Bangali (“a Bengali is made of fish and rice”): fish alone supplies about 60% of animal protein intake (Ahmed et al., 1997). The fisheries sector provides full-time employment to an estimated 2 million fishermen, small fish traders, fish transporters and packers, etc. (World Bank, 1989), and another 10 million people are partly dependent on fishing, e.g. part-time fishing for family subsistence (BFRSS, 1986). The sector contributes about 5% of GDP (Ali, 1998), 14% of Gross Agricultural Product (Amin, 1998) and about Tk.18 billion (9%) of export earnings, of which frozen shrimp constitutes about 82% while the rest are fish and other aquatic products such as frogs’ legs, shark and shark fins (Banik and Humayun, 1998). Fisheries exports comprise frozen shrimp, frozen frogs’ legs, frozen fish, dry fish, salted and dehydrated fish, turtles, tortoises and crabs, and shark fin and fish maws. Most of these products are coming from wild stocks. The foreign currency from wild fish and shell-fishes exporting has been decreased in recent years due to natural and man-made causes. 

The protection of threatened fish species is an important issue in today’s scientist society. Information on the life-history traits of threatened fishes is crucial to the implementation of proper management strategies for conserving the critically endangered commercially important fish like Eutropiichthys vacha (Hamilton, 1822), whose spawning aggregations are heavily exploited by local small- and large-scale fishers (Hossain et al., 2009a). 

The small fish E. vacha (Siluriformes: Schilbeidae) is a freshwater and brackish-water subtropical species which is commonly known as ‘River catfish’. This fish is also known as Bacha in Bangladesh (Rahman, 1989), Batchwa vacha in India (Talwar and Jhingran, 1991), Cherki in Nepal (Shrestha, 1994), and Challi in Pakistan (Soomro et al., 2007). The conservational status of this fish has been referred as critically endanger in Bangladesh (IUCN Bangladesh, 2000), and endangered in India (Lakra et al., 2010). In addition, Mijkherjee et al. (2002) reported E. vacha as vulnerable species and predicted that, the species will disappear from their natural habitat in West Bengal. It is a commercially important food fish in Asian countries and has gained popularity among consumers due to its high nutritional value and good taste (Hasan et al., 2002). The river catfish is an important target species for small scale fishermen in Bangladesh, who use a variety of traditional fishing gears (Hossain, 2010a). It is also a major source of animal protein and micronutrients in the diet of rural small-scale farmers (Hossain et al., 2009a). 

This fish is widely distributed through the Indian sub-continent including Bangladesh, India, Pakistan, Nepal, Myanmar, and Thailand (Talwar and Jhingran, 1991). The river catfish inhabits standing and running waters, usually in tanks, streams, rivers, and lagoon with mostly muddy bottoms (Froese and Pauly, 2011). Previously abundant in the rivers, streams, canals, reservoirs, lakes, swampland (beels, haors, and baors) and ponds of Bangladesh (IUCN Bangladesh, 2000), India and Pakistan (Froese and Pauly, 2011), but the populations have seriously declined or verge of extinction due to over exploitation and various ecological changes in its natural habits (Mijkherjee et al. 2002). Furthermore, in a recent study, Mishra et al. (2009) reported that overfishing is a potential major threat as this species is heavily utilized as a food fish, and they recorded a mean decline of 29.2% in wild catch in southern West Bengal for the period 1960-2000. However, IUCN Bangladesh (2000) identified habitat loss as a major threat to this species; though, this does not appear to be supported by any empirical data. Moreover, the culture practices of this species are not existing so far and the total demand for this fish in the domestic market is met through capture from wild populations; thus, the effective management of wild stocks is critical (Mishra et al., 2009). 

Successful fisheries management relies on understanding the regenerative ability of fish populations and having an accurate assessment of biological parameters, including reproductive traits (e.g., size and age at maturity) (Tracey et al., 2007). Determining the size at first sexual maturity in fish is important not only for distinguishing between different populations of the same species, but also principally for establishing a basis for later estimation whether eventual changes in length at first maturity are because of fisheries pressure or other reasons (Templeman, 1987). In addition, maturity size is of special interest in fisheries management and is widely used as an indicator of minimum permissible capture size (Lucifora et al., 1999).  

LWRs are effective in fishery assessments for predicting (i) length distributions into weights for biomass estimates (Gerritsen and McGrath, 2007), and (ii) a cost-effective alternative to direct, field-based weight measurements that can be time-consuming (Koutrakis and Tsikliras, 2003). Moreover, LWR parameters are important to assess fish-stock condition, etc. (Gonzalez Acosta et al., 2004). Indeed, an aquatic animal’s condition reflects recent environmental (physicochemical and biotic) circumstances, as it fluctuates by interaction among feeding conditions, parasitic infections, and physiological factors (Le Cren, 1951).

To my knowledge, biological traits such as size at first sexual maturity, length-weight relationships (LWRs), and condition factors are quite insufficinet for critically endangered fishes, nevertheless, a number of studies on biology, life history characteristics and conservation of many threatened species of Bangladesh are well documented (IUCN Bangladesh, 2000; Hossain et al., 2006a; 2006b; 2008; 2009a; 2009b; 2009c; Hossain, 2010a; 2010b). Furthermore, the natural populations of E. vacha are seriously decreasing due to high fishing pressure, leading to an alarming condition. Detailed information on the population structure of E. vacha is needed immediately to avert the alarming decline and initiate conservation measures for this important fish of the Padma River. 

Objectives

This study is the first complete and comprehensive description of size at sexual maturity and relative growth of the E. vacha in the Padma (main tributary of the Ganges) River, northwestern Bangladesh, which includes:

1. the size at first sexual maturity based on gonadosomatic index for males and females separately; 

2. the overall length-weight relationships (either isometric or allometric growth) for male and females, separately;

3. the length-weight relationships in relation to gonad weight for males and females separately;

4. the length-weight relationships based on size at first sexual maturity for males and females separately;

5. the Fulton’s condition factor and relative condition factor; and 

6. the results were compared with available literatures of same or other populations.

 

ABSTRACT

The critically endangered catfish Eutropiichthys vacha (Hamilton, 1822) is one of the commercially important small indigenous species in the Padma River of Bangladesh, but the population is badly decreasing due to high fishing pressure, leading to an alarming condition and deserving of high conservation importance. This catfish is an important target species for small scale fishermen in Bangladesh, who use a variety of traditional fishing gears. This study aims to estimate the size at first sexual maturity, length-weight relationships (LWR), and condition factors (Fulton’s, KF; and Relative condition, KR) of E. vacha in the Padma (main tributary of the Ganges) River, northwestern Bangladesh. Sampling was done using traditional fishing gears including cast net, square lift net and conical trap during January to December 2010. Total length (TL) was measured to the nearest 0.01 cm using digital slide calipers, and total body weight (BW) was measured using an electronic balance with 0.01 g accuracy. Whole gonads were removed from each individual and weighed (GW) with an electronic balance to an accuracy of 0.001 g. The gonadosomatic index (GSI) was calculated by the equation, GSI (%) = (GW/BW) × 100. The size at first sexual maturity of males and females were estimated by the relationship between gonadosomatic index and its total length. The length-weight relationship was calculated using the expression: W= a Lb, where W is the BW and L the TL. The Fulton’s condition factor (KF) and the relative condition factor (KR) were calculated using the equation, KF =100× (W/L3), and KR = W/ a× Lb, where W is the total body weight (BW, g), L is the total length (TL, cm), and a and b are the LWR parameters. A total of 583 specimens ranging from 8.30-27.00 cm TL (total length) and 3.16-159.50 g BW (body weight) were analyzed in this study. TL and BW did not show any significant difference between the sexes (P>0.05). The results showed a significant correlation between GSI and TL for males (rs = 0.387; P < 0.001) and females (rs = 0.479; P < 0.001) in the Padma River, indicating that GSI was dependent of body size. The sizes at first sexual maturity for males and females E. vacha were considered to be 13.15 cm and 14.00 cm TL, respectively in the Padma River. The allometric coefficient b for the LWR indicated isometric growth in males (~ 3.00), but negative allometric growth (< 3.00) in females. The analysis of covariance (ANCOVA) revealed significant differences in the regression line of the LWR between the sexes (F = 4.773, P = 0.029). The KF and KR showed no significant variations between males and females. The KF was not significantly correlated with TL for males (rs = 0.052; P = 0.378), but highly correlated for females (rs = -0.165; P = 0.005). Furthermore, KR was not significantly correlated with TL for males (rs = 0.006; P = 0.911) and females (rs = -0.028; P = 0.627), but highly correlated with BW for both sexes (P < 0.001). To my knowledge, this study presents the first complete and comprehensive description of size at first sexual maturity for E. vacha from Bangladeshi waters. This study would be useful for fishery biologists/managers to impose adequate regulations for conservation of this critically endangered fishery in Bangladesh and neighboring countries.

 

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CONTENTS

Acknowledgement 

Abstract 

Contents 

List of Tables

List of Figures

List of Plates

CHAPTER ONE: INTRODUCTION

CHAPTER-TWO: REVIEW OF LITERATURE

CHAPTER-THREE: MATERIALS AND METHODS 

3.1. Sampling site

3.2. Sampling and laboratory analysis

3.3. Size at sexual maturity

3.4. Length-weight relationships

3.5. Condition factors

3.6. Statistical analyses

CHAPTER-FOUR: RESULTS  

4. 1. Population structure

4.2. Size at sexual maturity

4.3. Length-weight relationships

4.4. Condition factors

CHAPTER FIVE: DISCUSSION

CHAPTER SIX: CONCLUSION

CHAPTER SEVEN: REFERENCES

 

LIST OF TABLES

Descriptive statistics on the length (cm), weight (g) and measurements of the Eutropiichthys vacha (Hamilton, 1822) in the Padma (main tributary of the Ganges) River, northwestern Bangladesh

Descriptive statistics and estimated parameters of the length-weight relationships (BW = a × TLb) of the Eutropiichthys vacha (Hamilton, 1822) in the Padma (main tributary of the Ganges) River, northwestern Bangladesh 

Gonadosomatic index, GSI % = 100 × (GW/BW), Fulton’s condition factor, KF= =100× (BW/TL3) and Relative condition factor, KR=BW/(a× TLb) of the Eutropiichthys vacha (Hamilton, 1822) in the Padma (main tributary of the Ganges) River, northwestern Bangladesh n, sample size; Min, minimum; Max, maximum; SD, standard deviation; CL, confidence limit for mean values; GSI, gonadosomatic index; KF, Fulton’s condition factor; KR, relative condition factor

Spearman rank correlation (rs) for Fulton’s condition factor (KF= =100×(BW/TL3) and Relative condition factor (KR=BW/a× TLb) with total length (TL) and body weight (BW) of the Eutropiichthys vacha (Hamilton, 1822) in the Padma (main tributary of the Ganges) River, northwestern Bangladesh 
 

LIST OF FIGURES

Sampling site of the Padma (main tributary of the Ganges) River

Relationship between gonadosomatic index and total length for male Eutropiichthys vacha (Hamilton, 1822)

Relationship between gonadosomatic index and total length for female Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (ln W = ln a + b ln L) of the male Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (W = a × Lb) of the male Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (ln W = ln a + b ln L) of the female Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (W = a × Lb) of the female Eutropiichthys vacha (Hamilton, 1822)

Total length-gonad free body weight relationships [ln (W-G) = ln a + b ln L] of the male Eutropiichthys vacha (Hamilton, 1822)

Total length-gonad free body weight relationships [ln (W-G) = ln a + b ln L] of the female Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (ln W = ln a + b ln L) of the male Eutropiichthys vacha (Hamilton, 1822)

Total length-body weight relationships (ln W = ln a + b ln L) of the female Eutropiichthys vacha (Hamilton, 1822)
 

LIST OF PLATES

Measuring weight of Eutropiichthys vacha

Measuring length of Eutropiichthys vacha

Measuring gonad length of Eutropiichthys vacha



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