Length-weight relationship and reproductive biology of Bombayduck Harpadon nehereus (Hamilton, 1822) from Veraval fishing harbour, Gujarat

Introduction

Bombay duck Harpadon nehereus (Hamilton, 1822) (Synodontidae: Aulopiformes) is a benthopelagic marine fish commonly inhabiting shallow coastal waters with muddy substrates, and it frequently enters estuarine and creek environments. The species is widely distributed throughout the Indo-Pacific region and supports important commercial fisheries (Ganga et al., 2016; Froese and Pauly, 2021) [7,6] . Within the northern sectors of the Indian EEZ, particularly along the coasts of Gujarat and Maharashtra in the Arabian Sea and West Bengal in the Bay of Bengal, H. nehereus constitutes a significant fishery resource. It supports traditional small-scale fisheries and is also regularly encountered as bycatch in various fishing gears operated in these regions. The species is locally referred to as "Bombil" in Maharashtra and "Bumla" or "Bumli" in Gujarat. The species is predominantly distributed in the northern regions of the Indian EEZ, and several researchers have associated this restricted latitudinal occurrence with different environmental factors. Hora (1934) [10] related its distribution to salinity, while Raj (1954) [13] associated the occurrence of Bombayduck with the 80°F isotherm and prevailing monsoon conditions in its distributional range. Later, Bapat (1970) [4] identified sea surface temperature as the primary factor influencing the unique distribution pattern of Bombayduck along the Indian coast.

Methodology

30 Bombayduck samples were collected every month from Veraval fishing harbour from March 2025 to February 2026. The major fishing crafts landing Bombayduck at this centre were dol netters and trawlers operating in the north-eastern Arabian Sea at depths ranging from 70 to 90 m. The collected specimens were preserved in ice and transported to the laboratory in insulated containers for detailed analysis.

Length-weight relationship

Length measurements, including total length (TL) and standard length (SL), along with body weight, were recorded to the nearest millimetre (mm) and gram (g), respectively, using a digital measuring scale and electronic balance. The length-weight relationship was estimated using the equation W = aL b (Le Cren, 1951) [12] , where W represents the fish weight in grams, L denotes the total length in centimetres, a is the regression intercept, and b is the regression coefficient or slope. The significance of differences between the regression coefficients of males and females was evaluated using ANOVA (Snedecor and Cochran, 1967) [14] .

Reproductive biology

The Gonadosomatic Index (GSI) was calculated using the formula proposed by Kume and Joseph (1969).

GSI = [Gonad weight/Bodyweight] × 100

Absolute fecundity (F) is the total number of ripe eggs in the ovaries just before spawning. Fecundity was calculated following the gravimetric method by preserving ovaries in 5% formalin, then the weight (g) and maturity stage (Stage IV and V) of the ovaries were recorded. The ovary was then divided into three sections: front (anterior), middle, and back (posterior). From each section, a small piece weighing 0.01 g was taken to count the number of eggs and estimate fecundity.

Results

Length-weight relationship

A total of 300 individuals, consisting of 196 females (158-355 mm TL) and 104 males (162-302 mm TL), were used for the calculation of the length-weight relationship. The relationship between weight (g) and TL (cm) for males, females and combined sexes is expressed by the following equations:

Length-weight relation (Males): W = 0.000000672 x TL 3.3 (R 2 = 0.89) Length-weight relation (Females): W = 0.00000131 x TL 3.5 (R 2 = 0.81) Analysis of covariance showed no significant difference in the regression coefficients of males and females at 1 and 5% levels. Hence, the sexes were pooled, and a length-weight relation was calculated and expressed as: Length-weight relation (pooled sexes): W = 0.000000867x TL 3.4 (R 2 = 0.85) The b value estimated was greater than 3, and the fish showed positive allometric growth

Gonadosomatic Index

Pooled GSl varied significantly between months and ranged from 0.1 to 7. The peak value was observed in March, and a higher percentage of mature specimens was observed during January to April, indicating the peak spawning season of the species.

Absolute fecundity (F)

A total of 62 mature females were observed in this study.

The absolute fecundity ranged from 25,485 to 1,42,336 eggs per fish, and relative fecundity from 252-435 eggs per gram.

Discussion

Knowledge of the length-weight relationship (LWR) is essential for stock assessment studies, as it serves as a fundamental input and provides insights into the growth pattern, condition, and overall fitness of fish (Abdurahiman et al., 2004) [1] . The LWR of H. nehereus obtained in the present study indicated positive allometric growth. Earlier reports on the length-weight relationship of H. nehereus are summarised in Table 2, and the findings of the present investigation are in agreement with previous studies conducted in the north-eastern Arabian Sea. Differences observed in the 'b' values across studies may be attributed to ecological variation, seasonal influences, feeding conditions, and differences in the composition and number of juvenile and adult specimens examined (C. Anulekshmi et al., 2024) [2] . Intense fishing pressure, coupled with the effects of climate change, has been influencing fish populations in the northern Arabian Sea. The susceptibility of fish species is largely governed by their biological characteristics, environmental conditions, and anthropogenic disturbances. Bombay duck H. nehereus has been identified as a species with high climate vulnerability and low adaptive capacity and is considered a non-hardy coastal species exposed to multiple environmental stressors (Dineshbabu et al., 2020) [5] .

During the present study period, immature, maturing, and mature ova were observed throughout the year in varied frequencies, suggesting that spawning is a continuous activity with a peak from January to April. Fecundity was estimated for gravid females, and the absolute fecundity ranged from 25,485 to 1,42,336 eggs per fish. Relative fecundity ranging from 252 to 435 eggs per g. The absolute fecundity ranges of 21,182-1,16,067, and the relative fecundity was estimated to be 314 ova/g body weight, were reported by Balli et al. (2006) [3] from Mumbai waters. Ghosh (2014) [8] reported a relative fecundity of 388 eggs per gram body weight for the species. C. Anulekshmi et al. (2024) [2] reported that the absolute fecundity ranged from 23,444 to 1,34,432 eggs per fish, with a mean of 82,884 eggs per fish, and the relative fecundity increased with body size and ranged from 235-430 eggs per g. [11] Pooled: a = 0.00117, b = 2.0279 Maharashtra Balli et al. (2006) [3] Male [9] Male: a = 0.0106, b = 2.8097 Female: a = 0.00867, b = 2.871 Pooled: a = 0.00535, b = 3.024 Saurashtra Ghosh (2014) [8] Male [2] Male: a = 0.

Conclusion

In the present investigation of H. nehereus from the Veraval coast, the length-weight relationship showed a positive allometric growth in this region (b > 3). High GSI values were observed during January to April, indicating the peak spawning season of the species. The absolute fecundity ranged from 25,485 to 1,42,336 eggs per fish, showing the high number of recruitments in the new population.

References

1. Abdurahiman KP, Nayak TH, Zacharia PU, Mohamed KS. Length-weight relationship of commercially important marine fishes and shellfish of the southern coast of Karnataka, India. NAGA WorldFish Center Quarterly. 2004;27(1-2):9-14.
2. Anulekshmi C, Nakhawa AD, Azeez PA, Akhilesh KV, Bhendekar S, Khandagle PA, et al. Biology of the Bombay duck Harpadon nehereus (Hamilton, 1822) from the north-eastern Arabian Sea, India. Indian J Fish. 2024;71(1):70-81.
3. Balli JJ, Chakraborty SK, Jaiswar AK. Biology of Bombay duck Harpadon nehereus (Hamilton, 1822) (Teleostomi: Harpadontidae) from Mumbai waters, India. J Indian Fish Assoc. 2006;33:1-10.
4. Bapat SV. Bombay duck, Harpadon nehereus (Hamilton). Technical report. Kochi, India: ICARCentral Marine Fisheries Research Institute; 1970.
5. Dineshbabu AP, Zacharia PU, Sujitha T, Shoba JK, Rajesh KM, Vivekanandan E, et al. Assessment of stock vulnerability of Indian marine fishes to past changes in climate and options for adaptation. Clim Res. 2020;79:175-192. doi:10.3354/cr01586.
6. Froese R, Pauly D. FishBase [Internet]. 2021 [cited 2026 May 16]. Available from: www.fishbase.org
7. Ganga U, Thomas JP, Sukumaran S. A new species of the genus Harpadon (Aulopiformes: Synodontidae) from the north-eastern Arabian Sea, India. Indian J Fish. 2016;62(4):1-9.
8. Ghosh S. Fishery, reproductive biology and diet characteristics of Bombay duck Harpadon nehereus from the Saurashtra coast. Indian J Geo Mar Sci. 2014;43(3):418-426.
9. Ghosh S, Pillai NGK, Dhokia HK. Fishery and population dynamics of Harpadon nehereus (Hamilton) off the Saurashtra coast. Indian J Fish. 2009;56:13-19.
10. Hora SL. Wanderings of the Bombay duck Harpadon nehereus (Hamilton-Buchanan) in Indian waters. J Bombay Nat Hist Soc. 1934;37:642-654.
11. Kurian A, Kurup KN. Stock assessment of Bombay duck Harpadon nehereus (Hamilton) off the Maharashtra coast. Indian J Fish. 1992;39:243-248.
12. Le Cren ED. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca fluviatilis). J Anim Ecol. 1951;20:201219. doi:10.2307/1540.
13. Raj B. The problem of the apparent discontinuous distribution of Harpadon nehereus (Hamilton). Proc Indian Acad Fish Res Inst. 1954;6:1-69.
14. Snedecor GW, Cochran WG. Statistical methods. 6th ed. Ames, Iowa, USA: Iowa State University Press; 1967.
15. Vladykov VD. Fecundity of wild speckled trout (Salvelinus fontinalis) in Quebec lakes. J Fish Res Board Can. 1956;13(6). doi:10.1139/f56-046.