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Biological Features of the Schilbid Catfish Pachypterus Atherinoides from the Payra River, Southern Bangladesh

FERDOUS AHAMED
Department of Fisheries Management, Patuakhali Science and Technology University, Patuakhali 8602, Bangladesh

MIMI SULTANA
Department of Fisheries Management, Patuakhali Science and Technology University, Patuakhali 8602, Bangladesh

ZOARDER FARUQUE AHMED
Dept. of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Some biological features including sex ratio, length-frequency distributions (LFDs), size at sexual maturity, spawning season, length-weight relationships (LWRs) and condition factor of Pachypterus atherinoides were studied. Samples were collected seasonally during March 2018 to January 2019 from a tributary of the Payra River. The overall sex ratiowas significantly different from the expected value of 1:1 (p<0.001) in favor of female specimens. Females were significantly largerin size than males. Size at sexual maturity was estimated at6.4 cm total length. Seasonal variations in the gonadosomatic index (GSI) indicate that the main spawning season is fromsummer to autumn. The LWRs showed positive allometric growth in males and isometric growth in females; however, with clear seasonal variation. Fulton’s condition factor varied in both sexes and was attributed to the variations in GSI with maturity.The findings of this study will be helpful to formulatemanagement and conservation strategies of P. atherinoides population.

Keywords: Pachypterus atherinoides, Spawning season, Length-weight relationship

Location: The Payra River, Bangladesh.

Start Date: 00-00-2018

End Date: 00-00-2019

Program Area: Conservation and Biodiversity

Commodity: Cat fish

Objectives:

To address some biological featuresincluding sex ratio, length-frequency distributions (LFDs), size at sexual maturity, spawning season, length-weight relationships (LWRs) and condition factor of P. atherinoides.

Methodology:

Study site and sampling:The samples were collected from a tributary (straddling 22º 35´ N and 90º 26´ E) of the Payra River (a river running through Patuakhali district of Bangladesh and finally falls into the Bay of Bengal as the Burishwar River). Samples were collected seasonally during March 2018 and January 2019 with the help of local fishers using push net (mesh size: 1.5–2.0 cm) and lift net (mesh size: 2.0 cm). Seasons were defined asspring (March–May), summer (June–August),autumn (September–November) and winter (December–February).The collected fresh samples were preserved with ice on site and fixed with 10% formalin upon arrival at the laboratory for further analysis. Fish measurement: Total length (TL) for each individual was measured to the nearest 0.1 cm using a measuring scale and body weight (BW) was measured using a digital balance (AND FSH, Korea) to 0.01g accuracy. Sex determinationwas done by abdominal incision of each individual and visual inspection of the gonad. In case of females, the gonad weight was measured to the nearest 0.001 g. Sex ratio and length-frequency distributions (LFDs): Sex ratio (male/ female) was calculated and the results were analyzed byχ² test (1:1; p<0.05). Length frequency distributions for both male and female P. atherinoides specimens were constructed using 0.5 cm intervals of TL. The normality of TL frequency distributions were fitted based on Hasselblad’s maximum-likelihood method (Hasselblad 1966). Size at sexual maturity and spawning season: The gonadosomatic index (GSI) was calculated as GSI (%)= (GW/BW)×100. Size at sexual maturity was estimated by the relationship between TL and GSI. Spawning season was estimated based on the seasonal variations of GSI. Length-weight relationships (LWRs) and condition factor:LWRs were calculated according to the equation: BW= a × TL^b, where BW is the body weight (g) and TL is the total length (cm). The parameters a andb were estimated by linear regression analysis based on natural logarithms: ln (BW)= ln (a) + bln (TL). Extreme outliers were removed from the analyses (Froese 2006). Significant deviation of b value from the theoretical isometric value (b = 3) indicates either positive (b> 3) or negative (b< 3) allometric growth (Tesch 1971), which was verified with Student’s t-test (Sokal and Rohlf 1981). Analysis of covariance (ANCOVA) (Zar 1984) was used to test for significant differences in slopes and intercepts between sexes. Fulton’s condition factor (K) was estimated using the following equation: K= (BW/TL³) × 100.

Source of Information: Bangladesh J. Fish. (2019) 31(2) : 173-180

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Achievement/Findings:

In the present study, the overall LWRs indicated positive allometric growth in males and isometric growth in femalesthough some seasonal variations in growth types were observed. However, Hossain and Afroze (1991) reported negative allometric growth, and Ahamedet al. (2018) reported isometric growth for combined sex of this species based on small data collected from occasional samples.The differences in b values could be related to season, diet, stomach fullness and sex (Tesch 1971,Bagenal and Tesch 1978). All allometric coefficients (b) estimated in the present study were within the expected range of 2.5 to 3.5 (Froese 2006). The condition factor (K) is an index reflecting interactions between biotic and abiotic factors on the physiological condition of the fishes; therefore, it can also be used as an index to assess the status of the aquatic ecosystem in which fish live (Anene 2005). K is generally correlated with the temporal changes of fish GSI (Ahamed et al. 2014, Hossain et al.2012& 2013). In the present study, the K value started to increase in summer and remained high in autumn, thereafter the K was low duringwinter and spring and summer for both sexes. On the other hand, the GSI value began to rise from spring and remained high during summer and autumn, thereafter the GSI decreased sharply in winter. Therefore, it appears that K of P. atherinoides started to increase with the start of reproductive period and decrease at the end of the reproductive period.In conclusion, the presentstudy provides some basic information on some biological features of P. ather inoides for the first time (except LWR); therefore, the results presented here constitute the baseline for future work.

Knowledge Management: Journal