Biometrics of the rare fish Rhinomugil corsula(Hamilton,1822)(Mugiliformes:Mugilidae)in the Ganges,Northwestern Bangladesh

Objective:To investigate biometrics of the Rhinomugil corsula(Hamilton,1822)(R.corsula),including length-weight relationships(LWRS),condition factors(Allometric,K_(A);Fulton's,K_(F);Relative,K_(R);Relative weight,W_(R)),and sex ratio and length-frequency distributions in the Ganges(Padma River),Northwestern Bangladesh.Methods:Monthly sampling was conducted using traditional fishing gears during June to August 2012.Total length was measured to the nearest 0.01 cm using digital slide calipers,and total body weight was measured using an electronic balance with 0.01 g accuracy.The LWR was calculated using the expression:W=a×L_(b),where the W is the body weight,L is the total length,a and b are the parameters of the regression.Results:A total of 350 specimens ranging from 8.59-15.71 cm in total length and 9.57-32.59 g in body weight were analyzed during this study.The overall sex ratio was not significantly different from the expected value of 1:1(X^(2)=2.57,P>0.05),but there was significant difference in the length-frequency distributions between the sexes(P=0.03).The allometric coefficient b for the LWR indicated negative allometric growth(b=3.00)in males,female and combined sexes.Results further indicated that Kr was not significantly different between the sexes(P=0.57).However,the mean W_(R)of R.corsula showed significant differences from 100 for males(P=0.03)and females(P<0.001)in this study,indicating the imbalance habitat with food availability relative to the presence of predators.Conclusions:This study reported the first description of biometric relationships for R.corsula,which would be useful for the sustainable conservation of this rear fishery in Bangladesh and also neighboring countries.