Length-weight and length-length relationships, sex ratio and condition factors of the Asian striped dwarf catfish Mystus tengara (Hamilton, 1822) (Siluriformes: Bagridae) in the Ganges River, Northwestern Bangladesh

The present study describes the sex ratio (SR), distribution of length-frequency (DLF), relationship of length-weight (RLW), relationship of length-length (RLL) and condition factors of Mystus tengara, a small indigenous freshwater fish species. A total of 881 specimens ranging from 4.3-11.4 cm LT (total length) and 3.8-9.6 g WB (body weight) were investigated in the Ganges River of Rajshahi, northwestern Bangladesh from January 2010 to December 2010. The overall sex ratio showed significant differences from the expected value of 1:1 (df=1, χ2=8.9, P<0.001). The significant difference was found in the DLF (LT) between the sexes (Two tailed, P<0.001). Overall, the allometric coefficient b of the RLW was closed to the isometric value (b=3.088), although it suggested negative allometric growth for males (b=2.956) whilst positive allometric growth for females (b=3.198). The results further indicated that the RLL were highly correlated (r2>0.91, distribution of length-frequency). The value of Fulton’s condition factor (KF) was ranged from 0.9 to 1.2 for male and 1.0 to 1.5 for female M. tengara. Also, relative weight (WR) was significantly higher in females (WR>100) than in males (WR<100) indicating imbalance habitat with food availability.