Length–length and length-weight relationships of critically endangered striped cat fish Rita rita (Hamilton) from the Padda River near Rajshahi of Northwestern Bangladesh

Abstract

The present study describes the length-length (LLR) relationships for critically endangered catfish Rita rita (Hamilton, 1822) from the Ganges River, northwestern Bangladesh. A total of 379 specimens used for this study were caught by traditional fishing gear from January to December 2011. Total length (TL), standard length (SL), fork length (FL), snout length (SnL), head length (HL), pre-dorsal length (PrDL), post-dorsal length (PoDL), Anal length (AnaL) and Anus length (AnsL) were measured and relationships were calculated by linear regressions. Parameters a and b of the weight-length relationship were estimated by least squares regression analysis. Most LLRs relationships were highly significant with 'r 2 ' values greater than 0.845. Exceptions were found incase of TL-HL relationship of female(r 2 =0.756); TL-SnL relationships of male(r 2 =0.701) and combined sexes(r 2 =0.656), TL-PrDL relationship for combined sexes(r 2 =0.692) and TL- AnsL relationship for female(r 2 =0.722) and combined sexes(r 2 =0.695). TL-BW relationships were highly significant with 'r 2 ' values greater than 0.845 for male, female and combined sexes. The calculated allometric coefficient ranged from 0.914 to 1.159(b<3), so the fish showed negative allometric pattern of growth. To the best knowledge of the authors, this study presented the first reference on LLRs for these species from Bangladeshi waters. Keyword: Ritha, Padma river, riverine catfish, LLRs, LWRs and morphometric characteristics