Life History Traits of the Gangetic scissortail rasbora, Rasbora rasbora (Hamilton, 1822) in the Payra River, Southern Bangladesh

The near threatened gangetic scissortail rasbora, Rasbora rasbora (Hamilton, 1822), is an economically important, and nutritionally valuable freshwater food fish in south Asian countries. The present study provides the first inclusive explanation on life-history traits of R. rasbora in the Payra River, southern Bangladesh. This species invites research interest due to its nutritional demand and IUCN red list status. Sampling was carried out using different traditional fishing gears during July to December 2019. For each individual, total length (TL) and standard length (SL) were measured to the nearest 0.01 cm using digital slide caliper, while body weight (BW) was taken by an electronic balance with 0.01 g accuracy. A total of 215 specimens were measured ranging from 2.6-12.5 cm TL and 0.2210.65 g BW during this study. The 4.00 to 4.99 cm TL was numerically leading group of the total population. The allometric coefficient (b) of the length-weight relationships (LWRs) indicates negative allometric growth pattern (b<3.00) for R. rasbora in the Payra River. The results also indicate that the LWRs were highly significant (p<0.001) with r2 values >0.963. In addition, The LLR (SL vs. TL) was highly significant (p<0.0001) with a coefficient of determination values of 0.988. The estimated form factor (a3.0) was 0.007 indicating this fish is elongated in body shape and the size at first sexual maturity (Lm) for combined sexes of R. rasbora was calculated as 7.96 (~8.00) cm TL in the Payra River. The allometric condition factor (KA) varied from 0.0063 to 0.0570 and Fulton′s condition factor (KF) varied from 0.3933 to 4.1844. However, KF tended to be lower after 9.0 cm for combined sexes, which may indicate the start of sexual maturation and therefore Lm could be around 8.0 cm TL for R. rasbora. The knowledge about the biological aspects of gangetic scissortail rasbora may be used for improved management tools in the future.