Temporal variations in bio-indices of Oreochromis niloticus (Linnaeus, 1758) in East Kolkata wetlands, India

Temporal variations in selected bio-indices of length-weight relationships (LWRs) like relative condition factor (Kn), relative length of gut (RLG), hepato-somatic index (HSI), gonado-somatic index (GnSI) and gastro-somatic index (GaSI) of Nile tilapia (Oreochromis niloticus) were carried out in 341 samples collected at fortnightly intervals in East Kolkata wetlands, a Ramsar site. The exponent b value of LWRs was 2.9869, 2.8316 and 2.9163 with r2 value being 0.938, 0.936 and 0.935 for male, female and the pooled sample respectively showing negative allometric growth of the fish. The Kn values ranged 1.01 to 1.09 and 1.05 to 1.12 for male and female samples respectively exhibiting significant difference (p<0.05) between sexes. Monthly mean RLG values fluctuated from 6.55 to 9.01 indicating herbivore feeding habits. Monthly mean GaSI values were in the range from 0.64 to 2.63 and that of HSI values from 0.53 to 1.41. Monthly mean GnSI values ranged from 0.19 to 1.27 and 0.35 to 3.01 for male and female fish respectively exhibiting significant (p<0.05) difference between the sexes, which was attributed to maturity and gradual gonadal development. Key words Oreochromis niloticus, Bio-indices, East Kolkata Wetlands, Ramsar site