Morphological features and length-weight relationships of Sarotherodon galilaeus from Oyan Lake, Southwestern Nigeria

Abstract

Oyan Lake is one of the major sources of fish protein supply to many parts of Southwestern Nigeria. Investigation was conducted on the biometrics, length-weight relationship and condition factor of Sarotherodon galilaeus in Oyan Lake. Fish samples were obtained from fishermen using gillnets, hook and line, cast nets and traps. One hundred and thirty samples of S. galilaeus were collected for the study, comprising eighty-three (83) males and forty-seven (47) females with sex ratio of 1:0.57 (male:female). The mean total lengths for combined sexes, males and females were 15.5±0.15, 15.7±0.19 and 15.3±0.26cm while the mean total weights were 81.0±2.78, 83.8±0.56 and 75.9±4.70g, respectively. No significant difference (p>0.05) was observed between mean total lengths of males and females. However, mean weight of males was significantly higher (p<0.05) than females. Mean eye diameter (EYD) and length of caudal peduncle (LCP) were significantly higher (p<0.05) in females. The range of number of pectoral rays (PRA) (12-14), number of pelvic rays (PVR) (4-5), number of anal spines (ANS) (2-3) and number of pelvic spines (PEVS) (1, no range) were the same in both sexes. There was strong correlation between weight/total length (r=0.93) and total length/length of dorsal fin base (r=0.72), while there was no correlation between body depth/head length. The mean condition factor (k) were 2.07±0.02 (combined sexes), 2.08±0.03 (males) and 2.03±0.03 (females). Growth was isometric for both sexes: males, 3.24 and females, 3.06. The results suggested that Oyan Lake is suitable for S. galilaeus.