Estimation of gillnet selectivity of Coptodon zillii in Asejire Lake, Oyo State, Nigeria
Gillnet selectivity of Coptodon zillii was estimated in this study to determine the appropriate mesh size for the exploitation of the fish in Asejire dam. Holt’s indirect method of estimation was used to estimate gillnet selectivity of C. zillii in Asejire dam. Three mesh sizes 50.8mm, 63.5mm and 76.2mm were used for the estimation. The result shows that these mesh sizes caught C. zillii that were significantly different in sizes and abundant (P < 0.05). The 63.5 mm mesh size of gillnet was the most efficient; it caught 150 C. zillii with length range of 13 – 22 cm. Also, 50.8 mm mesh size caught137 C. zillii with length range of 11 – 18 cm. Likewise, 76.2 mm mesh size caught 57 C. zillii with length range 16 – 24 cm. The optimum length of 50.8 mm mesh size was 14.78 cm, 63.5 mm was 18.48 cm and 76.2 mm was 22.17 cm. Mesh size of 63.5mm is recommended as the appropriate mesh size for the exploitation of C. zillii in Asejire dam for the sustainability of the fish. This is done to prevent both recruitment and growth overfishing of C. zillii in Asejire dam.
Key words: optimum length; exploitation; selection; sexual maturity; recruitment overfishing, growth overfishing