Length Base Structure and Growth Parameters of Sarotherodon galilaeus (Pisces: Cichlidae) in Tropical Coastal Estuary, Nigeria

摘要

Population dynamics and length frequency distribution of Sarotherodon galilaeus was investigated from commercial fishermen operating within Iken brushpark in the Ogun coastal estuary of Nigeria. The study was necessitated to provide information on S. galilaeus that has been listed in the IUNC as a threatened species. A total of 1,938 specimens with total length range of 11.0 – 11.9 to 41.0- 41.9 cm and corresponding weights of 27 g to 1,345 g were sampled. Mean TL ranged from 26.96±0.58 cm in February to 31.08±0.41 cm in June with corresponding mean weight of 517.20±26.45 g and 766.12±26.04 g. In terms of abundance, the month of April ranked as the highest (492) and the least abundance was observed in February (252).The contribution of size class 31.0-31.9cm dominates the stock. Bhattacharya’s Modal Class Progression Analyses depicts four distinct peaks representing age groups 1+ to 4+. The highest value of the exponent "b" of length-weight relationship and condition factor "K" was recorded in male fish. K value showed significant difference (p<0.05) within sex. The estimated growth parameters values using Von Bertalanffy Growth Equation from age lengths key data were: Asymptotic length (L∞) = 43.58 cm, Growth rate (K) = 0.81 yr-1, Total mortality (Z) = 2.64 yr-1, Natural mortality (M) = 1.42 yr-1, Fishing mortality (F) = 1.22 yr-1, Exploitation rate (E) = 0.46, longevity (Tmax) = 3.70 years, Length-at-optimum yield (Lopt) = 25.02 cm and Length-at-first maturity (L50) = 11.43 cm. Overview of the growth parameters analysis suggest that S. galilaeus is still under exploit and it longevity is also above the recommended limit of cichlids.