Population Dynamics of Cichlid Fish Species of Opi Lake, Nsukka. Enugu State, Nigeria.

Abstract

Studies on the population dynamics of cichlid fish species in Opi lake were carried out between August, 2014 and January, 2015. Also, physico-chemical parameters of the lake were analyzed using appropriate methods. Morphometric relationships and seasonal variations of the fish species were determined. A total of 235 cichlid fish, comprised of 5 species, namely: Tilapia zillii (28.09%), Sarotherodon melanotheron (51.49%), Oreochromis niloticus (14.04%), Pelmatochromis guentheri (5.96%) and Hemichromis fasciatus (0.43%) respectively were sampled and used for the study. The above listed cichlid fishes showed no correlation (P>0.01) and (P>0.05) with values of the physico-chemical parameters determined. S. melanotheron however, showed positive correlation (P<0.05) with phosphate. The fish species sampled showed that there were more females than males. Ripe gonads were recorded much in all the species except in O. niloticus where mature gonads were greater in number. In T. zillii, the smallest sexually matured females were 8.1 cm total length. The length–length relationship had a b–value of 0.76 when compared to the length–weight (L-W) relationship that showed positive allometric growth of b>3. Growth parameters of T. zillii showed asymptotic length of = 1.27 cm Tl, growth curvature (K) = 0.8 yr-1, growth performance index Q1 = 0.11, age–at–length zero (to) = 0.48 yr and the higher potential longevity (tmax) = 3.75 yrs. Mortality parameters showed that the total mortality (Z), natural mortality (M), fishing mortality (F) and exploitation rate (E) were 3.36 yr-1, 1.755 yr-1, 1.605 yr-1 and 0.48 yr-1 each. The smallest sexually matured female in S. melanotheron was 9.8 cm Tl. The length-length relationship had a b–value of 0.79 and L–W relationship showed positive allometric growth of b>3. The growth parameters showed that was 37.38 cm Tl, K = 0.8 yr-1, Q1 = 3.1, to = 0.188 yr and tmax = 3.75 yrs. Also, mortality parameters showed that Z = 4.54 yr-1, M = 0.70 yr-1, F = 3.34 yr-1 and E = 0.85 yr-1 respectively. O. niloticus had sexually matured female of 11.5 cm Tl. Whereas length-length relationship gave a b–value of 0.82 while L–W relationship showed positive allometric growth of b>3. Bertalanffy growth parameters were = 5.27 cm Tl, K = 0.8 yr-1, Q1 = 1.35, to = 0.32 yr and tmax = 3.75 yrs. Mortality estimate were Z = 3.39 yr-1, M = 1.175 yr-1, F = 2.21 yr-1 and E = 0.65 yr-1 respectively. Also P. guentheri had sexually matured female of 11.6 cm Tl. Length-length relationship had a b–value of 0.84 and L–W relationship showed negative allometric growth of b<3. The Bertalanffy growth parameters were = 22.0 cm Tl, K = 0.8 yr-1, Q1 = 2.59, to = 0.22 yr and tmax = 3.75 yrs. Mortality estimates were Z = 2.6 yr-1, M = 0.80 yr-1, F = 1.80 yr-1 and E = 0.21 yr-1. H. fasciatus was only sampled once towards the end of the study (January) which showed that the species appear endangered. Fishing mortality was substantially high in all the species sampled which is undesirable since it can lead to the collapse of the cichlid fish species in Opi lake.