WATER QUALITY, FISH DIVERSITY AND CATCH ASSESSMENT OF IKERE GORGE OYO STATE, NIGERIA

Abstract

Study of the physico-chemical parameters of Ikere gorge is one of the recently constructed man-made lake in Oyo state, Nigeria. The need to assess the fish diversity, water quality and catch assessment of this new water body was necessary. Data on fish species were collected on monthly basis using multi-stage gillnet sampling techniques for eighteen months. Four sampling stations were randomly selected from the entire gorge. In each sampling station (fishing villages) were randomly selected for the investigation of the fish composition and abundance. A variety of sampling methods were used at each site in order to reach every fish species. At the river channel and the floodplain sites, traps, cast nets (2.55cm mesh), seine nets (25.5x2m, cm mesh), monofilament nylon gillnets (15.55 cm mesh), and hook and line were employed. Effort were made in order to catch fish species in large abundance. Some sampled fish (dead) were collected and placed in cool boxes and examined within 18h of capture, others were preserved in 15% formalin and stored for later examination. Samples of catches from the commercial fishermen was in addition examined and assessed. A total of 5,736 fish specimens were caught during the study period. These were identified and classified into 34 species belonging to 13 families, and arranged according to Greenwood et al (1966). The percentage species composition of the harvest by numbers and weight for all fish species that contributed more than 1% in all the stations combine were computed. Data fish composition and abundance were collected. From field and Laboratory evaluation, Bagridae (25.1%), Cichlidae (37.1%) and Mormyridae (14.5%) were most abundant families contributing 76.7% by number and 75% by weight of the total catch followed by Characidae (9.6%), Cyprinidae (7%) and Centropomidae (3%) constituting (19.6%) by number and 8.7% by weight. Others; Schilbedae (1.1%) Clarridae (0.8%), Hepsetidae (0.7%0, Mochokidae (0.6%), Channidae (0.5%), Icthyoboridae (0.2%) and Malapteruridae (0.1%) were least represented (4% by number and 16.5% by weight of total catch). Study of the physico-chemical parameters such as dissolved oxygen ranged from 2.2 to 9.1mg/l; temperature, 24.2 to 30⁰C; alkalinity, 94 to 118ppm; conductivity, 81 to 86.7ohms/cm; pH, 6.04-8.62; transparency 50cm to 3.9m; nitrate, 258.15-532.6mg/l; total dissolved solids, 0.142-782mg/l; depth, 25-33.60m; pH and water temperature serve as variables since the fluctuation of one affects the values of others. The water quality parameters were favourable for fish production. The gillnet fisheries indicated that different mesh sizes of experimental gillnets were sensitive to different fish species. 78.4mm, 112mm, 67.2mm mesh sizes were efficient in catching C. nigrodigitatus L. niloticus and the cichlids respectively. Other gears used were cast net, traps, bamboo stems, spears and gura net. The study has shown that station iv was the most suitable habitat for fish in Ikere gorge. Water level and temperature were observed to guarantee high fish yield in the gorge.