Aspects Of The Biology Of Cichlids In The Brimsu Reservoir In Cape Coast, Ghana
Abstract
An investigation was conducted into the species composition, growth, reproductive biology and food spectrum of cichlids in the Brimsu Reservoir in Cape Coast, Ghana. Five species of cichlids: Sarotherodon melanotheron, Tilapia zillii, Tilapia guineensis, Hemichromis fasciatus and Oreochromis niloticus representing four genera were encountered. S. melanotheron was the most abundant with numerical composition of 44.80 %, while T. zilli, T. guineensis and H. fasciatus represented 26.57 %, 25.10 % and 2.65 % of the total sample respectively. Oreochromis niloticus was rare in the reservoir and represented by a single specimen of standard length of 12.0 cm. The fish sample ranged from 5.8 cm to 17.6 cm (SL). The modal size of S. melanotheron was 10.0 cm (SL), while T. zillii and T. guineensis had modal size of 9.0 cm and H. fasciatus, 8.0 cm. The blackchin tilapia, S. melanotheron, matured at a bigger size (11.26 cm and 11.34 cm for male and female respectively) than the other cichlids in the Brimsu reservoir. Male cichlids matured at a bigger size (11.26 cm) than females (11.34 cm). S. melanotheron and T. guineensis fed primarily on phytoplankton whereas T. zillii fed mainly on aquatic macrophytes. H. fasciatus is carnivorous and fed on other fish and invertebrates. The choice of food item was dependent on the abundance of that food item in the environment. There was seasonality in the condition index. However, all the cichlids exhibited isometric growth. The cichlids spawn in most part of the year, however, the wet season was the major breeding season. Observations on the ovum diameter distribution indicate that the cichlids spawn in batches.
