No abstract

Fish meal is widely used in commercial feed production because of its amino acids profile, and high protein content, however, its usage constitutes a major cost in fish feed production. It is therefore essential to source for a highly nutritious, cheap and readily available substitute which can supply the farmed fish with necessary dietary requirements for proper growth and development. The study utilised house fly maggots (Musca domestica) cultured from poultry waste at varying inclusion levels of 0 (no inclusion), 25, 50, 75 and 100% (maggot inclusions) to replace fish meal in the diets and replicated thrice. A total of 180 Clarias gariepinus juveniles catfish with initial average weight of 10.11±0.12 g were stocked at 12 fish per tank, acclimatised for 2 weeks and fed twice daily at 3% body weight for a period of 12 weeks. The proximate composition of wet maggots showed the presence of favourable amino acids similar to fish meal but had lower crude protein content (47.45%) with high ether extract (22.23%) and moisture content (83.52%). The water quality parameters such as ammonia, temperature and dissolved oxygen were monitored daily and showed no significant difference (P<0.05) among the treatments and were tolerable for fish culture. Sampling of fish was done weekly, the growth and nutrient utilisation, economic indices and haematological studies were done and analysis of variance was used for the statistical analysis. It was observed that 75% inclusion of wet maggot gave better results and rapid utilisation and conversion of feed to flesh and was evident in the weight gain (50.71 g), lowest feed conversion ratio (1.04±0.04), highest specific growth rate (1.99±0.00 g/day) and cheap in terms of cost of production (₦ 172.12). This shows that 75% of wet maggots can be recommended as an inclusion level in commercial fish feed for adequate utilisation by C. gariepinus juveniles.

The food habit and ecological balance of fish species in Osun River were investigated for a period of 12 months (November 2017 to October 2018) with monthly sampling of water and fish species in the river. Fish were sampled using monofilament gill nets of mesh size between 25mm and 101mm. A total of 4544 individuals belonging to 19 species and 10 families were captured. They were grouped based on their feeding habits into herbivores, carnivores, and omnivores. Carnivores dominated the River (38.63%) with Cichlids being the most abundant family (95.10%) and Oreochromis niloticus the most abundant fish species (14.10%). The Forage - Carnivore ratio (F/C) for the dry, wet and combined season was 0.64, 0.34 and 0.48 respectively. T-test showed significant differences (P < 0.05) between all the trophic groupings in relation to seasons. The mean values recorded across the sampling months were Temperature (18.70 oC ± 2.69), pH (7.10 ± 0.25) and Dissolved Oxygen (3.20 mg/L ± 0.54) while Ammonia (1.20 mg/L ± 0.18) was significantly different (P < 0.05) across the months of study. For the sampling points, mean values recorded were Temperature (17.90 oC ± 0.31), pH (7.20 ± 0.12), Dissolved Oxygen (3.20 mg/L ± 0.27 mg/L) and Ammonia (0.10 mg/L ± 0.21). The abundance of carnivores is not desirable, and it is therefore essential to maintain the ratio of forage and carnivorous fish species in the river for conservation of fish species.

The study assessed histopathological alterations in the organs of Oreochromis niloticus (Nile tilapia) and Clarias gariepinus (Catfish) harvested from Dandaru Pond, Ibadan, Nigeria. The histopathological effects were evaluated through biomarkings and heavy metals measurements of the fish organs and tissue. Results showed the kidney with sign of coagulated necrosis of the renal tubules. In the liver, there were hepatocytes which appeared foamy and contained large-sized vacuoles. The gills appeared with some congestion in their capillaries in addition to numerous bluish staining walled-off structures. There was severe thinning of the myocardial fibres in the fish heart. The chambers were moderately congested. The fish organs contained 0.06-0.90 µg/g lead. The Pb concentrations and those of manganese and iron exceeded the WHO permissible limit in fish. It is conclusive that the bioaccumulated heavy metals in the tissue and fish organs consequently impaired their histopathological condition, and thus affect fish health status.

No abstract