Biological assessment of Oreochromis niloticus (Pisces: Cichlidae; Linne, 1958) in a tropical floodplain river

Biological assessment o

Trophic ecology of commercially important fishes

ABSTRACT Diet composition, Food Richness, Diet Breadth and Gut Repletion Index of 47 fish species belonging to 28 genera and 16 families consisting of 14,837 individuals in the inland wetlands of Cross River, Nigeria, were studied monthly between January 2006 and December 2007. There was variation in the composition of food objects in the different species despite the similarity in the rank-order (r s = 0.996, p > 0.004). Major food item in the diet of the 46 species consist of detritus (79.9%), fish and fish fry (41.3%), insect and insect larva (41.3%), phytoplankton (26.1%), crustaceans (23.9%), mollusk (13%), macrophytes parts (13 %), seeds (10.9%), worms (0.04%), arachnids (0.02%) and amphibians (0.02%). Food Richness (N) varied between 5 and 20, Diet Breadth (D) from 0.22 to 0.88 and Gut Repletion Index (GRI) between 34% and 100%. This implies that most of the fish species in Cross River are detritivores with high feeding intensity and trophic flexibility, hence are capable of changing diet according to availability

Dynamics of the limnological features and diversity of zooplankton populations of the Cross River System SE Nigeria

Physico-chemical factors and zooplankton diversity were investigated over a two year period in three regions along the 200 km length of Cross River. The objective of the study was to quantify the relative importance of local environmental conditions and diversity of the principal zooplankton species within sampling sites. Mean conductivity, TDS and chlorides were highest upriver with values 289 ± 198 µs·cm–1, 322.9 ± 101 mg·L–1, and 105.8 ± 77.3 mg·L–1 and lowest downriver with 123.5 ± 78.9 mg·L–1, 45.8 ± 23.7 mg·L–1 and 109 ± 89 µs·cm–1 respectively. Values of wet season water conductivity (406 ± 178 µs·cm–1), TDS (420.4 ± 267 mg·L–1), alkalinity (289.9 ± 34.7), total hardness (205.8 ± 37 mg·L–1), BOD (1.7 ± 0.2), chlorides (205.8 ± 37) and ammonium ions (0.2 ± 0.1 mg·L–1) were significantly higher than dry season values of 156 ± 78.5 µs·cm–1, 0.2 ± 0.1, 123.8 ± 15, 101.4 ± 87.9, 0.2 ± 0.1, 78.1 ± 34.8 and 0.1 ± 0.1 mg·L–1 respectively. Out of twenty seven (27) zooplankton species identified Cladocerans (Ceriodaphnia, Evadne, Alona sp.) and Decapods (Lucifer, Penaeid nauphlius, and Hermit crab larva) were the most diverse taxonomic group, while Tintinnopsis was the only Ciliate. Rainfall value was positively correlated with hydrological characteristics (size of river, flow velocity, water level, and transparency), which in turn determined values of physico-chemical properties and explained the observed seasonal and spatial changes in zooplankton diversity. Though water quality parameters were within the limits set by the World Health Organization (WHO) and European Economic Community (EEC) for good water, the changes in hydrological features of Cross River could be suspected to provide highly unstable aquatic habitat that could subsequently affect the stability of zooplankton and other aquatic organisms

Dynamics of the limnological features and diversity of zooplankton populations of the Cross River System SE Nigeria

Physico-chemical factors and zooplankton diversity were investigated over a two year period in three regions along the 200 km length of Cross River. The objective of the study was to quantify the relative importance of local environmental conditions and diversity of the principal zooplankton species within sampling sites. Mean conductivity, TDS and chlorides were highest upriver with values 289 ± 198 µs·cm–1, 322.9 ± 101 mg·L–1, and 105.8 ± 77.3 mg·L–1 and lowest downriver with 123.5 ± 78.9 mg·L–1, 45.8 ± 23.7 mg·L–1 and 109 ± 89 µs·cm–1 respectively. Values of wet season water conductivity (406 ± 178 µs·cm–1), TDS (420.4 ± 267 mg·L–1), alkalinity (289.9 ± 34.7), total hardness (205.8 ± 37 mg·L–1), BOD (1.7 ± 0.2), chlorides (205.8 ± 37) and ammonium ions (0.2 ± 0.1 mg·L–1) were significantly higher than dry season values of 156 ± 78.5 µs·cm–1, 0.2 ± 0.1, 123.8 ± 15, 101.4 ± 87.9, 0.2 ± 0.1, 78.1 ± 34.8 and 0.1 ± 0.1 mg·L–1 respectively. Out of twenty seven (27) zooplankton species identified Cladocerans (Ceriodaphnia, Evadne, Alona sp.) and Decapods (Lucifer, Penaeid nauphlius, and Hermit crab larva) were the most diverse taxonomic group, while Tintinnopsis was the only Ciliate. Rainfall value was positively correlated with hydrological characteristics (size of river, flow velocity, water level, and transparency), which in turn determined values of physico-chemical properties and explained the observed seasonal and spatial changes in zooplankton diversity. Though water quality parameters were within the limits set by the World Health Organization (WHO) and European Economic Community (EEC) for good water, the changes in hydrological features of Cross River could be suspected to provide highly unstable aquatic habitat that could subsequently affect the stability of zooplankton and other aquatic organisms