Food habit and ecological balance of fish species in Osun river, Nigeria

Abstract

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.

Owalla Reservoir in South-western Nigeria: Assessment of Fish Distribution, Biological Diversity, and Water Quality Index

“…These values indicated that the dissolved oxygen concentration in the reservoir is tolerable for fish survival. Similar values were reported in Eleyele Reservoir [39] and Osun River [40]. These mean pH values recorded across the zones (7.00±0.00) and overall mean (7.00 ± 0.00) were within the range of 6.5 -9 as stated by USEPA [35].…”

“…Simpson's index was highest in May and least in September which indicated a low and high diversity, respectively. As stated by Shannon and Weiner [40], the higher the fish abundance the lower the diversity and vice versa. The Shannon diversity indices had most of the calculated values across the months higher than 1, which indicated a fairly high diversity of fish species across the months of study.…”

“…Similarly, the mean concentration measured across the sampling zones recorded similar increased values which were higher than the recommended values. These indicated that the organic activities and other forms of waste decomposition around the reservoir must be put to check [33].…”

“…The overall calculated WQI value from this zone was 152.72, and it implied that the quality of water is unsuitable because it exceeds the value of > 100 as recommended by Aigberua and Tarawou [16] The overall mean value was lower than values in zones A (155.97) and B (154.35) despite being exposed to similar anthropogenic activities. A possible reason is the flow of water from zone C which is upstream to zone A which is downstream, which washes all pollutants by gravity downstream [40]. 6).…”

Trophic diversity and ecological balance of ichtyofauna in three lentic ecosystems of Côte d’Ivoire: Kossou, Taabo and Faé Lakes

“…Thereby, values of F/C ratio obtained in Kossou and Taabo lakes (respectively 0.87 and 1.28) fell outside the expected range. This indicated the unsuitable ecological balance between carnivores and their prey populations in Kossou and Taabo lakes (Iyiola et al, 2020). The pressure of fishing evocated by Blé (2008) and Diarra (2020) could explain this situation.…”