Assessment of proximate composition, microbial loads and some heavy metals concentration in the sediment, water and organ of four commercial fish species from Oluwa River, Igbokoda, Ondo State, Nigeria

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The objective of this study was to evaluate the proximate composition, microbiological contamination, and levels of heavy metals in water, sediment, and four fish species (catfish (Clarias gariepinus), Nile tilapia (Oreochromis niloticus), snakehead (Parachanna obscura), and marine catfish (Arius gigas)) obtained from the Oluwa River. Water, sediment, and fish samples were collected monthly in the Oluwa River over a period of three consecutive months. The proximate composition, microbial loads, and heavy metal contents of water and fish samples were assessed utilizing established protocols. The proximate composition result shows that the moisture of the fish content ranges from 7.32 to 9.24%, the crude protein ranges from 82.16 to 85.32%, crude fiber ranges from 0.29 to 2.33%, fat ranges from 0.84 to 4.73%, ash ranges from 3.38 to 6.62%, and carbohydrates range from 0.00 to 0.11%. The findings from the analysis of microbial burdens in water and fish demonstrate a statistically significant distinction (P < 0.05) in the counts of Enterobacteriaceae and total viable counts between the chosen samples of fish and water. The average values (mg/L) of heavy metals in the water range between 0.01 ± 0.00 and 0.53 ± 0.01, with no detection of mercury or manganese. The measured values of the parameters fell within the acceptable limits set by the World Health Organization (WHO) (0.05 mg/L), except for lead, which exceeded the limits. The average concentration (mg/L) of heavy metals in sediment was above the permissible limits except for zinc, which fell within the acceptable range. The average values (mg/kg) of heavy metals range from 1.85 ± 1.15 to 31.75 ± 0.00; 0.03 ± 0.02 and 33.21 ± 0.02; 0.02 ± 0.00 and 29.57 ± 0.02; 0.01 ± 0.00 and 23.52 ± 0.02 for P. obscura, C. gariepinus, O. niloticus, and A. gigas, respectively, and were within the maximum permissible limits set by the WHO with the exception of manganese and copper. The concentrations of heavy metals identified in the Oluwa River may not present an imminent or severe risk to fish and human consumers, potentially leading to adverse health effects.

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