Journal of Agricultural Science and Food Technology
Research Paper|Published August 2024|Vol.10(2):12-19
https://doi.org/10.36630/jasft_24012
Stock Assessment of Oreochromis niloticus (Nile tilapia) from a Tropical Reservoir
Oluwale Femi V.1, Kelua Shedrach J2 and Odey Cristian A1
1Department of Zoology, University of Ibadan, Oyo, Nigeria.
2Department of Fisheries and Aquaculture, Federal University of Oye-Ekiti, Nigeria.
ABSTRACT
Artisanal fisheries in reservoirs sustain livelihoods and employment in developing countries like Nigeria, where fish is a primary source of animal protein. Using length composition data, a study on aspects of the stock status of the commercially important Oreochromis niloticus in Asejire Reservoir, Southwestern Nigeria, was conducted to promote the sustainability of both the species' benefits and the reservoir's ecosystem functions. A random sample of O. niloticus was collected each month from January to December 2023. The Total Length (TL) of each fish was measured in centimeters. Monthly length-frequency data were then analyzed using the TropFishR package within the RStudio environment. Oreochromis niloticus (n = 465) ranged from 6.0 to 26.5 cm TL, (16.38 ± 3.8 cm), and exhibited a length-frequency distribution with three modes at 10.2 cm, 14.4 cm, and 19.3 cm, corresponding to age groups 0+, 1+, and 2+
years, respectively. The species exhibited a moderate growth rate (K = 0.75) influenced by seasonal variations (seasonal coefficient C > 0.5), reaching an asymptotic total length (L∞) of 32.18 cm and a lifespan of 3 years. Estimated lower natural mortality rate (1.06 year−1) than fishing mortality (2.56 year−1) coupled with an exploitation rate that surpassed the optimum level of 0.5 confirming overexploitation of the species in the reservoir. An exploitation status exceeding the optimum threshold and fishing mortality surpassing natural mortality indicate that the Oreochromis niloticus stock is susceptible to overfishing, emphasizing the necessity for targeted conservation and management efforts for the species in the reservoir.
Key Words: Growth, Mortality, Stock status, Size composition, Nile tilapia, Asejire Reservoir.
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