Length-based estimates of growth parameters and mortality rates of Nile Tilapia (Oreochromis niloticus, L. 1758) in Lake Abaya, Southern Ethiopia

Abstract

The Nile tilapia, Oreochromis niloticus, is one of the most commercially important fish species in Ethiopia. Effective management is essential to sustaining their fisheries and providing benefits for the local communities. The study was aimed at determining the basic population characteristics (growth, mortality rates, and recruitment), size at first maturity, length at first capture, and stock status of O. niloticus in Lake Abaya. These basic quantitative population characteristics enable a fisheries manager to identify population changes resulting from fishing. The parameters were determined using length frequency data collected from 4089 samples of O. niloticus ranging from 23 to 47 cm in total length. The total length (TL) and total weight (TW) of O. niloticus samples were gathered between September 2021 and August 2022. The length-weight relationship parameters were (TW = 0.0157TL^3.0192, R² = 0.9603) and the condition factor K=1.69. The population parameters were determined using the ELEFAN I routine in FiSAT software. Estimated von Bertalanffy growth parameters were (L∞) = 49.35 cm, growth curvature (k) = 0.36 yr^-1, age at length zero (t_o) = -0.40, and growth performance index (Փ') = 3.0.The estimated values of total natural and fishing mortalities were Z= 1.34 yr^-1, M =0.34 yr^-1,and F= 1.0 yr^-1, respectively. The current exploitation rate (E) was 0.74, which is higher than the optimal (E = 0.5) and indicates that O. niloticus in Lake Abaya was overexploited. In order to maintain the sustainability of the fish population, it is advised that the local authorities establish regulations for the management of O. noloticus in Lake Abaya. These regulations should include protecting the use of small fishing gear and safeguarding fish that are caught smaller than their length at first maturity.