STUDY THE POPULATION DYNAMICS AND STOCK ASSESSMENT OF Oreochromis niloticus IN THE UNNICHCHAI IRRIGATION RESERVOIR , BATTICALOA DISTRICT

Abstract

The purpose of this study was to determine the population dynamics and stock assessment of the Nile tilapia. In Unnichchai Reservoir, it is the predominant fish that is highly preferred by consumers. The length-frequency distribution, length-weight relationship, growth and mortality parameters, and recruitment of the Unnichchai reservoir were investigated using length-frequency data and respective weight. The length-frequency distribution and length-weight relationship were computed from linear regression analysis by using MICROSOFT EXCEL Professional plus 2019 and growth mortality parameters and recruitment analyzed ELEFAN method incorporated in FISAT software. 360 fish specimens sampled two times per month, from Gill net haul over a period of 6 months starting from June 2023 to November 2023. Oreochromis niloticus exhibited negative allometric growth (b: 2.02 (l 3) and near to the strong positive correlation (t':0.8615). The von Bertalanffy growth constants for Oreochromis niloticus were TL- :38.40 cm, K: 0.69 yr-1, and with a derived growth performance index of $:3.00. The instantaneous rates of total mortality (Z), natural mortality(M),andfishingmortality(F)were l.45,l.29,and0.16peryearrespectively. The rate of exploitation (E : 0.ll) showed under-exploitation of this species. However, this reservoir be stocked annually that may be to balance the rate of exploitation of the Nile tilapia population. There might be a few possibilities for yearly stocking, which would suggest that the reservoir experiences predator attacks, heavy exploitation due to fishing, or inadequate natural recruitment. To solve that issue, implement a regular monitoring program to identify and record the O. niloticus population, improve natural recruitment, and increase public awareness of fisheries.