Kepadatan Populasi Ikan Oskar (Amphilophus citrinellus) di Danau Toba, Kecamatan Simanindo, Kabupaten Samosir

Abstract

Oskar fish (Amphilophus citrinellus) is an introduced species known that aggressive behaviour, high adaptability, and reproductive potential. Its population tended to increase in Toba Lake, particularly in Simanindo District area, Samosir Regency. High population of the species raised concerns regarding the survival of native species and the stability of the aquatic ecosystem. This study aimed to analyze the population density, length-weight relationship, sex ratio, and their correlation with the physico-chemical parameters of the water. The research was conducted from January to April 2025. Sampling sites were selected using a purposive sampling method based on surrounding anthropogenic activities. Samples were collected using gill nets with a 3.5-inch mesh size at three stations representing agricultural, residential, and natural areas. The observed parameters were population density, length-weight relationship, sex ratio, gonad maturity stage, and correlation analysis with water quality variables. The results showed that the highest population density was found at Station 1 (0.39 ind/m²) and the lowest at Station 3 (0.23 ind/m²). Growth patterns were negatively allometric at Stations 1 and 2, and positively allometric at Station 3. The sex ratio was male-dominated, and most female fish were at gonad maturity stage IV. Light penetration exhibited a very strong correlation with the population density of oskar fish. Therefore, the population density of oskar fish in Toba Lake, specifically in Simanindo District area, Samosir Regency remains relatively low.