POPULATION DYNAMIC OF ENDEMIC RICEFISH IN LAKE POSO IMPLICATIONS FOR CONSERVATION

Abstract

The aim of this study is to assess the population dynamics of medaka fish (Oryzias nigrimas) in Lake Poso. Three habitats of this fish were surveyed, including Watudilana waters, Tolambo village waters and Taipa village waters. Samples were collected at night using a petromax lamp to attract fish. The fishing gear used nets of 8 by 3 meters with a mesh size of 3 by 3 millimeters. A total of 685 individuals of medaka fish (Oryzias nigrimas) were used for population dynamics analysis. Standard length was used to compare the current size of the endemic medaka fish Oryzias nigrimas with its size 28 years ago, while total length was used to examine data on growth, mortality, exploitation rate, recruitment yield and potential reproductive ratio. The male to female sex ratio of this type of fish fluctuated each month, where females tended to be more abundant than males. The average length of this fish is smaller than the standard length in 1993. However, its average size is larger than the freshwater medaka species Oryzias asinua, Oryzias wolasi and Oryzias woworae from Southeast Sulawesi and Oryzias matanensis from Lake Sulaw Towuti. The mortality rate of the medaka fish Oryzias nigrimas is mainly caused by the presence of introduced species and overexploitation. Selectivity of fishing gear, especially by catching fish measuring more than 50.70 millimeters, is strongly recommended for the conservation effort of this fish species.