Sex Ratio, Size at First Maturity, and Egg Diameter of Yellow-finned medaka fish in Lake Towuti, Indonesia, as a Basis for Domestication

Nursyahran Syahran (Aquaculture Study Program, Balik Diwa Institute of Maritime Technology and Business, Jl. Perintis Kemerdekaan VIII No. 8, Makassar, South Sulawesi 90245)
Jayadi Jayadi (Department of Aquaculture, Faculty of Fishery and Marine Science, Indonesia Muslim University, Jl. Urip Sumoharjo KM. 05, Makassar, South Sulawesi 90231)
Andi Yusuf (Aquaculture Department, Pangkep State Polytechnic of Agriculture, Pangkajene and Islands, Jl. Poros Makassar-Parepare KM. 83, Mandalle, South Sulawesi 90655)
Heriansah (Aquatic Resources Study Program, Balik Diwa Institute of Maritime Technology and Business, Jl. Perintis Kemerdekaan VIII No. 8, Makassar, South Sulawesi 90245)

Journal of Aquaculture and Fish Health
Vol. 15 No. 2 (2026): JAFH Vol. 15 No. 2 June 2026

Yellow-finned medaka fish (Oryzias profundicola) is an endemic species in Lake Towuti and is often consumed by people around the lake. Despite the potential of this species, the problem of over-exploitation has led to a significant decrease in its population. Therefore, this study aims to analyze the sex ratio, first gonad maturity size, and egg diameter of yellow-finned medaka from Lake Towuti. Fish samples were caught using seser nets, and data were collected from January to June 2022 at stations located in Tanjung Timbala, Tanjung Lengkobutanga, Tanjung Bakara, Tanjung Saone, and Tanjung Tominanga. The sex of each fish was identified through the examination of body morphology and gonad. Measurement of egg diameter was carried out at gonad maturity levels III and IV, and a total of 200 eggs were observed at each station per month. The total length and total weight of samples were then measured. Data on sex ratio, size at first gonad maturity, and egg diameter were analyzed using several equations. The results showed that the sex ratio of yellow-finned medaka in Lake Towuti was balanced. The average size range at first gonad maturity of male and female fish was 32.65-39.96 mm and 25.82-33.08 mm, respectively. In addition, the frequency distribution of egg diameter showed peak mode at gonad maturity levels III (0.03-0.17 mm) and IV (0.93-1.07 mm). Based on these findings, yellow-finned medaka was included in the partial or long spawning categories. The results of this study were expected to provide information on the sustainable management, conservation, and domestication of yellow-finned medaka.