Penelitian dilakukan di kota tarakan pada bulan januari – maret 2021 dengan tujuan mengetahui bio-populasi ikan senangin dan ikan arut dari aspek sex ratio, pertumbuhan, tkg (tingkat kematangan gonad), ikg (indeks kematangan gonad), fekunditas, ukuran pertama kali matang gonad (lm) dan tertangkap (lc). total sampel penelitian 113 ekor yang terdiri dari ikan arut 81 ekor dan ikan senangin 32 ekor. sampel diukur panjang menggunakan penggaris dan ditimbang bobotnya menggunakan timbangan analitik. pengamatan jenis kelamin dilakukan secara anatomi dengan melihat gonad ikan. sex ratio ikan sampel selama penelitian adalah 1 : 4 (ikan senangin) dan 1 : 2 (ikan arut). berdasarkan model pertumbuhan ikan arut sebagai hasil tangkapan utama, diketahui parameter pertumbuhannya yaitu dugaan panjang maksimal tercapai (l?) 71.26 cm, koefisien pertumbuhan (k) 0.0127 cm dan dugaan umur pada panjang teoritis null (t0) sebesar -1.0665 hari. tkg ikan senangin jantan dominan tkg i dan betina tkg iv. sampel ikan arut jantan dominan tkg i dan betina tkg iii. kisaran ikg ikan senangin jantan 0.08 – 1.29 dan betina 0.11 – 3.47. ikg ikan arut jantan berkisar 0.08 – 1.62 dan betina 0.38 – 2.34. nilai lm ikan arut 30.6 cm dan ikan senangin 40.4 cm. nilai ukuran lc pada ikan arut 30.9 cm dan ikan senangin 34.7 cm. kata kunci: ikan arut, ikan senangin, matang gonad, rasio kelamin dan tarakan

The study was conducted in tarakan city in january to march 2021 with the aim of finding out the bio-population of the senangin fish and arut fish from the aspect of sex ratio, growth, tkg (gonadal maturity level), ikg (gonadal maturity index), fecundity, size at first gonadal maturity (lm) and caught (lc). the total sample of the study was 113 fish consisting of 81 arut and 32 senangin. samples were measured in length using a ruler and weighed using an analytical balance. observation of sex was done anatomically by looking at the fish gonads. the sex ratio of the sampled fish during the study was 1:4 (senangin fish) and 1:2 (arut fish). based on the growth model of arut fish as the main catch, it was known that its growth parameters reached the estimated maximum length (l?) 71.26 cm, gowth coefficient (k) of 0.0127 cm, and age estimation at null theoretical length (t0) of -1.0665 days. the male senangin was dominant of tkg i and female of tkg iv. the male arut was dominant of tkg i and female of tkg iii. the range of ikg of male senangin was 0.08-1.29 and the female was 0.11-3.47. the ikg of the male arut ranged from 00.08-1.62 and the female 0.38-2.34. the lm value of arut was 30.6 cm and senangin was 40.4 cm. the value of lc size in arut was 30.9 cm and senangin was 34.7 cm. keywords: arut fish, senangin fish, gonad ripe, sex ratio, tarakan