<![CDATA[Bonylip barb (Osteochilus vittatus Valenciennes, 1842) is an indigenous fish which is the main target of fishermen in lake Rawa Pening. This study aims to determine the biological parameters including length-weight relationship, con-dition factor, and sex ratio of bonylip barb in lake Rawa Pening, Semarang Regency. Fish sampling was conducted biweekly from October 2019 to March 2020, caught using bamboo blinds operated by local fishermen. Data collected consisted of total length, individual weight, and sex. Data on the length-weight relationship and condition factors were analyzed descriptively, while the sex ratio was analyzed with the chi-square test (χ2). The results showed that female bonylip barb was obtained as many as 392 individuals with a length-range between 10.0-26.0 cm and a weight range between 14.5-264.1 g. The male counted 255 individuals with a length range of 10.2-22.4 cm and a weight range of 15.0-160.9 g. The growth pattern was allometric negative. The equation of the length-weight relationship of female was W = 0.0186 L 2.9096 (R² = 0.9527), and the male was W = 0.0151 L 2.9689 (R² = 0.9386). The value of the average condition factor of females was 1.05, and the males was 1.02. The condition factor in females was in excellent condition (> 1.05), and males were in good condition (0.95-1.05). The overall sex ratio of male and female was 1:1.54. It means that females population was significantly higher than males. Abstrak Ikan nilem (Osteochilus vittatus Valenciennes, 1842) merupakan ikan asli yang menjadi target utama tangkapan nela-yan di Rawa Pening. Penelitian ini bertujuan untuk mengetahui parameter biologi yang meliputi hubungan panjang-berat, faktor kondisi dan nisbah kelamin ikan nilem di danau Rawa Pening Kabupaten Semarang. Pengambilan sampel ikan dilakukan dua minggu sekali dari bulan Oktober 2019 sampai Maret 2020, menggunakan kerai bambu yang dioperasikan oleh nelayan setempat. Data yang dikumpulkan terdiri atas panjang total, bobot individu, dan jenis kelamin. Data hubungan panjang-berat dan faktor kondisi dianalisis secara deskriptif, sedangkan nisbah kelamin dianalisis dengan uji chi-square (χ2). Hasil penelitian diperoleh jumlah ikan nilem betina sebanyak 392 ekor dengan kisaran panjang antara 10,0-26,0 cm dan kisaran berat antara 14,5-264,1 g. Ikan nilem jantan sebanyak 255 ekor dengan kisaran panjang antara 10,2-22,4 cm dan kisaran berat antara 15,0-160,9 g. Pola pertumbuhan ikan nilem di danau Rawa Pening bersifat allometri negatif. Persamaan hubungan panjang-berat ikan nilem betina yaitu W = 0.0186L2.9096 (R² = 0.9527), dan jantan yaitu W = 0.0151 L2.9689(R² = 0.9386). Nilai faktor kondisi ikan nilem betina rerata 1,05, sedangkan ikan nilem jantan rerata 1,02. Proporsi faktor kondisi ikan nilem betina terbanyak dalam keadaan sangat baik (>1,05), sedangkan ikan nilem jantan berada dalam kondisi baik (0,95-1,05). Rasio betina dan jantan secara keseluruhan yaitu 1,54 : 1, yang menunjukkan populasi betina secara nyata lebih banyak dari pada jantan.]]>
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