PENENTUAN UKURAN PERTAMA KALI MATANG GONAD (Lm) CAKALANG (Katsuwonus pelamis Linnaeus, 1758) DI SAMUDRA HINDIA SELATAN BALI

Abstract

Cakalang tergolong kelompok jenis ikan pelagis besar yang keberadaanya cukup melimpah di perairan Samudera Hindia termasuk perairan selatan Bali. Informasi biologi reproduksi sangat penting terutama untuk mengetahui kapan ikan tersebut memijah sehingga dapat digunakan sebagai dasar pengelolaannya. Cakalang memijah beberapa kali (multiple spawner), hal ini diketahui berdasarkan tingkat perkembangan oosit yang lebih dari satu tingkatan dalam satu gonad aktif. Sampel gonad cakalang betina diperoleh dari Pangkalan Pendaratan Ikan Kedonganan, Bali. Sebanyak 106 ekor cakalang betina dengan kisaran panjang cagak 37-71 cmFL dan kisaran bobot 902-7.214 gram yang teramati. Sampel gonad dalam keadaan segar langsung difiksasi menggunakan larutan buffer-formalin 10% kemudian dianalisis secara histologis menggunakan metode parafin dan pewarnaan HE (Harris-Haemotoxilin dan Eosin). Cakalang betina yang diklasifikasikan sebagai ikan yang belum dewasa (immature) memiliki karakteristik oosit unyolked (UY) yang lebih gelap pewarnaannya, memiliki diameter <156 µm dan Early yolked (EY) yang memiliki diameter 114-249 µm. Cakalang dewasa (mature) memiliki karakteristik perkembangan ovari berupa adanya oosit pada tingkat yang lebih tinggi yaitu advanced yolked (AY) dengan diameter oosit berkisar antara 180-448 µm, migratory nucleus (MN) 239-468 µm dan hydrated (Hy) dimana ukuran oositnya sangat besar yaitu sekitar 459-552 µm dan berbentuk seperti noda merah muda (pink stain). Cakalang betina di perairan Samudera Hindia selatan Bali memiliki perkembangan oosit yang asynchronous (tidak seragam) yang ditandai oleh munculnya beberapa tingkat perkembangan oosit dalam satu ovari. Ukuran panjang pertama kali matang gonad (Lm) cakalang betina yaitu 44,7 cmFL. Cakalang betina dewasa yang berstatus memijah aktif (actively spawning) ditemukan di setiap bulan pengamatan (April-September) dan diduga memijah sepanjang tahun. Skipjack tuna is classified as a large pelagic fish species and has abundant presence in the waters of the Indian Ocean including the waters of southern Bali. Information related to reproductive biology is very important especially to find out when the fish spawn so that they can be used as a basis for its management. Skipjack spawns several times (multiple spawner), this is known based on the level of oocyte development that was more than one level in one active gonad. Samples of female skipjack gonads were obtained from Kedonganan, Bali. A total of 106 female skipjack tuna with length range of 37-71 cmFL and weight range of 902-7,214 grams were observed. Gonad samples in fresh condition were immediately fixed using a 10% buffer-formalin solution then histologically analyzed using the paraffin method and HE staining (Harris-Haemotoxilin and Eosin). Female skipjack classified as immature fish has the characteristics of unyolked oocytes (UY) which are darker in coloration, have a diameter <156 ìm and Early yolked (EY) which has a diameter of 114-249 ìm. Adult skipjack (mature) has the characteristics of ovarian development in the form of oocytes at a higher level, namely advanced yolked (AY) with oocyte diameter ranging from 180-448 µm, migratory nucleus (MN) 239-468 µm and hydrated (Hy) where oocyte size is very large, which is around 459-552 µm and shaped like a pink stain. Female skipjack in the waters of the Indian Ocean south of Bali has an asynchronous (non-uniform) oocyte development which is characterized by the appearance of several levels of oocyte development in one ovary. Size at first maturity (Lm) of female skipjack in Indian Ocean southern Bali was 44.7 cmFL. Adult skipjack females with active spawning status are found every month of observation (April-September) and suspected to spawn throughout the year.