PERKEMBANGAN HISTOLOGI GONAD, FEKUNDITAS DAN PENDUGAAN PEMIJAHAN TONGKOL LISONG (Auxis rochei Risso, 1810) DI PERAIRAN SELATAN BALI

Abstract

Tongkol lisong (Auxis rochei Risso, 1810) adalah satu jenis ikan tuna neritik yang terdapat di perairan Samudera Hindia selatan Jawa. Tingkat pemanfaatan pada saat ini diduga telah mencapai fully exploited. Penelitian tongkol lisong dilakukan untuk memperoleh data biologi reproduksi meliputi perkembangan gonad betina, fekunditas dan pemijahan di perairan selatan Bali sebagai bahan masukan bagi pengelolaan. Penelitian dilakukan pada bulan Juni-November 2021, melalui pengambilan contoh dari hasil tangkapan yang didaratkan di PPI Kedonganan, Bali. Sebanyak 151 ekor ikan betina dari total sampel 317 ekor (panjang 15-35 cmFL) telah diteliti. Sampel gonad segar difiksasi dan dianalisis secara histologis melalui metode parafin dengan pewarnaan Harris-Haemotoxilin dan Eosin. Tongkol lisong mempunyai tipe pemijahan ganda dengan kematangan oosit tidak seragam, ditandai adanya beberapa tingkat kematangan oosit dalam satu ovarium. Tongkol lisong betina yang belum matang gonad memiliki oosit unyolked dan early yolked berdiameter antara 41-179 µm; gonad ikan betina dewasa memiliki oosit lebih matang yaitu advanced yolked (AY) berdiameter antara 275-328 µm, mempunyai migratory nucleus berdiameter antara 475-514 µm dan hydrated berdiameter sekitar 554 µm. Secara makroskopis tongkol lisong betina berpijah sejak bulan Juli dengan kontribusi 32%. Pengamatan mikroskopis menunjukkan pemijahan telah berlangsung sejak Juni hingga Oktober, puncak pemijahan Juli-Agustus denga kontribusi 52% dari total ikan betina yang diamati. Dugaan fekunditas dengan oosit migratory nucleus dan hydrated yang dikeluarkan berkisar antara 5.062-229.707 butir telur/ekor atau rata-rata 81.351 butir/ekor.

Bullet tuna (Auxis rochei) is one of the neritic tuna species in the Indian Ocean south of Java. At present, its exploitation rate of its has reached fully exploited. This study was conducted to obtain the data on reproductive biology related to the gonadal (ovaries) development, fecundity and spawning in the southern waters off Bali as the input for management. The research was conducted from June to November 2021 by biological fish sampling from the catch landed. About 151 females fish from a total of 317 fishes ranging between 15-35 cm FL could be observed. The fresh gonad samples were fixed and analyzed histologically by the paraffin method with Harris-Haemotoxilin and Eosin’s staining. Bullet tuna is a multiple spawner type with asynchronous oocyte development. The immature female fish have an unlocked and early yolked oocytes with 41-179 µm in diameter; the mature ovaries have oocytes in a higher level of maturity, namely advanced yolked (275-328 µm in diameter), migratory nucleus (475-514 µm in diameter), and hydrated oocytes (about 554 µm in diameter). Macroscopically, the female bullet tuna spawned in July, characterized by decreasing GSI value and the presence of ovaries in the maturity stage IV (mature) and V (spent), with a contribution of 32% of total females landed. The microscopic observations during the sampling periods showed that spawning, characterized by the emergence of spawning development classes, took place from June to October. The peak of spawning was around July-August, where 52% of the total females landed—estimating fecundity (number of mature eggs released during spawning) with that migratory nucleus and hydrated oocytes in between 5,062-229,707 eggs/individual with an average of 81,351 eggs/individual.