Reproductive Biology of Skipjack Tuna (Katsuwonus pelamis) in Indonesian Exclusive Economic Zone

Skipjack tuna (Katsuwonus pelamis) is a tropical tuna species and has been a historically exploited in the south and western part of Indonesia waters (south eastern Indian Ocean). The objective of this study was to determine length at first maturity (Lm50) of female skipjack obtained from area south of Bali. Samples were collected from April to September 2018, and April to October 2019. A total of 230 ovaries with length ranged between 33-72 cm FL. Fresh ovaries were immediately fixed using a 10% buffer-formalin solution then histologically prepared using the paraffin method and HE staining (Harris-Haemotoxylin and Eosin). Ovaries containing advanced yolked, migratory nucleus or hydrated oocytes and/or POFs were classed as mature, and ovaries with unyolked or early yolked oocytes as the MAGO but with maturity markers present were classed as mature as well. Ovaries containing unyolked and early yolked oocytes as the MAGO but no POFs, atresia or maturity markers were classed as immature. Size at first maturity (Lm50) of female skipjack in Indian Ocean southern Bali was 42 cm FL (41 - 42.9 cm FL).