Histopathology Laboratory, Regional Science Research Center, Office of the Vice Chancellor for Research and Extension, Mindanao State University General Santos
Corresponding author
johnchristianentia12@gmail.com
,
Glennville A. Castrence2,
Blessie Justine G. Arellano1 ,
Red Arthur Duke A. Amoncio1 ,
James T. Wetzel3, Edna P. Guevarra4
Organogenetic alterations described over the stages of gonadogenesis at the gross and microscopic scale can be used to determine spawning behavior in iteroparous fishes and provide finer details of the reproductive functions of commercially important species. This information can be used as the basis for stock assessment and maintenance of wild populations. In this study, the gross morphology of Eastern Little Tuna (Euthynnus affinis) gonads from Sarangani Bay, Davao Gulf, Moro Gulf, and Sulawesi Sea collected in 2020– 2022 was investigated along with its microanatomy through histotechniques. We determined four different size classes (FL): size 1 (≤ 30 cm), size 2 (30.1–40 cm), size 3 (40.1–50 cm), and size 4 (> 50 cm), and six stages for reproductive maturity: Immature, Onset Maturation, Developing/Maturing, Spawning, Spent, and Recovering/Resting. We observed that at the Spawning stage of the testis, the gonad appears creamy-white in color and soft in texture, with the contents freely released. The ovary is characterized by conspicuous blood vessels, a large ovum on the surface, and a pink-orange color. Histoarhitecture of the same stage showed the presence of lobular and tubular tissues, spermatozoa, primary and secondary spermatocytes, and proliferation of spermatids in the testis. In the female, the ovary is populated by secondary vitellogenic oocytes and yolk granules, indicating that the follicles are fully mature. Spawning was observed to commonly occur at Size 3 (40.1–50cm FL) in both males and females. Our paper is the first study that relates the gonadal sexual maturity of Euthynnus affinis in the southern Philippines to its fish length.