Knowledge of the reproductive biology of the toadfish is still limited. The present study therefore aimed to provide basic knowledge about ovarian histology in the mangrove toadfish Batrachomoeus trispinosus, a potential aquaculture species in Thailand. To this end, we performed histological analysis of the ovaries (n = 20, all females, total length 15 to 20 cm) obtained from the Pranburi River estuary, Thailand, during January to April 2017. The ovary of this species was a paired sac-like organ located in parallel to the digestive tract. We described histological details for the oocytes at following phases: oogonium, primary growth phase (further classified into perinucleolar and oil droplets-cortical alveolar steps) and secondary growth phase (early secondary growth, late secondary growth, and full-grown oocyte steps). The ovary contained oocytes at different developmental phases. Most oocytes were in the secondary growth phase (60%), although those in primary growth phase (33.33%) and a few oogonia (6.66%) were also observed. The primary growth phase was associated with accumulated lipid droplets and cortical alveoli, whereas oocytes at the secondary growth phase contained larger lipid droplets, spherical yolk granules, and associated changes of the follicular cell. Overall information from this study provided accurate ovarian features, which will support further works on the reproductive biology of this species.
