Reproductive anatomy, gonad development and spawning seasonality of nurseryfish, Kurtus gulliveri (Perciformes:Kurtidae)

Abstract

The nurseryfish, Kurtus gulliveri, of northern Australia, is remarkable for the fact that the males carry the egg mass on a supraoccipital hook on their forehead. Plankton samples of larval nurseryfish indicate a prolonged spawning season (June–November) that more or less corresponds with the dry season in the Northern Territory. The paired, elongate testes are located in the posterior portion of the body cavity suspended by the mesorchium. The gonadosomatic index (GSI) of males was small and highly variable (mean 0.14, range 0.01–0.27) from June to November. The histological structure of testicular lobes showed maturing and mature stages that contained spermatocytes, spermatids, and spermatozoa. The paired, bean-shaped ovaries contained about 5500 oocytes (1176–9783) and were located in the rear of the abdominal cavity. GSI averaged 1.58 (range 0.36–4.48). Ovarian histology revealed primary growth, cortical alveolar oocytes, vitellogenic oocytes, coalesced yolk, and atresia. The occurrence of postovulatory follicles and late vitellogenetic oocytes in the ovaries clearly indicate that nurseryfish females are batch spawners. Maturing testes showed signs of previous spawnings indicating that males are capable of spawning several times throughout the spawning season. We speculate that nurseryfish may spawn in a manner similar to their closest relatives, cardinalfishes (Apogonidae), with eggs carried on the male’s hook instead of orally.