Ultrastructural variations of the sagittae in two Anabantiformes fishes: Anabas testudineus (Bloch, 1792) and Trichogaster fasciata (Bloch & Schneider, 1801)

Abstract

The sagitta otolith is well-decorated with various species-specific peculiarities, used to support the relatedness in taxonomy and other aspects among fishes. Present study deals with the morphostructural variations of the sagitta in the Anabas testudineus and Trichogaster fasciata by light and scanning electron microscopy. As these two fishes are belonging to order Anabantiformes but their sagitta morphologies are much more varies. The sagitta of the A. testudineus is oval with complete dorsal and ventral marginal boundary, while the dorsal boundary is incomplete in the T. fasciata. The sulcus of the A. testudineus is ostio-pseudocaudal with spoon-headed ostium, whereas the sulcus in T. fasciata is ostio-caudal with a simply tubular ostium. The ostium and cauda are demarcated with a prominent constriction in the A. testudineus, while this demarcation is maintained by a virgule-like development in the T.fasciata. Presence of the orthorostrum patch, and hexangular stony pillars along the marginal sculpture in the T. fasciata is a species-specific peculiarity. A phylogenetic tree is made based on the sagitta features between these two fish species and five other Anabantiformes fishes and stated that the A. testudineus is characteristically more related to Channa sp than that of the T. fasciata.