Developmental variations of sagitta otolith in different body size groups of Trichogaster fasciata (Bloch and Schneider, 1801)

The Trichogaster fasciata (Bloch and Schneider, 1801) is a small, indigenous, tropical labyrinth perch of Osphronemidae family with a great value in the ornamental fish industry and biological experiment. Morphological descriptors of the sagitta otolith are used as an important tool in fish taxonomy and fish biology. Detailed morphological and morphometrical characteristics of almost all visible descriptors of sagitta otolith in different body length groups of T. fasciata are described. The sagitta contains a heterosulcoid, ‘J”-shaped, ostio-caudal sulcus with a distinct rostrum and orthorostrum patch. Different morphostructural development in the ortho-rostrum patch is directly proportional to the total length. The caudal fork is well-developed and its growth is directly proportional to the total length. The marginal sculptures of the sagittae comprised numerous scallops, whose shape and size are considerably changed with the increment of the total length. The Kruskal–Wallis H test revealed that some sagitta descriptors display important changes in different body length groups of T. fasciata. About nineteen sagitta descriptors among the studied structures display a significant developmental relationship to the increment of the total length and they might be used as an important predictor to evaluate the fish size. Different shape indices of the sagitta and the sulcus are analyzed, some of which have a significant relationship to the total length. These shape indices and the sagitta predictors might be useful in stock separation of the T. fasciata. The characteristics of the sagitta descriptors of T. fasciata are compared with the available data of other Anabantiformes fishes.