Histology and Histochemistry of the Female Sparrow Rasbora, Boraras urophthalmoides (Cypriniformes: Cyprinidae), an Important Small Fish in Thailand.

Despite extensive histology descriptions in fishes, comparable information for the sparrow rasbora (Boraras urophthalmoides), an important freshwater fish in Thailand, remains scarce. This study characterized the histology and histochemistry of the major organ systems in female B. urophthalmoides. Ten healthy adult females collected from freshwater habitats in Nakhon Nayok Province, Thailand, were examined using routine histological and histochemical methods. The results demonstrated the organization of the digestive, reproductive, respiratory, circulatory, nervous, integumentary, and urinary systems. The digestive system showed clear regional differentiation from the oral cavity to the intestine, together with the associated liver and pancreas. The ovary contained oocytes at various developmental stages, each with distinct histochemical features. The gills, heart, brain, spinal cord, integument, and kidney also exhibited well-defined tissue architecture, indicating functional specialization of the major organ systems. These findings provide baseline histological and histochemical information on B. urophthalmoides and contribute to a better understanding of its biology, ecological adaptations, and potential requirements for captive maintenance and aquaculture.