Histological Observations on Oocyte Development in the Fourfinger Threadfin (Eleutheronema tetradactylum)

Background: Comprehensive information on oocyte growth and ovarian development patterns (synchronous or asynchronous) is lacking. Therefore, the present study aimed to study oocyte growth and ovarian development patterns in Eleutheronema tetradactylum collected from the Gujarat coast of India from September 2021 to August 2022. Methods: 333 female E. tetradactylum were collected from the Navsari coast, Gujarat, India. Macroscopically, determined gonads were preserved in 10% neutral buffered formalin and processed for histology. Ovaries preserved in Gilson’s fluid were examined for oocyte size and development pattern, with 150-400 oocytes per fish measured in a microscope. Result: The results revealed that E. tetradactylum oocytes development stages were classified into five developmental stages. (i) pre-vitellogenic (ii) vitellogenic (iii) late-vitellogenic (iv) postvitellogenic and (v) follicular atresia. The oocyte attained the maturation stage at 550-650 µm. Histological observation and percentage distribution of oocyte types revealed that the E. tetradactylum is an asynchronous and multiple spawner fish species. In the various ovarian maturity stages, the presence of different stages of oocytes confirms asynchronous oocyte growth. Furthermore, the pattern of continuous oocyte size frequency in maturing to the ripe stage indicates a batch spawning strategy. The findings provide essential baseline data for assessing oocyte maturity and optimizing hormonal induction protocols in artificial breeding programs.