Feeding ecology of priapiumfish neostethus lankesteri regan, 1916 in Sirinart Rajini mangrove ecosystem learning center and Pranburi river, Prachuap Khiri Khan province

Abstract

The priapiumfish, Neostethus lankesteri is a dominant species of the Pranburi River ecosystem. It was hypothesized as a link between primary producer and higher consumer of the Pranburi River Estuary ecosystem, Prachuap Khiri Khan Province. However, the roles and utilization of N. lankesteri in the ecosystem have not been reported. In this study, I used gut content analysis and morpho-histology of the digestive tract and the gametogenesis to examine the habitat utilization of this fish. Thirty individuals of N. lankesteri were collected monthly by larval trawl from two sites: Pranburi River estuary and Sirinart Rajini Mangrove Ecosystem Learning Center (SRMELC), during Northeast Monsoon and Southwest Monsoon season. Based on the gut content of N. lankesteri, food items were categorized into four groups: diatoms, algae, dinoflagellates, and zooplankton. The index of relative importance, IRI showed that diatoms were a major component followed by zooplankton at Pranburi River estuary, whereas zooplankton was a major component followed by the diatoms at SRMELC during the two seasons. Moreover, Neostethus lankesteri has a superior mouth with canine teeth. The pharyngeal toothplates were numerous with canine-shaped. The intestine coefficient of N. lankerteri was 0.55. The results of the histology of the digestive tract in N. lankesteri showed that they were stomachless, which the intestine consisted of three regions: anterior intestine, middle intestine, and posterior intestine. Goblet cells were also observed among epitheliums and positively reacted to Periodic Acid Schiff staining method. The study of the gametogenesis of female N. lankesteri revealed that the mature ovary in these fish was an asynchronous development oocyte type which consisting of two phases: primary growth phase and secondary growth phase. Post-ovulatory phase was observed in the sampling periods as well. In male N. lankesteri, the mature testicular parenchyma was observed. The spermatogenetic stage was divided into three phases including spermatogonial, spermatocyte and spermiogenetic phases. Overall, based on gut content, morpho-histology of the digestive tract, and gametogenesis, I suggest that N. lankesteri is zooplankton feeder specialist (sensu lato) and utilized the Pranburi River estuary ecosystem for both feeding ground and spawning ground.