Tidal Fluctuation of Salinity and Distribution of Dominant Fish Species in Udara River Estuary, Amitori Bay, Iriomote Island.

A study in the brackish waters of Udara River Estuary, Amitori Bay, Iriomote Island, reveals distinct tidal-driven patterns in fish distribution linked to salinity fluctuations. The research found that the brackish-water species Neopomacentrus taeniurus (Ribbon Damselfish) dynamically shifts its habitat based on tidal cycles, occupying lower and mid-stream regions during high tide but restricting itself to low-salinity bottom layers (<50 cm depth) at low tide. In contrast, Fibramia amboinensis (Amami Stonefish) maintained a stable presence in mid-stream areas with salinity ranging from 19-32‰, while the diadromous species Kuhlia rupestris (Bigeye Glassy) consistently inhabited upstream zones with salinity below 3‰. These findings highlight interspecies differences in environmental adaptability, with some fish selecting optimal salinity conditions tidally and others exhibiting narrow salinity tolerance, suggesting nuanced ecological strategies in tropical estuarine ecosystems.

INOUE, H., MURAKAMI, T., NANJO, K., MIZUTANI, A., & KOHNO, H. (2016). TIDAL FLUCTUATION OF SALINITY AND DISTRIBUTION OF DOMINANT FISH SPECIES IN UDARA RIVER ESTUARY, AMITORI BAY, IRIOMOTE ISLAND. Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 72(2), I. https://doi.org/10.2208/jscejoe.72.i_1087