AbstractBased on seasonal investigations by block net in 1999, the dynamics of species diversity of fishes in creek tidal waters within mangrove swamps of Yingluo Bay, Guangxi, were studied. Fifty four species of fishes, belonging to 44 genera and 29 families, were recorded. The numbers of species occurring in one to four seasons were 27, 8, 11 and 8, respectively. The dominant species in each season were very obvious, but the most dominant species differed in different seasons. The most dominant species were Clupanodon punctatus in spring, Osteomugil ophuyseni in summer, Ambassis gymnocephalus in autumn and Leiognathus ruconius in winter. As to theirtemperature tolerances, the warm-water species absolutely occupied the largest percentage. Numbers of demersal species were greater than other ecological types. Thirty species in spring, 30 in summer, 26 in autumn, and 22 in winter were captured in the creek waters. Twenty species were shared between summer and autumn, which was higher than that between any other pairs of seasons. This was also reflected in the similarity index between the two seasons, which reached 55.6% for the summer autumn comparison. The indices of richness D , diversity H ′, and evenness J , were all higher in autumn than in other seasons. Numbers of fish species and the three biodiversity indices in creek tidal waters were all higher than that in mangrove fringed tidal waters. The species diversity of the fish community in these waters was low in comparison with that in tropical mangrove areas.