A monthly underwater visual census was conducted in the coral-dominated habitat of Yokonami, Tosa Bay, Japan, from June 2006 to January 2009. A total of 12,586 individuals belonging to 168 species in 43 families were recorded during the study period. The number of species and individuals increased from June－August (summer), the highest numbers occurring in September－December (autumn), thereafter decreasing from January (winter) to the lowest point in May (spring). Labridae was the most dominant family in terms of species numbers (28 species), followed by Chaetodontidae (21 species) and Pomacentridae (18 species). In terms of individual numbers, Chaetodontidae was the most abundant (56.3% of total individual numbers), followed by Labridae (15%) and Pomacentridae (12.5%). The most dominant species were Chaetodon speculum (33.4%), Pomacentrus coelestis (11.1%), and C. lunulatus (8.2%). The fish assemblage was divided into 4 groups: (1) temperate fishes (1877 individuals in 26 species), (2) (sub-)tropical fishes (10,648 individuals in 136 species), (3) temperate－tropical fishes (28 individuals in 2 species), (4) unknown fishes (33 individuals in 4 species). Species and individual numbers of temperate fishes were high in summer and low in winter, whereas those of tropical fishes were high in summer and autumn and low in spring, suggesting that typhoons in summer and autumn, and low water temperatures in winter might affect fish recruitment and community density. Moreover, at least 44 tropical species were observed throughout the year during the study period.
