Juvenile fish were sampled with a 10 m long net in a tide pool (17 000 m2) on the West margin of Boca Guarumal, Térraba-Sierpe Forest Reserve, Puntarenas, Costa Rica, from October 1992 through January 1994. Water temperature and surface salinity were recorded in each visit. The specimens were fixed in 5% formaldehyde and preserved in 70% ethanol. Abundance and size data were pooled based on precipitation, a main ecological influence in the Reserve. A total of 13 494 individuals from 18 species were captured. Eucinostomus currani, Gobionellus sagittula, Diapterus peruvianus, Agonostomus monticola and Atherinella sp. represented more than 97% of the captures. Although many species presented the tendency of concentrating during the dry season, significant differences in temporal abundance were found. The fish entered the estuary when their body length was between 20 and 60 mm.
Keywords: Composition, abundance, structure, tide pool, fish, Térraba-Sierpe, Costa Rica