Based on ichthyoplancton research along the southern Pacific coast of Colombia, which revealed high concentrations of fish larvae in this area, a juvenil fish survey was conducted in shallow waters « I O meter water depth) during the transition period from dry to wet season (July 21 to July 31 , 1 994). The twelve sampling stations, were distributed in fron! of the four main of this coastline, where the highest concentrations of juvenile fish were expected. At each sample station, three 15 min oblique hauls were conducted every g hours using a bottom trawl for juvenile fish of 4 mm mesh size; 53 species in 20 families were identified (21 not known as adults in the area). They were distributed as follows: Sciaenids (11), Ariids (7), Pristigasterids (6), Engraulids (6), Carangids (5), Clupeids (2), Soleids (2), Batrachoidids (2), Tetraodontids (2), Urolophids (1), Polynemids (1), Synodontids (1) and Taeniopedids (1). This ichthyofauna is cornmon in open tropical estuaries. Abundances and biomass were 0.35 ind.lm3 and 1 .61 g/m3 respectively, higher than in other tropical shallow water systems. The niches of ¡he 25 species whose abundance (A) and biomass (B) contríbuted 97.5 % and 93.3 % respectiveIy to the total catches were: (1) pelagic-neritic (53 % A, 34 % B); (2) demersal-pelagic (1 8 % A, 28 % B); (3) demersal (22 % A, 23 % B) and (4) benthic (8 % A, 1 5 % B). The Shannon-Weaver diversity index in the four subareas ranged from 0.89 to 1.1, within the range reported for other tropical American estuarine systems. An ordination analysis (non-metric Multi-Dimensional Scaling, MDS) of the data revealed significant differences in the species composition between day and night and an importan! association among sorne species. Station position, tides and environmental parameters did not markedly influence species composition. It is concluded Ihat: (1) The area surveyed represents an important nursery and growth habitat for juvenile fish of many species that are more common as adults over soft bottoms in deep waters of the continental shelf; (2) this shallow soft bot- 10m fish cornmunity is c1early separated from those species inhabiting intertidal salt marshes, interior bays and mangrove areas; and (3) sorne of the fish species commonly living in rocky and reef habitals in adult stages, spend their juvenile stage over shallow water soft bottoms. These results confirm a rather strong niche separation between juvenile and adults fish species stages in tropical waters.
Keywords: nurseries, juvenil fish assemblages, fish diversity, estuaries, multivariate analysis, colombían pacific coas