Comparative ecology of eleotrid fishes in Central American coastal streams

Abstract

The population structure, abundance, reproductive status, and feeding interrelationships of eleotrid fishes from two freshwater streams of the Caribbean coast of Costa Rica were investigated over 10 continuous months. Eleotris amblyopsis was abundant in both streams. Dormitator maculatus, Eleotris pisonis, and Gobiomorus dormitor were present in both streams but common only in the larger stream that contained dense growth of floating aquatic macrophytes. Dormitator maculatus is a detritivore and overlaps with the other three eleotrids, all of which had diets dominated by shrimp and fishes. Intraguild predation and cannibalism was documented with E. amblyopsis as the prey. Except for the benthic G. dormitor, eleotrids were associated with dense mats of floating macrophytes in the large stream, and leaf peaks in the small stream. Diet similarity among the three carnivorous eleotrids declined during the wet seasons, the period when their prey disperse at lower per-unit-area densities within the flooded forests that surround the streams. Analysis of population size distributions and gonadal maturation indicated that at least some reproduction occurs on a nearly year-round basis within these eleotrid populations. The spring dry period may be associated with migration of ripe eleotrids to estuarine habitats for spawning. Juvenile Eleotris are the dominant fishes in the ‘tismiche’, mass migrations of juvenile shrimp and fish larvae and juveniles that enter and ascend the estuary, especially during the summer wet season.