Niche specificities of eleotrid fishes in a tropical estuary

Abstract

Five species belonging to the teleost fish family Eleotridae (sleepers) are known to coexist in the Tortuguero estuary of Caribbean Costa Rica and adjacent estuaries. Three of these forms, Dormitator maculatus , Eleotris amblyopsis , and Gobiomorus dormitor are found amongst the root masses of water hyacinths along the borders of the lower estuary. The study was carried out to determine how these forms divide their environmental resources to avoid competition. Field investigations were carried out at Tortuguero in September of 1977. Results suggest that Eleotris amblyopsis is the dominant species in the hyacinth root masses and is largely carnivorous, feeding on invertebrates and larval fishes. Only small individuals of Dormitator milculatus are found in this habitat and these forms utilize plant materials in addition to invertebrates. Gobiomorus has feeding habits similar to E. amblyopsis but occupies benthic areas sheltered by the hyacinth mats. A fourth eleotrid in the system, Eleotris pisonis , has food habits similar to E. amblyopsis , but appears restricted to fresh-water tributarics of the estuarine system where E. amblyopsis is less abundant. The fifth eleotrid species, Leptophilypnus fluviatilis , appears to inhabit benthic arcasof the lower estuary, but is extremely uncommon in this system.