IMPACT OF PREDATION ON EARLY STAGES OF THE ARMORED CATFISH HOPLOSTERNUM-THORACATUM (SILURIFORMES-CALLICHTHYIDAE) AND IMPLICATIONS FOR THE SYNTOPIC OCCURRENCE WITH OTHER RELATED CATFISHES IN A NEOTROPICAL MULTI-PREDATOR SWAMP

This study investigated the role of predators in preventing competitiv e exclusion among three closely related armoured catfishes (Callichthy s callichthys, Hoplosternum littorale and H. thoracatum) that occur sy ntopically in multi-predator freshwater swamps of Suriname, South Amer ica. The potential impact of predation on armoured catfish was determi ned by combining laboratory measurements of predation rates on five ea rly developmental stages of the armoured catfish H. thoracatum for 24 aquatic predators with field studies of the density of the predators i n the swamps. The contribution of a particular predator to the total p redation pressure on its prey was determined to a large extent by the density of the predator in the swamp. Seemingly innocuous predators wi th low or moderate predation rates in the laboratory may be extremely important in the swamps due to their high abundance. Small-sized omniv orous fishes and aquatic invertebrates were major predators of early d evelopmental stages of armoured catfish. Both qualitative and quantita tive ontogenetic changes in the predation pressure on armoured catfish were observed. Major predation on eggs, larvae and juveniles of H. th oracatum resulted from a different set of predators in each developmen tal stage of the prey. In all developmental stages of H. thoracatum th e predation pressure involved several predator species and not a singl e, dominant predator. The potential predation pressure of the 24 preda tors taken together and the number of predators that were able to prey on N. thoracatum decreased sharply with increasing age (size) of the prey. Even if egg (nest) predation is prevented by the guarding male, the potential impact of the 24 predators on the populations of armoure d catfish is large. Predation may account for the high mortality of H. thoracatum observed in the swamps. The high predation pressure on cal lichthyid catfishes may help to explain the coexistence of three close ly related and morphologically quite similar armoured catfishes in Sur inamese swamps.