Seasonality and midscale spatial effects on Cichla ecology and fish species diversity in a neotropical floodplain river

Abstract

The influence of seasonal fluctuations in water levels on tropical fish species from fluvial environments was evaluated by comparing the ecology of resident piscivores and habitat use of prey fish within a floodplain river. Ecological data were collected for three species of sympatric Cichla (Cichlidae) from the Cinaruco River in Venezuela from November 1993 to June 1994. Cichla intermedia showed an affinity for structured habitats in the main channel. Cichla orinocensis and C. temensis were captured in both main channel and lagoon habitats. Cichla temensis was more numerous and significantly larger than the other two species. Hydrologic seasonality influenced prey availability, and consequently reproductive timing. Prey fishes from predator stomachs were significantly larger during the falling-water period than during rising water. All three species of Cichla had spawning peaks during the late low-water and early rising-water periods. Marginal increment analysis of saggita otoliths revealed a slow growth period that coincided with low water and peak spawning activity. Based on annuli counts from otoliths, Cichla from the Cinaruco system can live up to seven years. Increased fishing pressure at the Cinaruco, especially during the reproductive season, may disrupt adult reproductive success and survival of substrate-guarded young. Management activities aimed at maintaining healthy Cichla stocks should be directed at protecting spawning adults. Seine collections from sand beach habitats revealed high species diversity. One hundred and five fish species from 22 families and 8 orders were found in lagoon and main river beach habitats. The order Characiformes comprised 68.5% of the species and 83.5% of the individuals. Most samples were numerically dominated by 1-3 species of small characids. Perciforms were more diverse in lagoon beaches than in main or side channel areas. Many fish species were never numerically abundant but occurred in most collections. There was little similarity in species assemblages among lagoon samples, or among main river samples, suggesting little fine-scale habitat specialization for fishes inhabiting sand beach areas.