Evaluation of factors associated with dynamics of Cichla ocellaris invasion of the Upper Parana River floodplain system, Brazil

Invasion by Cichla ocellaris was studied in the Upper Parana River floodplain. Generalised linear models and the Akaike Information Criterion (AIC) were applied to standardised gill-net catch data (CPUE), with years, rivers, secchi depth, and their respective interactions. Generalised additive models and AIC were used to evaluate relationships of CPUE for C. ocellaris with standard length, sampling year and secchi depth. C. ocellaris was first recorded in 1992 in the Parana and Ivinheima Rivers. Nevertheless, the CPUE of individuals was very low in the latter until 2000, and the species was not recorded from the Baia River until 2000. In 2001, CPUE of C. ocellaris greatly increased (from 20 to 140) in all three rivers, and this coincided with changes in hydrology and suspended sediment. Greater secchi depth is thought to benefit foraging by these visually oriented, diurnal piscivores. The estimated annual growth rate for local populations was 21% for the Parana, 42% for the Ivinheima, and 73% for the Baia Rivers. Consequently, relative to other populations, C. ocellaris of the Baia River and, to a lesser degree, the Ivinheima River, appear to be less influenced by density-dependent factors given their more recent invasions of those areas.