Life history characteristics and recruitment of fish under the effect of different hydrological regimes in a tropical floodplain

With the aim to analyze intra- and interspecific variation in the life history characteristics and recruitment pattern of six fish species, samples were conducted in two different hydrological regime areas of Pantanal (synchronous/Norther and asynchronous/Southern regions - high temperatures and rainfalls are and are not coincident with the flooding period, respectively). In both regions, fish were sampled using sieve net and dragnet along the river and marginal lakes. In the synchronous regime (Cuiabá River), the combined data collected between the years 2005 and 2010 were utilized. In the asynchronous regime (Paraguay River), the collections were made between 2009 and 2011. Length frequency data were used in the FISAT program to estimate the parameters. Four species, in the synchronous regime, reached trend to longer values for the asymptotic length values (L∞) and trend to lower values in growth taxa (k) and mortality (Z), but the outcomes did not demonstrate significant intraspecific variation for L∞ and Z by length classes between the hydrologic regimes (except for Moenkhausia dichroura). The recruitment pattern did not show intra- and interspecific variation between the hydrological regimes, with long period of recruitment and greater pulse for all species between June and August. Thus, the correlation of species recruitment with river level in the asynchronous regime follows the flood pulse concept, where the flooding pulse is the main driving force for production of animal and plant biomass. In contrast, the pattern of recruitment in the synchronous regime follows the hypothesis of the low flow recruitment, where the recruitment is not influenced by flooding, despite the period of high temperature and rainfall being coincident with the period of flooding.