Abstract
Macrobrachium borellii is an abundant prawn of the Paraná River floodplain. Newly hatched juveniles have the general characteristics of adults, and they are proposed to have the same feeding habits. Its natural diet is composed mainly of animals' items rather than vegetals, of which dipteran larvae and oligochaetes are positively selected. However, the oscillations of the hydric cycle imply an adequacy of its selection according to prey availability in all seasons and moments of the ontogenetic development. This work verifies the predation behavior and the ontogenetic predation capacity of M. borellii feeding on three preys (cladoceran, dipteran larvae and oligochaetes) of different bioforms and mobility that represent its natural diet. The prawns were placed individually in containers where was offered one prey type in increasing amounts every 48 hours until any prawn ate the total amount offered. The predation behavior was recorded, and the amount consumed was verified after 24 hours. Both sizes of M. borellii were capable of preying on all food items used in this study. The search and catch was always made with the second queliped, suggesting a non-visual prey perception, and the handling was different for each prey. Cladoceran was the most consumed, followed by dipteran larvae and oligochaetes. The results show that, in both sizes, M. borellii has a trophic plasticity due to its capacity to prey on a variety of bioforms with differing mobility. This capacity could favor the ability of prawns to select the most profitable prey according to the changes in abiotic and ecological factors.
Highlights
Macrobrachium borellii (Nobili, 1896) is a widespread endemic prawn of the Paraná River system (Collins et al, 2004)
We proposed to verify the behavior and ontogenetic predation capacity of M. borellii on three preys of different bioforms and mobility of littoral-benthic communities that represent the natural diet of this prawn
When the preys were placed in the container, the prawn started the search almost immediately
Summary
Macrobrachium borellii (Nobili, 1896) is a widespread endemic prawn of the Paraná River system (Collins et al, 2004). The variety and availability of potential prey change with the unstable environment conditions of rivers with a floodplain These fluctuations influence the interspecific relationship of predator-prey, and feeding plays an important role because prawns may supply their nutrient requirements in each stage of ontogenetic development during all hydric cycles (Collins et al, 2006). Collins and Paggi (1998) found that M. borellii positively select oligochaetes and dipteran larvae, but, in winter, at low waters and low temperatures and in the absence of macrophytes, zooplankton might play an important nutritional role. This prawn must to be able to hunt prey of different characteristics, such as shape and mobility, in all stages of its life cycle
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