Endozoochory by an ilyophagous fish in the Paraná River floodplain: a window for zooplankton dispersal

Abstract

Fish can have an important role in the passive dispersal of freshwater zooplankton. In the Paraná River system the migratory fish Prochilodus lineatus (Valenciennes) constitutes about 60% of the fish biomass, the adult individuals have an ilyophagous feeding mode adapted to feed on soft bottom sediments. We hypothesize that P. lineatus ingests resting stages of zooplankton along with bottom sediments and that these resting stages are able to hatch after passing through the digestive tract. Forty adult P. lineatus individuals were caught in a lake located in the floodplain of Middle Parana River. Content of the last part of intestine was removed and divided into two equal portions and stored (3 months) at 4°C and at room temperature. Later, both portions were incubated for 27 weeks at 25°C. Hatching was controlled at 4-day intervals during the first 9 weeks of the experiment and later less frequently. At the end of the experiment, 8016 individuals were recorded, belonging to 18, mostly littoral species (15 rotifers, 2 cladocerans, and one copepod). Incubation preceded by a cooling period resulted in hatching of more species and individuals. Our results show that migratory fish may be an important vector for zooplankton dispersal.