Impact of the Planktonic Larvae of the Invasive Asian Bivalve Limnoperna fortunei on the Growth of Larvae of the “Sábalo”, Prochilodus lineatus (Pisces) in South America

PAOLUCCI, ESTEBAN; CATALDO, DANIEL; THUESEN, ERIK; BOLTOVSKOY, DEMETRIO

Nijmegen, Netherlands

Congreso; ICAIS 2007 (15th International Conference on Aquatic Invasive Species); 2007

ICAIS

ecent studies have shown that the larvae of at least 11 fish species of the Paraná-Río de la Plata watershed feed on larvae of the recently (1990) introduced Asian mussel Limnoperna fortunei. Larvae of “sábalo” (Prochilodus lineatus), whose adults represent over 60% of overall fish biomass in these rivers, have been observed to feed sometimes exclusively on L. fortunei veligers. In order to assess the effects of this dietary shift on the growth of this species, we conducted 28 days laboratory experiments feeding newly hatched P. lineatus larvae with 1) plankton artificially enriched with L. fortunei larvae, where these represented 90% of all zooplankton >100 μm; 2) natural zooplankton, where veligers accounted for 43% of the zooplankton; and 3) plankton artificially enriched with cladocerans and copepods, where L. fortunei accounted for 1% of the zooplankton. Fish larvae were collected in the Lower Paraná River near the city of Zárate, whereas plankton was collected every other day in the Rio de la Plata estuary, off Buenos Aires. Experiments were conducted in 3.5 L plastic jars with 35 fish larvae each at 22ºC. The average length, weight and gut contents of the fish larvae were assessed weekly. Proportions of L. fortunei biomass in fish gut contents paralleled veliger concentrations in the respective diets, but they were always higher than those of veligers in the food offered: 100%, 76% and 21% for diets 1, 2 and 3, respectively. This indicates that L. fortunei was always selected positively over the other prey items. L. fortunei larvae are slow and clumsy swimmers, and are therefore an easy prey for the fish larvae. Final average fish length and weight decreased when fed diets with lower proportions of veligers (average lengths: 10.6, 9.9 and 9.0 mm; average weights: 6, 4 and 2 mg, for diets 1, 2 and 3, respectively). Statistically significant differences were obtained between lengths of treatments 1 and 3 (ANOVA, á<0.05, Duncan test p=0.048), and between weights of treatments 1 and 3 and treatments 2 and 3 (ANOVA, á<0.05, Duncan test p=0.004). Our results indicate that L. fortunei veligers are consumed and assimilated by P. lineatus larvae, and that this new and abundant resource significantly enhances the growth of this species. Higher growth rates may stem from the higher energy supply represented by the veligers, and/or from the lower energy costs of capturing a slower prey.