Zoological Studies

Vol. 54, 2015

Selective foraging by non-native rainbow trout on invertebrates in Patagonian streams in Argentina

Cecilia Yanina Di Prinzio1,2,3*, Guillermo Omad1,2,3, María Laura Miserendino1,2,3 and Ricardo Casaux1,2,3,4

1Consejo Nacional de Investigación en Ciencia y Tecnología (CONICET), Rivadavia 1917, 1033 Buenos Aires, Argentina
2Centro de Investigaciones Esquel de Montaña y Estepa Patagónica (CIEMEP), Sarmiento 890, 9200
Esquel, Argentina
3Laboratorio de Investigación en Ecología y Sistemática Animal (LIESA), Universidad Nacional de la Patagonia, Sarmiento 890, 9200 Esquel, Argentina
4Instituto Antártico Argentino, Cerrito 1248, 1010 Buenos Aires, Argentina

Background: It is well known that fish predation alters ecosystem processes by top-down effects. Salmonids are described as aggressive, visually and size-selective predators. Thus, prey selection by the non-native rainbow trout was examined on a seasonal basis at two streams: Nant y Fall (NyF) and Cabeza de Vaca (CVA) at Patagonia, a region where this kind of information is lacking.
The benthos density at NyF was higher than that at CVA, and at both streams, riffles supported higher macroinvertebrate densities than pools. The diet of trouts from both streams was dominated by aquatic macroinvertebrates, was diverse, and was varied seasonally. The individuals represented in the stomach contents were among the largest available at the streams. Diet diversity peaked during spring at NyF and during summer at CVA, whereas at both streams, the niche width peaked during spring. Prey selectivity varied seasonally. The selected preys included both aquatic (Gasteropoda, Crustacea, Plecoptera, Trichoptera, Ephemeroptera, Coleoptera, Diptera, and Odonata) and terrestrial organisms (adult dipterans, Oligochaeta, Araneae, Homoptera, Hymenoptera, Orthoptera, and Hemiptera). Some infaunal invertebrates like oligochaetes and some small Coleoptera and Diptera larvae (mainly Chironomidae) were not selected by trouts.
Conclusions: Despite of the overall dominance of trichopteran species, the composition of the diet of the rainbow trout varied seasonally. This fish positively selected both aquatic and terrestrial organisms. We observed that in both streams, trouts consumed the larger individuals available in those environments.

Key words: Selective predation; Non-native fish; Stream; Patagonia.

*Correspondence: E-mail: laracar@posgradouatx.com.mx