Survival of Rainbow Trout Oncorhynchus mykiss Walbaum, 1792 (Salmoniformes -
Salmonidae) Eggs in an Altitude Stream in Southern Brazil
WINCKLER-SOSINSKI1, L.; SCHWARZBOLD1, A. & SCHULZ2, U.H.
1 Universidade Federal de Rio Grade do Sul, Av. Bento Gonçalves 9500, Inst. de Biociências. Depto. Ecologia, 91540-000 Porto Alegre, RS, Brasil.
2 Universidade do Vale do Rio dos Sinos, Lab. de Ecologia de Peixes C2, Av. Unsinos, 950, 930022-000 São Leopoldo, RS, Brasil.
ABSTRACT: The introduction of rainbow trout (Oncorhynchus mykiss) in a high altitude stream in Southern Brazil occurs every year in winter to support a put and take fishery of local economical importance. The effects of this introduction on the native fauna have not been investigated. To address the question whether rainbow trout might build up a self-sustaining population, we measured the survival of eggs in modified Whitlock-Vibert-Boxes. These artificial redds, filled with natural substrate and rainbow trout eggs, were incubated in the bottom substrate of the Silveira stream. After three weeks exposure mean survival was 10.7% (1.7 standard error). In the fourth week hatched larvae were found. The number of surving larvae decreased in the fifth week, indicating high larval mortality in the post-hatching phase. The overall survival rate at this time was 3.5 % (1.1 s.e.). Considering the low survival of eggs and the high water temperatures during summer which increase the mortality of adults, the build-up of a self-sustaining population is not probable.
Key-words: Oncorhynchus mykiss, reproduction, exotic species.