Chronic stress of rainbow trout Oncorhynchus mykiss at high altitude: a field study.

The stress response of Oncorhynchus mykiss in high-altitude farms in central Mexico was investigated over two seasons: the cool (9·1-13·7° C) dry winter season, and the warmer (14·7-15·9° C), wetter summer season. Fish were subjected to an acute stress test followed by sampling of six physiological variables: blood cortisol, glucose, lactate, total antioxidant capacity, haemoglobin concentration and per cent packed cell volume (VPC %). Multivariate analyses revealed that lactate and total antioxidant capacity were significantly higher in the summer, when water temperatures were warmer and moderate hypoxia (4·9-5·3 mg l(-1) ) prevailed. In contrast, plasma cortisol was significantly higher in the winter (mean ± s.e.: 76·7 ± 4·0 ng ml(-1) ) when temperatures were cooler and dissolved oxygen levels higher (6·05-7·9 mg l(-1) ), than in the summer (22·7 ± 3·8 ng ml(-1) ). Haemoglobin concentrations (mg dl(-1) ) were not significantly different between seasons, but VPC % was significantly higher in the summer (50%) than in the winter (35%). These results suggest that in summer, effects of high altitude on farmed fish are exacerbated by stresses of high temperatures and hypoxia, resulting in higher blood lactate, increased total antioxidant capacity and elevated VPC % levels.

Variation in scale shape among alternative sympatric phenotypes of Arctic charr Salvelinus alpinus from two lakes in Scotland.

Landmark-based geometric morphometric analysis was used to detect differences in scale shape between ecologically distinct phenotypes of Arctic charr Salvelinus alpinus coexisting in the same lake. Relative warp analysis and standard multivariate analyses of the partial warps, obtained after a Procrustes superimposition, showed that scale landmarks were efficient in discriminating among two closely related alternative phenotypes within each of the two lakes. In Loch Tay, S. alpinus exhibited a bimodal body size-frequency distribution among sexually mature fish, whereas in Loch Awe, S. alpinus are unimodal in body size but segregated into two distinct spawning phenotypes. In both lakes, alternative phenotypes showed significant differences in foraging ecology, habitat use and life history. It is probable that differences in scale shape reflect differences in ecology of these forms.