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A portion of the terrestrial subsidies to lentic habitats consists of arthropods. In high mountain, originally fishless lakes, terrestrial arthropods are an important seasonal food resource for introduced fish. Here we investigate how brook trout (Salvelinus fontinalis) can alter the input of terrestrial arthropods in 10 high mountain lakes contrasting for their stocking history (with and without fish or manipulated for fish eradication). We used a food consumption model to calculate the minimum and maximum number or biomass of arthropods consumed by fish, and we found that they can exceed, by several folds, the number or biomass of arthropods sinking into the lakes, at least under the metabolic rates expected for fish for most of the summer. We interpret this result as an indirect indication that arthropods usually cannot overcome the surface tension at the lake surface and that fish can work as a vector across the water-air interface. We infer that pathways for dead and live arthropods to leave the lakes do exist and fish can transfer into the water column many arthropods whose fate was leaving the lakes, which may have overlooked ecological and conservation implications. Les arthropodes constituent une partie des apports terrestres dans les habitats lentiques. Dans les lacs de haute montagne initialement sans poisson, les arthropodes terrestres constituent une importance ressource alimentaire saisonniere pour les poissons introduits. Nous examinons comment des ombles de fontaine (Salvelinus fontinalis) peuvent modifier l'apport d'arthropodes terrestres dans 10 lacs de haute montagne caracterises par differents historiques d'empoissonnement (avec ou sans poisson, ou manipules pour en retirer les poissons). Nous employons un modele de consommation d'aliments pour calculer le nombre ou la biomasse minimum et maximum d'arthropodes consommes par les poissons et constatons que ce nombre ou cette biomasse peut etre plusieurs fois superieur au nombre ou a la biomasse d'arthropodes qui calent dans le lac, du moins pour les vitesses de metabolisme prevues pour les poissons durant la majeure partie de l'ete. Ce resultat est interprete comme indiquant de maniere indirecte que les arthropodes ne peuvent habituellement pas contrer la tension de surface du lac et que les poissons peuvent constituer un vecteur pour le passage de l'interface eau-air. Nous inferons qu'il existe des voies permettant aux arthropodes morts et vivants de sortir des lacs et que les poissons peuvent transferer dans la colonne d'eau de nombreux arthropodes dont le destin etait de quitter les lacs, un processus qui pourrait avoir des consequences ecologiques et pour la conservation qui ne sont generalement pas prises en consideration. [Traduit par la Redaction], Introduction Terrestrial subsidies to aquatic habitats include all nutrients of terrestrial origin that are incorporated into the aquatic food web, becoming available in the form of dissolved or particulate organic [...]

Carotenoid-based signals may function as indicators of individual quality because, being exclusively obtained from the diet, they indicate the ability of individuals to intake high-quality food. Moreover, carotenoids are involved in several important physiological functions, including antioxidant defense, so that carotenoid-based colorations have been suggested to reflect the antioxidant status of their bearers. The present correlative, cross-sectional study aimed at investigating if the skin carotenoid-based coloration is a signal of antioxidant defenses in the brown trout (Salmo trutta Linnaeus, 1758). We investigated the relationships between carotenoid-based coloration traits (including the number, density and redness of red spots, as well as the ventral yellowness), and both non-enzymatic (plasma and liver total antioxidant capacity) and enzymatic antioxidant defenses (activity of hepatic superoxide dismutase —SOD, catalase —CAT and glutathione peroxidase —GPx). We found significant positive covariations between antioxidant defenses and carotenoid-based skin coloration, in terms of ventral yellowness. Brown trout individuals displaying intense carotenoid-based coloration (i.e., ventral yellowness) had a high non-enzymatic antioxidant capacity both in plasma and in liver and, interestingly, an elevated activity of hepatic SOD and CAT. Our data suggest that carotenoid-based skin colorations may be considered a signal of individual quality in terms of antioxidant defenses in the brown trout. [ABSTRACT FROM AUTHOR]

Introduced fish are a major threat for high altitude aquatic habitats and Salvelinus fontinalis have been widely used throughout the Alps for stocking lakes and rivers. Understanding its feeding ecology is a basic, but essential tool for interpreting its impact. To assess which factors determine the diet of S. fontinalis we analyzed more than 500 stomachs from several introduced populations from the Gran Paradiso National Park (GPNP, Western Italian Alps) and we measured the availability of several prey groups (zooplankton, aquatic invertebrates, terrestrial invertebrates). We complemented the study with a short, but exhaustive literature review on the S. fontinalis feeding ecology. In general the food composition reflected the availability of prey -confirming that S. fontinalis is an opportunistic predator-and was influenced by habitat type (stream vs lake), fish size, and seasonality. The obtained results were discussed in the light of the existing literature on the feeding ecology and ecological impact of S. fontinalis. Large benthonic insects account for a substantial part of the diet of stream dwelling brook trout, while they are almost absent both in the diet and in the prey species pool of lake-dwelling brook trout, probably reflecting a stronger ecological impact in the lakes. [ABSTRACT FROM AUTHOR]