Résumé: Two stocking densities, “low” (L, between similar to 19 and similar to 25 kg m(-3)) and “high” (H, between similar to 75 and similar to 100 kg m(-3)) were compared for effects on specific growth rate (SGR), feed conversion, energetics and welfare of rainbow trout reared at 14 degrees C either in static water (S) or swimming in a gentle current of similar to 0.9 bodylengths s(-1) (C). Trout (initial mass similar to 110 g) were reared for 9 weeks in circular tanks (volume 0.6 m(3)), in triplicate of four conditions (LS, LC, HS, HC). Fish were fed ad-libitum daily: waste pellets were swirl-collected at the outflow to calculate feed intake. SGR was measured each three weeks for the last six weeks of the trial. The tanks functioned as intermittent-stopped flow respirometers, to permit metabolic rate to be measured as instantaneous oxygen uptake once per hour. Mean (+/-SD) SGR was significantly lower at H than L (1.51 +/- 0.03 vs 1.44 +/- 0.04% day(-1), respectively, n = 6) and lowest in HC. When compared over a similar interval of mass gain, H groups had approximately 25% higher metabolic rates than L, with the highest rates in the HC condition. As a result, fish in the H groups dissipated a greater amount of feed energy as metabolism and, across all groups, there was a direct negative relationship between the quantity of energy dissipated and their SCR. There was no evidence of a neuroendocrine stress response, plasma cortisol was around 1 ng ml(-1) in all conditions. An acute crowding stress increased plasma cortisol to above 120 ng ml(-1) in all groups, but C groups recovered to control levels within 8 h whereas S groups required 20 h. Respirometry on individuals revealed that H fish had approximately 14% higher metabolic rates than L fish, indicating that increased metabolic rate in rearing tanks was in part physiological. The H groups had approximately 15% lower critical swimming speeds than the L groups which, together with their raised metabolic rate, indicated a physiological impairment Thus, high density reduced SGR by raising energy dissipation, at least partially as a physiological response by the fish, although there was no evidence of an endocrine stress response. The only beneficial effect of C was in recovery from acute stress. (C) 2012 Elsevier B.V. All rights reserved.

Résumé: Salmonids are ecologically, economically, and culturally important fish species in North America, but whether contaminants in the environment play a role in their population decline is unclear. We tested the hypothesis that bisphenol A (BPA) deposition in eggs, mimicking a maternal transfer scenario, compromises the stress axis functioning and target tissues stress response in two generations of a model salmonid species, rainbow trout (Oncorhynchus mykiss). Eggs were enriched with 0, 4, or 40 ng of BPA, fertilized, and reared in clean water for two generations. The fish were subjected to an acute stressor after a year in both generations to test their stress performances. Trout raised from BPA-enriched eggs showed impaired stressor-mediated plasma cortisol and lactate response in the Fl and F2 generations, respectively. Key genes involved in cortisol biosynthesis in the head kidney, as well as stress- and growth-related transcripts in the liver and muscle, were impacted either in the F1 and/or F2 generations. Our results underscore the long-term impact associated with BPA in eggs, mimicking a maternal transfer scenario, on the stress performance of trout in two generations. The results highlight the need for developing novel biomarkers to predict long-term and generational toxicities in salmonids.