Résumé : European water legislation enforces increasingly restrictive measures with regards to reduction of water consumption and waste emission in order to minimise the potential environmental impact of the agro industry sector. Fish farms are particularly concerned, but legislation covering effluent...European water legislation enforces increasingly restrictive measures with regards to reduction of water consumption and waste emission in order to minimise the potential environmental impact of the agro industry sector. Fish farms are particularly concerned, but legislation covering effluent discharge varies significantly from country to country. However, recommendations and directives from institutional, national or regional bodies suggest the enforcement of increasingly strict waste reduction measures and the development of waste treatment. Before treatment, it is necessary to evaluate waste production in terms of composition and quantity. The waste quantification methods used today for fish culture systems are either based on direct measurements of nutrient and suspended solid fluxes or on indirect evaluation based on the digestibility coefficients of the feed constituents. The objective of the present study is to evaluate the waste of a freshwater flow through farm using both approaches and to discuss their applicability, drawbacks and advantages from the viewpoints of fish farmers and control authorities. Waste production on the farm was monitored during several 24 hour cycles in order to characterise the effluents of the system. The predictions and measurements for the total nitrogen (TN) parameter were well correlated, but measured and predicted suspended solids (SS) and total phosphorus (TP) values presented a weaker correlation coefficient. The hydrobiological method gives details on the N and P forms of waste but this method is heavy and it is difficult to obtain representative samples and flow rate measurements. The nutritional method is the simplest to use, provided that feed data are available.
Résumé : Although effects of hypoxia and, in a lower extent, effects of hyperoxia, have been widely studied, very few data is available regarding the effect of oxygen concentration around normoxia. Moreover, the effect of rearing oxygen level around normoxia on flesh quality, and a possible interaction...Although effects of hypoxia and, in a lower extent, effects of hyperoxia, have been widely studied, very few data is available regarding the effect of oxygen concentration around normoxia. Moreover, the effect of rearing oxygen level around normoxia on flesh quality, and a possible interaction with stress at slaughter, have never been investigated. Rainbow trout were reared during 18 weeks up to pan size (mean weight 400 g) at 76, 98 or 117% of oxygen saturation. Afterwards they were slaughtered according to two procedures: a minimal stress (NS group), or after a 15 min confinement stress (S group). Fish characteristics (weight, condition factor, fat-meter value, plasma cortisol level, hepato-somatic index, and hepatic glycogen content) and quality criteria of fillets (color, initial muscle pH, and muscle glycolytic potential) were recorded at slaughter time, whereas mechanical resistance, ultimate pH and dry matter content of the flesh were measured at 24 h and 48 h post-mortem. Muscle fiber size was analyzed on histological samples from white and red muscles. In our study, rearing oxygen level had no impact on the morphological characteristics of the fish except a higher hepato-somatic index and hepatic glycogen content for trout reared at 97% oxygen saturation. Rearing oxygen level affects slightly flesh quality at the lowest oxygen level (76% saturation) with a lower force for low deformation mechanical resistance measurement in the anterior part of the fillet. Stress before slaughter highly increased plasma cortisol concentration (by more than 18 in mean), and decreased fat-meter values (of 14% in mean) and the mean diameter of red muscle fibers (of 6.4% in mean). Stress before slaughter also decreased fillet lightness (L*, -1.1 unit), yellowness (b*, -0.76 unit), and initial pH (-0.15 unit) of the flesh but had no effect on ultimate pH measured at 24 or 48 h post-mortem. Stress before slaughter induced a softer flesh as shown by lower mechanical resistance at high deformation measured on samples from both anterior and caudal part of the fillet. The post-mortem measurement time (24 or 48 h) was the main factor affecting the mechanical resistance of the flesh, with a significant softening of the flesh between 24 and 48 h. Nor oxygen level, nor slaughter stress affected the size of white muscle fibers. No major interaction between rearing oxygen level and slaughter stress was formally demonstrated. (C) 2008 Elsevier B.V. All rights reserved.
Résumé : The objective of this study was to characterize the body composition, nutrient utilization, energy storage sites and major economic traits of trout selected at pan-size for or against body weight corrected muscle fat content (fat line, FL and lean line, LL respectively). The study focused on the...The objective of this study was to characterize the body composition, nutrient utilization, energy storage sites and major economic traits of trout selected at pan-size for or against body weight corrected muscle fat content (fat line, FL and lean line, LL respectively). The study focused on the effect of selection in fish size larger than the size where selection has been applied, and the possible effect of diet composition on the differences between lines. FL and LL trout were fed two diets differing for energy content and protein/lipid ratio during 62-days. The feeding trial (day 370 to day 432) started with 327g fish. Dietary protein and lipid contents were 58.7% and 8.3% dry matter (DM) respectively for diet D8 and 47.7% and 26.7% DM for diet D27. Growth, feed intake, feed utilization and traits related to body shape and composition were recorded. In both lines diet D27 improved growth rate, feed efficiency, protein retention and fat gain (P < 0.05), and was associated with a higher viscero-somatic index, fillet fat content and lower trimmed fillet yield than diet D8. At the end of the trial, LL fish were slightly heavier than FL ones (P = 0.02, no line x diet interaction). The main differences between lines were observed in lipid gain and retention. Values of lipid retention (% of intake) were higher in FL fish (P = 0.04) regardless of diet, and suggested a greater ability of FL fish in de novo lipid synthesis. Fat deposition (% of weight gain) was greater in FL fish during the trial and occurred in fillet (P = 0.04), on internal side of the belly flap (P = 0.04), as well as in other sites of the body, as indicated by higher overall body lipid content at day 432 (P = 0.02, no line x diet interaction). Nevertheless, carcass and fillet yields were not different between lines regardless of diet. In conclusion, selection for body weight corrected muscle fat content modified the ability of the fish to utilize nutrients and to store more or less fat in the different body sites. The differences were expressed in a large range of dietary protein/fat ratios. Line x diet interactions were recorded for a very limited number of traits, indicating that the combined use of genetic and nutritional tools should be efficient to manage carcass quality (growth, body shape, processing yields) and fat deposition (quantity and body location) in trout, with no need to adapt diet formulation according to lines. (C) 2007 Elsevier B.V. All rights reserved.