Abstract
The aim of this study was to replace 75% of total fish oil (FO) and alter digestible protein/digestible energy (DP/DE) in rainbow trout feeds to minimize potentially hazardous environmental contaminant exposure. Two diets differing in DP/DE ratios (18 and 25) were combined with soybean (SO), canola (CO), and a blend of canola oil and Schizochytrium sp. (COS). Dietary lipids and DP/DE ratios did not affect apparent digestibility, growth, and somatic parameters. The n-3/n-6 levels decreased significantly in the growth trial, especially for the SO groups. A short washout trial restored n-3/n-6 levels for the CO and COS groups, irrespective of the DP/DE ratio, but not for the SO groups. At all sampling events, contaminant concentrations in fish flesh were lower than limits set by regulatory agencies in Canada, the US, and Europe. Contaminants were lower in the oil replacement diets compared to FO for toxaphenes, organochlorine pesticides, and PCBs but not flame retardants during the growth phase. At the end of the washout phase, no differences were detected. Thus, this study revealed that replacing 75% of total fish oil in rainbow trout feed by CO and COS, combined with a 25 DP/DE ratio, with a washout period seems to be the most efficient approach in terms of maximizing the total FO replacement and contribute to reducing POPs exposure.
Highlights
Bell et al [16] concluded that replacing fish oil in the aquaculture feed by vegetable oils plus a washout period is efficient in reducing persistent organic pollutants (POPs) accumulation in Atlantic salmon
While the level of fish meal was not altered in vegetable oil-based diets, total fish oil was reduced by 75%
These diets must contribute in maintaining growth and somatic parameters, as well as the high quality of the flesh in terms of fatty acid content. e average fish mass increased continuously through the experiment without mortality, and no effects of dietary treatments on weight gain, thermal growth unit coefficient (TGC), condition factor, and hepatosomatic index were observed in this study (Table 3)
Summary
Tanks were stocked with 45 fish per tank in order not to exceed a density of 60 kg/m3 per tank at the end of the trial, based on known growth rates. E lipid sources were herring oil (FO), soybean oil (SO), canola oil (CO), and a blend of canola oil and Schizochytrium sp. E COS blend was formulated to provide an equivalent level of DHA versus FO, while providing equivalent energy to other FO replacements via CO. E following diets were formulated: 18 DP/DE with 100% FO (18 FO); 18 DP/DE or replaced with 75% SO (18 SO); 18 DP/DE with 75% CO (18 CO); 18 DP/DE with 75% of a blend of CO and Schizochytrium sp. To restore beneficial n-3 LC-PUFA levels in fillets, fish oil-based diets were fed for a three-month washout period. Fish were fed diets containing 100% fish oil
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