Interactive effects of dietary protein/lipid level and oil source on growth, feed utilisation and nutrient and fatty acid digestibility of Atlantic salmon

Although the use of fish meal (FM) and fish oil (FO) has been extensive in Atlantic salmon culture, there is a growing need for less reliance on these commodities. Moreover, it is crucial for the aquafeed industry to optimise the use of dietary protein and to improve the protein utilisation in salmon diets. The interactive effects of the dietary protein/lipid level and rapeseed oil (RO) inclusion on growth, feed utilisation, nutrient and fatty acid (FA) digestibility and whole body chemical composition of large Atlantic salmon (Salmo salar L.), reared at summer water temperatures (11.6 °C), were investigated in a ten week feeding trial. The fish (initial weight 2053 g) were fed six isoenergetic diets in a factorial design containing 350 g kg−1/350 g, kg−1, 330 g kg−1/360 g kg−1, 290 g kg−1/380 g kg−1 of protein/lipid for high protein (HP), medium protein (MP) and low protein (LP) diets, respectively. At all protein/lipid levels the oil source was either FO or RO (60% of the added oil). At the end of the trial the final weights ranged from 3340–3664 g and the FCR from 0.99– 1.10. The protein level did not affect significantly any of the growth parameters but the oil source had a significant effect on final weight, specific growth rate (SGR) and thermal growth coefficient (TGC), showing improved growth with RO inclusion. This could be explained by the significantly higher lipid digestibility of the fish fed the diets containing RO (86.1 vs. 92.2%) which was probably affected by the diet FA composition; the apparent digestibility coefficient (ADC) of saturated FA, and to a lesser extent of unsaturated FA and especially monoenes, was improved by RO inclusion. The protein ADC was significantly affected by the protein level indicating a higher ADC for the HP diets compared to the LP (80.1 vs. 77.7%, respectively). Regarding the whole body composition, moisture was significantly affected by both factors, the fat content was significantly affected only by the oil source, while significant interactions were shown for the protein content. In conclusion, the results of this study suggest that low protein/high lipid diets can be used with no negative effects on the growth, FCR and chemical composition of Atlantic salmon reared at high water temperatures. Moreover, the replacement of FO with RO can enhance the growth of the fish as well as the nutrient and FA digestibility of the diets

Effects of dietary protein and fat level and rapeseed oil on growth and tissue fatty acid composition and metabolism in Atlantic salmon (Salmo salar L.) reared at low water temperatures

A 12 week feeding trial was conducted to elucidate the interactive effects of dietary fat and protein contents and oil source on growth, fatty acid composition, protein retention efficiency (PRE) and β-oxidation activity of muscle and liver in Atlantic salmon (Salmo salar L.) at low water temperatures (4.2 oC). Triplicate groups of Atlantic salmon (initial weight 1168 g) were fed six isoenergetic diets formulated to provide either 390 g kg-1 protein and 320 g kg-1 fat (high protein (HP) diets) or 340 g kg-1 protein and 360 g kg-1 fat (low protein (LP) diets); within each dietary protein/fat level crude RO comprised 0, 30 or 60% (R0, R30, R60, respectively) of the added oil. After 12 weeks the overall growth and FCR were very good for all treatments (TGC; 4.76 (±0.23), FCR; 0.85 (±0.02)). Significant effects were shown due to oil source on SGR and TGC only. The liver and muscle FA compositions were highly affected by the graded inclusion of RO. The PRE was significantly affected by the dietary protein level, while no significant effects were shown in total β-oxidation capacity of liver and muscle. The results of this study suggest that more sustainable, lower protein diets with moderate RO inclusion can be used in Atlantic salmon culture at low water temperatures with no negative effects on growth and feed conversion, no major detrimental effects on lipid and fatty acid metabolism and a positive effect on protein sparing

Effects of increasing replacement of dietary fishmeal with plant protein sources on growth performance and body lipid composition of Atlantic salmon (Salmo salar L.)

The effects of high levels of replacement of dietary fish meal (FM) by mixtures of plant protein (PP) sources on growth performance, lipid composition, protein and lipid digestibility and fatty acid profile were investigated in Atlantic salmon, Salmo salar. Experimental diets containing 35% protein and 28% lipid were formulated with a low level of FM that was replaced by increasing levels of PP resulting in four diets of 25/45 ((% FM/% PP, F25), 18/50 (F18) 11/55 (F11) and 5/60 (F5). Dietary oil was supplied by a fish oil (FO) and rapeseed oil blend at a ratio of ~40/60 so this formulation was effectively a dual replacement of FO and FM. Diets were supplemented with crystalline amino acids, to compensate for the reduction in indispensible amino acids due to reduced FM content, and all diets were supplemented with lecithin. Salmon, initial weight 1.30 ± 0.1 kg, were fed one of the four experimental diets for 19 weeks. Feed consumption decreased as PP inclusion in diets increased, probably as a result of reduced palatability. Fish fed the F18, F11 and F5 diets had significantly lower final body weights than fish fed the F25 diet, with SGR decreased by 5 %, 11 % and 23 %, respectively. The lower growth as FM inclusion in diets decreased was associated with decreased feed intake throughout the trial. In contrast, nutrient utilization was significantly affected in the first phase with increased FCR and decreased PER as FM inclusion decreased. However, there were no significant differences in these parameters in the second phase suggesting that there was metabolic adaptation to the diets. Changes in feed physical texture and/or chemical olfactory attractants possibly reduced the palatability of the diets. Essential fatty acid composition, in particular EPA, DHA and ARA in salmon flesh and liver were not negatively affected by dietary treatment and there was some evidence of increased retention and/or synthesis of LC-PUFA