No abstract

A 24‐week growth trial was conducted to evaluate the effects of feeding levels of corn gluten meal (CGM) on growth performance and pigment deposition in the muscle of rainbow trout (Oncorhynchus mykiss). Three isonitrogenous and isoenergetic (digestible energy basis) experimental diets were formulated to contain increasing levels of CGM (0%, 9% and 18%) and 50 mg kg−1 of astaxanthin. Each diet was fed in triplicate to groups of 75 fish (initial average body weight = 549 g fish−1) reared at 8.5°C. The inclusion of CGM did not significantly (P > 0.05) affect final body weight, thermal growth efficiency (TGC) or feed efficiency. Carotenoid concentration determined by liquid chromatography showed a significant (P < 0.05) linear reduction in the concentration of one astaxanthin isomer, all‐trans astaxanthin and all‐trans lutein in the muscle of fish in response to increasing levels of CGM. Tristimulus colour analysis of the muscle showed a significant (P < 0.05) linear reduction in a* (redness) and C*ab (chroma). Salmofan™ score showed a significant (P < 0.05) linear and quadratic reduction in response to increasing levels of CGM. In conclusion, the inclusion of CGM up to 18% does not significantly impact growth performance of rainbow trout. However, the concentration of all‐trans astaxanthin as well as the expression of important colour attributes of the muscle can be negatively affected at levels exceeding 9% of CGM in the diet. More research on this topic is needed to discern the mechanism(s) behind the negative effects of dietary CGM and/or its intrinsic yellow pigments on muscle pigmentation of rainbow trout.

A digestibility trial was conducted to assess the effect of dehulling, steam-cooking and microwave-irradiation on the apparent digestibility of nutrients in white lupin (Lupinus albus) seed meal when fed to rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Six ingredients, whole lupin seed meal (LSM), dehulled LSM, dehulled LSM steam-cooked for 15 or 45 min (SC15 and SC45, respectively) and LSM microwave-irradiated at 375 or 750 W (MW375 and MW750, respectively), were evaluated for digestibility of dry matter, crude protein (CP), lipids, nitrogen-free extractives (NFE) and gross energy (GE). The diet-substitution approach was used (70% reference diet + 30% test ingredient). Faeces from each tank were collected using a settlement column. Dehulled LSM showed higher levels of proximate components (except for NFE and crude fibre), GE and phosphorus in comparison to whole LSM. Furthermore, SC15, SC45, MW375 and MW750 showed slight variations of chemical composition in comparison to dehulled LSM. Results from the digestibility trial indicated that dehulled LSM, SC15, SC45 and MW375 are suitable processing methods for the improvement of nutrients' apparent digestibility coefficient (ADC) in whole LSM. MW750 showed a lower ADC of nutrients (except for CP and lipids for rainbow trout) in comparison with MW350 for rainbow trout and Atlantic salmon, suggesting a heat damage of the ingredient when microwave-irradiation exceeded 350 W.

Whole lupin seed meal was evaluated as partial replacement for fishmeal in extruded diets for rainbow trout, with particular emphasis on the effect on growth performance and apparent digestibility coefficient (ADC) of protein, lipids, carbohydrates, and energy. Effect on muscle fatty acid composition was also evaluated. All diets were formulated to be isonitrogenous and isoenergetic and to contain approximately 45% crude protein and 5.5 kcal energy g/diet. Diets were formulated to include whole lupin seed meal at 0, 10, 15, and 20%. Triplicate groups of fish weighing 65.9 ± 15.1 g on average were fed twice a day until apparent satiation during 12 wk. Growth, feed intake, hepatosomatic index, hepatic histology, proximate composition of whole body, and muscular fatty acid profile were determined. Growth and feed utilization were similar in all treatments and whole-body composition did not vary among treatments. Polyunsaturated fatty acids of the n-6 and n-3 series remained constant in muscle as the amount of lupin in diets increased. Furthermore, the ADCs were similar among all diets. These results suggest that inclusion of whole lupin seed meal up to 20% in extruded diets for rainbow trout do not have any negative effect on growth, feed performance, or flesh quality.

Saez, P. J., Abdel-Aal, E. M. and Bureau, D. P. 2015. Reduction of carotenoids in corn gluten meal: Effects on growth performance and muscle pigmentation of rainbow trout (Oncorhynchus mykiss). Can. J. Anim. Sci. 95: 79–92. Corn gluten meal (CGM) is an ingredient widely included in aquaculture feeds. The use of significant levels of CGM in diet formulation has been anecdotally related to the suboptimal pigmentation of the muscle of salmonid fish. The results of a few scientific studies that have examined the effect of CGM on muscle pigmentation in salmonids remain inconclusive. Therefore, a bench-scale study was carried out to reduce the content of yellow xanthophyll carotenoids in CGM using white soy flake flour as a bleaching agent. A 12-wk growth trial was then conducted to assess the effects of treated CGM on growth and muscle pigmentation of rainbow trout (Oncorhynchus mykiss) in comparison with regular CGM. Results of the pigment reduction study indicated that the concentration of lutein, zeaxanthin, β-cryptoxanthin and β-carotene was reduced by 86, 97, 100 and 100%, respectively, in the treated CGM. Results of the growth trial showed that the inclusion of treated or regular CGM in the diet did not significantly affect growth performance. However a significant (P<0.05) reduction in astaxanthin deposition was observed in the muscle of fish fed the diet supplemented with 190 g kg−1 of regular CGM when compared with the fish fed the control diet (0 g kg−1 of CGM). The muscle of fish fed the diet containing 190 g kg −1 of treated CGM showed the lowest astaxanthin deposition. This could be attributed to the presence of reactive peroxy radicals produced during the reduction of carotenoids in the treated CGM. Further research is underway to improve the processing method for the reduction of carotenoids in CGM.