Introduction
The cereal industry generates large amounts of residual by-products with high potential as feed ingredient for aquafeeds. Such raw materials could help to substitute protein and lipids from less sustainable sources such as soy concentrate, wheat flour or oils and reduce the competitiveness between the production of aquafeeds and the use of food for human consumption. In this study, one of these by-products, corn gluten feed, has been tested in dose-response experiments as ingredients in on-growing feeds for two European species (greater amberjack, Seriola dumerili; gilthead seabream, Sparus aurata). The final aim was to examine to what extent this more-sustainable and low-cost product can be used as alternate ingredient for fish feeds.
Materials and methods
Corn gluten feed was provided by Roquette (Corex, 18% crude protein). The experimental diets had increasing proportions of this novel ingredient. Diets were manufactured by SPAROS Lda and were tested in greater amberjack and gilthead seabream. The inclusion level increased from 0 to 25% on weight basis (control: 0%, 12.5%; and 25%) replacing wheat flour and rapeseed oil. All diets contained 47% of crude protein and 20% of crude fat. Greater amberjack juveniles (average body weight 92.25 g) were distributed in 9 tanks in RAS and fed until apparent satiation three times a day for 97 days at 22 ºC. Gilthead sea bream juveniles (average body weight 93.36 g) distributed into 9 tanks in RAS were maintained for 57 days at 24 ºC and fed in excess with automatic feeders twice a day. Feeding and growth performance were measured at the end of the trials with both species. Intestinal integrity, oxidative stress biomarkers (catalase activity CAT, lipid peroxidation LPO and mitochondrial reactive oxygen species mROS) in liver as well as fillet composition and organoleptic characteristics were also analyzed in greater amberjack. Statistical differences were tested by one-way ANOVA followed by Tukey’s test (p < 0.05).
Results
Experimental diets were well-accepted by both fish species and the fish grew up in all cases. In greater amberjack, the voluntary feed intake (VFI) was lower, but not significantly different, in fish fed diet with 12.5 inclusion of corn gluten feed than in fish fed the other two diets. Growth parameters and feed conversion ratio (FCR) with the two experimental diets were similar to those of the control diet. The hepatosomatic index (HSI) was also similar among treatments. However, the viscerosomatic index (VSI) was higher with diet containing 12.5% of corn gluten feed (Table 1). Oxidative stress parameters (CAT and mROS) were higher with 12.5%-diet than with the other two diets, but LPO was similar among treatments though with a trend to be lower with the control-diet (Table 2). Organoleptic analysis of fresh and cooked fillet samples revealed no differences among treatments for all sensory attributes and a good acceptance for fillets coming from fish fed diet with the new ingredient. No histological alterations associated to inflammatory processes in the intestine were observed in fish fed the experimental diets. In gilthead sea bream, VFI was significantly lower in fish fed on diet with 12.5% of corex inclusion, but growth parameters and FCR were similar in juveniles fed on the three diets. Likewise, no statistical differences were detected for VSI (Table 3).
Discussion
The inclusion up to 25% of corn gluten feed in diets for greater amberjack and gilthead seabream allowed similar growth and feed utilization than the control, even a tendency for a more favorable utilization of the diet with 25% inclusion was observed in greater amberjack. With the 12.5%-corex diet, fish required to activate higher antioxidant defences to prevent damage by oxidative stress. In addition, fish fed with the new ingredient maintained the integrity of the intestinal mucosa as well as the flesh quality. These results support the potential of corn gluten feed to be used as an ingredient for fish diets. This by-product has a good protein content and is also rich methionine, a limiting amino acid in feeds with high proportion of plant derived ingredient. The use of this ingredient would increase the sustainability of growing stage in the aquaculture industry without affecting the zootechnical performances and reducing competition with human food chain resources.
Acknowledgements
Project SUSTAINFEED, EIT Food 21168, Co-funded by the European Union.