Various studies have confirmed the effects of the processing conditions on both ingredients and aquafeed quality. Temperature represents without any doubt one of the main factors affecting the nutriment availability and digestibility. Most of the raw protein sources are denatured during heat cooking process, which reduces amino acid and peptide use.
Fish larvae are extremely sensitive to the feed quality as their digestive system may not be fully in function. Development of effective weaning and starter diets is facing therefore various challenges for fulfilling the nutritional requirements with the proper physical quality adapted to the larval behavior.
In a recently published study conducted on tuna juveniles (see below reference), Cho has evaluated the effects of krill and squid-based diets and their heat treatment on the biochemical composition and growth performance. The 2 ingredients were incorporated in the complete diets as either raw (non-heated) or heated (freeze-dried meals were kept for 12 h under 105°C). After the 10-days trial, there were significant differences in the growth performance between the heated and non-heated diets either for krill and squid. The water-soluble proteins and total amino-acid profile were significantly lower in the Heated versus Non-Heated diets. It can be concluded that the highly water-soluble protein contained in the non-heated diets has been more effectively absorbed and assimilated in the early stages of tuna juveniles.
Formulation of weaning and starter diets requires severe selection of ingredients and care on their processing conditions.
Reference:
Cho, J.-H.; Kurimoto, T.; Haga, Y.; Kamimura, Y.; Itoh, A.; Satoh, S. Effects of Non-Heated and Heat Processed Krill and Squid Meal-Based Diet on Growth Performance and Biochemical Composition in Juvenile Pacific Bluefin Tuna Thunnus orientalis. Fishes 2022, 7, 83. https://doi.org/10.3390/fishes7020083