T. Synnøve Aas1,5*, Bendik F. Terjesen1, Trygve Sigholt3, Marie Hillestad3, Jørgen Holm4, Ståle Refstie1,6, Grete Baeverfjord1, Kjell-Arne Rørvik2, Mette Sørensen2,6,7, Maike Oehme1,5, Gaojie He5,7, Torbjørn Åsgård1,5
1 Nofima, NO-6600 Sunndalsøra, Norway
2 Nofima, Postboks 5010, NO-1432 Ås, Norway
3 BioMar, AS, NO-7484 Trondheim, Norway
4 BioMar A/S, Mylius Erichsensvej 35, DK-7330 Brande, Denmark
5 Centre for research based innovation in aquaculture technology (CREATE), SFI, SINTEF Sealab, NO-7645 Trondheim, Norway
6 Aquaculture Protein Centre (APC), CoE, P.O.Box 5003, NO-1430 Ås, Norway
7 Norwegian University of Life Sciences (UMB), Department of Animal and Aquacultural Sciences, P.O. Box 5003, NO-1432 Ås, Norway
Handling, storing and transport of feeds lead to attrition of the pellets. Undersized particles represent loss and poor utilisation of feed resources. Thus, feeds with high physical pellet quality are demanded. However, the physical properties affect the nutritional value of feeds. In a 48 days trial, two feeds, with high (feed A) or low (feed B) water stability, were fed to rainbow trout (Oncorhynchus mykiss) kept in sea water (salinity 32-34 ppm, temperature 12 °C , O2-saturation >80%). The feed intake was 23% higher in trout fed feed B than in those fed feed A. Introducing a daily period of lowered salinity (< 10 ppm), temperature (6 °C ) and oxygen saturation (50-60%) resulted in a severe drop in feed intake in both dietary groups. However, the apparent digestibility of macronutrients was highest in feed A, but at fluctuating environment the difference between the dietary treatments was small. Furthermore, the stomachs of trout fed feed B, particularly of those kept at stable environment, contained large amounts of free water and oil, which could potentially lead to fat belching. Both apparent digestibility and free water and oil in the stomach seemed to be related to feed intake, and were thus indirectly caused by feed and environmental conditions. In another trial, pellet degradation of three commercial feeds (12 mm pellet size) during pneumatic conveying, which is commonly used in cage culture to transport the feed from the storage silo to the sea pens, was measured. The three feeds, chosen especially for having different physical properties, showed different degradation patterns during conveying. Furthermore, high air speed (m/s) in the conveying system, which is used to spread the feed pellets well in the cage, increased pellet degradation, whereas high feeding rate (kg/min) protected the pellets from breakage. In all runs, less than 1% of the sample ended up as small particles. In conclusion, feed intake appears to be a main factor when evaluating pellet quality, but several other factors, such as pellet durability, nutrient digestibility and fat belching must be taken into consideration when searching for the most economical and sustainable pellet quality.
