Utilization of alternative protein sources in aquafeeds

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Protein component of the aquaculture feeds is the single most expensive portion and important dietary nutrient. However, recent quick decline of sardine catch in Japan has resulted in the shortage of quality fish meal and has made it necessary to increase the use of alternative protein in practical feeds. This research was, therefore, conducted to investigate the availability of various protein sources such as soybean meal (SBM), corn gluten meal (CGM), meat meal (MM), meat born meal (MBM), etc., in diets for yellowtail, red seabream, striped jack, rainbow trout.In yellowtail it has been demonstrated that fish meal could be replaced up to 62% by combinations of SBM,CGM and MM in newly developed soft-dry pellets (SDP) for both juvenile and adult yellowtail without any adverse effect. But the SDP with 50% soy protein concentrate showed feed performances and physiological conditions slightly inferior to the fish meal diet group. These protein sources were also found to be able to replace around 50% fish meal in single moist pellets (SMP). SBM,CGM,MM,MBM were also found to be included in SMP at levels of 20-30% as sole alternative protein. Dietary value of raw SBM was improved by heat treatment, further by alcohol treatment. In red seabream, utilization of different types of SBM,with or without extrusion processing, was investigated using high energy dry pellets, with 30% SBM.Palatability and acceptability of diets were influenced by inclusion of 30% SBM.There was no marked difference in growth and feed gain ratio between the control and SBM diets, although feed performances were slightly better for the control. The feed utilization of SBM diets was not improved by extrusion processing. In striped jack, SBM and defatted wheatgerm meal were found to be included at a 30% level in DP without ill effect. The same kinds of results were also obtained in rainbow trout.