WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2015 45 into the mash (IN) before extrusion or coated on the outside of the pellet (OUT) after extrusion. Groups of 60 rainbow trout Oncorhynchus mykiss (average weight = 11 g) were stocked in tanks (15-1,300 L) supplied with 20 L/min, constant temperature (15 C) second-use water. Treatments were a control (no SDP), 3 percent or 6 percent SDP IN and 3 percent or 6 percent SDP OUT. All diets were isonitrogenous and isolipidic and met or exceeded the nutritional requirements of rainbow trout. Diets were fed for 84 days. The results indicated increased crude protein digestibility in diets containing SDP (Fig. 2). Biomass was greater for trout fed with 6 percent IN, and 3 and 6 percent OUT, compared to control; while 3 percent IN was slightly reduced. Overall survival of trout fed diets with SDP either IN or OUT compared to trout fed the control diet (Fig. 2). Inclusion of SDP improved survival, protein digestibility and biomass, irrespective of being incorporated inside or applied outside the feed, demonstrating that SDP could be applied prior to extrusion and maintain improvement of performance. These results are significant in terms of feed manufacturing and the optimal inclusion of SDP in commercial diets for rainbow trout. Enhanced Growth, Size Distribution, and Health Condition of Sea Bream A study evaluated the inclusion of SDP as a functional protein ingredient in commercial feeds for gilthead sea bream Sparus aurata fry in terms of growth performance, feed utilization, organization of the intestinal mucosa, activity of oxidative stress enzymes in liver and intestine, and non-specific serum immune parameters (lysozyme, bactericidal activity) (Gisbert et al. 2014). Diets (cold extruded, 0.8-1.5 mm pellet size) were manufactured by substituting high-quality fishmeal with 0, 3 or 6 percent SDP (AP820P, APC Europe, Inc.), fed for 60 days at 22 C. Fish (1.3 g initial weight) were fed to satiation and each diet was tested with four replicates (400-L tanks, 150 fry/tank). Dietary SDP promoted fish growth; the final weight of sea bream fed with pellets supplemented with 3 percent SDP was 10.5 percent greater than those fed the control diet (Fig. 3). In improved size distribution could reduce the task of size selection during processing and also diminish hierarchical dominance situations that ultimately maximize harvested biomass and reduce the cost associated with growing fish to harvest size. Based on feed conversion ratio (FCR) and protein efficiency ratio (PER), the optimal dietary inclusion level of SDP in diets for Atlantic salmon parr was calculated to be 4.1 percent. Fish Feed Processing with Plasma Most fish feeds are pelleted by extrusion temperatures greater than 100 C to improve nutrient digestibility and increase buoyancy. This begs the question: will typical aquafeed processing conditions affect the potential response of fish species fed diets containing SDP or should the SDP be applied to feed pellets post-processing? Past research related to pelleting temperature of animal diets containing SDP demonstrated that: • Conditioning at 77 C or lower did not negatively affect pig performance response to diets containing SDP (Steidinger et al. 2000). • Broilers fed SDP in feed that had been processed with conditioning temperatures of 85-95 C and expander temperatures of 149 C had improved growth response (Campbell et al. 2006). • When SDP was included in the mash of dry dog food pellets before extrusion, improved dry matter digestibility was observed (Quigley et al. 2004). These results suggest that animal responses to SDP in diets was not impaired by feed processing conditions for broilers or dogs, but could be affected in pig diets if pellet conditioning temperature exceeded 77 C. The different response between pigs and those of poultry and dogs are likely due to differences in the matrix for pig diets, which typically contain more carbohydrates and sugars that could impact the Maillard reaction when processing into feed. Increased Survival, Protein Digestibility and Biomass of Rainbow Trout A study was designed to evaluate the effects of feeding graded levels of SDP on digestibility and rainbow trout performance (Campbell et al. 2014). In this study, SDP was incorporated (CONTINUED ON PAGE 46) FIGURE 3. Final body weight (left) and goblet cell density (right) in red sea bream fed diets with graded levels of SDP (0, 3 or 6 percent) for 60 days.
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