46 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG addition, fish fed SDP had a more uniform size distribution, better condition and were more efficient in converting feed than those fed the control diet. These results are consistent with previous results observed in Atlantic salmon. Further, nutrition provided by SDP reduced oxidative stress levels in the liver and intestine, improving the health condition status of the fish. Further, sea bream fed diets containing SDP have a greater density of goblet cells in the intestine that benefit the fish by providing an effective immune barrier against gut pathogenic microbiota, suggesting an enhancement of the intestinal innate immune function (Fig. 3). These results were supported by enhancement of blood nonspecific immune parameters, which were greater in fish fed diets containing SDP compared to fish fed the control diet. Stress and Disease Management with SDP In addition to the benefits of dietary supplementation of SDP on animal growth performance, the nutrition provided by SDP also improves the health condition of terrestrial animals by enhancing immune competence (Torrallardona et al. 2003, Moreto and Perez-Bosque 2009, Che et al. 2012), reducing the redox status in the intestine (Gao et al. 2011) and improving the animal’s ability to cope with stress (Peace et al. 2011). Several studies have reported the beneficial effects of feeding diets with SDP on the immune response and disease resistance of shrimp Penaeus japonicus and P. vannamei (Russell and Campbell 2000), European eel Anguilla anguilla (Jensen and Nielsen 2003) and rainbow trout (Aljaro 1998). The results obtained in these challenge studies are in agreement with the immune modulatory effects (increased density goblet cells in the intestinal mucosa, antioxidant defense system and innate immune function) observed in sea bream. Increased Survival of Shrimp with White Spot Syndrome Virus An experiment was done to determine the effect of 0, 2, 4 or 6 percent SDP on immune parameters of shrimp. Penaeus japonicus were stocked at 15 shrimp per tank (60 cm × 30 cm × 40 cm) and water temperature maintained at 25 C. Hemolymph samples were collected on days 0, 3 and 7 of the study. Activity of isolated hemocytes was determined by measuring the rate and extent of latex bead phagocytosis as measured by fluorescent microscopy. Initially (day 0) there was no difference between treatments. On days 3 and 7, there was an increase in the phagocytic activity of isolated hemocytes, corresponding to increasing levels of SDP (Russell and Campbell 2000). In a second study, Russell and Campbell (2000) intended to determine the protective effect of SDP during a challenge of White Spot Syndrome Virus (WSSV). Penaeus japonicus with an average weight of 13 g were fed one of four diets containing 0, 2, 4 or 6 percent SDP. Laboratory tanks, similar to those used in the first experiment were stocked with 15 shrimp per tank and maintained at 25 C during an 18-d feeding period. Feed was offered at 2 percent body weight per day. On day 8, the shrimp were exposed to WSSV by immersing them in a contaminated tank and then returning them to the original tank. The WSSV challenge was severe because all control shrimp (0 percent SDP) died before the end of the 10-d observation period. However, survival of shrimp that consumed diets containing SDP ranged from 33 to 67 percent (Fig. 4). Another study conducted with juvenile eel Anguilla anguilla assessed the effect of feed containing SDP (APC internal data, 2000) under challenge conditions. Juvenile eel were fed a control diet (CON), a diet containing 4 percent SDP added with vacuum coating (SDP 4 percent) or a diet containing 4 percent SDP coated externally (SDP 4 percent Coat). The eel were distributed into 12 tanks (4 replicates per treatment) containing 0.5 kg of juvenile eels. After 6 wk of feeding with the test feeds, weight was measured (2.0±0.1 g) and redhead disease was introduced to the tanks. Redhead disease normally causes low appetite and on some farms increased mortality. The duration of the trial was 40 days after challenge and the parameters analyzed were survival, growth rate, appetite index and feed to gain ratio (F:G). The results indicated that feeding SDP in the diet, irrespective of feed processing method, improved growth rate compared to eels fed the control diet (Table 1). Feed to gain ratio was only improved when SDP was added to the diet with vacuum coating but not when it was externally coated. Survival in all groups was almost 100 percent, indicating the low stress conditions during the trial. The average appetite levels did not differ much between treatments despite improved growth of eel fed diets with SDP. There was a high appetite level in general due to optimum water conditions and a very limited negative effect from the redhead challenge. Reduced Mortality of Rainbow Trout Challenged with Yersinia ruckeri A study was conducted to evaluate the effect of 4 percent dietary SDP on survival and growth of rainbow trout challenged with Yersinia ruckeri (Aljaro 1998). Five hundred rainbow trout fingerlings (initial BW, 20 g) were assigned to 10 circular tanks (1.0 m3) with 50 trout per tank. Tanks were randomly assigned to 10 treatment groups (Table 1). All groups were fed a control diet for a 14-d acclimation period prior to initiation of the study. Two experimental diets consisting of a commercial trout feed containing 0 percent or 4 percent SDP (replacing fishmeal in the formula) were fed during the 30-d study period. Feed with 4 percent SDP was prepared by mixing SDP with oil and topically coating the pellets prior to feeding. The feed allocation per group was adjusted daily and was around 2.5-3.5 percent of body weight FIGURE 4. Effect of dietary SDP on survival of Penaeus japonicus during a WSSV challenge.
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