Dietary nucleotide supplementation enhances immune responses and survival to Streptococcus iniae in hybrid tilapia fed diet containing low fish meal

AbstractA feeding trial was conducted to evaluate the effects of nucleotide (NT) supplementation in diet on immune responses and disease resistance of juvenile hybrid tilapia, Oreochromis niloticus×Oreochromis aureus. Nucleotide was added at 0, 120, 240, 360, 480 and 600mg NT/kg to low fish meal (6%) and high soybean meal (56%) basal diet for a total of 6 experimental diets. Each diet was fed to triplicate groups of tilapia (initial body weight 0.15±0.005g) in a recirculated freshwater rearing system for 10 weeks. Head kidney leukocyte superoxide anion production ratio was higher (P<0.05) in fish fed diets supplemented with ≥240mg NT/kg than that in fish fed the NT unsupplemented control diet. Fish fed the diet supplemented with 240mg NT/kg had higher plasma lysozyme activity than fish fed diets supplemented with ≤120mg NT/kg. The stimulation index (SI) of head kidney leukocyte stimulated with ConA was higher in fish fed diets supplemented with ≥120mg NT/kg than that in fish fed the control diet. The SI of leukocyte stimulated with PHA-P was higher in fish fed diets supplemented with ≥240mg NT/kg than in fish fed diets supplemented with ≤120mg NT/kg. After the feeding trial, 10 fish were randomly selected from each aquarium and were challenged with Streptococcus iniae for 7 days, higher survival (>80%) were observed in fish fed diets supplemented with NT than fish fed the NT unsupplemented control diet (56.7%). These results suggest that nucleotides supplemented at 120–240mg NT/kg in diet enhances immune responses and survival of tilapia fed low fish meal and high soybean meal diet

Effect of feeding strategy and carbohydrate source on carbohydrate utilization by white sturgeon (Acipenser transmontanus) and hybrid tilapia (Oreochromis niloticus X O-aureus)

Two 8-week growth trials were conducted to determine the effect of continuous (CF) versus 2 meals day(-1) (MF) feeding and 30% starch versus 30% glucose diets on the carbohydrate utilization of 9.0-g white sturgeon and 0.56-g hybrid tilapia. The two trials were conducted under similar conditions except that sturgeon were kept at 18.5 degrees C in a flow-through system and tilapia were kept at 26 degrees C in a recirculating system. Significantly (P less than or equal to 0.05) higher specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), body lipid content and liver glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activities were observed in the CF than MF sturgeon. Only SGR, FE and PER were higher in sturgeon fed the starch than the glucose diets. Only higher liver G6PDH and malic enzyme (ME) activities were observed in the CF than MF tilapia but higher SGR, FE, PER and liver G6PDH, 6PGDH and ME activities were observed in tilapia fed the starch diet than those fed the glucose diet. This suggested that carbohydrate utilization by sturgeon was more affected by feeding strategy whereas tilapia was more affected by carbohydrate source. Furthermore, white sturgeon can utilize carbohydrates better than hybrid tilapia regardless of feeding strategy and carbohydrate source