Cross-effects of dietary probiotic supplementation and rearing temperature on growth performance, digestive enzyme activities, cumulative mortality and innate immune response in seabass (Dicentrarchus labrax)

Probiotic influence on fish immune response and digestive capacity is extensively discussed in aquaculture. In this experiment, a feeding trial was carried out for 100days to evaluate the cross-effects of probiotic supplementation and rearing temperature (17, 20 and 23 degrees C) in juvenile seabass (Dicentrarchus labrax). The experimental diet was supplemented with a commercial probiotic blend (Biomin AquaStarGrowout) at 3g/kg diet (5.23x10(8)CFU/kg diet), and tested against a non-supplemented diet (control). Growth performance and innate immune responses were analysed at 70 and 100days of feeding, whereas digestive enzyme activities were determined at 100days of feeding. At the end of the feeding trial, fish were subjected to a handling stress and cumulative mortality was recorded. Digestive enzyme activities were influenced by temperature, with -amylase and lipase activities peaking at the higher temperature (23 degrees C) and trypsin at the lower temperature (17 degrees C). Immune parameters showed a significant temperature versus feeding duration effect, with complement system (ACH50) and peroxidase peaking at 70 and 100days of feeding, respectively. Poststress cumulative mortality was higher at the lowest temperature (17 degrees C), especially in fish fed the control diet. In conclusion, water temperature was the main variable affecting the studied parameters, whereas the dietary probiotic supplementation had influence on the chymotrypsin activity and survival rate in seabass reared at 17 degrees C.