Search

Rainbow trout (23.1 ± 0.4 g) were fed either a fishmeal- or plant-based diet supplemented with various levels of zinc (0, 15, 30, 60 or 120 mg kg−1) for 12 weeks. Trout fed the fishmeal diet had significantly higher weight gain than with the plant-based diet. Zinc supplementation in the fishmeal diet had no effect on growth performance, suggesting that additional dietary supplementation of zinc is not required. However, in trout fed the plant-based diet, growth increased significantly up to 30 mg kg−1 zinc after which growth was not affected. Trout fed the plant-based diet containing no zinc exhibited severe growth retardation, and in fish fed the 0 and 15 mg kg−1 zinc diets, cataracts were present. Use of broken-line quadratic modelling suggests that dietary supplementation of zinc needed to prevent deficiency and promote adequate growth in rainbow trout fed the plant-based diet in this study was 30.1 mg kg−1 (80 mg kg−1 total dietary zinc). This is higher than the NRC (2011, Nutrient Requirements of Fish and Shrimp) dietary recommended level of 15 mg kg−1 for rainbow trout. Following the NRC recommendation could lead to zinc deficiency in rainbow trout fed a plant-based diet. [ABSTRACT FROM AUTHOR]

Summary Juvenile channel catfish, Ictalurus punctatus, were fed diets supplemented with yeast or yeast subcomponents (YYS) as commercial preparations of β-glucan (MacroGard® and Betagard A®), mannan oligosaccharide (Bio-Mos® Aqua Grade), or whole-cell Saccharomyces cerevisiae (Levucell SB20®) at the manufacturers' recommended levels. Fish were fed experimental diets for 1 or 2 weeks prior to disease challenge (pre-challenge feeding periods) and sampled at the end of each feeding period to measure haematological and immune parameters and to determine the effects of dietary YYS on resistance to Edwardsiella ictaluri, the causative agent of enteric septicaemia disease (ESC). Feeding of experimental diets continued for 3 weeks post-challenge. In channel catfish fed diets supplemented with MacroGard®, Betagard A®, or Levucell SB20®, survival in the 1 week pre-challenge feeding group and antibody titres in the 2 week feeding group were significantly higher post- E. ictaluri challenge in relation to catfish fed with the control diet. In fish fed these same three diets, survival to ESC was significantly higher after 1 week vs. 2 weeks feeding, while the antibody response was significantly higher after 2 weeks vs. 1 week. Lysozyme activity was also higher in the 1 week feeding group, but the increased activity was unrelated to diet. Feeding YYS-supplemented diets for a shorter duration of 1 week prior to challenge may prove beneficial in increasing resistance to ESC in channel catfish. However, we cannot discount that feeding YYS diets during the recovery period may have contributed to 'glucan overload' and reduced survival in the 2 week feeding group. [ABSTRACT FROM AUTHOR]