The role of dietary L‐ascorbyl‐2‐polyphosphate on the growth and physiological functions of beluga, Huso huso (Linnaeus, 1758)

Effects of dietary ascorbic acid (AA) supplementation were carried out on growth performance and physiological indices in juvenile beluga Huso huso fed different levels of dietary L-ascorbyl-2-polyphosphate as AA source consisting of 0 (control), 100, 200, 400, 800 and 1600 mg AA kg−1 diet for 16 weeks. No significant differences were found in growth performances between treated groups except for condition factor. Using AA caused significant differences in haemoglobin, number of red blood cells, white blood cells, aspartate aminotranspherase and lactate dehydrogenase, while no significant difference was found in haematocrit, mean corpuscular haemoglobin concentration, differential white blood cells count and alkaline phosphatase activity at the end of the experiment. Lysozyme activity after 8 weeks was significantly affected by dietary treatments with the lowest value in fish fed control diet, but not at completion of 16-week feeding trial. Liver AA concentration showed a significant increase in correlation with dietary AA increase. Air exposure stress test showed significant differences among the treatments in case of cortisol and glucose concentrations. Also between pre- and post stress, significant changes were observed in some of treatments. The lowest and highest levels of cortisol were 9.2 ± 3 (in 200 mg kg−1) and 16.8 ± 5.1 ng mL−1 (in control), 6 h post stress (P < 0.05) respectively. Also, the lowest and highest levels of glucose were measured in fish fed 200 and 800 mg AA kg−1 respectively. The obtained results showed that most growth parameters were not affected by dietary AA, but some physiological and immunological parameters of this species were influenced by this vitamin. We suggest that under rearing conditions, AA should be added to the diet especially during early life stages for improving health status and resistance to stressors.