Ascorbic acid turnover in rainbow trout, Oncorhynchus mykiss: Is there a vitamin enrichment effect during embryonic period on the juvenile fish “sensitivity” to deficiency?

Abstract

Proper feeding results in the transfer of nutrients from broodstocks to eggs and alevins and consequently in better growth and survival throughout the early ontogeny. In the present study, however, following fertilization, rainbow trout eggs had been exposed to different forms and levels of vitamin C enrichment that included 0, 1000 mg L − 1 ascorbic acid (AA) neutralized (N) with NaOH, 1000 and 2000 mg L − 1 ascorbyl phosphate (AP). Fertilized eggs were immersed in water containing ascorbate at above concentrations and forms. After hatching and yolk absorption, feeding trials were carried out on offspring with different vitamin exposure history in two separate experiments of 6 week duration each. Two casein-gelatin based experimental diets were formulated. The first diet contained 500 mg/kg ascorbyl phosphate (AP) (+ C) and the second diet was the negative control with no ascorbic acid (− C). In the first experiment (first 6-week period), dietary treatments did not have a significant effect on growth performance and survival of fish. However, the fish fed + C diet had significantly higher ascorbic acid (TAA) levels in the whole body and viscera ( P < 0.05) than those on − C diet. After exposure to hypoxia, survival and oxygen consumption did not differ significantly between dietary treatments. In the second experiment (the second 6-week period), all experimental fish were pooled into two groups (+ C and − C) based on the dietary treatments they were previously allocated regardless of the vitamin C exposure at the beginning of embryonic development. At the end of experiment 2, fish fed − C diet had a lower final mean weight (2.08 ± 1.12 g) than those fed + C diet (2.37 ± 0.11 g). Survival was significantly lower in fish fed − C diet (91.6 ± 6.8%) than those fed + C diet (100%) ( P < 0.05). Liver TAA concentration was significantly higher in fish fed + C diet than those on − C diet ( P < 0.05). Deficiency symptoms, including exophthalmia, anorexia and lethargy, lordosis, and scoliosis were observed. Our results suggest that dietary ascorbic acid supplementation plays more important role than enrichment of rainbow trout eggs with ascorbic acid through immersion bath and it is unlikely that “rebound-scurvy” might occur in alevins and juveniles. No signs of enhanced ascorbic acid degradation (turnover) were observed based on body ascorbate depletion following ascorbate-free diets.