Ascorbic acid deposition in rainbow trout ( Oncorhynchus mykiss) eggs and survival of embryos

Abstract

The effects of feeding broodstock rainbow trout (initial individual weight 977 ± 220 g) diets devoid of ascorbic acid (-AA) or supplemented with equivalent amounts (300 ppm) of ascorbic acid (AA) or ascorbate monophosphate (AP) on ascorbic acid deposition in eggs and hatching rate were examined. There was no significant difference in overall average body weight among groups during the 8 month experiment. However, maturing females of the -AA group had a significantly lower increase in body weight (33.6 ± 14.7%) than those in the AP group (74.3 ± 9.2%). Fish were kept at prolonged light cycles to delay spawning and increase the length of feeding on the experimental diets. Mortality was not related to the dietary treatments. Total ascorbic acid concentrations in eggs from females fed the -AA diet, AA or AP supplemented diet amounted to 82 ± 32, 276 ± 33 and 316 ± 43 μmg/g wet weight, respectively. The hatching rate of embryos from females fed the -AA diet was 16.0 ± 6.6%, which was much lower, although not significantly different from 36.0 ± 10.7%, for AP females. Fish from the hatchery had a hatching rate of 60.8 ± 29.6%. There was a high correlation between ascorbic acid concentrations in eggs and newly hatched fry which suggested that 37% of ascorbic acid reserves were utilized during embryonic development regardless of the initial concentration. We conclude that ascorbic acid deficiency in a broodstock diet for several months prior to spawning considerably depletes ascorbic acid reserves in eggs and has a negative effect on the growth of maturing females.