Effects of season and dietary ascorbic acid on some biochemical characteristics of rainbow trout (Oncorhynchus mykiss) semen.

During the reproductive season, rainbow trout spermatozoa are stored in the sperm ducts for several months. There is no sperm production at this time since spermatogenesis is completed before spawning. To leam more about characteristics of semen during such a long storage, we analyzed changes in protein concentrations, anti-proteinase activity in seminal plasma and sperm aspartate aminotransferase activity during an extended reproductive period during which fish were fed diets supplemented with various ascorbic acid concentrations. Seminal plasma protein concentration and anti-proteinase activity declined toward the end of the reproductive season. These phenomena may be related to oncoming proteolytic events leading to degradation of the sperm. Protein concentrations and anti-proteinase activities were strongly correlated within groups of different ascorbic acid supplementations and several sampling dates (r=0.6-0.9 in most cases, p<0.05). Ascorbic acid deficiency resulted in a decrease in both parameter levels as compared to levels in groups with vitamin C supplement (p<0.08). Deficiency also resulted in lower stimulation of aspartate aminotransferase by an exogenous pyridoxal 5'-phosphate in comparison to fish fed vitamin C-supplemented diets (p<0.05). These results support earlier studies suggesting a protective role of ascorbic acid toward maintaining sperm quality.