Relationships between dietary ascorbic acid status and deficiency, weight gain and brain neurotransmitter levels in juvenile rainbow trout,Salmo gairdneri.

A study was conducted to determine the interrelationships between dietary ascorbic acid (AA) concentrations, brain neurotransmitter levels and weight gain in juvenile rainbow trout. At the end of 4 weeks and until the end of 12 weeks of feeding test diets of varying AA concentrations (0-320 mg AA/kg diet), increased weight gain was noted in fish fed the AA-free diet. However, by the end of 13 weeks and until the end of the experiment this phenomenon was no longer evident; instead the fish showed the more classical deficiency signs of anorexia and decreased weight gain. After 12 and 24 weeks, there were no significant differences in brain serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE) or dopamine (DA) between fish reared on the different test diets. However, after 12 weeks of feeding the test diets, brain 5-HT, brain AA and weight gain were significantly correlated with one another. No such relationships were found for brain NE or brain DA. After 24 weeks of feeding the diets, the relationships between brain 5-HT, brain AA and weight gain were no longer apparent. Similarly, after 24 weeks brain NE and DA were also unrelated to brain AA and weight gain. These results provide evidence that in very young rainbow trout, AA deficiency, brain 5-HT levels and weight gain were related. However in fish reared on the diets for 24 weeks these relationships were no longer evident.