Modification of Carbohydrate Metabolism and Liver Vitellogenic Function in Brook Trout (Salvelinus fontinalis) by Exposure to Low pH

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Abstract
Brook trout (Salvelinus fontinalis), 1+ yr old, were exposed to pH 4.48 from February to December. Compared with control fish maintained at pH 7.34, acid-stressed fish generaly had elevated blood glucose levels. Plasma cortisol concentration, measured only in males, was significantly increased in the acid-treated trout up to July. Although somatic growth decreased by about 30% by the end of the experiment, peritoneal fat was unchanged. During the reproductive season, female plasma levels of oestrogen and vitellogenin were the same at both pH levels. When immature fish were implanted with oestradiol-17.beta. and then maintained for 21 d either in pH 7.34 (control) or 4.48, acid-treated fish again showed increased blood glucose levels. Liver weight increased at both pH levels, but liver glycogen was depleted and plasma vitellogenin was significantly increased by exogenous oesterogen only in control fish. It is postulated that before acclimation occurs, acid stress increases cortisol secretion, diverts nutrients normally used for growth to maintain a high blood sugar level, and affects the liver''s ability to metabolize carbohydrates and synthesize vitellogenin.