TISSUE CONCENTRATIONS OF RNA AND PROTEIN FOR JUVENILE BROOK TROUT (SALVELINUS-FONTINALIS) - LAGGED RESPONSES TO FLUCTUATIONS IN FOOD AVAILABILITY

To be useful as short-term indices of nutritional status when food ava ilability varies, wet weight-at-length and tissue concentrations of nu cleic acids and protein must covary closely with a fish's recent feedi ng history. We measured changes in these indices for young brook trout (Salvelinus fontinalis) (fork length: 20-34 mm) reared under alternat ing, 4 to 5 d periods of food provisioning and food deprivation. Weigh t-at-length corresponded closely with current feeding conditions, bein g higher when the trout were fed than when they were deprived. Concent rations of RNA and protein, however, did not correspond closely with c urrent feeding conditions. Instead, there were significant carry-over effects whereby responses to feeding conditions experienced in one tre atment period were not exhibited until the following treatment period. Food provisioning had positive carry-over effects on concentrations o f RNA and protein while food deprivation had negative carry-over effec ts. Consequently, food-deprived trout sometimes had higher concentrati ons of RNA and protein than well fed trout. Since wild fish may experi ence short-term fluctuations in food availability, lagged responses in concentrations of nucleic acids or protein like those reported here c ould hamper attempts to use these biochemical measures to assess the n utritional status of juvenile fish in the field.