RNA–DNA Ratios as Indicators of Recent Growth Rates of a Fish

When golden shiners (Notemigonus crysoleucas) were fed at 0, 2, and 6% body weight for 15 days, the mean RNA–DNA ratios for defatted tissues (whole, eviscerated fish) were 2.18, 2.83, and 4.32, respectively, in association with mean weight changes of −16.1, 2.2, and 21.3%.Food deprivation for 30 and 45 days resulted in mean ratios of 1.66 and 1.36, in association with mean weight losses of 20.6 and 35.6% body weight. Feeding at 2% body weight for 30 and 45 days resulted in a leveling off of ratios (3.15 and 3.03, respectively) with a continued gain in body weight (19.9 and 45.6%); feeding at the 6% rate for the same durations resulted in a decline in ratios (3.91 and 3.08, respectively) with a continued gain in body weight (57.9 and 90.9%).Depriving golden shiners of food for 14 days and then resuming feeding for 6 days demonstrated that RNA–DNA ratios change rapidly, the changes being attributed primarily to changes in RNA concentrations. Mean ratios declined from 3.56 after 4 days to 2.30 after 14 days of food deprivation. When feeding was resumed, ratios averaged 3.45, 4.93, 5.07, 5.73, 5.00, and 5.14 after 1–6 days feeding, respectively.