Evidence is given that the average daily rations (R) and fortnightly growth increments (ΔW) of six weight groups ofPleuronectes platessafed onMytilus edulisare related as in the power equation ±(ΔW−ΔWm) = ±b(|R–Rm|)B. Rmis the daily ration associated with the growth increment (ΔWm) at maximum growth efficiency;band B are parameters. The power B has a mean value of about 0.5 and shows significant deviations from the mean especially in the case of smaller fish.