EFFECT OF DIETARY-PROTEIN CONTENT ON GROWTH OF JUVENILE MUSSELS, MYTILUS-TROSSULUS (GOULD 1850)

Juvenile mussels, Mytilus trossulus, were fed for 3 weeks on either lo w-protein (LP) algae, high-protein (HP) algae, or a combination of LP algae and protein microcapsules (PM). Growth rates of mussels fed a sa tiation ration of 27.5% body weight (bw; ash-free dry weight of algae/ ash-free dry tissue weight of mussels) per day of LP algae (28% protei n percent weight per weight) were significantly (P < 0.05) lower than growth rates of mussels fed a satiation ration (27.5% bw d-1) of HP al gae (43% protein weight per weight). However, growth rates of mussels fed LP algae (27.5% bw d-1) supplemented with one of three different r ations (6, 12 and 18% bw d-1) of PM increased proportionally to PM rat ion size. Mussels fed a diet containing LP algae with the highest leve l of PM supplementation grew at rates that were not significantly diff erent from those of mussels fed a diet of HP algae alone. Growth rates of mussels fed LP algae alone were not improved if the ration of LP a lgae was increased (34.1% bw d-1), indicating that the positive growth response of mussels fed PM supplements was due to an increase in diet ary protein content and not simply due to an overall increase in food (energy) availability. In addition, mussels fed LP algae had O/N ratio s > 18, indicating that they were conserving dietary protein from cata bolism; whereas mussels fed protein-rich diets had O/N ratios < 10, in dicating that they were catabolizing dietary protein. These results su ggest that dietary protein contents below 40% w/w and dietary C/N rati os above 10 can qualitatively limit growth rates of juvenile M. trossu lus.