Effect of Dietary Protein Content on Growth of Juvenile Mussels, Mytilus trossulus (Gould 1850).

Abstract

Juvenile mussels, Mytilus trossulus, were fed for 3 weeks on either low-protein (LP) algae, high-protein (HP) algae, or a combination of LP algae and protein microcapsules (PM). Growth rates of mussels fed a satiation 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% protein 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 algae (43% protein weight per weight). However, growth rates of mussels fed LP algae (27.5% bw d-1) supplemented with one of three different rations (6, 12 and 18% bw d-1) of PM increased proportionally to PM ration size. Mussels fed a diet containing LP algae with the highest level of PM supplementation grew at rates that were not significantly different 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 algae was increased (34.1% bw d-1), indicating that the positive growth response of mussels fed PM supplements was due to an increase in dietary protein content and not simply due to an overall increase in food (energy) availability. In addition, mussels fed LP algae had O/N ratios > 18, indicating that they were conserving dietary protein from catabolism; whereas mussels fed protein-rich diets had O/N ratios <10, indicating that they were catabolizing dietary protein. These results suggest that dietary protein contents below 40% w/w and dietary C/N ratios above 10 can qualitatively limit growth rates of juvenile M. trossulus.