RESUMEN
We have investigated the interactions between dietary vitamin C levels (at 33, 79, 135, and 424 mg kg-1 of wet mass feed) and growth rate on the collagen and cross-link contents of fast muscle in farmed juvenile Atlantic salmon (Salmo salar L.). The growth rate was measured over an 11 week period using the thermal growth coefficient (TGC). Alkaline-soluble (0.1 M NaOH) (a-s) hydroxyproline (HYP) and alkaline-insoluble (i-s) HYP were determined as a measure of collagen content and hydroxylysyl pyridinoline (PYD) as a measure of mature collagen cross-link concentration. There was a approximately 5-fold increase in muscle vitamin C concentration at similar feed conversion ratios ( approximately 0.82) as dietary vitamin C levels increased from 39 to 424 mg kg-1 of wet mass feed. However, even the lowest dietary vitamin C was sufficient for normal skeletal development and growth. The lowest dietary vitamin C level tested resulted in a approximately 27% decrease in the a-sHYP concentration relative to the other diets, whereas there was no significant effect of vitamin C on the i-sHYP and PYD concentrations. ANOVA revealed no significant interaction between vitamin C and growth rate, whereas the covariate TGC was significant for i-sHYP and PYD but not for a-sHYP. Pyridinoline cross-link and i-s HYP concentrations were 11.1 and 7.7% lower, respectively, in high (TGC > 3.9) mass than low (TGC < 3.9) growth rate fish. These small differences in collagen cross-linking were associated with a 15.6% decrease in fillet firmness measured with an instrumental texture analyzer. It was concluded that for healthy juvenile salmon reared under controlled growth conditions, the dietary vitamin C inclusion of 79 mg kg-1 of wet mass feed was sufficient to produce the required synthesis of soluble muscle collagen. Furthermore, post-translational modifications of the collagen leading to cross-linking showed a small decrease with increasing growth rate but was independent of vitamin C concentration in the diet at these levels.
