| White muscle fiber growth dynamics and protein synthesis were studied in diploid and triploid rainbow trout to understand mechanisms underlying growth differences between triploid and diploid teleosts. Muscle fiber hyperplasia and hypertrophy in full-sib, all-female, diploid and triploid rainbow trout (100-400 mm, TL) were assessed by means of conventional morphometry, and protein and DNA concentrations. Differences between diploids and triploids in muscle fiber distribution were observed in smaller trout (100-300 mm, TL). Triploid trout had relatively few fibers normally considered to be hyperplastic (diameter ;There was no difference between diploids and triploids in the mean size of muscle fibers; however, the number of fibers per unit area was reduced by 10% in triploids. No differences were observed in protein or DNA concentrations in muscle tissues between the two genetic groups. Since triploid nuclei have 1.5 times more DNA than diploid nuclei, this deviation from the expected muscle DNA concentration (1.3-1.4 times more DNA in triploids when the 10% reduction in fiber density is considered) suggests that the number of nuclei present in individual muscle fibers is reduced in triploids. This reduction, however, does not lower the protein synthetic ability of triploid muscles: they contained RNA and protein concentrations similar to diploid muscles. This implies that the third set of chromosomes is active in triploids, compensating for the reduced number of nuclei. RNA-based biochemical growth correlates were valid predictors of growth in small (mean size, 65 g) and large (mean size, 650 g) triploids. The study also demonstrated that DNA and protein concentrations can be used to assess hyperplasia and hypertrophy in muscle tissues. |
