The Physiological Effects of Exercise on California Yellowtail (Seriola dorsalis) White Muscle

Abstract

California yellowtail (Seriola dorsalis) is a species of ray-finned fish that demonstrates a significant increase in muscle mass in response to sustained exercise at optimal swimming speed. In this study, three groups of yellowtail have been analyzed for a 6-month period to determine if the length of exercise affects white muscle fiber development and if these changes persist when the exercised fish have been returned to a normal "resting" condition. Gene analysis was performed to test if MyoD, a myogenic regulatory factor, was upregulated in response to exercise. To test these questions, the groups compared included a control group (not exercised), a 3-week exercise group, and a 4-week exercise group. Samples of the yellowtail white muscle were taken monthly and analyzed microscopically to measure fiber areas and to determine if any of the groups were undergoing hypertrophy or hyperplasia. Hypertrophy is arbitrarily classified as fibers 7000+ μm 2 and hyperplasia is marked by presence of newly recruited fibers (0-1000 μm 2). The results show that immediately following the exercise period, the 4-week exercise group had the highest average fiber area (3365.5 ± 113.5 μm 2) and the control group had the smallest (3034.8 ± 103 μm 2). However, at the end of the 6-months, the average fiber area of the 4-week exercise, 3-week exercise, and control were more similar in size (4249.4 ± 149.2 μm 2 , 4046.1 ± 134.6 μm 2 , 4121.4 ±161.7 μm 2) with no significant difference. When comparing the patterning of the fibers, all three groups demonstrated a general trend of hypertrophy over the 6month period. In contrast, the control group had the greatest amount of hyperplasia, but there was not a noticeable trend in the amount of fibers that were recruited over the 6-month period. MyoD was upregulated at the start of the racing procedure compared to samples that were collected one month post-exercise.