Scaling and Sex-Related Differences in Toadfish (Opsanus Beta) Sonic Muscle Enzyme Activities
Male toadfishes (genus Opsanus) use a sonic muscle on the swimbladder to produce a mating call — the boatwhistle — for extended periods during the mating season. Previously, we noted significant differences in sonic muscle mass and activities of metabolic enzymes of the sonic muscles between male and female gulf toadfish, Opsanus beta, of a limited size range (12-130 grams). Notably, males had larger sonic muscles and elevated aerobic capacity, as indicated by higher mass-specific activities of citrate synthase (CS) and malate dehydrogenase (MDH). The present study examined the patterns of sonic muscle mass and activities of these enzymes (and lactate dehydrogenase) in sonic muscle and skeletal muscle as a function of a larger range of body size (7–400 grams) in an effort to determine the point of growth and development that these mate-female differences occur, and to shed light on the possible functional significances of these differences. Sonic muscle mass differences were apparent in the smallest toadfish, and identical rates of increase in sonic muscle mass in males and females maintained these differences throughout the size range examined. In contrast, mass-specific CS and MDH activities were similar in smaller toadfish and began to diverge when fish were about 25 g. While mass-specific MDH activity increased at different rates in males and females, mass-specific CS activity increased in males and decreased in females. The results are discussed in the context of possible control by steroid sex hormones, size at sexual maturity, and success in mate attraction.
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Document Type: Research Article
Publication date: 1989-07-01
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