Effect of size and sex on buoyancy in the oyster toadfish

✍ Scribed by M. L. Fine; J. W. McKnight; C. R. Blem

• Publisher: Springer-Verlag
• Year: 1995
• Tongue: English
• Weight: 897 KB
• Volume: 123
• Category: Article
• ISSN: 0025-3162
• DOI: 10.1007/bf00349218

✦ Synopsis

In 1991 we examined the developmental consequences of swimbladder growth and sexual dimorphism on specific gravity (SG) and percent buoyancy (%B) in the oyster toadfish (Opsanus tau Linnaeus collected in the York River, Virginia) and tested the hypothesis that large ovaries compensate for the buoyancy conferred by a smaller swimbladder in females. Weight in water (Ww) increased as a linear function of weight in air (Wa) for both sexes, and there were no sexual differences between regressions. SG and %B did not change with Wa, indicating proportional growth of body and swimbladder. SG averaged 1.049 _+ 0.002 and %B 3.183 __ 0.160. Removal of the gonads had no significant effect on Ww, SG or %B, indicating that the larger ovaries did not compensate for buoyancy associated with a smaller swimbladder. In fact testis and ovary SG did not differ significantly from values for intact fish. However, gonad composition changed with development: testis SG and % fat decreased with gonosomatic index, whereas ovary SG and % fat increased, but % water decreased. Removal of the swimbladder significantly increased SG to 1.083 and %B to 6. Swimbladder volume increased linearly with Wa and was significantly larger in males; adjusted means were 11.40 _+0.83 and 8.94 _+0.83 ml for males and females, respectively. Variability in bladder volumes contributed to the absence of sexual differences in SG and may be permissible because negative buoyancy imparts minimal selective advantage for precise volume and buoyancy control. The absence of a relationship between fish buoyancy and sexual dimorphism in bladder size supports evidence that sexual dimorphism in the swimbladder relates to its function in sound production.