FASTING CONFINEMENT EFFECTS ON SHARKS 631 



of inanition, total serum lipid concentrations approximate those of freshly 

 caught Squalus (Homo, 360-820 mg%; Harper 1969). During starvation, the 

 turnover rate for serum fatty acids is under 8 min (Newsholme and Start 

 1973). This is in contrast to the situation in fasting elasmobranchs. Total 

 serum lipids decline, and the turnover rate for serum fatty acids in starved 

 Squalus is about 48 h (Sargent, Gatten, and Mcintosh 1972). 



Thus, it appears probable that circulating lipid components do not play a 

 major role in the support of fasting elasmobranchs. Baldridge (1972) 

 examined animals (Carcharhinus milberti, Negaprion breuirostris) starved in 

 laboratory pens, and concluded that liver lipids were mobilized, but not in 

 preference to tissue proteins. He suggested that lipids were conserved to 

 meet buoyancy requirements. The normal liver of Squalus acanthias contains 

 triglycerides, diacyl-glycerols, and wax esters (Sargent, Gatten, and Mcintosh 

 1971.) The latter components are of low density and are presumably most 

 important in buoyancy regulation. Malins and Barone (1970) placed weights 

 on dogfish and found a significant increase in the ratio of diacyl-glycerols to 

 triglycerides after 50 h of weight stress. They suggested that buoyancy was 

 regulated by increasing the amount of low-density lipids in the liver. As 

 Baldridge (1972) has observed, starvation would tend to increase underwater 

 weight, since the denser tissues of the body, such as denticles, teeth, and 

 calcified cartilage, are not metabolically available. Thus, while the mobiliza- 

 tion of triglycerides and free fatty acids during starvation would provide 

 some metabolic fuel, mechanisms may be present to conserve or even 

 augment those lipids responsible for buoyancy. This has been suggested 

 elsewhere by Sargent et al. (1972), following studies on the patterns of liver 

 lipid synthesis in Squalus. 



As in higher vertebrates, carbohydrate metabolism in elasmobranchs is 

 subject to endocrine control. The hyperglycemia of depancreatized animals 

 (Mustelus) was eliminated after pituitary extirpation (Dodd 1961), and 

 ACTH administration to hypophysectomized animals elevated blood glucose 

 (Grant and Banks 1967). The basic responses of serum glucose to insulin, 

 glucagon, ACTH, corticoids, and catecholamines are similar in form to those 

 of higher vertebrates (deRoos and deRoos 1972; Patent 1970). 



Blood glucose levels are subject to a variety of influences, and variability is 

 anticipated both between animals and, over time, in individuals. Normal 

 serum glucose levels in elasmobranchs have been reported as ranging from 

 17-80 mg% (Denis 1922; Scott 1921; Patent 1970; deRoos and deRoos 

 1972). Patent (1970) sampled groups of freshly caught animals (Squalus 

 acanthias) with blood glucose levels of 30 mg%, and felt that this reflected a 

 poor nutritional state. Scott (1921) reported only "trace" amounts of 

 glucose present in some animals held "until needed" in live cars; these 

 animals generally appeared to be in poor condition. 



In the present study, serum glucose levels declined during starvation. 

 Decreases in glucose during fasting were also observed by deRoos and 

 deRoos (1973) in Squalus acanthias, Kern (1966) in Scyliorhinus canicula, 

 and Hartman et al. (1941) in rajids. However, Patent (1970) reported that 

 blood glucose levels in Squalus acanthias remained stable during at least two 

 weeks of starvation. 



