632 ECOLOGY AND BEHAVIOR 



Glycogen reserves in the liver may not play a significant role in 

 maintaining blood glucose during starvation. Patent (1970) reported that 

 liver glycogen levels of freshly caught Squalus acanthias averaged 62.4 mg%. 

 The liver of a 4-kg animal would approximate 400 g (Burger 1967b); thus 

 liver glycogen reserves would total only about 250 mg (about 1000 calories). 



Stimpson (1965) has suggested that the glycogen and lipid reserves of 

 goldfish are made available solely under the influence of adrenaline, but not 

 during starvation, when tissue proteins appear to be used preferentially. In 

 elasmobranchs, liver glycogen has been shown to be unresponsive to 

 corticoids and ACTH, though serum glucose levels were elevated (Patent 

 1970); administration of adrenaline decreased liver glycogen levels in 

 addition to raising serum glucose levels (Grant and Banks 1967). Patent 

 (1970) suggested that corticoids act through gluconeogenesis from liver 

 lipids. However, deRoos and deRoos (1972) failed to find a significant 

 decrease in liver lipids during cortisol-induced hyperglycemia, and suggested 

 gluconeogenesis from protein precursors. 



In the present study, serum protein levels declined steadily. The rapidity 

 of this decline agrees with data of Cordier, Barnoud, and Brandon (1957), 

 who found reductions in serum protein levels of Scyliorhinus canicula, 

 starved over a two-week period, comparable to those in carp starved for six 

 months. The increases in total body water (Baldridge 1972), intercellular 

 fluid (present study, from histological interpretations), and rising serum 

 potassium levels may also indicate protein catabolism and decreased plasma 

 oncotic pressure. (The apparent muscular atrophy has been considered 

 above.) 



In elasmobranchs, urea levels are responsive to a variety of factors 

 encountered in physiological studies, and thus are probably poor indicators 

 of metabolic activities. As adrenaline administration increases urinary urea 

 clearance some 15 times (Forster, Goldstein, and Rosen 1972), such factors 

 as the stresses of capture and aggressive interactions in the pen, which 

 influence the sympathetic nervous system, would depress serum urea levels. 

 Moreover, the average water temperature over the experimental period 

 (16°C) was close to the temperature at which urea clearance at the gills 

 increases markedly (Boylan 1967: Squalus acanthias). And if the animal is 

 gaining water, fluid shifts would affect the extracellular fluid concentration 

 of a number of substances, urea included. 



Metabolic Regulation 



The regulation of secretion of the interrenal gland in elasmobranchs is 

 mediated in a manner analagous to that of "higher" vertebrates. ACTH is 

 present in the hypophysis (deRoos and deRoos 1964, 1967), and interrenal 

 tissues respond to the presence of ACTH, or pituitary extracts, by an 

 increase in steroid synthesis (Macchi and Rizzo 1962). The effects of 

 pituitary extirpation, corticoid injection, and ACTH administration upon 

 blood glucose levels have been noted above. Cortisol treatment decreases the 

 secretory rate of the rectal gland (Chan and Phillips 1967) and in the present 



