624 ECOLOGY AND BEHAVIOR 



This is attributed to seasonal differences in temperature and the metabolic 

 reserves of the animals. 



Identification of a general trend in total serum osmolarity was difficult 

 due to the variations in chloride and urea levels, reported below, which 

 contribute significantly to the total osmolarity of the serum. Figure 6a pre- 

 sents a scatter diagram of the data, with data points from five animals 

 connected. 



Serum levels of sodium and potassium consistently increased over the 

 experimental period. Figure 6b, c presents scatter diagrams of the data 

 points; these figures also present the computer-determined patterns that best 

 fit data collected from all the individuals sampled. Serum levels of both cal- 

 cium and iron also increased as the animals approached death (Figure 7a, 7b). 



Serum chloride levels rose in most of the animals (Figure 7c). 



Serum glucose gradually decreased over the period of confinement. Excep- 

 tions existed principally among animals that had remained on the longline 

 for prolonged periods. This was presumably due to the attendant exertions; 

 in these instances blood glucose was low at capture but increased by the 

 second sampling. Thereafter it declined. Occasionally, a marked elevation in 

 blood glucose appeared immediately prior to the death of an animal (Figure 

 8a). 



Serum cholesterol levels were variable within the population and, to a 

 lesser extent, within a single animal over time. The general trend was a 

 decline in serum cholesterol as the animals approached death (Figure 8b). 



The total quantity of serum lipids fell rapidly, much more dramatically 

 than the serum cholesterol values (Figure 8c). 



No statistically significant trend was apparent in serum levels of urea 

 (Figure 9a). 



Serum protein concentrations declined steadily during the period of con- 

 finement (Figure 9b). 



DISCUSSION 

 Histological Alterations 



The only consistent change in the digestive system over the experimental 

 period was destruction of the acinar cells of the exocrine pancreas. 



Kern (1966) treated starving Scyliorhinus canicula with alloxan and found 

 no lesions in the endocrine pancreas. He did observe degeneration in the 

 exocrine pancreas of all experimental animals. These alterations, and those 

 of the present work, may represent responses to starvation. In mammals, 

 ligation of the pancreatic ducts produces destruction of exocrine cells with- 

 out damage to the endocrine pancreas (Banting and Best 1922). 



Epithelial compression was reported by Oguri (1964) as accompanying 

 regressive alterations in rectal glands of freshwater elasmobranchs, and Chan 

 and Phillips (1967) described cellular vacuolation in rectal glands of low 

 secretory activity. 



