FASTING CONFINEMENT EFFECTS ON SHARKS 639 



potassium, calcium, chloride, and iron. Decreases were observed in serum 

 protein, total lipids, glucose, and cholesterol. Serum urea and total 

 osmolarity were variable. 



5. Atrophy of skeletal muscle was apparent in the starved animals. 



6. A drastic reduction in hematocrit values occurred, associated with 

 alterations in hematopoeitic tissues. Erythroblasts and hemocytoblasts 

 formed up to 24% of the circulating red blood cells. Other alterations in the 

 blood over the experimental periods included eosinophilia, lymphocy- 

 topenia, thrombocytopenia, and leukocytosis in the presence of immature 

 erythrocytes, erythroblasts, and hemocytoblasts. Alterations in the spleen 

 over the period of confinement included increased phagocytic activity of 

 reticuloendothelial cells, reticuloendothelial hyperplasia, lymphocytopenia, 

 and a progressive expansion of the red pulp. 



7. The interrenal tissue evidence an increase in secretory activity. 

 Nuclear enlargement and an increase in the vascularity of the gland were 

 followed by a gradual depletion of lipid contents, and in some cases total 

 disorganization of the glandular parenchyma. The lack of extensive liver lipid 

 mobilization, the decline in serum protein and glucose, and the preferential 

 utilization of tissue proteins during starvation parallel the responses of other 

 vertebrates to hyposecretion of glucocorticoids. These results are consistent 

 with the hypothesis that interrenal secretions of Squalus possess little or no 

 glucocorticoid activities. 



8. Histological alterations in the rectal gland were indicative of 

 decreased secretory activity. Nephric tissue generally appeared normal 

 histologically, but in animals sacrificed with low hematocrits, or sampled 

 immediately after death, tubular degeneration was apparent. 



9. No obvious changes were observed in the tissue of the endocrine 

 pancreas; the exocrine pancreas displayed marked cellular atrophy. No 

 consistent alterations were observed in the epithelium of the digestive tract. 



10. When considered in combination with data of other authors on 

 captive elasmobranchs, it is apparent that the alterations induced by fasting 

 confinement are of sufficient magnitude to demand more rigorous criteria 

 for the selection of experimental subjects. 



11. Recommendations are presented for the capture, care, maintenance, 

 and selection of elasmobranchs for use in experimental investigations. 



12. In the light of this study, it is possible that many physiological and 

 behavioral investigations of captive elasmobranchs should be reconsidered. 



ACKNOWLEDGMENTS 



The author expresses his appreciation to the following persons for their 

 assistance in the course of this study: To Drs. P. W. Gilbert, W. A. Wimsatt, 

 and W. N. McFarland for their time, equipment, and laboratory space; to the 

 staff of the Tunison Laboratory of Fish Nutrition, Cortland, N.Y., the 

 Cornell Veterinary College, Ithaca, N.Y., the Star Island Corporation and its 

 employees, and to Dr. J. M. Kingsbury and the staff of the Shoals Marine 



