614 ECOLOGY AND BEHAVIOR 



With the passage of time, periods of inactivity increased both in frequency 

 and duration. During isolation for sampling, the animals struggled weakly or 

 not all all. Eventually, the sharks were unable to right themselves, and lay 

 ventral side up. Abortions were common at this time. Subsequently, the 

 animals became rigid and appeared unable to move any but the pharyngeal 

 muscles necessary to maintain a weak respiratory current across the gills. 

 Clotting of blood samples was extremely slow, and the serum frequently 

 showed a distinct discoloration. Death followed within 24 h. Dissection 

 indicated extreme emaciation, with wrinkling of the skin. 



Histological Alterations 



Figure la, lb illustrates the effects of prolonged starvation on muscle fibers 

 of the ventrolateral abdominal wall. The muscles have atrophied, inter- 

 cellular fluid has increased, and cellular organization appears disrupted. 



No consistent alterations were observed in the mucosa of the esophagus, 

 stomach, or spiral intestine. Sections of liver stained for glycogen showed a 

 faintly positive reaction in one of the sections from a wild control; all other 

 tests were negative. 



The exocrine portion of the pancreas was greatly modified. Figure lc, d 

 compares the acinar cells of a freshly caught animal with those of a shark 

 sacrificed after two weeks in captivity. A marked reduction in the size of the 

 acinar cells occurred, accompanied by cytoplasmic vacuolation. Cell height 

 was reduced, partly due to decreases in secretory granulations and nuclear 

 size. 



No histological changes were seen in the opisthonephroi of experimental 

 animals until they were near death. Figure le, f compares the appearance of 

 the kidney of a control animal (group IVa) with that of an animal sacrificed 

 after 18 days in captivity. A dense precipitate was frequently present in the 

 tubules. Tubular damage was evident, and disaggregate cells and cellular 

 debris occasionally occluded a tubule. 



Measurements were taken of the nuclear diameters of tubular cells in the 

 rectal glands of eight animals; the results are presented in Table 2. 



A significant decrease in nuclear diameter occurred during the experi- 

 mental period. This was accompanied by increasing density and basophila of 

 the chromatin in the nucleus, an increase in the density of the cytoplasm, 

 and some cytoplasmic vacuolation (Figure lg, h). Similar observations gen- 

 erally accompany a decrease in secretory activity (Ham 1969). 



The interrenal organ of Squalus acanthias is an elongate structure located 

 dorso-medial to the opisthonephros. The cells of the gland are arrayed in 

 anastomosing cords, which are delineated by narrow, tortuous vessels. In 

 histological preparations, after paraffin embedding the cells of the normal 

 gland appear columnar in form, with basal nuclei which contain prominent 

 nucleoli. The lightly basophilic cytoplasm appears lacy and vacuolated. It 

 can be demonstrated, using frozen sections of formalin-fixed tissue, that 

 these cells contain abundant lipid inclusions. Histochemical procedures in- 

 dicate the presence of cholesterol. 



