636 ECOLOGY AND BEHAVIOR 



Lower hematocrit values for captive animals have been reported in other 

 studies. Burger (1967) mentions "wild plasma" as having hematocrit values 

 of 17-32, while "live car plasma" had hematocrits ranging from 6 to 33. 

 Lenfant and Johansen (1966) found hematocrits from 13 to 26 in 

 aquarium-held Squalus, and Robin et al. (1966), mentioned that "healthy 

 fish, in the experience of this laboratory, have hematocrits greater than 

 15%." Dawson (1933) reported that captive Mustelus had a greater 

 percentage of erythroblasts than did wild animals (up to 33%). 



Since 90% of the oxygen transport in Squalus occurs via the hemoglobin 

 of the red blood cells (Lenfant and Johansen 1966), a reduction in 

 hematocrit and an increased percentage of erythroblasts would necessarily 

 decrease the oxygen-carrying capacity of the blood. The behavioral changes 

 reported in the study- are comparable to those described for elasmobranchs 

 subjected to hypoxic conditions over relatively brisf periods (Fishman 1967; 

 Piiper et al. 1970), and many other alterations observed in captive Squalus 

 appear similar to those induced in other fishes by reductions in the oxygen 

 content of the surrounding water. 



It may be significant that species that adapt to confinement for long 

 periods are adapted for life on or near the bottom. They can provide strong 

 respiratory currents while motionless and are the species that accept food 

 shortly after capture. 



Catfish subjected to periods of low oxygen tension showed a loss in 

 appetite and a cessation of digestive processes (Bouck and Ball 1965); 

 elasmobranchs starved in captivity for weeks occasionally regurgitate, or 

 display upon autopsy, pieces of food in the digestive tract undisturbed by 

 digestive processes (Patent 1970; Martini, personal observations). 



Blood glucose levels in captive animals occasionally rose to above normal 

 values (158 ± 10 mg%, n = 9) shortly before the death of an animal. 

 Hematocrit values for these animals averaged 10%. Denis (1922) and Scott 

 (1921) described hypoxic hyperglycemia in elasmobranchs following their 

 removal from the water or maintenance in aquaria with low oxygen 

 concentrations, and tench subjected to suffocation by confinement showed a 

 gradual increase in serum glucose to more than 300 mg% over a 2-day period 

 (Bange-Barnoud 1965). 



The relationship between the gradual reduction of oxygen and histological 

 changes in the kidney and interrenal are unknown. In mammals, chronic 

 hypoxia results in extensive kidney necrosis (Pitts 1966), but in fishes 

 extreme interrenal disorganization has been described following acute stress 

 (Rasquin and Rosenbloom 1954, Astyanax mexicanus; Weatherley 1963, 

 Perca fluyiatilis). 



Implications for the Researcher 



More rigorous criteria should be applied to the maintenance and selection of 

 elasmobranchs for use as experimental animals. Because of the similarity of 

 trends observed in several species of elasmobranchs while starving in captiv- 

 ity, it would appear that this study has significance for those working with 



