The respiration of other aquatic animals, including marine inverte- 

 brates, also has been investigated to some extent. Oxygen consumption of 

 seven species of marine invertebrates, scallops, and Crustacea was com- 

 pared with regard to their environmental temperature (Fox 1936 and Fax 

 and Wingfield 1937). Measurements of oxygen consumption have also been 

 made on the fiddler crab (Demeusy 1957) and on numerous species of other 

 crustaceans, including the kelp crab (Weymouth et al 19hh)» By means of 

 staining techniques, using neotetrazolium and tetrazolium, Nayar and 

 Parameswaran (1955) detected succinic dehydrogenase in neurosecretory 

 cells of the thoracic ganglion of the crab. 



Humphrey (19U7) has studied endogenous respiration and succinoxidase 

 activity of homogenates of oyster muscle. The large increase in respira- 

 tion observed when succinate was added indicates that oyster muscle pos- 

 sesses an active system for succinate metabolism. The inhibitory effects 

 of certain narcotics on respiration of oyster-muscle homogenate also were 

 studied (Humphrey I9U8). 



Jodrey and Wilbur (1955) have demonstrated that a major portion of 

 the TCA cycle is present in the oyster. Specific assays for aconitase, 

 isocitric dehydrogenase, succinic dehydrogenase, malic dehydrogenase, 

 cytochrome oxidase, and fumarase were made, using homogenates or acetone 

 powders of oyster tissue. With the exception of aconitase, positive re- 

 sults were obtained for these TCA-cycle enzymes j however, their activities 

 were considerably lower than in mammalian tissue. Of possible special 

 significance in the process of carbonate deposition is oxalacetate de- 

 carboxylase activity, which was found to be more than 100 times greater 

 in oyster mantel than in mouse liver (Jodrey and Wilbur 1955). The effects 

 of several TCA-cycle acids on the respiration of strips of mantel tissue 

 also were studied. Succinate, malate, and oxalacetate brought about sig- 

 nificant increases in consumption of oxygenj pyruvate had only slight 

 effect; and citrate was without effect. Heavy-metal catalysis in oyster 

 mantel is indicated by strong inhibition of respiration by cyanides hcw- 

 ever, the inability of methylene blue to reverse this inhibition suggests 

 that the cytochrome system may not be of major importance in respiration 

 of this tissue. Inhibition of oxygen uptake by the metal-complexing agent, 

 diethyldithiocarbamate, indicates the presence of a metal respiratory 

 catalyst, perhaps copper (Jodrey and Wilbur 1955). 



Evidence for the occurrence of the TCA. cycle in oyster eggs was 

 shown by Cleland (195o)j preparations of homogenized oyster eggs could 

 bring about the complete oxidation of pyruvate. Uptake of oxygen was 

 also stimulated by glutamate and various TCA intermediatest succinate, 

 citrate, a-keto-glutarate, fumarate, and malate (Cleland 195l)« 



Consumption of oxygen by oyster spermatozoa is increased by the ad- 

 dition of certain o-keto acids such as a-ketoglutaric, oxalacetic, pyruvic 

 and isocitric acids and amino acetic acid (Humphrey 1950 a and Humphrey 

 and Jeffrey 195U). No significant effect on respiration was noted, however, 

 when other TCA-cycle intermediates were used as substrates. To overcome 

 possible problems of permeability, esters of these acids were tried. The 



15 



