POIKILOTHERMIC ADAPTATIONS 



striking enzymic increases in fish tissues in the cold are in those of 

 glycolysis. However, intermediate acids must ultimately be oxidized 

 and the relatively small changes in electron transport enzymes are 

 difficult to explain. 



The preceding evidence indicates that some enzymes change and 

 others are unaltered in the compensatory acclimation of fish, that 

 corresponding enzymes differ for different tissues, and that enzymes 

 may either increase or decrease according to temperature. The 

 meaning of inverse acclimation (e. g., malic dehydrogenase in gold- 

 fish liver and catalase in eel liver) is not clear. In general, the more 

 an animal is taken apart, the less is the apparent acclimation. In our 

 laboratory Murphy recently examined the activity of numerous en- 

 zymes of goldfish liver and has had difficulty obtaining statistically 

 significant differences between those from cold- and warm- acclima- 

 ted fish. The range of variability is very great for those genetically 

 heterogeneous fish and reproducibility of experiments poor. Cer- 

 tainly there is no evidence for a general change in activity of all me- 

 tabolic systems, and major effects are probably in the integration of 

 metabolism. 



Non- enzymatic Chemical Changes 



Other changes besides those in enzymes of intermediary meta- 

 bolism havebeennotedincold-acclimation. Changes in water content 

 may be significant for marine fish. At 1.6 C in sea- water the tide- 

 pool fish Girella lost 23% of their water, and they survived only 2 

 days, whereas in 45% sea- water at the same temperature no water 

 loss was observed and survival was prolonged (Doudoroff, 1938). In 

 fresh- water fish, however, an increase of 2% in water content was 

 reported for goldfish after 2 days at4 C (Meyer et al., 1956) and a 

 decrease after 25 days at 5° C (Hoar and Cottle, 1952). Goldfish 

 liver showed no significant difference in water content for 5 C and 

 30 C acclimation (Murphy, 1961). 



o 

 Protein content of liver from goldfish acclimated at 5 C was 



9.9% and from those at 30° C was 12.5% (Murphy, 1961); no change 



was found in the protein content of muscle. 



21 



