Serial Determinationa of Metabolic Rate: 24-Hour Experiments 



Procedur e. --Preliminary oxygen consumption tests indicated that a more or less 

 consistent level of metabolic activity was reached after 1 to 2 hours in the container. It is not 

 claimed that this represents a "basal" level of metabolisnn for iao, since the fish are not at com- 

 plete rest, and furthermore it is obvious froin the experiments described below that there is 



considerable fluctuation from 

 hour to hour in the rate of oxy- 

 gen uptake. It appears, how- 

 ever, that any great increase 

 in metabolic rate due to the 

 handling of the fish in setting 

 up the experiment is dissipated 

 after 1 to 2 hours. 



In the actual 

 experiments, 10 or more fish 

 were carefully transferred to 

 the iar and water was allowed 

 to flow for 1 hour with the lid 

 removed. The rubber cork 

 with its connections was then 

 inserted and the flow rate was 

 adjusted to 12 liters /hour. 

 Water samples were taken at 

 1-hour intervals for the first 

 3 or 4 hours, and approxi- 

 mately at 2-hour intervals 

 thereafter. 



Results. --The 



Figure 2a.-- Diagraim of the apparatus used for measuring 

 rate of oxygen consumption in iao. A - sea 

 water line; B - reservoir; C - overflow jar; 

 D - siphon for inlet sannples; E - thermo- 

 meter; F - connection for outlet samples. 

 1, 2, and 3: adjustable hose clzunps. 



Figure 2b. -- Assembly used for obtaining different 



temperature levels. A - inlet to experi- 

 mental container; B - outlet from experi- 

 mental container; C - inlet to copper coils: 

 D - outlet from copper coils; E - cold bath; 

 F - centrifugal pump; G - heating unit; 

 H - stirring rod. 



Figure 2c. --Diagram of the experimental container used 

 in the flow rate experiments. A - inlet to 

 experimental container; B - outlet from 

 experimental container; C - plastic observa- 

 tion window; D - threaded brass rod; E - 

 thernaometer. 



results of three successful 24- 

 hour experiments, all per- 

 formed in January and Febru- 

 ary of 1952, are reported in 

 table 3 and figure 3. Although 

 the data are quite variable, 

 they seem to point to the ab- 

 sence of consistent diurnal 

 cycles in the metabolic rate. 

 In experiments 2 and 3, the 

 rate of oxygen consumption 

 fluctuates irregularly for about 

 6-8 hours, and then undergoes 

 a slow, but nonetheless notice- 

 able, decline for the remainder 

 of the experiment. In both ex- 

 periments, there is at the end 

 of the 24 hours a small rise in 

 the metabolic rate for which 

 there is no apparent explana- 

 tion. These tests, then, show 

 only that there is an irregular, 

 apparently non-cyclic, fluctu- 

 ation in metabolic rate during 

 the first 24 hours in the jar. 

 Attention is called to the 

 marked rise in oxygen con- 

 sumption which occurred at 



