Two additional factors 

 regarding stock "condition" must be 

 considered. First, fish with injured 

 tails, presumably chewed by other 

 fish, were sometinnes seen in the 

 tanks. Their swimnaing behavior ap- 

 peared to be normal. Secondly, an 

 ectoparasite was occasionally found 

 attached to the underbelly of the fish. 

 To estimate the incidence of this kind 

 of parasitism, two aannples taken near 

 the laboratory were examined. In the 

 first sample, 1 fish out of a total of 95 

 showed ectoparasites; and in the second 

 sample, only 2 fish out of 390 posses- 

 sed externally visible parasites. Oc- 

 casionally, one or two fish with para- 

 sites or chewed tails were discovered 

 at the end of an experiment, but the 

 presence of these fish did not appear 



to change the pattern of the results. 

 Figure 1. --Holding box for iao at the main 



laboratory j^ ^-^^ ^f j^e delicate 



nature of these fish, considerable 



care was taken in selecting and handling experimental animals. Fish dissociated from the main 



school and swimming weakly at the surface were removed as quickly as possible fronn the stock 



tanks. In transferring the fish, they were first lifted from the tank in a fine -meshed net, dipped 



into a beaker, and then poured through a plastic funnel into the experimental container. 



MEASUREMENT OF DISSOLVED OXYGEN 



The unmodified Winkler procedure was used to measure dissolved oxygen for all the 

 experiments in which the water in the experimental container was continually being renewed. The 

 method is standardized and widely used and, therefore, needs no detailed description. Essential- 

 ly, the steps outlined by TuUy et al. (1950) were followed both in the preparation of reagents and 

 in the collection and preserving of samples. In those experiments where the fish were allowed to 

 use up the dissolved oxygen in sealed jars, the permanganate modification of Winkler's method 

 was employed to avoid possible nitrite error. The procedure foll'owed that outlined by Welch 

 (1948). 



Several methods are available for standardizing sodium thiosulfate solutions, and their 

 relative utility has recently been compared (Thompson and Robinson 1939). Potassium bi-iodate, 

 as recommended by Thompson and Robinson, was used as a standard in the present study. This 

 substance is expensive, but is relatively stable and, furthermore, consistent in its results. To 

 standardize the thiosulfate solution, 10 ml. of 0.01 normal bi-iodate was diluted to 50 ml. with 

 sea water, alkaline -iodide and sulfuric acid added in that order, and the released iodine titrated 

 as usual. 



METABOLIC RATE UNDER VARIOUS CONDITIONS 



Although oxygen uptake is not the only index of activity of an organism, it is correlated 

 quantitatively with rate of metabolism and heat production and is the generally accepted standard 

 measure of nnetabolic processes. In the present work the terms "metabolic rate", "oxygen con- 

 sumption", and "oxygen uptake" will all be taken to mean the rate of oxygen consumption, ex- 

 pressed as cc./gram wet weight/hour. The following problems are taken up in this section: (1) 

 the extent of normal fluctuations in rate of oxygen consumption and the presence or absence of 



