Discussion 



A striking feature of the serial observations of rate of oxygen consumption (table 3) 

 is the great variability from hour to hour. Such fluctuations are apparently not uncomnnon, how- 

 ever, having been observed by several workers (Chapman 1939: Clausen 1936; Shlaifer 1939; Wells 

 1935a). The following statement of Wells (1935a) is perhaps apropos: "Duplication of results with 

 the sanne animals at two different times is not a measure of the efficiency of the apparatus, nor is 

 a failure to duplicate results a reflection upon the method." Krogh (1916) mentions that the res- 

 piratory exchange in a normal animal may vary 100 percent or more. Over the 24-hour period 

 during which serial observations were made, no consistent rhythms in metabolic rate were evi- 

 dent. Daily cycles in metabolic rate have been claimed for a few freshwater fish (Clausen 1936; 

 Oya and Kimata 1938; Higginbotham 1947) but have not received extensive confirmation. 



10 



20 



30 



40 



50 



RATE OF FLOW(GAL/MIN) 



Figure 6. --Results of a field experiment 



testing the influence of flow rate 

 (gal. /min. ) on rate of oxygen con- 

 sumption (cc. /gm. /hr.). Open 

 circles represent the average of 

 two determinations of oxygen con- 

 sumption (represented by crosses) 

 at each flow. 



The temperature-oxygen 

 consumption curve (fig. 4) in general resem- 

 bles those for other fish but nnust, of course, 

 be interpreted entirely upon its own merits, 

 particularly since a relatively narrow temp- 

 erature range was studied. The curve may be 

 said to represent an experimentally deter- 

 mined relationship of temperature to rate of 

 oxygen consunnption in iao ranging in size 

 from 34 to 50 mm. for the temperature inter- 

 val 19 -29 C. In view of the apparently 

 valid arguments of Ege and Krogh (1914) and 

 Wells (1935a) against the unrestricted use of 

 Van't Hoff's Q and the Arrehenius relation, 

 no attempt was made to calculate either Q,_ 

 values or "thermal increments, " Ege and 



Krogh, for example, found that Q,. varied 



o 5 ol d o 



from 9.8 at -5 C. to 2.2 at 23 -28 C. in 



the goldfish. 



At the higher temperatures in the 

 range tested, the effect of temperature upon 

 metabolic rate appears somewhat more pro- 

 nounced. Since the local fishery is conducted almost entirely during the summer and early fall, 

 when water temperatures often rise to 27 -28 C. and higher, it may be advisable to watch for 

 sudden changes in the water temperature of the live-wells. Even a small rise in temperature 

 might considerably increase the activity and consequently the rate of oxygen consumption of the 

 fish. 



That the rate of oxygen consumption should rise with increase in rate of flow is perhaps 

 not surprising, inasmuch as the fish would presumably exert more energy in swimming as the 

 current of water through the jar increases in intensity. In curve 1 (fig. 5), representing small 

 aggregations of fish and based on the most extensive collection of data, oxygen consumption in- 

 creases linearly with flow rate over the range from 7 to 37 liters /hour. The points appear less 

 scattered at the extreme flow values. This may be a chance variation or the fish, for some reason, 

 may exhibit a uniform metabolic response to the environment at the extreme flow rates. This ex- 

 planation is easier to accept in the case of the high flow values (35-37 liters/hour), where the fish 

 might all be exerting approximately the same amount of energy in maintaining their position against 

 the strong current. 



When larger numbers of fish are used (curve 2, fig. 5), the overall level of metabolism 

 is lower. An analysis of covariance (tables 4b and 4c) on the data making up curves 1 and 2 yields 

 the following statistical conclusions: 1) the difference between the mean values for metabolic rate, 

 adjusted to a common flow value, of group 1 (20-45 fish, adjusted mean 0.431 cc. /gm. /hr, ) and 

 group 2 (75-83 fish, adjusted mean 0. 320 cc. /gm. /hr. ) is highly significant (P < 0. 01), indicating 



