food consumption at the low oxygen concentrations in the ponds. However, 

 since the bass in the ponds were obviously unable fully to satisfy their 

 appetite for food at any of the tried oxygen levels, this reduction of 

 their food consumption must have been due primarily to their reluctance to 

 expend as much energy in pursuing their prey at the low oxygen levels as 

 they expended in the presence of more dissolved oxygen. 



The amount of energy that the bass expended in capturing and assimila- 

 ting their food in the ponds at like temperatures and high oxygen concen- 

 trations was virtually independent of the density of the prey. In other 

 words, the average rate of their metabolism was not appreciably affected by 

 changes in availability of the food. As food became less available, so 

 that less was consumed, less energy had to be expended in the process of 

 assimilation of the food ingested and more could be expended, therefore, in 

 pursuing the prey, but the total energy expenditure did not increase or de- 

 crease demonstrably. The average metabolic rate of the bass in the ponds 

 was estimated by the energy balance (or caloric apportionment) method. The 

 caloric value of the unassimilated portion of the food and of metabolic 

 wastes (estimated through laboratory experiments, using small aquaria) and 

 the measured increment in caloric value of the bodies of the growing bass 

 were subtracted from the caloric value of the food found to have been 

 consumed by the bass during an experiment; the remainder, in calories, was 

 then divided by the mean caloric value of the bodies of the bass, in kilo- 

 calories, and by the duration of the experiment, in days. Fairly uniform 

 values of about 26 cal/kcal per day were thus obtained at temperatures near 

 21 C (Lee, 1969; Doudoroff and Shumway, 1970). 



At moderately reduced oxygen concentrations the feeding activity of the 

 bass was reduced evidently because the metabolic rate was limited by the 

 oxygen supply, and this must have been the reason also for the reduction of 

 the appetite of the bass in aquaria at the same oxygen concentrations. 

 When held in aquaria with an unlimited food supply (easily captured 

 mosquitofish), the bass had at high oxygen concentrations an average 

 metabolic rate approximately equal to that of more active bass in the 

 ponds. Reduction of the oxygen concentration thus can be expected to limit 

 the appetite of fish whenever it impairs their feeding, and vice versa. 

 Effects of some toxic substances on feeding activity and appetite may be 

 similarly related, but those of other poisons may be quite unrelated 

 phenomena. It is highly probable that some toxic substances, at concen- 

 trations that impair neither the appetite nor the gross food-conversion 

 efficiency of fish held in aquaria or even improve one or both of them, 

 nevertheless reduce the rate of growth of the fish under natural conditions 

 by limiting their feeding activity. Such an effect has not yet been 

 clearly demonstrated, probably only because the appropriate experiments 

 have not been performed. But we surely may not assume that a reduction of 

 feeding activity will always be accompanied by an impairment of appetite as 

 it apparently is when oxygen concentrations are reduced. 



As I have pointed out already, cyanide poisoning can greatly restrict 



one kind of activity of fish, at least, while causing an increase of their 



appetite for food; for reasons to be soon apparent, I believe that it can 



restrict spontaneous (not enforced) activity also without impairing the 



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