appetite. Also, we certainly may not assume that feeding activity cannot 

 be materially restricted at cyanide levels that have very little or no ad- 

 verse effect on the efficiency of utilization of food for growth by fish in 

 laboratory aquaria and on their consumption of food that can be procured 

 with almost no effort. Although extremely low cyanide concentrations 

 greatly impaired the swimming ability of young coho salmon, Oncorhynchus 

 kisutch (Broderius, 1970), much higher concentrations not far below lethal 

 levels were found, in a sinlgle experiment performed by Leduc (1966), to 

 have no persistent, adverse effect on their food consumption and conver- 

 sion efficiency to aquaria. Indeed, after an initial reduction of both 

 food intake and food-coversion efficiency during the first 12 days of ex- 

 posure the gross conversion efficiency considerably exceeded that of 

 controls. This result needs verification, but there is no very good reason 

 to doubt its validity. The efficiency of food conversion probably 

 increased, as compared with that of the controls, because of reduction of 

 the activity of the usually quite active fish in the cyanide solutions, in 

 which more of the assimilated food consequently could be utilized for 

 growth. Had the fish been required to remain normally active, a very 

 different result probably would have been obtained. To ensure complete 

 validity and comparability of laboratory measurements of food-conversion 

 efficiency, uniform, moderate activity of all test subjects must be somehow 

 enforced, but this is very difficult to accomplish. When this is not done, 

 the results of detailed studies of food-conversion efficiency at a number 

 of different levels of food intake and toxicant concentrations are 

 certainly not without interest or value, but, for the reasons indicated, 

 such a laborious study may not be quite as profitable an exercise as it may 

 appear to be. I believe that effort devoted to feeding-activity studies 

 can be more profitable, and that whenever an impairment of the efficiency 

 of food utilization for growth is masked in aquarium tests by a depression 

 of activity, the harmful effect of a poison will be revealed by appropriate 

 tests for reduction of feeding activity. The activity of fish in the 

 aquaria is largely spontaneous and unrelated to feeding, but feeding 

 activity, which is not enforced activity, can be expected to be depressed 

 by a poison whenever spontaneous activity is suppressed. 



I have discussed in much detail the relation and distinction between 

 appetite for food and feeding activity or foraging efficiency, and how they 

 can be affected by water quality changes, because I believe that many 

 biologists do not sufficiently realize the need for food-consumption 

 studies designed to measure something other than the appetite or 

 assimilative capacity. Very few studies of effects of water pollution on 

 the foraging activity and success have been undertaken in the past. I 

 believe that much effort can be profitably devoted to the development of 

 methods for such investigation. 



Sufficiently instructive tests for impairment of the feeding activity 

 or efficiency of small fishes that feed on plankton or on benthic inverte- 

 brates such as amphipods in standing or gently flowing waters apparently 

 can be quite simple, requiring little space and no elaborate facilities. 

 One can introduce a limited number of the food organisms into each of 

 several large aquaria and determine how many of them are consumed in a 

 certain period of time by hungry fish that have been held in the aquaria 



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