Pygmy Killifish and Mosquitofish 97 



to yield consumption during the period (adapted from Elliott and 

 Persson 1978): 



C t = ((S t +l)-(S -H)e- rt )rt 



l-e~ rt 



Daily food consumption, £C t , is the sum of consumption rates over 

 each period. For G. affinis in summer, the graph of consumption versus 

 time (bottom panel of Fig. 1) indicates that peak consumption occurred 

 in the afternoon. 



Gambusia affinis in winter samples showed feeding trends similar 

 to those in summer but at lower levels. Evacuation rate and daily food 

 consumption were lower in February than in August (Table 2). There 

 was a single feeding peak in late afternoon, as in summer. Low daily 

 food consumption combined with low fish biomass to produce very low 

 area-based consumption. 



Leptolucania ommata. Leptolucania ommata showed diel feeding 

 patterns similar to those of G. affinis. Foregut content in summer 

 peaked in late afternoon (Fig. 2). Consumption showed one daily peak, 

 in the afternoon. In winter (March 1984), L. ommata also consumed 

 maximally in the afternoon, as other species-season combinations had 

 done. 



Leptolucania ommata had seasonal feeding dynamics similar to 

 those of G. affinis. The evacuation rate in summer was 0.279/ hour, 

 similar to the 0.262/ hour calculated for G. affinis in summer (Table 2). 

 The evacuation rate in winter was also similar in the two species, 0.143 

 and 0.1 57/ hour, respectively. In both species, daily food consumption 

 increased from winter to summer by a factor of about 4 (3.85 for L. 

 ommata, 4.62 for G. affinis). This increase might be largely a result of 

 temperature-dependent feeding: If the "Q 10 " for food consumption were 

 about 2, the approximately 20° C difference from winter to summer 

 would give an increase of about 4 times. Such a doubling of feeding for 

 every I0°C is consistent with the results of Salvatore et al. (1987), who 

 found that the feeding rate of Dorosoma cepedianum Lesueur approxi- 

 mately doubled when laboratory water temperature increased from 10 

 to 20° C. Thus such differences in feeding rates may be largely attributed 

 to the environmental temperature. 



DISCUSSION 



The two fishes fed on similar kinds of foods. This should not be 

 surprising, because I captured them in the same areas and observed 

 them feeding at about the same depth (near the surface). Diets, 

 evacuation, and consumption in this study were similar to values 



