508 BENNETT AND GOODYEAR 



directly related to temperature since other factors can also affect 

 brood size in mosquitofish. Krumholz indicated that body size, time 

 of year, previous brood size, and fertility can affect the number of 

 young per brood. We feel that although brood size is comparable to 

 that reported in the literature the number of generations per year is 

 probably increased in mosquitofish from thermally affected areas. 

 Discussion and data presented by Ferens and Murphy (1974) support 

 this hypothesis. 



Size at sexual maturity and sex ratios are parameters that vary 

 greatly among populations. Krumholz (1948) found that females 

 reproduced at 31 mm in one population and at 24 mm in another. 

 The variation in size at sexual maturity (23 to 33 mm) that we found 

 agrees with these data. The sex ratios found in this study (1.6 : 1 and 

 2:1) were also within the range reported by Krumholz. He found 

 that females doubled males in "standing" populations, whereas new 

 populations were generally 1 : 1. It is interesting to note that the 

 lowest proportion of males was found at PC2, the station subjected 

 to the highest temperatures (Table 1). Krumholz also found that 

 males were generally less resistant to stressful conditions than 

 females. 



Percentages of body fat were generally similar for the popula- 

 tions studied, with the exception of the Par Pond samples, which had 

 significantly lower amounts of body fat (Fig. 2a). The results of our 

 analyses of body fat content were generally similar to those of Falke 

 and Smith (1974), except that we found lesser amounts of body fat 

 in females than in males. Falke aiid Smith reported higher percent- 

 ages of fat in females. Since their fish were sampled in August, time 

 differences may be responsible for the disparity. 



Fish exhibit changes in body fat content generally associated 

 with changes in metabolism and reproductive activity (Nikolsky, 

 1963). Peaks in fat content are usually found in late summer (Maki, 

 1967) or fall (Dahlberg, 1969) and are probably associated with high 

 quality and quantity of food ingested and assimilated (Love, 1957) 

 and with reduced channelization of energy into reproduction. 

 Although fish are actively reproducing in Pond C and are subjected 

 to abnormally high temperatures, which should increase metabolic 

 demands, percentages of body fat were similar to those for fish from 

 unaffected areas. One possible explanation is that elevated- 

 temperature regimes increase productivity at lower trophic levels, 

 which increases the available food supply. Thus fish are able to ingest 

 and assimilate enough food to store fat even though temperatures are 

 abnormally high and reproduction is generally occurring throughout 

 the year. Our data support the conclusion of Falke and Smith (1974) 



