RESPONSE OF MOSQUITOFISH TO THERMAL EFFLUENT 505 



TABLE 3 



MEAN NUMBERS OF EMBRYOS PER FEMALE 



Gambusia affinis FROM FIVE 



SAMPLE POPULATIONS* 



Sample timet 



Sample 



station Feb. June Oct. Dec. 



PCI 11.8(70) 5.0(10) 13.8(11) 27.9(12) 



PC2 9.2(68) 12.2(12) 23.2(8) 27.4(12) 



PCS 5.6(78) 8.8(21) 10.0(18) 0.0(12) 



PP 0.0(45) 23.0(21) 0.0(11) 0.0(11) 



RP 12.0(65) 24.5(12) 6.0(12) 0.0(5) 



*Stations PCI, PC2, and PC3 are in thermally affected 

 areas; PP and RP are in areas at natural temperatures. 



fNumbers in parentheses are numbers of females 

 examined. 



areas. Female mosquitofish from all stations, however, contained 

 similar amounts of fat. Juvenile mosquitofish from thermally 

 affected areas had the highest mean percentage of fat (14 to 18% dry 

 weight). 



Seasonal variation in percentage of fat was found in fish from 

 thermally affected and unaffected areas (Fig. 2b). Percentages of fat 

 were significantly higher (a = 0.05) in fish from affected areas than 

 in those from unaffected areas in February and were similar in June 

 and October. Body fat content was lower in June and higher in 

 October. 



The period of reproductive activity was altered in Pond C as a 

 result of the thermal effluent (Table 3). Embryos were found in 

 female mosquitofish from PCI and PC2 in February, June, October, 

 and December. This indicates that fish were reproductively active 

 throughout the year. Mean brood size generally increased at PCI and 

 PC2 as water temperatures decreased. Embryos were found in female 

 mosquitofish at PCS in all sampling periods except December. 

 Several embryos in the early development stage were found in one 

 female at Risher Pond in February, but the stage of development and 

 the small proportion of gravid females indicated that the reproduc- 

 tive period had not commenced at the time the February sample was 

 taken. Although water temperatures were suitable for reproduction 

 in October (Table 1), few embryos were found in female mosquito- 

 fish from PP and RP (Table 3). The maximum number of embryos 

 per female (61) was found in a female from Par Pond. 



