500 BENNETT AND GOODYEAR 



Station PCI was the nearest to the effluent canal, followed by PC 2 

 and PCS. Station PCI was separated by about 300 m of open water 

 from PC2, and PCS was approximately 650 m from PCI and PC2. 

 Mosquitofish populations at PCI and PC2 appeared to be inhabiting 

 waters at similar thermal regimes, whereas the population at PCS had 

 access to a small inlet stream at temperatures "natural" for the area. 

 Two control or unaffected populations were also sampled, one from 

 an unheated section of Par Pond, a 1120-ha cooling pond, and the 

 other from Risher Pond, a 0.1-ha farm pond (stations PP and RP, 

 respectively). Also during the February sampling period a second Par 

 Pond population was sampled, but, because of its similarity to that at 

 the other Par Pond station, it was not sampled for the remainder of 

 the study period. Station PP was approximately 2 km from the 

 Pond C populations. Mosquitofish populations in RP were about 

 20 km southwest of the Par Pond and Pond C populations. 



METHODS 



Mosquitofish populations were sampled with a 2-m seine and a 

 dip net in February, June, October, and December 1970. Fish were 

 transported alive to the laboratory in Styrofoam coolers and were 

 processed within 24 hr. All fish were measured (total length to 

 0.1 mm), weighed (nearest milligram), and sexed by the absence or 

 presence of a gonapodium, and females were examined internally for 

 embryos in the oviduct. The stage of development of the embryos 

 was classified as: stage 1, no enlargement— no development; stage 2, 

 enlarged embryo without development; stage S, embryo with eye- 

 spots; stage 4, embryo with well-developed eyes; stage 5, embryo at 

 late yolk sac; stage 6, embryo mobile and capable of surviving 

 externally from the female. For comparative purposes, stages 1 and 

 2, S and 4, and 5 and 6 were combined as early, intermediate, and 

 advanced stages, respectively, of embryo development. 



Samples from February, June, and October were separated by 

 sex, quickly frozen, and lyophilized in a freeze dryer. Samples were 

 considered dry when consecutive daily weighings were identical. 

 Dried samples were homogenized in a small blender and placed in 

 dessicators until fat determinations were made. Fat content was 

 determined by hot ether extraction for S hr. Ether was evaporated 

 from samples in drying ovens (30°C), and the weight of the extract 

 was recorded. Results were expressed as percent of dry body weight. 

 Data were log transformed and tested by analysis of variance, and 

 class means were compared using the Student— Neuman—Keuls test 

 (P < 0.05) (Sokal and Rohlf, 1969). 



