SEA LAMPREY OF CAYUGA LAKE 



571 



the gill openings increased from about ninety one- 

 thousandths of the total body length in Septem- 

 ber-October to approximately one hundred and 

 ten one-thousandths in June. 



Body depth. — Body depth of male and female 

 specimens was approximately equal in September- 

 October and June, but in May, before egg deposi- 

 tion, the females were considerably deeper bodied 

 than males (table 9). Males increased in body 

 depth at a nearly constant rate from September- 

 October through June. However, the females in- 

 creased in depth very rapidly prior to spawning 

 (May), but changed very little thereafter. 



Disc length. — Males and females had discs 

 (mouths) of about the same relative size during 

 September-October and May (table 10). In June, 

 the proportional disc length of male specimens was 

 considerably larger than that for females. The disc 

 size remained nearly constant throughout the en- 

 tire year except for a slight decrease in both sexes 

 in May and a great enlargement in male specimens 

 in June. This difference was distinct enough to be 

 useful in the field as an aid in determining sexes. 



Snout length. — Length of the snout changed in 

 much the same manner as the disc length (table 

 11). Only in June did the proportional snout 

 length differ greatly between the sexes; in this 

 month the males possessed the larger snouts. Only 

 minor seasonal changes were evident except for the 

 June specimens, at which time the size of the snout 

 of males increased considerably. 



Table 9. — Relative body depth of Cayuga Lake sea lampreys 



in 8 collecting periods 



[Expressed as thousandths of the total length] 



Table 10. — Relative length of the disc of Cayuga Lake sea 

 lampreys in 3 collecting periods 



[Expressed as thousandths of the total length] 



Table 11. — Relative length of the snout of Cayuga Lake sea 



lampreys in 3 collecting periods 



[Expressed as thousandths of the total length] 



Tail length. — Tail length of male lampreys aver- 

 aged larger than that for females during each col- 

 lecting period (table 12). The differences were 

 not large, however, until June. As the seasons 

 progressed from fall to spring, the relative tail 

 length consistently decreased. Tail length was 

 the only body section in which relative size de- 

 creased. From September-October to May the 

 change was small, but a marked decrease took 

 place between May and June, especially in 

 females. 



Summary. — Sexual dimorphism during Septem- 

 ber-October was exhibited only by the length over 

 the gill openings. In May, only body depth 

 showed any appreciable differences in the sexes. 



