SEA LAMPREY OF CAYUGA LAKE 



593 



mens captured in August had a mean intestinal 

 diameter of 0.67 inch. In 55 spent lampreys cap- 

 tured in June the mean intestinal diameter was 

 0.06 inch. Since the intestine had no noticeable 

 taper, this measurement was taken at approxi- 

 mately the midregion. These values indicate a 

 shrinkage of nearly 94 percent in the diameter of 

 the sea lamprey's intestine prior to and during the 

 spawning period. 

 Loss of Body Weight and Length 



Length measurements and weights of 27 male 

 and 37 female sea lampreys that were tagged on 

 then upstream migration and recaptured after 

 spawning, provided information on the absolute 

 and percentage loss in weight and length (table 33) . 



Loss in weight during the spawning season 

 amounted to 8.5 percent for males and 34.1 per- 

 cent for females. There is little evidence of cor- 

 relation between prespawning weight and subse- 

 quent percentage loss of weight. 



Greater weight of sex products discharged by 

 females at spawning accounts for part, but by no 

 means all, of the sex difference in total loss of 

 weight (table 34). In prespawning samples the 

 testis made up 2.9 percent of the total weight of 

 males and the ovary 17.5 percent of the total 

 weight of females. The gonads did not disappear 

 entirely, however, at spawning. An estimated 

 26 percent of the testis and 1 percent of the ovaries 

 were present in the postspawning lampreys; con- 

 sequently, the maximum estimated losses through 

 discharge of sex products were 2.1 (2.9X0.74) 

 percent for males and 17.3 (17.5X0.99) percent 

 for females. Additional weight losses are accord- 

 ingly 6.4 (8.5 — 2.1) percent for males and 16.8 

 (34.1 — 17.3) percent for females. The loss of 

 weight in females, in addition to that attributable 

 to discharge of sex products, is between 2 and 3 

 times that of males. 



Table 33. — Losses in length and weight of mature sea 

 lampreys during the spawning season 



Table 34. — Mean percentage composition of total weight 

 made up by gonads and percentage losses in weight due 

 to deposition of reproductive products and from other causes 



[Figures in parentheses are the number of specimens 

 upon which the mean values are based] 



Loss in length was 11 percent in males and 17.9 

 percent in females. In absolute measures this 

 shrinkage amounted to a loss of several inches in 

 total length. The sex difference in percentage 

 loss of length was smaller than in percentage loss 

 in weight. The percentage loss in length tended 

 to be greater among the longer than among the 

 shorter males, but in females no correlation be- 

 tween length and relative decrease in length was 

 detectable. 



EGG DEVELOPMENT AND HABITS OF 

 AMMOCOETES 



Egg Development 



Freshly deposited sea lamprey eggs are light tan 

 or cream color, nearly spherical, and have an aver- 

 age diameter of approximately 1 millimeter. This 

 small size permits them to fall into the interstices 

 of the gravel in the nest bottom where they are 

 covered and protected during incubation. 



An experiment in artificial propagation was con- 

 ducted at the Cornell Experimental Fish Hatchery. 

 One large partially spent female and several ripe 

 male sea lampreys were used. Milt from one male 

 lamprey was expelled into a basin which con- 

 tained approximately one teaspoonful of water. 

 Then the eggs, an estimated 15,000, were dis- 

 charged into the basin, and milt from another male 

 was added. The eggs were stirred with a feather 

 for 1 minute. Next 1 cupful of water was added 

 and the contents stirred for 10 minutes. The 

 liquid was then decanted and replaced by 1 quart 

 of water. After the eggs were stirred rather 

 slowly for one-half hour they were placed in a 

 Downing hatching jar. The water volume passing 

 through the jar was adjusted to keep the eggs in 



