85 percent of the fish caught; in 1954, 71 percent as 

 II-group; and in 1955, 11 percent as Ill-group. 



Males made up 45.6 to 49.7 percent of the fish 

 in the four younger age groups (O-III). They 

 were less abundant (36.6 percent) in the age 

 groups IV-VI combined. During the spawning 

 season the percentage of males on the inshore 

 spawning site was greater than normal but that in 

 the open lake was less. 



The length-weight relation of gizzard shad 

 varies from year to year, from season to season 

 within the year, according to sex during the 

 spawning season, and among the females accord- 

 ing to the state of the ovaries during the spawning 

 season. 



Equations were derived for length-weight data 

 and from them was obtained the general length- 

 weight equation, log \V=— 4.81765 + 3.07053 log 

 L, in which W is the weight in grams and L the 

 standard length in mm. Gizzard shad from Lake 

 Erie were heavier than those reported from Illinois 

 and Missouri. 



Fish of the same length had the. greatest weight 

 in August-October. Males were lightest in June; 

 females in May. The spawning-season female 

 was heavier than the male; this difference in 

 weight was not traceable to the gonadal develop- 

 ment in the female, but may result from the 

 greater activity of the male at this period. Among 

 the females in the spawning season, those which 

 would not spawn during the current season were 

 the heaviest, those approaching spawning were 

 next, and spent fish were the lightest. The 

 percentage loss in weight during spawning 

 averaged 10.7. 



Annual differences in shad weight from rela- 

 tively heaviest to lightest ran: 1952, 1954, 1955, 

 1953. 



Most of the growth in length for the O-group 

 (which hatched in June) occurred in July-Septem- 

 ber; for the I-group during June-August; and for 

 the II-group during July-September. Gizzard 

 shad of the II-group and older commence their 

 rapid growth in length about a month later than 

 the I-group fish. Shad lengths remain practically 

 stationary from November until the time of 

 annulus formation. 



Males and females had almost the same length 

 at the end of the first year (140 mm.) but after 

 about June of the second year of life the females 

 were consistently longer than males of correspond- 



ing ages. The sizes of males and females at the 

 start of different growing seasons were: third, 

 males, 273 mm. and females, 285 mm.; fourth, 

 males, 313 mm. and females, 335 mm.; fifth, 

 males, 343 mm. and females, 364 mm. ; sixth, 

 males, 349 mm. and females, 386 mm. 



The seasonal growth in weight resembles that of 

 the growth in length except that weight decreases 

 during winter while length remains nearly con- 

 stant. This loss of weight begins about the start 

 of the year and continues until about May. 



Differences among the lengths of individuals of 

 an age group at the end of a calendar year tend to 

 be reduced by later compensatory growth. At 

 the end of succeeding years those fish that were 

 the longest of their year class maintain a length 

 advantage, but this advantage decreases. 



The stage of egg development varied from fish 

 to fish throughout most of the year, but with the 

 approach of the spawning season, the retarded 

 shad increased their pace of development while 

 the advanced ones slowed down so that the con- 

 dition of the ovaries became much more nearly 

 uniform. 



A brief description is given of the testis and of 

 various stages of the ovary. The developing egg 

 and the seasonal changes in the saccular ovary 

 also are described. 



Not all mature eggs are expelled at the same 

 time. Eggs which are not mature are held over 

 for next year, and those which develop to the 

 spawning stage too late to be expelled are resorbed. 



Only rarely were I-group female shad ripe. 

 Most of them (an estimated 80 percent) spawn for 

 the first time as II-group fish. The age of sexual 

 maturity could not be determined for the male; 

 males examined in January had motile sperm — 

 even the new I group. The number of II-group 

 males on the spawning site suggests that most 

 mature as the II-group — the few I-group in- 

 dividuals present may be termed precocious. 



A spawning site in the vicinity of Fishery Bay, 

 South Bass Island, was a sandy, rocky bar covered 

 with 2-4 feet of water. Gizzard shad were 

 captured here only during the spawning season — 

 almost all during the evening and night. Spawn- 

 ing was limited in the open lake. The females 

 that are ready to spawn migrate to inshore 

 spawning sites. After spawning, they return to 

 the deeper water. Males also migrate to the 

 spawning sites where they are two or three times 



GIZZARD SHAD IN WESTERN LAKE ERIE 



423 



