Table 6. — Empirical weights and weights calculated by the, 

 general length-weight equation for gizzard shad in western 

 Lake Eric, 1952-55 



50 100 150 200 250 300 350 



STANDARD LENGTH (MILLIMETERS) 



Figure 7. — Length-weight curves for gizzard shad from 

 Lake Erie, Missouri, and Illinois. Left curve, Lake 

 Erie; middle curve, Missouri; right curve, Illinois. 



Empirical weights and the weights calculated by 

 the general length-weight equation (table 6 ; fig. 6) 

 agreed well in view of the heterogeneous nature of 

 the materials (records of weight were combined 

 without regard to season, year, sex, maturity, or 

 method of capture). Largest disagreements in 

 measurements concerned the longest fish. 



Patriarche and Lowry (1953) determined the 

 length-weight equation to be log W= — 2.2071 

 + 2.9812 log L for gizzard shad in the Black River 

 Basin of Missouri. Lagler and Van Meter (1950) 

 reported the equation to be log W= — 2.2789 

 + 3.034 log L for shad in Illinois. In both equa- 

 tions, the units are weight in ounces and total 

 length in inches. The curves based on these 

 equations show the Lake Erie shad to be heavier 

 for corresponding lengths than those in Missouri 

 and Illinois (fig. 7). 



The weights of male and female gizzard shad 

 were closely similar except in June and July, 

 when the females were consistently heavier than 

 males of corresponding length. This difference 

 frequently has been explained on the basis that 



GIZZARD SHAD IN WESTERN LAKE ERIE 

 774-711 O— 66 8 



the female's ovaries are heavy with eggs soon to 

 be spawned. Although the weight of the ovaries 

 contributes strongly to the heavier total weight 

 of the female gizzard shad, it does not explain 

 it entirely. To investigate this point, the body 

 weight (exclusive of gonad weight) of both sexes 

 should be compared. Unfortunately, I had 

 taken relatively few gonad weights of males — 

 and these over a period of several months which 

 cut across the seasonal changes of weight. How- 

 ever, since the testis weight averaged 1.4 percent 

 of the body weight for these males, I thought I 

 could eliminate the greater part of the weight 

 advantage offered by the ovary by adjusting the 

 female shad's weight to include ovaries weighing 

 only 1 percent of her body weight. 



The adjusted weights of these fish were still 

 greater than those of male shad of corresponding 

 length (table 7). The lesser weight of males may 

 result from their greater activity during the 

 spawning season. 



Effect of State of Ovaries on Weight 



The study of the effect of the state of develop- 

 ment of the ovaries on the weight of the fish was 

 based on records for three categories of fish caught 

 in June 1955: will not spawn, will spawn, and 

 spent. 



The gizzard shad that would not have spawned 

 were the heaviest ( cble 8). The average weight 

 of females which would have spawned was 96 per- 

 cent of that of the shad which would not have 

 spawned. It appears that the production of ma- 

 ture eggs for spawning reduces the fish's total 

 weight — possibly because some food is stored as 



401 



