Figure 8. — Newly hatched tomcod larvae from various incuba- 

 tion salinities. Note the larger amounts of yolk remaining, the 

 higher the salinity of incubation. A. Freshwater; B. 10%o; C. 

 20%o. Yolks have shrunk due to (Formalin) fixation effects. Mag- 

 nifications 13 X . 



Table 6. — Egg diameters (millimeters) for various incubation 

 salinities and incubation times. Each value is the mean of 10 

 measurements, v = calculated egg volume (microliters). Stan- 

 dard deviations given in parentheses. 



Days of 

 incubation 



0%0 



1 0%o 



20%o 



30%o 



higher salinities toward the end of the incubation 

 period did not lead to measurable swelling, al- 

 though slight swelling within experimental error 

 probably occurred. The mean diameters of FW, 10, 

 20, and 30%o eggs were 1.87, 1.78, 1.77, and 1.78 

 mm, respectively. The standard deviations for lots 

 of 10 eggs varied from 0.02 to 0.09 mm, and were 

 0.04-0.05 in most cases. The greater diameter of 

 the FW eggs is no doubt related to the higher 

 water content of these eggs. 



FISHERY BULLETIN: VOL. 78, NO. 1 

 Specific Gravity of Egg Solids 



The sp. gr. of FW egg solids (lipids included) was 

 constant at 1.27 for the first 27 d of incubation 

 (Figure 9), then rose linearly to about 1.36 just 

 before hatching. This increase in sp. gr. of egg 

 solids may be due to increase in compact tissue, 

 such as cartilage. It could also reflect a rapid in- 

 crease in embryonic tissue and a corresponding 

 decrease in yolk solids. The sp. gr. of solids of 

 Atlantic salmon alevins also increases during de- 

 velopment (Peterson and Metcalfe 1977). This was 

 shown to be due to increase in embryonic mass, the 

 solids of which had a higher sp. gr. than did yolk 

 solids. 



The sp. gr. of 10%o egg solids was identical to 

 that of FW eggs throughout. Apparently, in- 

 sufficient salt penetrated these eggs to change the 

 solids' sp. gr. measurably. This apparent lack of 

 difference between FW and 10%o eggs should be 

 accepted with some caution, since an error of 0.01 

 mg/egg in estimating dry weight (averaged over 

 the first five measurements) could result in a shift 

 in solids' sp. gr. by 0.2 units. Since the dry weight 

 of 10%o eggs was some 0.02 mg greater than that of 

 FW eggs (Table 4), some salt may well have en- 

 tered the 10%o eggs. 



The sp. gr.'s of egg solids for 20 and 30%o eggs 

 during early development were much higher than 

 for the two lower salinities (Figure 9), and they 



L38 

 1.36 



"O 



o 



CO 



^ 1.34 



LU 

 O 



^ 1.32 



O 



•^ 1.30 



ir> 



I 28 



26 



30% 



«-« — « — ft — ft 



_L 



J_ 



10 20 30 40 50 



Time from Fertilization (Doys) 



60 



Figure 9. — The specific gravity of egg solids (as calculated from 

 water content and egg specific gravity) at various times from 

 fertilization for various incubation salinities. Lines fitted by eye. 



154 



