PETERSON ET AL.: EARLY LIFE STAGES OF ATLANTIC TOMCOD 



Table 3. — Water content (milligrams per egg) and percentage 

 water (parentheses) in tomcod eggs at various incubation 

 salinities and days from fertilization. Each value represents 10 

 eggs. Sampling periods were fewer at 20 and 30%o due to earlier 

 hatch. 



Days of 

 incubation 



9 

 12 

 17 

 22 



27 



27-d mean 



32 

 37 

 42 



47 

 52 

 Newly hatched 

 larvae 



0%o 



10%o 



20%« 



2.86(86.7) 

 2.87(87.2) 

 2.72(86.6) 

 2.94(85.5) 

 2.78(86.1) 

 2.83(86.4) 



2.78(86.8) 

 2.87(87.5) 

 2.86(89.4) 

 2.88(87.8) 

 2.76(89.0) 



1.41(85.5) 



2.19(82.3) 

 2.14(84.3) 

 2.36(81.9) 

 2.22(81.5) 

 2.34(83.9) 



2.25(82.8) 

 240(84.5) 

 2.44(85.3) 

 266(86.0) 

 258(85.4) 

 2.91(88.2) 



250(84.7) 

 2.48(83.5) 

 2.47(83.4) 

 2.39(83.9) 

 2.30(82.7) 



2.43(83.6) 

 241(84.0) 

 2.44(84.5) 

 2.60(86.1) 

 2.65(85.8) 



30%<i 



2.35(81.9) 

 2.32(82.9) 

 2.54(83.6) 

 2.29(79.8) 

 2.40(82.2) 

 2.38(82.0) 



2.42(83.0) 

 2.55(84.7) 



The water content of newly hatched FW larvae 

 was 1.41 mg (85.5%), so about half of the water in 

 the FW egg is associated with perivitelline fluid 

 and zona radiata. 



Dry Weight 



No measurable change in egg dry weight oc- 

 curred over the first 27 d of incubation (Table 4). A 

 one way ANOVA indicated significant differences 

 among the mean dry weights for the first 27 d of 

 incubation (F = 3.9, P<0.05). The mean dry 

 weight of 30%o was significantly greater than 

 those of FW and 20%o eggs (Duncan's Multiple 

 Range Test). 



Table 4. — Dry weights (mg) for various incubation salinities and times from fertilization 

 (d). Each value is averaged from 10 pooled eggs. Values to the left of the bracket for the first 

 27 d of development are means for that period. 



Table 5. — Statistical parameters for regressions of percentage 

 water content vs. time (d) and dry wt vs. time (data given in 

 Tables 3, 4). Times are for days 27-52, inclusive, b = slope of 

 regression equation, r = correlation coefficient, df = degrees of 

 freedom. 



of incubation. The water content of 10%o eggs in- 

 creased over the last 25 d of incubation at 0.023 

 mg/egg per d (P<0. 05, Tables 3, 5), until the water 

 content at hatching approached that of FW eggs. 

 The 20%o eggs took up water after 27 d incubation 

 at 0.018 mg/egg per d (P<0.01), but the water 

 content of these eggs was still lower than for eggs 

 incubated in FW and 10%o. The 30%o eggs may 

 have taken up slight amounts of water, but the 

 data are insufficient to be tested statistically. 



Dry weight decreased significantly over the last 

 25 d (Tables 4, 5). This decrease was greatest in 

 freshwater, about 0.1 mg/egg compared with 0.07 

 and 0.04 at 10 and 20%o, respectively. Although 

 sample size is inadequate for statistical analysis, 

 it would appear that the 30%o eggs lost about 0.05 

 mg/egg. Yolk content of newly hatched larvae was 

 not measured; however, larvae hatched from 

 higher incubation salinities appear to have more 

 yolk (Figure 8), an observation supported by the 

 fact that hatching is earlier at higher salinities. 

 The lesser amount of yolk of FW eggs is in agree- 

 ment with the greater loss of solids by these eggs. 



About 25% of the dry weight of FW eggs is lost at 

 hatching, and is thus contributed by the chorion 

 and the perivitelline fluid. 



Egg Diameter 



The diameters of 10 eggs from each incubation 

 salinity were measured at the time intervals indi- 

 cated in Table 6. There was no indication of any 

 change in egg diameter with length of incubation 

 (Table 6), so that the water uptake at the three 



153 



