PETERSON ET AL.: EARLY LIFE STAGES OF ATLANTIC TOMCOD 



Zotin (1965) reported that eggs of freshwater 

 teleosts (e.g., loach, zander (Lucioperca)) took up 

 no water after water hardening until the chorion 

 began to stretch due to weakening by the hatching 

 enzyme. The mullet egg took up water during the 

 second half of development during which time the 

 perivitelline space first appeared. With the tom- 

 cod, water uptake occurred in the latter stages of 

 development in the three higher salinities. It is 

 not known where this water was distributed 

 within the egg, but it was probably incorporated 

 into embryonic tissue. 



It is inferred, from calculated specific gravity of 

 egg solids, that tomcod embryos osmoregulated to 

 some degree, becoming more proficient as de- 

 velopment proceeded. This may be simply a func- 

 tion of embryonic size, resulting in more 

 osmoregulating tissue. It has been suggested by 

 Holliday ( 1965) that plaice embryos can regulate 

 osmotic concentration after gastrulation, which 

 occurs in 9 d or less in these tomcod eggs. Holliday 

 (1969) also showed that flounder eggs could regu- 

 late yolk sodium from fertilization. Unfortu- 

 nately, we did not make measurements here be- 

 fore 9 d of incubation. 



Holliday and Blaxter (1960) and Forrester and 

 Alderdice (1966) observed development to proceed 

 faster at higher salinities for herring and Pacific 

 cod, respectively. While tomcod hatched earlier at 

 higher salinities, there is little suggestion that 

 development occurred more rapidly. Rather, it ap- 

 peared that the freshwater larvae grew larger 

 prior to hatching. Some structures were delayed, 

 or never appeared in 30%o embryos, but this is due 

 to abnormal development at this salinity. Abnor- 

 mal development has frequently been recorded at 

 abnormally high salinities. Usually the defor- 

 mities are skeletal as are observed for tomcod, or 

 involved body cavity deformities (Holliday 1965; 

 Alderdice and Forrester 1971). 



Although the tomcod is a physoclist species, the 

 pneumatic duct is apparently functional in the 

 newly hatched larva. In <24 h the duct is closed, 

 and the larva can no longer fill the swim bladder 

 by air ingestion. Larval loss of the pneumatic duct 

 has been implied for physoclists generally (Har- 

 den Jones 1957). Whether or not the duct is 

 utilized in initial filling of the bladder is apparent- 

 ly quite variable (Johnston 1953; Schwarz 1971). 



ACKNOWLEDGMENTS 



We wish to acknowledge P. Harmon for assist- 



ing in some aspects of field studies; P. W. G. 

 McMullon and F. Cunningham for performing the 

 photography and drafting; A. Sreedharan for pro- 

 viding statistical analyses of the data; and D. W. 

 McLeese and M. J. Dadswell for reviewing the 

 manuscript. 



LITERATURE CITED 



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1971. Effects of salinity, temperature, and dissolved oxy- 

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Galat, D. L. 



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Harden Jones, F. R. 



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157 



