FISHERY BULLETIN: VOL. 78, NO. 1 



RESULTS AND DISCUSSION 



Developmental Stages 



To assess development of eggs under natural 

 conditions, a series of embryological stages was 

 constructed (Table 1; Figure 3, lower) based on 

 systematically sampled, laboratory-reared eggs. 

 We attempted to make them consistent with those 

 published previously for other species (e.g., Bon- 

 net 1939 for Atlantic cod), although comparisons 

 were difficult in more advanced embryos. For 

 example, Atlantic cod lack a well-differentiated 

 lower jaw at hatching, but it is well developed in 

 tomcod. The stages are also referred to comparable 

 figures in Hardy (1978:278-289) where possible 

 (Table 1). Sampling eggs more frequently would 

 have been useful in some instances; e.g., many 

 anatomical features appeared between days 10 

 and 13, and are grouped into stage 11. The earliest 

 stages were missed by taking the first sample at 24 

 h. Stages 3-6 were observed from field samples. 



Table 1. — Summary of development stages and day of first 

 appearance of anatomical features for tomcod eggs incubated at 

 different salinities. For temperature regime see Figure 3. The 

 stages are for eggs developing in freshwater. Stages 3-5 and 9 

 were observed in field-collected material only. 



Irregularities in development were seen in the 

 later stages of development at 30%o. The snout 

 failed to develop normally, and the development of 

 pectoral fin buds and brain lobes was delayed. 



Field Observations 



Largest numbers of tomcod eggs were sampled 

 by the drift samplers (Figures 4, 5) in the 15- to 

 20-d period after spawTiing. The numbers corre- 

 lated fairly well with stream water level for 

 1977-78 when water levels were measured ( Figure 

 5). Largest numbers of drifting eggs may also be 

 related to spawning activity rather than stream 

 water levels per se. Typical numbers of eggs col- 



*3 0- 



o. tl 



-10 



•^""""'y Febfaoty 



MofCh 



Sea Surfoce Temp 



Fresh Water Temp 



1000 



100 



Eqqs ond 

 Larvae 



Larvae 



30 45 60 



Doys from Dec 29 



Figure 4. — Movements of tomcod eggs and larvae out of Frost 

 Fish Creek. Upper: Environmental conditions and numbers of 

 sampled tomcod eggs and larvae are shown for the 3 mo of egg 

 and larval stream residence in 1976-77. Freshwater tempera- 

 tures (solid line) and sea surface temperatures (dashed line) for 

 January- April 1976-77. Lower: Histogram of numbers of tom- 

 cod eggs and larvae caught in drift samplers. Open bars, eggs; 

 solid bars, eggs and larvae; hatched bars, larvae. 



150 



