FISHERY BULLETIN: VOL. 78, NO. 1 



southwestern New Brunswick, with a midsummer 

 discharge ca. 80 1/s and a drainage area of 570 ha 

 (Symons and Martin 1978; Symons and Harding^). 

 The drainage basin is typical spruce-fir boreal 

 forest with no human habitation. Portions of it 

 farther upstream have been recently logged. 



Tomcod spawn in a 10 to 1 5 m stretch at the head 

 of tide in Frost Fish Creek (Figure 1). This area is 

 freshwater for most of the tidal cycle, but has a 

 variable bottom salinity (depending upon the 

 height of the particular tide) during high tide. 

 Extreme neap tides do not invade the spawning 

 area. The stream substrate in the spawning area 

 varies from ledge to boulders and cobbles. Most of 

 the eggs settle in substrate interstices. 



^Symons, P. E. K., and G. D. Harding. 1974. Biomass 

 changes of stream fishes after forest spraying with the insec- 

 ticide fenitrothion. Fish. Res. Board Can. Tech. Rep. 432, 47 

 p. Fisheries and Environmental Sciences, Fisheries and 

 Oceans Canada, Biological Station, St. Andrews, NB EOG 2X0. 



7oo -* 



I .0%o 

 13.5 7oo 

 23.5 7oo 



25.0 %o;r^ 



26.5 7oo-^ 



\\S\\\\ v\ \ 



Edge of 

 Trees 



=p^epth  12 cm 



Marsh ;^v'v 



Spawning 

 Area 



;^ Depth = 60 cm 



3 Metres 



Rood 

 Culvert 



Depth Gauge 

 1977-78 



Drift Sampler 



977-78 



1976-77 



rSolt^: 

 Marsh^ 



.\\\S\V\S 



Figure l. — Diagram of tomcod spawning area in Frost Fish 

 Creek in the Digdeguash River estuary. New Brunswick. Depths 

 and salinities are for a "typical" high-tide situation. Salinities 

 were measured at the stream bottom. Hatched area indicates 

 spawning area. 



148 



Drift samples were installed downstream of the 

 area of egg deposition (Figure 1) near cessation of 

 spawning (26 Dec. to 2 Jan.) to sample egg and 

 larval drift. The samplers consisted of a 

 galvanized-metal funnel, the narrow opening (5 x 

 20 cm) facing upstream, with a cloth bag attached 

 to the downstream end (10x20 cm). The eggs and 

 larvae accumulated in a 250 ml plastic beaker, 

 with a screened, 2.5 cm diameter hole in one side, 

 clamped to the bag. The sampler was threaded 

 onto an iron rod driven into the stream bottom. A 

 meter stick was installed to measure stream water 

 levels, and stream salinities were measured with a 

 salinity meter. Stream temperatures and drift 

 samples were taken twice weekly at low tide, with 

 the numbers of eggs collected averaged on a per- 

 day basis. Eggs and larvae sampled were pre- 

 served in 10% Formalin^ or 70% ethanol, those 

 preserved in Formalin being cleared later (Galat 

 1972) to determine degree of development. 



One sample of eggs was taken from the area of 

 egg deposition with a Surber sampler in January 

 1977 to see if development of drifting eggs was the 

 same as those that were not. 



Egg Collection 



Adults (1 female:2 males) anaesthetized in 

 MS-222 were stripped of eggs and milt in the field. 

 Immediately, the eggs were fertilized by the "dry" 

 method and were washed with stream water 30 s 

 after mixing (temperature at fertilization near 0° 

 C). This water was fresh and was taken from a part 

 of the stream where tomcod were spawning at the 

 time (although spawning may continue into high 

 tide conditions when the water would be of vari- 

 able salinity). After 1 min the water was changed, 

 and the bottle of eggs was packed in ice and trans- 

 ported to the laboratory. The eggs were trans- 

 ferred to the various incubation salinities 30 min 

 after fertilization. The eggs are weakly adhesive 

 initially, but this adhesiveness disappears if the 

 eggs are separated. 



Laboratory Studies 



Eggs were incubated in columns of PVC pipe 

 and fittings holding 190 ml of water (Figure 2). 

 Screened floors and lids retained eggs and larvae. 

 Water flowed through the columns at 100 ml/min 



"Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



