FISHERY BULLETIN: VOL. 83, NO. 1 



METHODS 



Alevins 



Fish used in the experiments described below 

 originated from the 1981 brood of the Canada De- 

 partment of Fisheries and Oceans Capilano 

 Hatchery. Eggs were transferred to incubation 

 facilities at Simon Fraser University at the "eyed" 

 stage of development, corresponding to 347 Cel- 

 sius degree-days. Prior to transfer, the eggs were 

 held under a 12:12 LD photoperiod and at a con- 

 stant 8°C water temperature. The eggs were held 

 for 5 d in our laboratory at 8.5°C before exposure to 

 diel water-temperature regimes. 



Two lots of 100 fish were exposed as eggs and 

 later, as alevins, over a 69-d period to a water- 

 temperature regime whose diel amplitude aver- 

 aged 2" and 4°C (range 1.8°-2.4° and 3.0°-4.5°C) 

 above a daily average minimum temperature of 

 8.5°C. These temperatures were similar to those 

 observed in May-June 1981 in the Deadman River, 

 B.C., a stream supporting an O. tshawytscha 

 population. All eggs hatched by day 29. Eggs or 

 alevins in = 10) were sampled at days 19, 40, 55, 

 and 69. On day 39, 20 alevins were transferred 

 from a temperature regime with a 4°C amplitude 

 and 24-h period to a regime with the same temper- 

 ature amplitude but a 12-h period. A fourth group 

 was held at a constant 8.5°C. The constant water 

 temperature corresponded to that of the cool 

 period of the diel water-temperature regimes. 



Sagittal otoliths were removed from preserved 

 fish and prepared following the methods of Neilson 



and Geen (1981). Otolith sections were examined 

 using a light microscope or scanning electron mi- 

 croscope (SEM) as described in Neilson and Geen 

 (1982). 



Fry 



Fry used in these experiments were about 90-d- 

 old posthatch and originated from Capilano River 

 hatchery stock. Prior to transfer to 25 1 aquaria at 

 Simon Fraser University, fish were held under 

 natural light at a constant 8°C and fed once every 

 24 h. After transfer to our laboratory, fry were held 

 for 2 wk in flow-through aquaria supplied with 

 aerated and dechlorinated water at 6°C before ex- 

 periments commenced. During this period the 50 

 fish in each aquarivun were fed to satiation with 

 Oregon Moist Pellets once per 24 h and exposed to 

 a 12:12 LD photoperiod. 



Experimental feeding and temperature regimes 

 to which fry were exposed are summarized in 

 Table 1. Amplitude of daily temperature fluctua- 

 tions was 4°C (range 3.6°-4.4°C) above the average 

 minimum of 6°C. The diel temperature cycle in 

 relation to photoperiod and feeding events is 

 shown in Figure 1. The activity of one group offish 

 was artificially increased to examine the effects of 

 activity on otolith increment formation. These fish 

 were forced to evade a slowly moving aquarium 

 net for 10-min beginning at 1900 h daily. The in- 

 duced activity level appeared similar to that as- 

 sociated with feeding. Ration provided to experi- 

 mental lots of fish was maintained as a constant 

 proportion (4% or 8% ) of average fish dry weight by 



105- 



9.5- 



O 



0) 



2 

 « 

 a. 



E 

 ® 



0) 



IS 

 $ 



w 8 5" 



7.5- 



6.5- 



5.5 



0100 0500 f 1000 1500 f 2000 0100 0600 f 



1 1 00 1 600 



t 2100 



2400 



Time (24-h clock) 



Figure \. — Did water-temperature cycle in relation to photoperiod and feeding events (f) 

 for Oncorhynchus tshawytscha fry. Light and dark periods are indicated by the open and 

 solid bars respectively. 



92 



