FISHERY BULLETIN: VOL. 74, NO. 1 



emerging from simulated stream redds are de- 

 scribed. Light and current responses; length, 

 weight, and condition; remaining yolk reserves at 

 emergence; and changes in photoresponse were 

 investigated. The possible effects on photore- 

 sponse of repeated testing, previous exposure to 

 light, and feeding experience were also examined. 



MATERIALS AND METHODS 

 Emergence from Simulated Redds 



The emergence of coho salmon fry of known 

 parentage (two males x one female) from four 

 simulated redds was investigated in two pairs of 

 wooden channels (Figure 1) located outdoors. 

 Each channel was divided into three equal-sized 

 compartments, and to simulate a redd, each 

 center compartment was filled to a depth of 27 cm 

 with stream pebbles 2-5 cm in diameter. A stand- 

 pipe terminating at its lower end in a 10 cm x 10 

 cm platform on 10 cm stilts so as to enclose a 

 chamber of 100 cm^ volume was buried in each 

 redd at this time. In each redd the gravel surface 

 was entirely underwater, but a shallow median 

 depression served to concentrate the surface flow 

 issuing through the V-notch openings. 



The frames of the inner partitions were covered 

 with a double layer of fine plastic screen to allow 

 for circulation through the redds. Water flow 

 through each channel was 12 liters/min, about 

 30% of which passed through the redds. 



Ten days after hatching, 150 alevins from eggs 

 incubated and hatched in standard baskets and 

 previously unexposed to light were introduced 

 into each redd at night via its standpipe and al- 

 lowed to emerge spontaneously. Each standpipe 

 was cleared of fry 1 h after stocking the redd by 



inserting a wire rod capped with rubber stoppers 

 at either end and leaving the rod in place. Emerg- 

 ed fry could enter either the upstream or down- 

 stream compartments by way of the V-notch 

 openings and were collected there daily at dawn 

 and dusk. 



Emerging fry were anesthetized with MS-222,2 

 fork length was measured to the nearest 0.1 mm 

 using a dissecting microscope, weight determined 

 to the nearest 0. 1 mg on a Mettler Grammamatic 

 balance after blotting, and the fry then preserved 

 in 5% Formalin. For each redd, samples of 20 fry 

 were extracted from each quartile of the emerg- 

 ing population (total of 80 fry per redd) divided 

 between fry moving upstream or downstream fol- 

 lowing emergence. Yolk reserve at emergence 

 was determined by dissecting out the yolk ma- 

 terial, drying both yolk and fry to constant 

 weight at 80°C, and expressing yolk reserve as a 

 percentage of total dry weight. 



The resulting data were processed by regres- 

 sion and analysis of variance techniques to ex- 

 pose possible correlations between length, 

 weight, condition {K) and yolk reserve with time, 

 directional movement in current, and emergence 

 during the daylight or darkness. 



Photoresponse Tests 



Ten days after hatching, sibling alevins from 

 the same experimental stock as those used for the 

 emergence study but denied the redd experience 

 were separated into five groups of 50 fish each 

 and held indoors in wire baskets except during 

 testing. Two groups were held in complete dark- 

 ness. One of these groups was tested frequently 

 (dark experimental, DE); the other was tested 

 once then not retested until 15 days later (dark 

 control, DC). The three remaining groups were 

 held in baskets partly exposed to daylight of 

 about 200 ft-candles peak intensity from an ad- 

 jacent window and were given three different 

 treatments. One group was tested frequently 

 (light experimental, LE); one was tested once 

 then not retested until 15 days later (light con- 

 trol, LC). The remaining group was not tested 

 until the 18th day and, in contrast to the other 

 groups, was fed frozen ground beef liver three 

 times daily from day 9 onward (light control 

 plus food). 



Figure l. — Compartmentalized wooden channels. Center 

 compartments contained the simulated redds. Dotted areas 

 signify screens. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



168 



