reflect the environment of young salmon, we 

 also compared length and weight frequencies, 

 length-weight relationship, and general ex- 

 ternal appearance. 



A second approach to the problem of sep- 

 arating wild from hatchery fish is the arti- 

 ficial marking of the hatchery fish. Because 

 of the large numbers of fish involved (approxi- 

 mately 3 million young sockeye are planted 

 each year) techniques, such as fin clipping, 

 which require handling each fish, are time 

 consuming and expensive. 



A review of the literature suggested that 

 "marking" the scales of hatchery fish by a 

 short period of starvation might be a more 

 promising method. Gray and Setna (1931) and 

 Bhatia (1931, 1932) successfully modified the 

 circuli spacing on the scales of rainbow 

 trout (Salmo irideus \_gairdneTii\) by manipu- 

 lating the food intake. Circuli are the con- 

 centric rings which occur naturally on the 

 scales of many fish including salmon and 

 trout. When growth is fast, circuli are rela- 

 tively wide-spaced; and when growth is slow, 

 they are more closely set and sometimes 

 broken. Slow winter growth is denoted by 

 series of closely spaced circuli called annuli. 



As the first step to determine whether a 

 starvation-marking technique could be de- 

 veloped as a means of separating Lake 

 Wenatchee wild from hatchery-reared fish, 

 we conducted hatchery experiments in 1959 

 and 1960. The primary objective of these 

 experiments was to determine whether or not 

 a recognizable alteration (mark) could be 

 imprinted on the scales by short periods of 

 starvation. Other objectives were: (1) to 

 measure the mortality caused directly by 

 starvation, (2) assess the effect of starvation 

 on growth, and (3) determine the optimum 

 time and duration of starvation for obtaining 

 the desired modification, 



METHODS AND MATERIALS 



The experimental procedure was essentially 

 the same each year. Initially, we selected a 

 representative sample of approximately 1,200 

 fish from an outdoor pond and halved the 

 sample into two lots of 600, one a control lot 



for regular feeding and the other a test lot 

 for starvation. Every 2 weeks ' thereafter, 

 we removed 100 fish from the starvation lot, 

 placed them in a separate trough and reintro- 

 duced food. At the end of the experiment then, 

 we had fish that had been starved for 0, 2, 4, 6, 

 and 8 weeks (the latter in 1959 only). All lots 

 were sampled approximately every 2 weeks — 

 lengths and weights recorded and scales taken. 

 Mortality was recorded daily. 



The 1959 experiment was conducted with 

 fish that (representative of the bulk of the 

 hatchery fish for that and preceding years) 

 had been reared on a wet-type diet. Most of 

 the hatchery fish were changed to a dry diet 

 in 1960, and mainly because of this the tests 

 were repeated to determine whether or not 

 similar results could be obtained with fish 

 fed the new diet. 



To determine whether seasonal timing of 

 starvation and recovery periods influenced 

 marking success, we ran three variations of 

 the 2-week starvation period in 1960. We 

 chose the 2-week interval for this purpose 

 because it had produced the best marking 

 success in 1959. 



A more detailed description of the methods 

 and materials is presented in the following 

 subsections. 



Trough specifications and water supply 



The experiments were conducted inside the 

 main hatchery building in cement troughs, 

 187j inches by 16j inches by 16M inches, 

 filled to an average water depth of 10 inches. 

 The main source of the hatchery water supply 

 is nearby Icicle Creek, although some well 

 water is occasionally used in the summer for 

 cooling purposes. Water temperature is re- 

 corded continually by a thermograph. 



Feeding 



All feeding was at the prescribed hatchery 

 rate based on the weight of the fish in a trough. 



SThe 2-week periods described in this report varied 

 from 13 to 18 days. There is no evidence that the varia- 

 tion affected the experimental results. 



