prepare. In the 1950's, conversion ratios as low as 5.6 lb 

 (25 kg) of food fed per pound (0.45 kg) of weight gained 

 were reported from the ground-meat base diets used at 

 several FCO hatcheries. At most hatcheries today, less 

 than 2 lb (0.91 kg) of food are required for a 1 lb (0.45 kg) 

 gain in weight. Another disadvantage of the meat diets 

 was the spread of bacteria and viral diseases, to young fish 

 from diets that included salmon carcasses. Although the 

 diets did have disadvantages, they still allowed larger 

 fish to be reared. 



Several developments in the late 1950's had important 

 effects on rearing practices. Improved pasteurization 

 methods were developed to treat salmon viscera, an im- 

 portant component of many meat based diets. This pro- 

 cess was used to kill disease-causing organisms that 

 would otherwise have affected the young fish. Commer- 

 cial, dry, pelletized trout diets received much attention 

 experimentally as a salmon diet. Few of the standard 

 trout feeds showed promise and all required meat diets to 

 be used while the fish started feeding. 



In 1959, after many years of experimentation, the FCO 

 began feeding Oregon moist pellets (OMP) to fish at 16 of 

 their salmon hatcheries. The OMP diet, developed joint- 

 ly by the FCO and Oregon State University scientists 

 with funds supplied by the U.S. Bureau of Commercial 

 Fisheries (now National Marine Fisheries Service), was a 

 breakthrough in the area of hatchery nutrition. This easi- 

 ly fed diet does not require any preparation at the 

 hatchery and is readily accepted by the fish. It consists of 

 a combination of cereals, fish meals, fish oils, dried skim 

 milk, and vitamin supplements. Fish fed this diet have 

 shown, in almost all cases, better survival and contribu- 

 tion to the fishery than fish fed old ground meat type 

 diets (Hublou et al. 1959, Hublou 1963). Development of 

 the OMP has opened the way for other types of diets in- 

 cluding the Abernathy dry pellet developed at Abernathy 

 Salmon Cultural Development Center. These new diets 

 have made hatcheries biologically and economically 

 feasible ventures. 



Size at Time of Release 



One of the most interesting trends of hatchery pro- 

 duction over the last 17 yr has been the change in release 

 size of migrant coho, spring chinook, and fall chinook 

 salmon. Until the early 1960's hatcheries emphasized 

 numbers of fish liberated. It was common for a hatchery 

 to take more eggs than could be reared to migrant size. 

 As fish grew and crowding occurred, fish in excess of 

 hatchery capacities were released. Out of an egg-take of 

 over 13 million fall chinook salmon eggs in 1959, Spring 

 Creek NFH produced only 7.8 million migrants in May of 

 1960. The other 5.8 million were thinned out 3 mo earlier 

 CWahle et al. 1975). The average size for all species of mi- 

 grant salmon released from Pacific coast rearing facili- 

 ties in 1960 was 88 fish/lb (5.2 g/fish) (Fig. 14a). Fall chi- 

 nook salmon, reared for 5 or 6 mo, averaged 211 fish/lb 

 (2.29 g/fish) (Fig. 14b). Spring chinook and coho salm- 

 on, reared for an average of 20 mo, both averaged 33 

 fish/lb (13.8 g/fish) (Fig. 14c,d). 



I960 65 



C Spring Chinook 



Figure 14. — Average size of various species of Pacific coast anad- 

 romous salmonid releases (all species combined), 1960-76. (1 lb 

 equals 0.454 kg.) 



In the early 1960's, a trend developed away from maxi- 

 mizing numbers at hatcheries. Instead, the philosophy of 

 raising less fish to a larger size began to gain acceptance 

 among the fish rearing agencies. Marking experiments 

 showed that these larger fish had better survival and 

 contribution to the fisheries (Senn and Noble 1968; John- 

 son 1970; Wallis 7 ; Senn et al. 8 ; Washington Department 

 of Fisheries 9 ). Numbers of migrant fish released actually 

 declined slightly from 1960 to 1962 (Fig. 15) even though 

 the number of facilities increased (Fig. 12). While mi- 

 grant numbers held fairly constant from 1960 to 1976, the 

 number of migrant pounds increased almost six times 

 (Fig. 15). In 1976, fall chinook salmon smolts averaged 59 

 fish/lb (7.7 g/fish) (Fig. 14b). Spring chinook and coho 

 salmon showed similar size change, going from approxi- 

 mately 32 fish/lb (4.2 g/fish) to 11 fish/lb (41.2 g/fish) and 

 from 33 fish/lb (13.6) to 17 fish/lb (26.7 g/fish), respec- 

 tively (Fig. 14c, d). During this time, the average size for 

 all species combined went from 88 fish/lb (5.2 g/fish) to 

 26 fish/lb (17.5 g/fish) (Fig. 14a). 



? Wallis, J. 1968. Recommended time, size and age for release of 

 hatchery-reared salmon and steelhead trout. Fish. Comm. Oreg., Clacka- 

 mas. Proc. Rep., 61 p. 



8 Senn, H. G., R. C.Hager, and C. W. Hopley, Jr. 1975. The effects 

 of experimentally varying the size and time of release of hatchery-reared 

 coho salmon. Unpubl. manuscr., 14 p. Washington Department of 

 Fisheries, Olympia, Wash. 



"Washington Department of Fisheries. 1977. 1972-brood Toutle 

 River coho time/size at release study. Unpubl. manuscr., 16 p. Wash- 

 ington Department of Fisheries, Olympia, Wash. 



33 



