GROWTH OF PREMIGRATORY CHINOOK SALMON IN SEAWATER 



Bernard M. Kepshire, Jr., and William J. McNeil^ 



ABSTRACT 



A potential demand exists in sea farming for premigratory juvenile Pacific salmon that have been 

 acclimated to seawater. This paper reports experiments on growth of premigratory chinook salmon 

 (Oncorhynchus tshawytscha) acclimated to water of 33^r salinity and lower and describes a simple 

 mathematical model to evaluate rate of growth. Although chinook salmon raised in these experiments 

 experienced low mortality in water of high salinity, their growth slowed. Reasons for slow growth at 

 high salinity are discussed. 



Pacific salmon reproduce in fresh water, but only 

 two species — pink (Onchorhynchus gorbuscha) 

 and chum (0. keta) salmon — survive direct 

 transfer as fry from fresh water to full-strength 

 seawater (Weisbart, 1968). The ocean serves 

 as the early nursery ground for these two spe- 

 cies. The other species — including sockeye (0. 

 nerka) , coho (O. klsutch) , and chinook (0. 

 tshawytscha) salmon — require freshwater nur- 

 sery areas. 



Juvenile salmon undergo a period of adjust- 

 ment when they first enter the sea in order to 

 regulate water and salts in body fluids and tis- 

 sues. This adjustive phase for chum salmon fry 

 lasts about 30 hr and is characterized by an 

 immediate depression of activity, increased con- 

 centration of salts in body fluids, and dehydra- 

 tion of body tissues (Houston, 1959) . A slightly 

 longer adjustive phase of 36 to 40 hr has been 

 reported for yearling coho salmon (Conte et al., 

 1966; Miles and Smith, 1968). 



Early exposure to water of low salinity can 

 "trigger" the physiological adaptation to sea- 

 water of salmon species which typically remain 

 in fresh water for several months as juveniles. 

 Acclimation of premigratory young chinook 

 salmon to water of 30^( salinity by exposing 

 them to gradual increments in salinity has been 

 described by Wagner et al. (1969). Black 

 (1951), Coche (1967), and Otto (1971) found 



^ Department of Fisheries and Wildlife, Oregon State 

 University, Marine Science Center, Newport, OR 97365. 



also that coho salmon fry were better able to 

 tolerate water of high salinity after having first 

 been exposed to water of low salinity. 



Other evidence suggests that the growth of 

 juvenile coho and chinook salmon is influenced 

 by salinity. Coho salmon fry were observed by 

 Canagaratnam (1959) to grow faster in water 

 of 12 to 18^;, than in fresh water. Otto (1971) 

 reported faster growth of juvenile coho salmon 

 at 5 and 10'/,r salinity than at higher salinities 

 or in fresh water. Bullivant (1961) found no 

 significant diflPerence in growth of juvenile chi- 

 nook salmon in water of and W/U salinity. 

 However, Bullivant's fish grew more slowly at 

 35/^f salinity than at the two lower salinities. 



This paper reports comparisons of the growth 

 of juvenile chinook salmon raised in water rang- 

 ing in salinity from to 33/i:f . The experiments 

 were conducted at the Oregon State University 

 Port Orford Marine Research Laboratory, Curry 

 County, Oreg. 



GENERAL PROCEDURES 



Two groups of chinook salmon used in these 

 experiments were obtained as eyed eggs from 

 the Fish Commission of Oregon, Elk River 

 Hatchery, in winter 1969. Group I fish were 

 divided into five subgroups of 200 each on Feb- 

 ruary 24 (47 days after hatching). Group II 

 fish were divided into six subgroups of 300 each 

 on March 5 (18 days after hatching). Indi- 

 vidual subgroups were introduced to water of 



Manuscript accepted August 1971. 



FISHERY BULLETIN: VOL. 70, NO. 1, 1972. 



119 



