50 FISH HATCHERY MANAGEMENT 



PEN REARING 



Marine culture of salmon and trout in cages is called "pen rearing." Pen 

 culture developed in Scandinavia and Japan, and commercial operations 

 began recently in Washington state. Rainbow trout and Atlantic, chinook, 

 and coho salmon have been cultured in sea water. Coho salmon have been 

 the most popular in the United States because they are relatively resistant 

 to disease and can be fed formulated feeds. After initial rearing in fresh 

 water, the juvenile fish complete their growth to marketable size in saltwa- 

 ter pens. 



The term "sea ranching" is used when hatchery-reared salmon are 

 released as smolts and allowed to migrate to the ocean to complete the ma- 

 rine portion of their life cycle. 



Pen rearing relies on tidal currents to supply oxygen and flush out meta- 

 bolic wastes. The pens and floating structures cost less than a fish hatchery 

 on land, but must be protected from storms and high winds, and some type 

 of breakwater may be necessary. Some freshwater facilities must be avail- 

 able on land, however, to incubate the salmon eggs and initially rear the 

 fry. 



Water temperatures should not fluctuate greatly during pen culture; 

 50— 57°F are best for salmon. Prolonged higher temperatures lead to disease 

 problems. Although disease has been a serious problem in saltwater farm- 

 ing, recent developments in immunization of fish with vaccines show great 

 promise for overcoming this (Chapter 5). 



SELECTION OF REARING FACILITIES 



No single pond type will meet all requirements of fish hatcheries under all 

 rearing conditions. Topography of the land, water source, species of fish 

 being reared, and availability of funds and material will influence the selec- 

 tion of the rearing unit. There is a wealth of literature describing the 

 strong and weak points of various hatchery rearing facilities, much of it 

 conflicting. Personal preference based on experience tends to play a key 

 roll in making a selection. As pointed out previously, all of the types of 

 rearing units described successfully raise fish. 



In any hatchery construction there are several important objectives that 

 must be kept in mind: (l) to provide a compact rearing unit layout that 

 will allow future development of the hatchery; (2) to provide adequate 

 intake and outlet water supply facilities to meet the special requirements of 

 pond cleaning, treatment of fish for disease, and collection and handling of 

 fish; (3) to allow sufficient slope on pond bottoms for complete drainage 

 and provide for a practical and efficient means of collecting fish for 

 removal, sorting, or treating; and (4) to provide adequate water and rearing 

 space to safely accommodate the anticipated production of the hatchery. 



