BROODSTOCK, SPAWNING, AND EGG HANDLING 193 



Transportation of Eggs 



Eggs can be shipped at four developmental stages: as immature eggs in the 

 living female; as mature unfertilized eggs; as recently fertilized and water- 

 hardened eggs; and as eyed eggs. 



Live females may be shipped, but this method requires more extensive 

 transportation facilities than is required to ship eggs. Transportation of live 

 fish is covered in Chapter 6. 



The shipping of mature unfertilized eggs requires some precautions. 

 Sperm should be shipped separately in sealed plastic bags with an air space 

 in the sperm container of at least 10 parts air to 1 part sperm. No air re- 

 quirements are necessary for eggs. Both eggs and sperm should be kept re- 

 frigerated. With these techniques, the fertility of Pacific salmon sperm and 

 eggs is not affected by storage for 4 hours at temperatures of 47-52°F be- 

 fore they are mixed. Eggs that are fertilized and then shipped under the 

 same conditions can suffer high losses. When newly spawned and fertilized 

 eggs are shipped the eggs must not be shaken in transit. Therefore, no air 

 space should be allowed in the container. 



Eggs should not be shipped during the tender stage. They may be 

 shipped over long distances after the eyed stage is reached, if they are kept 

 cool and shipped in properly insulated boxes (Figure 66). 



Types of Incubators 



Many systems have been developed for incubating fish eggs. Basically, all 

 of them provide a fresh water supply with oxygen, dissipate metabolic 

 products, and protect the developing embryo from external influences 

 which may be detrimental. 



HATCHING TRAYS 



Hatching trays are perhaps the simplest type of incubation unit used. 

 They have been used successfully for many species of fish. The screened 

 hatching tray is sized to fit inside a rearing trough. The screening has rec- 

 tangular openings that will retain round eggs but permit newly hatched fry 

 to fall through. The wire mesh may be obtained in a variety of sizes and is 

 called triple warp mesh cloth. The triple warp cloth should have nine meshes 

 per inch for eggs that are 400 to 700 per ounce; seven meshes per inch for 

 eggs 240 to 390 per ounce; six meshes per inch for eggs 120 to 380 per 

 ounce; and five meshes per inch cloth for eggs that are 60 to 90 per ounce. 

 Eggs are placed on the tray no more than two layers deep, and the tray is 

 inclined and wedged at an angle of approximately 30 degrees, slanting to- 

 ward the incoming water in the trough. When all the eggs have hatched 



