BROOUSTOCK, SPAWNING, AND EGG HANDLING 159 



water is added to wash the eggs for incubation. In the wet method, a pan is 

 partially filled with water before the eggs are expressed from the female 

 fish. The milt from a male is then added. Because the sperm will live less 

 than 2 minutes in water after being activated, considerable speed is neces- 

 sary by the spawn takers. The dry method generally is accepted as the best 

 procedure. 



Eggs are washed or rinsed thoroughly after they have been fertilized and 

 before they are placed in the incubator. In some species, the eggs are allowed 

 to water- harden before being placed in an incubator. Water- hardening is the 

 process by which water is absorbed by the eggs and fills the perivitelline 

 space between the shell and yoke, causing the egg to become turgid. Precau- 

 tions should be taken to protect eggs from exposure to direct rays of bright 

 light, because both sunlight and artificial light are detrimental. 



Some species, such as walleye and northern pike, have eggs that are ex- 

 tremely adhesive. Often during the water- hardening process of adhesive 

 eggs, an inert substance is added to prevent the eggs from sticking togeth- 

 er. Starch, black muck, clay, bentonite clay, and tannin have been used as 

 separating agents. Starch, because it is finely ground, does not have to be 

 specially prepared, but muck and regular clay must be dried and sifted 

 through a fine screen to remove all coarse particles and then sterilized be- 

 fore they can be used. Starch or clay first must be mixed with water to the 

 consistency of thick cream. One or two tablespoons of this mixture is ad- 

 ded to each pan of eggs after fertilization is completed. When the separat- 

 ing agent has been mixed thoroughly with the eggs, the pan is allowed to 

 stand for a minute. Water is then added, the separating agent is washed 

 from the eggs, and the eggs placed in a tub of water to harden. Constant 

 stirring during water hardening helps prevent clumping. The water should 

 be changed at least once an hour until the eggs are placed in the hatchery. 



Striped bass also may be hand-stripped as an alternative to tank spawn- 

 ing. Both males and females of this species usually are injected with hor- 

 mones, as described in a later section of this chapter. An egg sample 

 should be taken and examined between 20 and 28 hours after a hormone 

 injection. Egg examination and staging requires microscopic examination. 



The catheter used for extraction of the egg sample is made of glass tub- 

 ing, 3 millimeter O.D., with fire- polished ends. The catheter is inserted ap- 

 proximately 2 inches into the vent and removed with a finger covering the 

 end of the tube to create a vacuum that holds any eggs in place in the 

 tube. Extreme care is needed while the catheter is inserted into the ovary. 

 The catheter should be instantly removed if the fish suddenly thrashes; 

 such thrashing usually is immediately preceded by a flexing of the gill cov- 

 ers. Careful manipulation will permit the catheter to be inserted into the 

 vent with a minimum of force, preventing damage to the sphincter muscles. 

 If these muscles are torn, eggs at the posterior end of the ovary will water- 

 harden. The plug thus formed will prevent the flow of eggs. 



