Fish Hatchery Management - fisheries & aquaculture

t66 FISH HATCHERY MANAGEMENTsystems, as introduced by Australian workers and used on some troutspecies in this country, have made spawning fast, easy, and efficient (Figure57). Two to four pounds of air pressure injected into the body cavityby means of a hollow needle will expel the eggs. The needle is inserted inthe area between the pectoral and ventral fins midway between the midventralline and the lateral line. The possibility of damage to the kidney byneedle puncture is reduced if the posterior section of this area is used. Theneedle should be sterilized in alcohol for each operation to reduce the possibilityof infection. It is imperative that a female be ripe if the eggs are toflow freely. When a fish is held in the normal spawning position, a feweggs should flow from the fish without pressure on the abdomen.It is important that the fish be relaxed before the air pressure method isattempted. An anesthetic should be used. The fish should be rinsed andwiped fairly dry to prevent anesthetic dripping into the egg-spawning pan.Air should be removed from the body cavity before the fish is returnedto the water. This is best done by installing a two-way valve and a suctionline to the needle. A supplemental line may be used to draw off the air bymouth, or the air may be forced out by hand when a check is made forremaining eggs, although these methods are generally not as effective.FIcunr 56. Spawning Pacific salmon. Left, female is opened with a spawningknife (cutting edge indicated by arrow). Right, milt is hand-stripped from a maledirectly onto the eggs.