156 FISH HATCHERY MANAGEMENT 



The pen method has several advantages. It provides close control over 

 the time of spawning, allows the pairing of selected individuals, facilitates 

 removal of spawned fish from the pond, protects the spawning pair from 

 intruding fish, and allows the injection of hormones into the broodfish. 



The aquarium method of spawning catfish is a modification of the pen 

 method. A pair of broodfish is placed in a 30- to .50-gallon aquarium with 

 running water. The broodfish are induced to spawn by the injection of hor- 

 mones. Tar-paper mats are placed on the bottom of the aquarium. As the 

 eggs are deposited and fertilized, they form a large gelatinous mass, and 

 adhere to the mat. The eggs readily can be removed with the mat. It is an 

 intensive type of culture; many pairs of fish can be spawned successfully in 

 a single aquarium during the breeding season. Each spawn is removed im- 

 mediately to a hatching trough for incubation. 



In methods involving the use of hormones, only females ready to spawn 

 should be used. Males need not be injected with hormones, but should be 

 about the same size or larger than the females with which they are paired. 

 If the male attacks the female, he should be removed until after the female 

 has been given one to three additional hormone injections. He then may be 

 placed with the female again. Males may be left to attend the eggs in the 

 aquarium or, preferably, the eggs are removed to a hatching trough. 



Striped bass have been spawned in circular tanks. This method generally 

 requires a water flow of 3 to 10 gallons per minute per tank. Six-foot diam- 

 eter tanks are most desirable. Broodfish are injected with hormones and at 

 least two males are put in a tank containing one female. After spawning, 

 the broodfish are removed. Striped bass eggs are free-floating, and if the 

 males have participated in spawning, the water will appear milky. The eggs 

 can be left circulating in the tank until they hatch or removed with a 

 siphon to aquaria for hatching. Some egg loss can be expected due to 

 mechanical damage if they are transferred from tank to aquaria. When fer- 

 tilized eggs are allowed to hatch in the tank, the fry will become concen- 

 trated around the edge of the tank after 4 or 5 days and they can then be 

 dipped out and transferred to rearing facilities. 



Artificial Spawning Method 



The artificial method of spawning consists of manually stripping the sex 

 products from the fish, mixing them in a container, and placing the fertil- 

 ized eggs in an incubator. The following description of egg stripping and 

 fertilization is widely applicable to many species of fish, including coolwa- 

 ter and warmwater species (Figure 49). 



Any spawn- taking operation should be designed to reduce handling of 

 the fish. Anesthetics should be used when possible to reduce stress. In 

 hand- stripping the eggs from a female, the fish is grasped near the head 

 with the right hand, and the left hand grasps the body just above the tail. 



