The physical injury and physiological stress of capturing, handling, transporting, injecting and holding brood fish can have a greater detrimental effect on spawning success than almost any other factor. Fish must be handled carefully and optimum water conditions must be maintained to minimize stress.
The importance of proper handling and water quality cannot be overemphasized. Female brood fish ready for spawning are in a particularly delicate condition. When female fish are stressed or injured, they may undergo rapid physiological changes that can result in the break-down (resorption) of the eggs in the ovary.
Fluctuations in temperature and low dissolved oxygen can hasten the resorption of eggs. Suboptimum conditions, while not immediately lethal, may stress brood fish, resulting in delayed mortality or failure to spawn.
Capture of brood fish:
Always check with your state conservation department to determine legal capture methods and obtain proper permits.
Haul seine:
Haul seines are effective for fishing large areas to collect brood fish. While this collection method is probably the most versatile and popular, the area to be seined must be free of bottom snags or obstacles.
Mesh size is dependent on fish size, and seine depth determines the depth of water that can be fished. Bag seines with extra lead weight are usually more effective than straight seines for brood fish capture.
Brood fish raised in ponds are usually captured by haul seine. Partial draining of the pond can simplify capture. Water level should not be lowered during the heat of the day. The temperature of shallow water increases rapidly, stressing the fish.
Dissolved oxygen should be checked frequently, before and during draining. If the dissolved oxygen drops below 4 mg/L while draining brood fish ponds, stop draining, refill and aerate.
If additional brood fish are still in the pond after seining, the pond should be flushed with fresh water to counteract the effects of disturbing the bottom sediments on reduced dissolved oxygen and the release of hydrogen sulfide and other toxic chemicals.
Dip net:
Dip nets can bean effective capture method when brood fish are concentrated on the spawning grounds or in tailwater areas. This method inflicts minimal damage to fish. Brood fish raised in tanks are usually captured with dip nets.
A crowding net should be used in large tanks to simplify capture. Dip nets are also used when transferring fish from seines, trap nets, hauling tanks, etc. Knitted smallmesh dip nets are recommended for handling brood fish to minimize scale loss and injury.
Gill net:
Both stationary and drift gill nets are effective for brood fish capture. They allow a large area of water to be fished to determine migratory routes and areas of brood fish concentration. However, these nets often cause physical damage and stress. Mortality may be appreciable, but losses can be reduced by checking the nets and removing fish every 15 to 30 minutes.
Trap net:
Trap nets such as pound nets, fyke nets and hoop nets have also been used to capture brood fish during the spawning migration. However, entrapment gear is usually limited in its application because of site selection, manpower requirements, mobility, and equipment expense.
Electrofishing:
When brood fish are concentrated on the spawning grounds or in tailwater areas below dams, electrofishing is an efficient method of capture. Fish collected in this manner usually will not struggle vigorously and, in most instances, are immobile for 1 to 3 minutes during the critical pickup and initial transportation period. Various types of electrofishing gear can be adapted to widely differing habitats.
Electrofishing, however, is restricted in all states and a special collecting permit is required.
Angling:
Mature fish may often be taken by hook and line in tailwater areas or where fish are concentrated and vulnerable to fishing pressure. For many fish species, this may be the only option for commercial fish farmers.
Authors:
R.W. Rottmann, J.V. Shireman, and F.A. Chapman
