SRAC Publication No. 422

Southern Regional Aquaculture Center

November 1991

Capturing, Handling, Transporting, Injecting and Holding Brood Fish for Induced Spawning

R.W. Rottmann, J.V. Shireman, and F.A. Chapman*

The physical injury and physi- must be free of bottom snags or ob- ferring fish from seines, trap nets, ological stress of capturing, han- stacles. Mesh size is dependent on hauling tanks, etc. Knitted small- dling, transporting, injecting and fish size, and seine depth deter- mesh dip nets are recommended holding brood fish can have a mines the depth of water that can for handling brood fish to mini- greater detrimental effect on be fished. Bag seines with extra mize scale loss and injury. spawning success than almost any lead weight are usually more effec- other factor. Fish must be handled tive than straight seines for brood Gill net carefully and optimum water con- fish capture. Both stationary and drift gill nets ditions must be maintained to Brood fish raised in ponds are usu- are effective for brood fish cap- minimize stress. The importance ally captured by haul seine. Partial ture. They allow a large area of of proper handling and water qual- draining of the pond can simplify water to be fished to determine mi- ity cannot be overemphasized. Fe- gratory routes and areas of brood male brood fish ready for spawn- capture. Water level should not be lowered during the heat of the fish concentration. However, these ing are in a particularly delicate day. The temperature of shallow nets often cause physical damage condition. When female fish are water increases rapidly, stressing and stress. Mortality may be ap- stressed or injured, they may un- preciable, but losses can be re- dergo rapid physiological changes the fish. Dissolved oxygen should be checked frequently, before and duced by checking the nets and that can result in the break-down during draining. If the dissolved removing fish every 15 to 30 (resorption) of the eggs in the oxygen drops below 4 mg/L while minutes. ovary. Fluctuations in temperature draining brood fish ponds, stop and low dissolved oxygen can Trap net draining, refill and aerate. If addi- hasten the resorption of eggs. Sub- tional brood fish are still in the Trap nets such as pound nets, fyke optimum conditions, while not im- pond after seining, the pond nets and hoop nets have also been mediately lethal, may stress brood should be flushed with fresh water used to capture brood fish during fish, resulting in delayed mortality to counteract the effects of disturb- the spawning migration. How- or failure to spawn. ing the bottom sediments on re- ever, entrapment gear is usually Capture of brood fish duced dissolved oxygen and the limited in its application because release of hydrogen sulfide and of site selection, manpower re- Always check with your state conser- other toxic chemicals. quirements, mobility, and equip- vation department to determine legal ment expense. capture methods and obtain proper Dip net permits. Electrofishing Dip nets can bean effective cap- Haul seine ture method when brood fish are When brood fish are concentrated concentrated on the spawning on the spawning grounds or in tail- Haul seines are effective for fish- grounds or in tailwater areas. This water areas below dams, elec- ing large areas to collect brood method inflicts minimal damage trofishing is an efficient method of fish. While this collection method to fish. Brood fish raised in tanks capture. Fish collected in this man- is probably the most versatile and are usually captured with dip nets. ner usually will not struggle vigor- popular, the area to be seined A crowding net should be used in ously and, in most instances, are * Institute of Food and Agricultural Sciences, large tanks to simplify capture. immobile for 1 to 3 minutes dur- University of Florida Dip nets are also used when trans- ing the critical pickup and initial transportation period. Various during capture and handling. Oxy- Holding brood fish at the types of electrofishing gear can be gen bottled or liquid is recom- hatchery adapted to widely differing habi- mended for reviving fish immedi- tats. Electrofishing, however, is re- ately following capture. For long Environmental factors in the stricted in all states and a special hauls, water agitators should be brood fish holding tank such as collecting permit is required. used in addition to oxygen to dissolved oxygen, water tempera- drive off the carbon dioxide that ture and absence of disturbance to Angling accumulates in the water. The com- the fish following hormone injec- Mature fish may often be taken by bination of aerators also provides tions are believed to play an im- hook and line in tailwater areas or a backup in case of system failure. portant role for successful induced where fish are concentrated and Water in small containers can spawning. The handling stress vulnerable to fishing pressure. For warm quickly, resulting in tem- and the physiological processes of many fish species, this may be the perature shock. Warm water also final maturation of eggs and only option for commercial fish reduces available oxygen and in- sperm increase the oxygen de- farmers. creases the metabolic rate of the mand of the brood fish. High tem- fish, adding further physiological perature accelerates egg Handling brood fish stress. Capture and transport maturation, resulting in an even brood fish during cool evening or greater oxygen demand by the Handling of brood fish should be early morning hours to minimize fish. Elevated temperature will kept to an absolute minimum. stress. Ice may be added to the also increase the rate of develop- Gentleness when handling fish is water during hauling to prevent ment of disease organisms. How- of utmost importance to prevent an increase in water temperature. ever, if the temperature is too low, physical injury and physiological Salt (0.3 -1.0 percent) may be used spawning will be delayed or in stress. Damage to the slime in the transport water to minimize many cases completely inhibited. (mucus) layer, scales, and skin of osmotic stress and infection. Anes- the fish can result in infection. It Holding tanks should be large thetics have also been used suc- also causes excessive uptake of enough to allow complete free- cessfully during transport of fish. water by freshwater fish or loss of dom of movement to the brood water from marine species (os- Injecting brood fish fish. Round tanks or tanks with motic stress). Knitted fine-mesh rounded corners are preferable be- dip nets are recommended for han- Females that have eggs in a suffi- cause they minimize injury to the dling fish to minimize injury and ciently advanced stage of develop- fish. Holding tanks should be cov- scale loss; do not use knotted dip ment for successful hormone- ered to provide shading that will nets. Minimize the number of induced spawning (See Determin- help quiet excitable species and times the fish are lifted from the ing Sexual Maturity of Broodstock for prevent the fish from jumping to water, and work as quickly as pos- Induced Spawning of Fish) should their death. sible when transferring fish. Time be injected as soon as possible. spent with the fish out of the Any delay in injecting the brood Conclusions fish greatly diminishes the chance water during handling can mean Brood fish must be handled care- for a successful spawn. While in- the difference between a good fully to minimize physical injury jecting the fish, every effort must spawn, no spawn, or death. and stress. Speed and gentleness be made to minimize stress and in- during fish capture and handling Transporting brood fish jury. It is unnecessary to remove are of utmost importance. Crowd- the fish from the water when giv- ing, dissolved oxygen depletion, Fish crowded in a transport tank ing injections. Brood fish are usu- can rapidly become stressed due rapid changes in temperature, and ally captured and gently osmotic imbalance are well known to physical injury, deteriorating restrained in a net for injections. water quality, rapid changes in causes of stress and must be Avoid squeezing or forcefully water temperature, and osmotic avoided when transporting fish. holding the fish. Fish may be anes- imbalance. Handling tanks in cap- Females that have eggs in a suffi- thetized with MS-222 if necessary. ture boats and transport trucks ciently advanced stage of develop- The fish may struggle less if a ment for successful hormone- should be large enough to allow cloth is placed over its head. Un- complete freedom of movement to induced spawning should be in- derwater injections while the fish jected as soon as possible. Any the brood fish and have no sharp is stationary or swimming slowly delay greatly diminishes the corners or edges that might injure are sometimes used for large, deli- the fish. Hauling tanks are usually chance for a successful spawn. Dis- cate species of fish because it elimi- solved oxygen content of the aerated with oxygen (bottled or liq- nates the stress of forcible restraint. uid) with air stones, electrical agi- water, proper temperature, and ab- tators (12-volt), or both. A high sence of disturbance to the fish fol- level of dissolved oxygen is crucial lowing hormone injection(s) are for rapid recovery of the brood believed to play an important role fish from the oxygen debt incurred for successful induced spawning.

The work reported in this publication was supported in part by The Southern Regional Aquaculture Center through Grant No. 89-38500-4516 from the United States Department of Agriculture.