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Techniques for Taking and Fertilizing the Spawn of Fish

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Techniques for Taking and Fertilizing the Spawn of Fish SRAC Publication No. 426 Southern Regional Aquaculture Center November 1991 Techniques for Taking and Fertilizing the Spawn of Fish R.W. Rottmann, J.V. Shireman, and F.A. Chapman* Following hormone injection, the During ovulation, the connection tion of egg quality for some eggs and milt of fish can be taken between the female fish and the species of fish commonly spawned by several different methods: eggs in the ovary is eliminated. In by hormone injection. warm-water fishes, egg quality ■ tank spawning, can deteriorate rapidly if eggs are Tank spawning not taken shortly after ovulation; ■ hand stripping, and they become “overripe” and can no Tank spawning is the simplest ■ surgically removing the eggs. longer be fertilized. In general, the method for obtaining a hatchery eggs of tropical and sub-tropical spawn. Brood fish of both sexes The method of choice depends on species of fish become overripe are placed together in the spawn- the fish species, hatchery facilities, more quickly than those that ing tank following injection(s). experience and skill of the hatch- spawn at cooler water tempera- Brood fish should not be disturbed ery staff, and the desired manipu- tures. The eggs of cold-water spe- and subdued lighting is recom- lations of eggs, sperm or fertilized cies remain viable for several days mended. The female ovulates eggs. after ovulation. Table 1 presents when she is physiologically ready. the reported maximum period be- The males stimulate the female to Taking the eggs tween ovulation and the deteriora- Ovulation is the final phase of nor- mal egg development. The time Table 1. The maximum period between ovulation and deterioration of between the final or resolving the egg quality for various species of fish. dose of hormone and ovulation is referred to as the latency period. Bighead carp (Hypophthalmichthys nobilis) 50 to 80 minutes This is usually dependent on the species of fish, water temperature, Common carp (Cyprinus carpio) 50 to 80 minutes and hormone preparation used, It is especially important to know Grass carp (Ctenopharyngodon idella) 30 to 45 minutes the latency period when hand Rainbow trout (Salmo gairdneri) 7 days stripping or surgically removing the eggs. Check the literature for Red-tailed black shark (Labeo bicolor) 15 to 30 minutes the latency period for the fish spe- cies you are spawning. Snook (Centropomus sp.) 15 to 30 minutes Striped bass (Morone saxatilis) 15 to 30 minutes * Institute of Food and Agricultural Sciences, Sturgeon (Acipenser sp.) 2 hours University of Florida White bass (Morone chrysops) 30 to 45 minutes release the eggs and fertilize the spawn. WATER INLET Better fertilization occurs if males are accustomed to the tank, and have been injected with a prepara- tory dose of hormone several days prior to and again at the same time as the female. Males can be used SPAWNING for several tank spawns, week TANK after week, until their milt flow di- minishes. Unless the males are aggressive toward each other, it is advisable to put two or three males for each female in a tank to ensure fertilization. If the spawning tank is of suffi- cient size, more than one female may be spawned in the same tank. Figure 1. Round spawning tank with screened egg collector. The presence of other individuals may help stimulate fish that are mass spawners. However, too many breeders in a small tank ■ might be disruptive to the spawn- Tank spawning has both advan- the surface area of substrate in ing process. tages and disadvantages. Advan- tanks is insufficient for large tages are: species that release large quanti- A round tank is advantageous for ties of sticky eggs. The-eggs species with non-sticky, floating or skill on the part of the hatchery clump together, resulting in fun- semi-buoyant eggs that spawn in a staff in predicting the exact time gus problems and poor hatch; river or estuary. The circular flow of ovulation or checking fe- and simulates the current in which males to verify ovulation is un- these fish naturally spawn. The necessary; ■ this method cannot be used if in- vigorous swimming action of the duction of polyploidy or other rapid deterioration of eggs in female in the swift water current is manipulations of eggs, sperm, the ovary after ovulation is not believed to assist in emptying the or fertilized eggs are a problem; ovaries. The eggs are carried with desired. the drain water from the spawning there is less potential of injury tank to a screened collector (Figure to the brood fish because it is Hand stripping 1). Eggs are then transferred to an unnecessary to check and strip incubator. the fish; and Hand stripping is commonly used for taking the spawn of many spe- Nest breeders and substrate less labor is required. cies of fish. Brood fish are sepa- spawners can also be tank rated by sex prior to hormone spawned if suitable nesting sites Disadvantages are: injection to prevent spawning in - - or spawning material are ■ the holding-tank. provided. When tank spawning a screened egg collector or suit- species that scatter sticky eggs, it is able spawning substrate is re- It is important to determine the advisable to place spawning mats quired; exact time of ovulation when hand stripping. However, the eggs of or brushes on the bottom of the ■ dirt and debris may be mixed tank. The eggs will attach to the cold-water species may remain vi- with the eggs, potentially caus- able for several days after ovula- substrate. Brood fish are removed ing problems during incubation; from the tank after spawning, un- tion; for example, in trout, eggs are less they provide parental care to ■ some females may not release usually stripped within 3 to 4 the eggs. Fertilized eggs are usu- all their eggs; days. The eggs of some species ally incubated in the spawning such as striped bass and white tank. ■ it is more difficult to accurately bass progressively clear or become estimate the number of eggs; transparent as they near ovulation. This visual cue is used by hatchery eggs until after the milt is added Surgically removing the workers to estimate the approxi- and mixed. Water and slime from eggs mate time of ovulation. An egg the vent and tail area of the female sample is taken by carefully insert- fish are dried with a towel. Water Because the internal anatomy of ing a tube (catheter) into the uro- activates the sperm and also fish varies greatly, hand stripping genital opening and examining the causes the opening through which may be difficult in some species. sample under a microscope (See the sperm enters the egg (micro- Sturgeon and paddlefish have no SRAC Publication No. 423, Deter- pyle) to close. For many fish, this ovarian sac; the eggs are released mining Sexual Maturity of Brood- closure takes place within only 45 into the abdominal cavity during stock for Induced Spawning of Fish). to 60 seconds. ovulation. The best method for tak- Eggs taken more than 15 hours be- ing the spawn in many of these fore ovulation cannot be accu- To strip the eggs, the fish is held species is to surgically remove the rately staged using this method. slightly on her side, tail down; gen- eggs. The first indication of ovula- tle hand pressure is applied to the tion for sturgeon and paddlefish is For most species, ovulation can abdomen, moving toward the vent the appearance of several eggs best be verified by checking the fe- (Figure 2). The stream of eggs is stuck to the sides or bottom of the male to determine when eggs flow directed into a clean, dry bowl tank. The brood fish are usually freely from the vent. At least one positioned so that water from the left undisturbed for an additional hour prior to the earliest antici- fish does not drip onto the eggs. 1 to 2 hours, depending on the size pated time of spawning, female The head of small fish can be held of the female (small females 1 hour fish are captured and the process by one hand while the eggs are and large females 2 hours), to in- of checking to verify ovulation is stripped with the other. A cloth sure complete ovulation. initiated. Tropical species are usu- glove may be worn to help hold ally checked every 45 minutes the fish while stripping. Larger If the female sturgeon or paddle- until ovulation is verified, temper- species are either wrapped in a fish is to be saved, it is first anes- ate water species are usually towel and held by one or more thetized. The fish is temporarily checked every hour. It is not neces- hatchery workers while another placed in an aerated holding tank sary to take the fish out of the strips the eggs, or the fish maybe with MS-222. When opercular water to verify ovulation. The fish restrained on a padded table or movement slows and the fish is un- is turned belly up and gentle fin- stretcher for stripping. able to right herself when turned ger pressure is applied to the abdo- over, she-is then placed belly-up men starting at the pectoral fins, Good quality eggs usually flow on a stretcher. Two hoses are used moving slowly toward the vent. readily from the genital opening of to ventilate the gills during sur- Do not try to squeeze or force the the female and have little ovarian gery. One hose delivers aerated eggs from the fish; this will only in- fluid. If the ovarian fluid is wa- hatchery water, and the other de- jure the female. Frequent or rough tery or milky and many of the livers water from a recirculating handling of females retards ovula- eggs are cloudy white, this indi- tank containing aerated water tion, reduces spawning success cates poor quality eggs.
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