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Home , Fish reproduction, Spawn (biology)

SRAC Publication No. 421

Southern Regional Aquaculture Center

November 1991

Introduction to -Induced Spawning of

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

The demand for fish for food, rec- redfish, snook, and . In ad- ing are in a particularly delicate reation, and ornamental aquari- dition to breeding other desirable condition. When female fish are ums is steadily increasing. fish , induced spawning stressed or injured, they may un- Natural fish populations have de- can be used to: dergo rapid physiological changes clined during the last several dec- that can result in the breakdown produce hybrids that are differ- ades because of environmental (resorption) of in the . ent from the parent species; degradation and over-. Crowding, dissolved oxygen de- This has resulted in an increased produce sterile polyploid fish pletion, rapid changes in tempera- effort in the development of tech- (for example, sterile triploid ture, and osmotic imbalance are niques for hatchery production of grass for aquatic weed con- well known causes of stress and fish. Traditional aquaculture spe- trol); must be avoided. Suboptimum cies such as , , common conditions, while not immediately carp, golden shiner, and synchronize of lethal, may stress brood fish, re- reach and large numbers of fish for simul- sulting in delayed mortality or fail- in hatcheries or , when con- taneous spawning, thereby sim- ure to spawn. Reducing stress and ditions are appropriate. plifying production and injury to brood fish can greatly in- marketing of the fish; crease the success of hormone- However, a number of fish species induced spawning. that have or potentially have great produce fry outside the normal economic significance for aquacul- spawning season for maximum Determine sexual maturity ture do not reproduce spontane- hatchery production and to pro- ously in captivity. Many of these vide fish when the price and The external appearance of brood fish spawn in environments that market demand is greatest; and fish has long been used to assess are nearly impossible to simulate maximize survival of fry under the stage of sexual development. in a hatchery. Hormone-induced controlled hatchery conditions. In some species, males change in spawning is the only reliable appearance during the spawning method to induce reproduction in Proper fish handling season. These physical changes these . make it relatively easy to identify The physical injury and physi- sexually mature males. However, Hormone-induced spawning of ological stress of capturing, han- secondary female charac- fish has been used for almost 60 dling, transporting, injecting, and teristics such as plumpness of the years. Surprisingly, the same pro- holding brood fish can have a abdomen and redness of the vent cedures, with only minor modifica- greater detrimental effect on are extremely subjective and can tions, have been used to spawn an spawning success than almost any be misleading. Sampling the eggs entire range of fishes from the an- other factor. Fish must be handled and of the brood fish elimi- cient and to carefully and optimum water con- nates the guesswork in determin- carp, catfish, , sea bass, ditions must be maintained to ing the stage of sexual develop- minimize stress. The importance ment. of proper handling and water qual- * Institute of Food and Agricultural Sciences, ity cannot be overemphasized. Fe- can usually be stripped from University of Florida male brood fish ready for spawn- males of most species when they are ready for spawning by apply- photoperiod; and testes; (3) LHRH analogs ing gentle pressure to the abdo- (LHRHa) alone or in combination water temperature; men between the pelvic fins and with (4) dopamine blockers which the vent. Sperm viability usually water quality (e.g., dissolved enhance the potency of LHRHa to can be determined by observing oxygen, pH, hardness, salinity, stimulate the pituitary; or (5) ster- motility with a microscope. alkalinity); oids to stimulate the di- rectly. The appropriate hormone Several methods are available to flooding and water current; preparation should be selected on determine the developmental tides and cycles of the moon; the basis of the species to be stage of the eggs in the fish’s spawned and the availability y of ovary. The diameter and appear- weather cycles (e.g., atmos- the . ance of the and the position of pheric pressure, rainfall); the nucleus in the egg are visual in- Preparation of hormones dicators of development. The ster- spawning substrate (e.g., oid assay procedure determines aquatic plants, sticks, gravel, The hormones must be mixed and the physiological response of the spawning caverns); stored properly to prevent con- tamination and preserve potency. eggs to hormones. Both require nutrition; that an egg sample be collected. The proper dosage must be calcu- The ovary can be sampled with disease and parasites; and lated for the brood fish, and the optimum injection schedule must either a rigid or flexible tube presence of other fish. (catheter). An egg sample can also be used for best results. To calcu- be taken by making a small inci- These factors do not function inde- late the proper dosage, (1) the re- sion along the belly or side of the pendently of each other, but are in- commended dose, (2) approximate fish. This technique is commonly terrelated. weight of the brood fish, and (3) used for sturgeon and paddlefish. the desired volume of the injection The internal mechanism that regu- must be determined. The quantity An understanding of sperm viabil- lates the process of reproduction ity and egg stage development of hormone to be injected can then in fish is the brain-hypothalamus- be calculated from the weight of will greatly improve the success of pituitary- chain (Figure 1). hormone-induced spawning of each individual brood fish and the Hormone-induced spawning tech- appropriate injection schedule. fish. niques influence this sequential Control of reproduction mechanism at several levels, by Taking the spawn either promoting or inhibiting the Reproduction in fishes is regulated process. The primary substances The eggs and milt of fish can be taken by several different meth- by external environmental factors used for hormone-induced spawn- that trigger internal mechanisms. ing have been: (1) pituitary ex- ods: (1) tank spawning; (2) hand stripping, and (3) surgically re- The final event of the reproductive tracts and (2) purified gonado- moving the eggs. The method of cycle, the release of eggs and tropin to stimulate the sperm resulting in spawning, can choice depends on the fish species, be controlled by either placing the fish in an appropriate environ- ment or by changing the fish’s in- Environmental Stimuli ternal regulating factors with injected hormones or other sub- stances. The internal mechanisms that regulate spawning are similar for most fishes. The external envi- Brain ronmental factors that control re- Releasing production, however, vary Hormone considerably among species. For this reason, more is known Gonadotropin about the internal regulatory Hormones mechanism of than the specific environmental re- Steroids and quirements for spawning each spe- cies. Environmental factors that Prostaglandins have been shown to play a signifi- cant role in the reproductive cycle are: Figure 1. Mechanism that regulates reproduction in fishes. hatchery facilities, experience and Because the internal of suspension, urea and salt solution, skill of the hatchery staff, and the fish vary greatly, hand stripping and tannic acid solution are prepa- desired manipulations of eggs, may be difficult in some species. rations commonly used to deacti- sperm, or fertilized eggs. Sturgeon and paddlefish have no vate the sticky layer of fish eggs. ovarian sac; the eggs are released In addition, the gelatinous matrix Tank spawning is the simplest into the abdominal cavity during of catfish egg masses can be dis- method for obtaining a hormone- . The best method for tak- solved with sodium sulfite so the induced spawn. Brood fish of ing the spawn of these species is to eggs can be incubated in hatching both are placed together in surgically remove the eggs. For jars. the spawning tank following injec- delicate species that seldom sur- Induced hatchery spawning of fish tion(s). The female ovulates when vive the rigors of hand stripping, requires a continuous series of de- she is physiologically ready. The humanely killing them and surgi- cisions, any of which if improperly males stimulate the female to re- cally removing the eggs may be made, can diminish or completely lease the eggs and fertilize the the best option. In addition, more obliterate the success of the pro- spawn. eggs can usually be obtained by ject. There are many ways to fail this method than by hand strip- Hand stripping is commonly used at each step and only a very few ping. for taking the spawn of many spe- that are productive. Consistent cies of fish. Brood fish are sepa- Fertilizing the spawn performance requires strict atten- rated by sex prior to hormone tion to detail. injection to prevent spawning in The eggs obtained by hand strip- the holding tank. It is important ping or surgical removal are usu- Additional SRAC fact to determine the exact time of ovu- ally fertilized with fresh milt. sheets on induced lation when hand stripping. In Males are captured, wiped off, and spawning many species, egg quality can dete- held belly down over the bowl riorate rapidly if the eggs are not containing the eggs. The portion SRAC 422 Capturing, Handling, taken shortly after ovulation. For of the abdomen posterior to the Transporting, Injecting, and Holding most species, ovulation can best be pelvic fins is gently massaged to Brood Fish for Induced Spawning verified by checking the female to extrude the milt onto the eggs. SRAC 423 Determining Sexual determine when eggs flow freely Milt can be collected from males Maturity of for Induced from the vent. To strip the eggs, and stored up to three weeks prior Spawning of Fish the fish is held slightly on her side, to stripping eggs. tail down; gentle hand pressure is SRAC 424 Hormonal Control of Re- Ovulated eggs of many species applied to the abdomen, moving production in Fish for Induced Spawn- such as white bass, sturgeon, pad- toward the vent. The stream of ing eggs is directed into a clean, dry dlefish, and become bowl positioned so that water sticky after water is added. During SRAC 425 Hormone Preparation, from the fish does not drip onto natural spawning, this stickiness Dosage Calculation, and Injection the eggs. It is important to insure causes the eggs to become at- Techniques for Induced Spawning of that no water comes in contact tached to rocks, sticks, or aquatic Fish with the eggs until after the milt is plants. Catfish eggs are connected by a sticky matrix that holds the SRAC 426 Techniques for Taking and added and mixed. Water activates Fertilizing the Spawn of Fish the sperm and also causes the eggs together in a mass. In the opening through which the sperm hatchery, this stickiness causes SRAC 427 Induction and Verification enters the egg to close. problems during incubation. Silt- of Triploidy in Fish clay, Fuller’s earth, or bentonite 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.