Spawning pens. movement, but they are still capable of swimming. Fry can be carefully caught with a small fine-mesh net or gen- tly poured into a bucket of pond water and transferred to the nursery. After counting the fry (see "Counting Fry"), they should be released into the nursery by slowly submerging the bucket. If the water temperature of the nursery differs from that of the brood pond, be sure to properly acclimate the fry as during hauling and stocking. 4. Pen Spawning Pen spawning uses submerged enclosures made of wood, concrete, wire mesh, or a combination of materials. Although this method requires additional construction and labor costs, it has the advantage of allowing selec- tive mating. Pen spawning techniques are not currently in wide use in Florida, but there may be good potential for this method in pit ponds, canals, sinkhole and solu- tion lakes, reclaimed phosphate pits, and other aquatic systems unusual or unique to the state. Pens are usually built in at least 3 feet of water along a bank to minimize the amount of materials needed and for ease of observing and handling fish. Galvanized chain link fence, plastic-coated wire mesh, or other nonrusting materials should be used to construct rectangular pens about 4 x 6 feet and extending 12-24 inches above the water surface, with the narrow side open against the shoreline. Adjacent pens can have common sides to fur- ther reduce construction costs. Sides of the pen must be embedded in the bottom to prevent brood fish from escaping. Mesh size must be large enough to allow for good water circulation, but not so large as to permit the escape of brood fish; meshes of V2-2 inches are usually satisfactory. A spawning container is placed in the pen, usually with the receptacle opening toward the center of the pond. A pair of ripe brood fish of similar size should be in- troduced into each pen. It is important to select fish, especially females, that are nearly ready to spawn. Some producers who use this method prefer to inject brood fish with spawning hormones a day or two before placing them in the pens. Cages should then be checked daily and any female that is being harassed or injured by a male should be removed at once. It is very important to transfer the female soon after spawning to prevent her from being seriously injured or killed by the male. Following spawning, eggs may be moved to the nursery or the male may be allowed to incubate them to hatching. If spawning does not occur in one to two weeks, double- check the sexes of the pair and exchange brood fish if necessary. 5. Tank Method Tank or aquarium spawning is the most intensive method of spawning management because it requires considerable investments of time, labor, and facilities. Aquaria, tanks, or troughs of at least 50 gallons (200 liters) are used as spawning enclosures. A pair of ripe brooders is selected and spawning is induced by injecting the female or both fish with pituitary extract or HCG. Depending on the dose of hormone, spawning usually ensues within a day or two of injection, but some females may require addi- tional injections. As soon as spawning is completed, the eggs are transferred to the hatchery and the aquarium can be stocked with a new brood pair, or the same male can be used with a fresh female following a resting period. The tank method has several advantages over other techniques: (1) variables such as temperature, light, and water chemistry can often be controlled more easily; (2) spawning period can sometimes be altered, allowing for earlier seasonal production of fry or limiting spawning to times that are convenient for the culturist; (3) fish that might not otherwise spawn may often be induced to; (4) diseases and parasites can be more easily controlled; (5) selected matings can be performed and easily recorded. Major disadvantages of the tank method are that (1) there are greater risks of losses from power outages, plugged pipes, and other mechanical failures; (2) the number of eggs produced per man-hour may be lower than other methods; (3) the tank method is comparatively expensive. The Hatchery The most efficient hatcheries use incubation chambers for hatching eggs, since predation, cannibalism, and disease can be reduced and stocking rates can be easily monitored. Hatcheries range from simple wooden pad- dlewheel troughs to more sophisticated devices available through commercial equipment suppliers. Hatcheries need not be elaborate, so long as good water quality and disease control measures are maintained. Trough Construction A typical incubation chamber consists of a flat- bottomed wooden, fiberglass, aluminum, or stainless steel (14-gauge) trough about 8 to 10 feet long, 18 to 24 inches wide, and 10 to 12 inches deep (about 100 gallons).