Within 45 minutes of spawning all the eggs can be sieved on a 50-?m screen to remove debris. When females appear to have finished spawning, they should be removed from the containers and the containers aerated. As oysters begin to spawn, males and females should be placed in separate containers (1 gallon or 2.2 L) containing treated sea water to prevent uncontrolled fertilization. Males release a near constant stream of sperm and females release eggs during periodic shell closures. When oysters begin releasing gametes, the whitish sperm and eggs can be easily seen against the black background of the tank. These sperm should be checked under a microscope to be sure there is no motility. To prevent unwanted fertilization, sperm used in this procedure can be placed in a microwave oven for 20 to 40 seconds to eliminate viability. If this fails to produce results in a reasonable time (about an hour), sperm stripped from a male can be delivered by pipette to the shell opening of several oysters to stimulate spawning. Cycling ambient and warm water a few times may also stimulate spawning. After the oysters have had time to acclimate and open their shells, warm water (generally 9 ✯ or 5 ✬ above ambient) is introduced into the tank to induce spawning. Therefore, 20 to 30 large oysters are thoroughly cleaned and scrubbed, then placed in a shallow, black tank containing 4 to 6 inches (101 to 153 mm) of filtered, treated seawater at the same salinity as the broodstock holding tank. Mature eggs are pear shaped, 55 to 75 ?m long, and 35 to 55 ?m wide.Ī significant amount of eggs and sperm can be produced by just a few oysters, but not every oyster may spawn and it is a good practice to have the eggs and sperm from several oysters. Gonads may also be cut and scraped and the material examined under the microscope for sperm and eggs. Ripening gonads have many branching tubules or prominent genital canals. Experienced hatchery personnel can judge the state of “ripeness” by removing the right or upper shell and noting the development of the gonads. In either case, oysters larger than 3 inches (76 mm) are selected, although males may be smaller, and then a sample is examined for reproductive readiness. The process begins with selecting broodstock, which may be oysters taken from the wild or oysters bred and maintained under controlled conditions for selective breeding. Spawning is typically undertaken in the spring when water temperatures rise above 77 ✯ (25 ✬) in southern waters. Approximately 10 million spat can be expected from the 25 million eyed larvae. Natural mortality and the need to thin out the larvae to proper densities should leave about 25 million eyed larvae ready for setting. Under good conditions 200 million eggs can result in 100 million or more early-stage larvae, which require 2,600 gallons (10,000 L) of treated water. As a rule, ten average females produce about 200 million eggs. Spawning oysters is the first step in the production of spat. Because of the rich array of organisms in Gulf of Mexico waters, mechanical filtration down to 1 ?m with UV treatment can assist in successful spawning and larval production. Mechanical filtration is usually done with a pressurized sand filter, cartridge filters for smaller volumes, or fine-mesh bags. Large-scale operations and “low-tech” or “back yard” facilities may forgo UV treatment but will use some mechanical filtration. Water used for spawning, mixing eggs and sperm, and growing larvae is typically filtered mechanically and treated with ultraviolet radiation. Good water quality is essential to successful hatchery production (see Site Selection) but even high-quality water must be treated to remove unwanted organisms. Another larger space with special lighting, separate from the main hatchery, is needed to grow larger volumes of algae. If algal cultures are to be produced, there must be a clean room with special lighting for starting cultures. Aeration throughout the hatchery is supplied by an appropriate size blower, overhead PVC piping, vinyl tubing, and good quality air stones. Shallow rectangular tanks with drain pipes provide nursery space for juvenile oysters. 4) that can handle the maximum expected water flow helps keep water off the floor. Drain pipes make it convenient to drain water and sieve larvae. Tanks for larval production are circular, generally 250 gallons (946 L) or larger, and have center drains and sloping or conical bottoms.
Treated sea- water is then suitable for larval and algal production. The plumbing is designed with a water filtration and treatment system consisting of some combination of rapid sand filters, cartridge filters, activated carbon, ultraviolet (UV) sterilization or pasteurization (Fig. Small cartridge and ultraviolet sterilizer filter system for treating seawater.
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