The value of global aquaculture was estimated at US$98.4 billion in 2008, with China largely dominating the market, but the value of aquaculture hatcheries and livestock production is yet to be estimated. Also, additional hatchery production for small domestic or conservation programs, particularly prevalent in Southeast Asia, has yet to be quantified. There is great interest in supplementing exploited fish stocks by releasing wild-caught and nursery-raised juveniles for later transplantation or exclusively producing them in hatcheries. Finfish larval cultures have been used extensively in resource improvement efforts in the United States to replenish natural populations. The US Fish and Wildlife Service have established a national fish hatchery system to help protect native fish species. Hatcheries produce juvenile fish and juveniles for transfer to aquaculture facilities, where they are "raised" to reach harvest size. A continuous supply of fish from aquaculture facilities is a key market requirement. Parent fish conditioning can extend the natural spawning period and thus the supply of young animals to farms. Supply can be obtained by procuring hatcheries in other hemispheres. Still guaranteed in the opposite season. Some hatcheries use genetic modification to improve breed quality and yield. Artificial insemination facilitates selective breeding programs aimed at enhancing production traits such as increased growth rate, disease resistance, survival, body colour, fertility, and/or reduced maturity. Genetic improvement is mediated by selective breeding, hybridization, or other genetic engineering techniques. Some hatcheries collect and condition wild adults, while others maintain permanent breeding stocks. Spontaneous spawning can occur in hatcheries during the normal spawning season, but adult spawning can be induced by a variety of methods when better control over the timing of spawning is required. Prior to fertilization, eggs can be gently washed to remove debris and bacteria that may contaminate the culture. To maintain the genetic diversity of the hatchery-produced population, it is necessary to encourage cross-fertilization among large numbers of individuals. Batches of eggs are kept separately, fertilized with sperm from multiple males, and left for 1-2 hours before analysing samples under a microscope to confirm high fertilization rates and numbers transferred to larval rearing tanks. Estimate. Rearing of early-stage larvae generally takes place in hatcheries that are closely associated with fish hatcheries, whereas shellfish hatcheries typically exist separately. Producing or purchasing live food on-site is one of the biggest costs for hatcheries as it is a labour-intensive process. Shellfish hatcheries also include an important settlement stage during which free-swimming larvae settle out of the water onto the substrate and metamorphose under suitable conditions. Once the metamorphosis has taken place, the hatchlings are commonly called spit, and this stage is taken to a facility where they continue to grow. Colonization behaviour is determined by many cues, including substrate type, water flow, temperature, and the presence of chemical cues that indicate the presence of adults and food sources. Therefore, hatcheries must understand these cues to induce settlement, and also substitute artificial substrates for easy handling and transport with minimal mortality. Many hatcheries are small and associated with larger, growing businesses, while others only produce hatcheries for sale.