time by over four months and is cheap and straightforward to achieve. Broodstock managers can use or select for traits such as fast growth rates or disease resistance over generations to produce more desirable fish. This ability for genetic improvement of stocks is more efficient and produces higher value stock. Broodstocks also enable you to selectively plan and control all matings. Selective breeding is an important part of the domestication of aquaculture species. Pond-reared broodstocks benefit from the removal of predation which can be a significant cause of mortality in natural populations. They further benefit from the removal of variable environmental impacts. Holding broodstock in an accessible pond or tank offers readily available breeding adults whenever required. Disadvantages When broodstocks are used to supplement natural populations they face different selective pressures to normal. Thus they may not have adequate fitness to survive the natural environment, or can alter and decrease natural genetic diversity due to the bottleneck nature of breeding from a smaller population. Broodstocks require supplementation from outside sources regularly to prevent negative effects of closed populations. Domestication of broodstocks in hatcheries can reduce reproductive capabilities and alter other genetic characteristics. For example, a trout stock maintained as a closed population for 20 generations showed reduced number and size of egg production. Examples Penaeidae Shrimp, particularly of the family Penaeidae, are one of the largest internationally traded species. Native stocks are usually collected as sources of broodstock supply . There are also examples of pond-reared Penaeidae broodstocks. These shrimp are raised in suitable environmental conditions including a 12–14 hour/day photoperiod, a water temperature of 25–29 °C and full seawater salinity with high water exchange rates. Sydney rock oyster The Sydney rock oyster, Saccostrea glomerata, has been farmed in New South Wales, Australia for over 100 years. Due to declines in the supply in the past 30 years, New South Wales introduced a selection program in 1990 to breed faster growing stocks. The utilised broodstocks are held in artificial ponds of around 0.11 ha in size, and at low densities. Broodstocks provided higher numbers of larvae and could be spawned readily providing a more definite source of Sydney rock oysters. Rainbow trout Global production of rainbow trout, Oncorhynchus mykiss, requires over 3 billion eggs per year. This number is met because of broodstocks which undergo selection and conditioning in hatcheries. Trout have been reared artificially for over 80 years. Rainbow