stylistic:style_transfer, quality:correction
Breeding

Selective breeding programs for the common carp include improvement in growth, shape, and resistance to disease. Experiments carried out in the USSR used crossings of broodstocks to increase genetic diversity, and then selected the species for traits such as growth rate, exterior traits and viability, and/or adaptation to environmental conditions such as variations in temperature. Selected carp for fast growth and tolerance to cold, the Ropsha carp. The results showed a 30 to 77.4% improvement of cold tolerance, but did not provide any data for growth rate. An increase in growth rate was observed in the second generation in Vietnam, Moav and Wohlfarth (1976) showed positive results when selecting for slower growth for three generations compared to selecting for faster growth. Schaperclaus (1962) showed resistance to the dropsy disease wherein selected lines suffered low mortality (11.5%) compared to unselected (57%).

The major carp species used traditionally in Chinese aquaculture are the black, grass, silver and bighead carp. In the 1950s, the Pearl River Fishery Research Institute in China made a technological breakthrough in the induced breeding of these carps, which has resulted in a rapid expansion of freshwater aquaculture in China. In the late 1990s, scientists at the Chinese Academy of Fishery Sciences developed a new variant of the common carp called the Jian carp (Cyprinus carpio var. Jian). This fish grows rapidly and has a high feed conversion rate. Over 50% of the total aquaculture production of carp in China has now converted to Jian carp.