portant to prolong its growth period, reduce mortality for overwintering and decrease
costs.
Previous research indicates that tilapia has genetic variation for cold tolerance in tilapia.
Khater (1985) and Khater and Smitherman (1988) demonstrated that differences existed
among the Egypt, Ghana and Ivory Coast strains of Nile tilapia. The further the geographic
location from the equator, the more cold tolerance possessed by the strain of Nile tilapia.
Apparently, natural selection affects cold tolerance in tilapia.
Selective breeding can alter the cold tolerance of tilapia. Behrends and Smitherman
(1984) used introgressive backcrossing to successfully transfer the cold tolerance of blue
tilapia, O. aureus, to red tilapia. The use of pure blue tilapia or its hybrids could enhance cold
tolerance of tilapia in China. However, Nile tilapia are the most commonly grown tilapia in
China, probably because of their rapid growth during the warmer part of the seasons. Since
Nile tilapia are the most common tilapia in China, study of their cold tolerance is important.
The GIFT line of Nile tilapia is being distributed throughout Asia, therefore, documentation
of its performance for important traits such as cold tolerance is needed as a single trait
does not measure a genotypes overall aquaculture value. Also, cold tolerance of Nile tilapia
developed in a tropical climate then transferred to a temperate climate where Nile tilapia
already exists needs evaluation. Cold tolerance has not been previously studied for Nile
tilapia in China.
The objective of the current study was to compare the cold tolerance of three strains of
Nile tilapia grown in China. One strain was a recent introduction and others were earlier
introductions.