They also occur in other regions of the U.S.A. in water bodies which are
warmed above normal ambient temperature during the winter by geothermal
water sources or artificial heating in conjunction with the operation of
power plants. Some tilapias have excellent aquaculture potential because of
their fast growth, herbivorous or omnivorous feeding habits, high food
conversion efficiency, high tolerance to low water quality, ease of spawning,
ease of handling, resistance to disease and parasites and good consumer
acceptance.TemperatureOne of the problems of using tilapia for pond culture is their inability, in
general, to survive water temperatures below 10°C for more than a few days.
The influence of temperature on survival and growth has been studied
through field observations, laboratory investigations and a few physiological
experiments designed specifically to determine thermal effects. There is a
large variation in the reports of thermal tolerance in tilapias, stemming from
a lack of standardized methods. Other variations in results might be attributed
to differences in: 1) acclimation time, 2) water quality such as total dissolved
oxygen (DO), total dissolved solids and salinity, 3) age, size, sex and health
of the fish, and 4) duration of the drop in temperature.
Activity and feeding of tilapias become reduced below 20°C and feeding
stops completely around 16°C. Although tilapias may be able to resist short-
term exposure (a few hours) to temperatures of 7 to 10°C,death can occur
(in some species) at temperatures as high as 12°C after long-term exposure.
Some tilapias are more tolerant to low temperatures than others. Tilapia
sparrmanii is a hardy fish, capable of withstanding much lower temperatures
than those tolerated by other species. The lowest water temperature tolerance
recorded for this species was 7OC in Zambia (Maar et al. 1966) and the same
temperature was recorded in South Africa (Hofstede 1955). T. rendalli was
able to survive a temperature of 11°C in Zambia (Sklower 1955).
Of the mouthbrooding fish, Sarotherodon aureus seems to be the most
resistant to low temperature. Yashouv (1960) found that at temperatures
below 10°C, S. aureus (reported as T. nilotica) ceases all motion, while at 6 to
7°C it loses its ability to maintain body position. However, when exposed
to low temperatures for only a few hours the fish recovers. Sarig (1969)
found that local S. aureus in Israel was able to tolerate temperatures of
8.0 to 8.5"C. S. vulcani, which was introduced to Israel from Lake Rudolf,
dies at temperatures of 11 to 13°C. On the other hand, its hybrid with
S. aureus had a lower temperature tolerance limit of 8.0 to 9.0°C. Denzer
(1968) recorded a temperature of 11°C as the lower lethal limit of S. nilo-
ticus. Chervinski and Lahav (1976) showed that the hybrids between S.
niloticus 9 x S. aureus d and S. vulcani 9 x S. aureus d have temperature
limits similar to S. aureus. Similar experiments conducted by Lee (1979)
showed that S. aureus is more tolerant to low temperature (6.7"C) (criteria,
of the fish lost equilibrium) than S. hornorurn (lO.O°C) and S. niloticus
(7 .S°C). The crosses between S. niloticus 9 p S. aureus d and S. hornorurn 9
x S. aureus d were similar to S. aureus in their low temperature tolerance.