which corresponds well to the naturally occurring minimum in Lake Huleh.
Hauser (1977) also reports a minimum temperature for reproduction of
20°C in T. zillii. S. aureus, S. niloticus (introduced) and S. galilaeus, which
occur with T. zillii in Lake Huleh and Lake Kinneret, Israel, are almost as
resistant to low temperatures as this latter species. In ponds S. niloticus and
S. galilaeus tolerate winter temperatures of 8°C for several hours each night
(Yashouv 1958), while S. aureus died at 8-9°C during experiments (Sarig
1969). It may be mentioned, however, that Chervinski and Lahav (1976)
reported an improved low temperature resistance of the local Israeli S.
aureus over that of S. niloticus imported from Africa.
The southernmost natural occurrences of tilapia include S. mossambicus
in coastal waters near Port Elizabeth (33'42'5). This has been attributed by
Jubb (1967, in Beadle 1974) to the fact that the southeastern coast of Africa
is swept by a warm current (the Agulhas) which maintains subtropical
conditions at a latitude at which tilapias would not normally occur (cf. their
absence at the same latitude on the west coast). In Africa T. sparrmanii is the
species which occurs at the lowest latitude naturally, tolerating winter
temperatures of 7°C and needing a minimum of 16°C for reproduction
(Chimits 1957). As a result of introductions, T. sparrmanii and S. aureus
have been established in the Cape region (Caulton pers. comm.).
Table 5 lists the tilapias which occur naturally, or after having been
introduced, in lakes of Africa and Madagascar at altitudes higher than
1,000 m. In natural environments 2,000 m seems to represent the limiting
altitude. The species which tolerate best the climates occurring at 1,500 to
2,000 m are S. niloticus, S. leucostictus and T. zillii. In ponds T. zillii has
been reported from an altitude of 2,500 m in Uganda (Chimits 1957), T.
rendalli from up to 1,400 to 1,500 m in Mexico and Colombia (FA0 1977~)
and S. mossambicus from up to 2,400 m in Ecuador (FA0 1977~). For
similar altitudes rivers tend to have minimum temperatures during the cold
season that are lower than those in lakes, which explains why few tilapias
occur in rivers above an altitude of 1,300 m. Studies by Gaigher (1973) have
shown that T. sparrmanii occurs in rivers above 1,220 m in the upper reaches
of the rivers of the Limpopo basin, but that T. rendalli and S. mossambicus
are limited to warmer rivers, below 1,220 m.
In addition to their temperature tolerance, the distributions of tilapias can
be related to their maximum swimming performance, which occurs at 24°C
in T. sparrmanii, 28°C in T. zillii and S. macrochir, 28 to 32°C in S. niloticus
and 32" C in S. mossambicus and S. galilaeus (Fukusho 1968).
A few tilapias have colonized hot springs. S. spil'urus percivali occurs in
the hot springs of the northern Uaso Nyiro system where the temperature
reaches 42.4"C (Trewavas 1966). S. alcalicus grahami is endemic in Lake
Magadi where it can live close to the hot springs (35 to 40°C), tolerating
short periods at 40 to 44OC (Coe 1966, 1967; Reite et al. 1974), and S.
shimnus chilwae, endemic to Lake Chilwa (Malawi) can tolerate 40 to
42°C for short periods (Morgan 1972). It may be mentioned for comparison
that North American species such as Notropis lutrensis and Barbus callensis
occur in hot springs of 40°C (Castenholz and Wickstrom 1975) and that
species of desert pupfish (Cyprinodontidae) may be found at temperatures
of 42°C (Brown 1971).
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