The Biology and Culture of Tilapias

Table 2. Tilapia introductions in natural waters of Africa.

Lake Victoria (Lake Kyoga) (Uganda-Kenya-Tanzania)

• two indigenous endemic species: S. esculentus and S. variabilis


• four introduced species: S. leucostictus, S. niloticus, T. zillii and T. rendalli (acci-
  dentally with zillii) between 1951 and 1954.


• good acclimatization of introduced species favored by the existence of empty eco-
  logical niches, notably the niche for a macrophage herbivorous tilapia: T. zillii
  underwent a large development and became almost as abundant as S. variabilis
  which was one of the main exploited species (Welcomme 1967a).


• but negative effects (see Fryer and Iles 1972; Fryer 1961a; Welcomme 1964,1967a):
  i. in the first stages of its growth, T. zillii shared the same niche as the alevins
  of S. variabilis, then competed with them and supplanted them due to more
  rapid growth and greater aggression.
  ii. T. zillii competed with and also supplanted S. variabilis for the occupation
  of breeding grounds.
  iii. S. niloticus competed with S. esculentus and hybridized with S. variabilis.
  iv. T. zillii hybridized with T. rendalli, naturally allopatric.

Koki lakes (Uganda)

• no indigenous tilapias


• complete failure with the introduction of S. spilurus niger and S. esculentus but
  satisfactory success with S. niloticus (see Lowe (McConnell) 1958)

Lake Bunyoni-Lake Nkugute (Uganda)

• no indigenous tilapias


• complete failure of S. spilurus niger introduction (Lake Bunyoni) and S. esculentus
  (Lake Nkugute) (Lowe (McConnell) 1958) and success of S. niloticus in the two lakes


• but hybridization S. niloticus x S. spilurus niger and S. niloticus x S. esculentus;
  excessive development of S. niloticus populations with, in consequence, retarded
  growth, nanism, infestation by parasites and finally a very poor result from the
  fishery point of view (Beadle 1974, p. 83).

Lake Naivasha (Kenya)

• no indigenous tilapias


• introduction of S. spilurus niger in 1925 and of T. zillii and S. leucostictus (acci-
  dental) in 1956


• good initial acclimation in S. spilurus niger which formed the mainstay of the fishery
  during the years 1950-60; in 1961 appearance of hybrids of S. spilunur niger x S.
  leucostictus; increase in their number (57% of catches in 1962) followed by their
  regression particularly marked after 1971, date of the total disappearance of S.
  spilurus niger; after this date, great development of S. leucostictus which became
  the dominant species in the lake and of T. zillii (Elder et al. 1971 ; Siddiqui 1979b)

Lake Lusiwashi (Zambia)

• no indigenous tilapias


• introduction of S. macrochir (1949) and T. rendalli (1959)succeesful (catches: 80 t,
  Fryer and Iles 1972) because ecologically complementary species (p&~ophagous
  and macrophagous) transplanted close to their original area of distribution in a
  milieu offering vacant niches.