Out of ten S. aureus females, one spawned 8 times, one 7 times, two 6 times,
one 5 times, four 4 times and one 3 times. Out of nine S. niloticus Ivory
Coast one spawned 5 times, five 4 times and three 3 times. Yashouv (1958)
stated that in Israeli fish ponds, two-year old S. aureus usually spawn three
or four times from May to October.Table 2. The spawning frequency and egg production of isolated individual Sarotherodon niloticus B
(400-500 g each) studied from February 1, 1973 to January 1,1974 (after Mires 1977 and Mires unpub-
lished data).Female no. Date of spawningTotal Average No. Average
egg eggs/ of interval
count spawn* spawns (days)Date 712- 413- 315- 516- 617- 3017- 519-
1 No. eggs 200 1,600 ** ** ** 1,000 ** 2,800 933 7
Interval 25 57 33 31 24 35 34
(days)
Date 2612- 2414- 215- 2915- 2317- 2018-
2 No. eggs 900 ** ** ** 1,300 ** 2,200 1,100 6
Interval 57 8 27 56 28 35
(days)
Date 2015- 916- 1317- 418-
3 No. eggs ** ** ** 1,000
Interval 15 34 21
(days)
Date 413- 2913- 415.
4 No. eggs ** ** 700
Interval 25 36
(days)
Date 2415- 1816- 219.
5 No. eggs 1,090 1,600 **
Interval 25 76
(days)
Date 2116- 2617-
6No.eggs ** * * 2
Interval 35 35
(days)
*Based on the number of eggs in fertile spawns only.
**Infertile spawns: eggs not counted.Interspecific Spawning- AQUARIA AND TANKS
The successful crossing of two different tilapia species in aquaria has
always been a serious challenge to researchers and hatchery operators.
It was made easier with the help of induced spawning techniques (Rothbard
and Pruginin 1975) but it seems improbable that this can be used widely.
Recently interspecific spawns have been obtained in tanks (Hulata et al.
1980). Hulata and co-workers have been studying interspecific spawns in
600-liter tanks since 1978 and have kindly permitted the use of some of
these data (Tables 3,4 and 5). As in Tables 1 and 2, there is an enormous vari-
ability in fecundity between females of the same group, even with constant
environmental conditions year-round.