Table 1. The spawning frequency and egg production of isolated individual Sarotherodon vulcani females
(400-500 g each) studied from February 1,1973 to January 1,1974 (after Mires 1977 and Mires unpub-
lied data).
Female no. Date of spawningTotal Average No. Average
egg eggs1 of interval
count spawn* spawns (days)Date 2413- 2414- 1515- 316- 2416- 2617- 519-
1 No. eggs 1,600 ** ** ** ** ** ** 1,600 1,600 7
Interval 31 21 19 21 32 40 27
(days)
Date 1013- 814- 2715- 2416- 317- 518-
2 No. eggs 1,400 ** 1,500 1,200 ** 1,000 5,100 1,275 6
Interval 39 47 28 9 33 31
(days)
Date 2513- 414- 915- 718-
3 No. eggs 1,000 ** 1,150 **
Inted 10 35 90
(days)
Date 2713- 2814- 1817-
4No.e~ ** *+ **
Interval 32 81
(days)
Date 2513- 2119-
5No.eggs ** *+
Interval 150
(days)
Date 1413-
6No.eggs **
Interval
(days)
*Based on the number of eggs in fertile spawns only.
**Infertile spawns: eggs not counted.Unfortunately, some of the females died during the experiment and
the times of death were not recorded. It is therefore impossible to know
whether the spawning of some of the females ceased because of their death
or because of other reasons. It is, however, interesting to observe that here
again, although an optimal temperature was maintained throughout the
experiment, the spawning frequency of the females differed.
In the Kibbutz Ein Hamifrats fish hatcheries, where several families
of S. niloticus and S. aureus are kept in 500-liter aquaria, individual females
of both species have never spawned more than six or seven times in one
year and the average spawning frequency of any given group of females
in a family has not exceeded four. Moreover the period over which spawning
occurs is restricted to five or six consecutive months even when the tem-
perature is optimal year-round.
In other intraspecific spawns in aquaria (Lee 1979) very big differences
were observed in the spawning frequency and fecundity of various females.