possible to select for the elimination of band 8 in order to avoid any over-
lap with S. aureus. Bands 5 and 6 are sometimes present. The differential
identification of these two species and their hybrids is based on the constant
presence of bands 7 and 9 in all S. niloticus and their total absence in S.
aureus. In the hybrids, however, all possible combinations occur (Plate 3).
There are also some slight differences in this respect between S. niloticus (G)
and S. niloticus (V). While both of them possess bands 7,8 and 9, band 7 is
quantitatively more intense in S. niloticus (G), whereas band 9 is more
intense in S. niloticus (V) (Plate 4).
EnzymesA study of some allozymic variations in Tilapia and Sarotherodon was
carried out by Chen and Tsuyuki (1970). They studied serum esterase (SE),
glucose-6-phosphate dehydrogenase (G6PD) in the liver and erythrocytes
and lactate dehydrogenase (LDH) from serum and other tissues (muscle, eye,
intestine, liver, ovary, heart, kidney and erythrocytes). Two species of
mouthbrooder, S. mossambicus, S. hornorum and their hybrids, and two
other species of substrate-spawners (Tilapia zillii and T. rendalli) were
tested. No significant interspecific variations, in both SE and LDH were
obtained within the Sarotherodon species, although enough variability
was found to distinguish between Tilapia and Sarotherodon. On the other
hand, the erythrocyte and liver G6PD showed significant interspecific
polymorphism.
Isoenzymic variations in different cichlids from the sea of Galilee were
investigated by Komfield et al. (1979). Six different species were tested,
three tilapias (S. aureus; S. galilaeus and T. zillii), two Tristamella species
(Tr. sacm and Tr. simonis) and a species of Haplochromis (H. flaviijosephi).
The interspecific similarities within these species were determined, mainly by
investigating the interspecific variations in different enzyme systems (e.g.,
adenylate kinase, esterase, isocitrate dehydrogenase, lactate dehydrogenase,
6 phosphogluconate dehydrogenase). Twenty-one allozyme loci were resolved
in all these species. Using Nei's coefficient (IN) of genetic identity (Nei
1972), interspecific similarities, ranging from IN = 0.95 within Tristamella
and 0.92 within Sarotherodon to less than 0.25 for Haplochromis, were
determined. A phenogram derived from these similarities shows that Trista-
mella is closely related to, but equidistant between, Sarotherodon and
Tilapia.
Two serum enzyme systems (LDH and SE) are being studied in our labo-
ratory in order to evaluate the interspecific variations in Sarotherodon spp.
(Avtalion et al., in prep.). At least three different LDH bands could be
shown, presenting an interspecific polymorphism, but no species-specific
pattern could be shown. For this reason, LDH is not utilized in our systematic
control test of broodstocks. The SE system shows no intraspecific poly-
morphism but S. aureus has a unique species-specific esterase band, located
in the transferrin region of the electropherograrn, having an Rm of 77.6%.
The most interesting finding was that all the different S. niloticus tested,