The Biology and Culture of Tilapias

and geographic situation it is believed to be a maternal mouthbrooder
like its neighbors S. pangani and S. mossambicus.
It is commonly believed that systematic conclusions are based on ana-
tomical considerations involving dissection and the use of the microscope.
Such evidence is indeed most important, but there is no aspect of an organ-
ism's biology that a systematist can afford to ignore. In defining the sub-
genera Sarotherodon and Oreochromis the main evidence is behavioral,
backed by geographical. The geographical evidence is well set out by Thys
(1963). Many observers have contributed to the behavioral evidence briefly
summarized above.
I do not know of any structural character that trenchantly separates
the two subgenera. Some members of Oreochromis, including S.(O.) hunteri
have four anal spines, either in all or in some individuals, but others have
only three; all species of subgen. Sarotherodon have three. In no species of
subgen. Sarotherodon are the jaws enlarged in sexually mature males. They
are enlarged in several species of subgen. Oreochromis but not in all. The
vertebral numbers range from 26 to 32 in subgen. Sarotherodon, 27 to 34 in
Oreochromis. Parallel adaptations to various feeding regimes have developed
in species of the two subgenera. If we do not know the breeding habits of
a species we can place it in a subgenus only if its overall characters add up to
a-general resemblance to a geographically-close member of one or other of
the subgenera.
The development of a tassel on the male genital papilla is a conspicuous
feature that characterizes a number of related species (S. macrochir, the
Malawi flock, ek.) and for these we may use a subgeneric name Nyasalapia
Thys (1968).
In the case of S. tanganicae, of whose breeding habits little is known,
the fact that its ventral scales are very small suggests relationship to Oreo-
chromis. But it has very specialized teeth and as it has been given a sub-
generic name of its own, I propose to use it and to call it Sarotherodon
(Neotilapia) tanganicae.
Another peculiar species in the same kind of limbo is the little S. fran-
chettii of Lake Afrera (= Giulietti) in Dancalia, eastern Ethiopia. Its outer
teeth as well as the inner are tricuspid and it has only 27 vertebrae and 10-
lower gill-rakers. It has been given its own subgeneric name by Thys (196B)
and so I propose to leave it as Ssrrotherodon (Danakilia) franchettii. (Dana-
kilia is now raised to genus; see Addendum).
For zoologists who are not systematists and for fish culturists there
is no need to use subgeneric names, and for these all the mouthbrooding
tilapias may be referred to by the generic name Sarotherodon followed by
the specific name.
Peters (1979) and Thys (1968, 1971a, 1971b) would prefer to leave the
tilapias undivided for the general and applied zoologist and to lump substrate-
spawners and mouthbrooders alike in a broad genus Tilapia. If I interpret
them rightly their reason for this is:
S. melanotheron and S. galilaeus, the two best known species of subgen.
Sarotherodon, have breeding habits distinct not only from those of
Oreochmmis but also in some ways from each other. Specifically, S.
melanotheron has large yellow eggs brooded normally by the father alone,