The Biology and Culture of Tilapias

Roberts and Sommerville note that the diseases of tilapias have not been as
well studied as those of other cultured species, both because their culture has
only recently been developed to an intensive level where disease problems
are more evident, and because diagnostic facilities are, in general, poorly
developed in areas where tilapia culture is most common.
Tilapia polyculture systems are discussed in some detail by Hepher and
Pruginin, and Coche mentions one instance, in Lake Victoria, of S. esculentus
and T. zillii being cultured together in cages, and two instances of S. niloticus
being cultured with common carp. It would seem that there is less reason for
polyculture in cage systems than in ponds, though others may recognize the
availability of distinct niches in cages. In ponds, Hepher and Pruginin suggest
that in Israel polyculture is especially advantageous when low to moderate
stocking densities of young-of-the-year tilapia are used. At high stocking
densities, which are more typical of intensive production systems with
hybrid fish, the natural food component is negligible, and hence the feeding
synergisms are less important. The use of predators in tilapia culture is
perhaps a special case as such use is primarily for controlling recruitment.
Hepher and Pruginin suggest that common carp may carry out this latter
function to some degree, as well as that of increasing the utilization of
natural food.
Dr. Roberts draws attention to the recent demonstration of a biochemical
compound in water in which S. mossambicus had been intensively cultured,
which produces a kind of "shock syndrome" in this and other tilapias. The
production of such substances by fish has been frequently referred to else-
where, but seems not to have been given much attention by culturists. There
is some evidence that such substancesmay be important in spawning behavior.