In intensive culture, the establishment of hatchery technology, which
allows detailed observations to be made on young fishes, has shown the
prevalence of particular larval anomalies. Rothbard et al. (1980) have de-
scribed the commonest of these in Sarotherodon niloticus, but others
are also found.
Mortality Associated Specifically with High DensityIt has long been a recognized phenomenon that in high density culture
the growth rates of many tilapias tail off and there are unexplained mor-
talities. Such growth inhibition has been attributed to the presence of some
inhibitory factor in the water. The phenomenon was first defined for Tilapia
by Chen and Prowse (1964) and is discussed by Balarin and Hatton (1979) in
relation to the "space factor" requirement defined by Swingle (1956) for
goldfish (Carassius auratus) and other extensively farmed species. Recently
some more specific information on the phenomenon (which is not universally
recognized) has become available with the publication of preliminary findings
by Henderson-Arzapalo et al. (1980) on a biochemical compound which
they isolated from mucus and culture water of intensively cultured S.
mossambicus which induced a syndrome suggestive of an acute anaphylactic
reaction in S. mossambicus, S. aureus, S. niloticus and T. zillii but had no
such effect on Ictalurus punctatus. This phenomenon shows a number of
similarities with the findings of Scott (1977) who described a phenomenon
which he called "shock syndrome" in Sarotherodon spilurus spilurus which
he observed to go into an anaphylactoid state in high density stocking in
Kenya (Plate 4).
Plate 4. Sarotherodon spilurus in state of shock from high density intensive tank culture.
Photograph courtesy of Mr. P.W. Scott.