from which it is probably invalid to extrapolate to large culture ponds
Editors). The so-called "paradoxical stunting" reported at lower or inter-
mediate stocking densities, ascribed to the action of "living space on growth"
seems at best apost hoc attempt to explain the situation. Our hypothesis not
only predicts the supposedly anomalous responses at different densities, but
makes specific predictions as to the manipulation of tilapias for management
purposes.
We feel our approach may be more rational than the great variety of
attempts to produce monosex cultures of tilapias for pond culture, to
produce all-male hybrid broods, to chemically or surgically castrate fish to
inhibit reproduction, or the search for growth-inhibiting factors that operate
differentially at different densities. Since it is based on the evolutionary (and
ecological) features of the life histories of these fish, and manipulates their
biology with a minimum of intervention requiring high technology or direct
human action, it should also be the desired course of action for those with a
solely practical interest in these fish, particularly in developing countries.
It is rewarding to find that the activities of basic science, particularly
taken from first principles and theory, may in the end yield something of
value comparable to that normally expected only from so-called mission-
oriented research. If our efforts have such an effect in this case, we would
view them as a success.
AcknowledgmentsThe support for our research which has allowed us to develop our ideas in
this area has come from the National Science and Engineering Research
Council of Canada and the Ontario Ministry of Natural Resources. Final
preparation of the manuscript was carried out by DLGN while in the Animal
Behavior Research Group, Department of Zoology, University of Oxford,
with the financial support of a Faculty Research Leave Award from the
University of Guelph. Thanks to Pat and Jeff for their understanding, and to
Dr. D.J. McFarland for providing space and facilities.
We thank collectively a number of colleagues who have suffered through
and at times contributed to the development of our ideas. One of us (DLGN)
profited from time spent as a Research Fellow at the Zentrum fur Inter-
diszipliniire Forschung, Universitat Bielefeld, B.R.D. in an interdisciplinary
project on early development in animals and man. The other (EKB) benefitted
from a research leave spent at the Senckenberg Institut and Museum, Frank-
furt, B.R.D. and in Southeast Asia. We thank Joan Cunningham for her
efforts in preparing the figure, and Marilyn White for her assistance with
photographic material. In preparing this review we have drawn extensively,
and depended heavily upon the published material of a number of well-
known authorities on tilapias. Drs. Fishelson, Fryer, Greenwood, Iles,
Lowe-McConnell and Trewavas deserve our special acknowledgement in this
regard. All our extrapolations and flights of fancy from their data remain
entirely our responsibility.