As we have outlined, the biology of these fishes is such that under 4hese
conditions of rapid turnover, simple ecological community, and frequent
environmental perturbations (e.g., draining ponds for stocking, harvest, etc.)
they are forced strongly into a more altricial life style. This tends to result in
fish showing earlier sexual maturation, and directing much of their resources
into reproduction, with consequent lack of somatic growth (especially in
females, in the bearers). In fact, these circumstances might well favor one of
the guarding species over any of the bearers, since the former are, as a guild,
more altricial.
The task in this case would be to select a guarder species that would not
mature (sexually) so rapidly as to cancel the inherent benefits of its life style
(high fecundity, general ability as an "invader" species). Furthermore, there
might be disadvantages associated with the guarding guild (substrate require-
ments for breeding, decreased likelihood of producing hybrids between
species because of prolonged, monogamous courtship and pair formation)
that would mitigate against them. However, some evidence (Caulton, this
volume, pers. comm.) suggests that under appropriate circumstances, a
guarder species (in his case T. rendalli) may have considerable potential for
aquaculture.
"Stunting" : A Misunderstood Phenomenon
Perhaps the most striking aspect of the literature on the culture of tilapias
is the so-called "stunting" problem (Balarin and Hatton 1979 ; Avtalion, this
volume; Hepher, this volume; Jalabert and Zohar, this volume; Lowe-McCon-
nell, this volume) encountered in many attempts at intensive aquaculture. In
fact, as we and some others have indicated (e.g., Fryer and Iles 1972),
the problem is not one of inhibited somatic growth but one of accelerated
ontogeny (sexual maturation).
Not only has the problem apparently been widely misinterpreted, and
therefore misunderstood, it is also perhaps the clearest possible verification
of the predictions of our hypothesis of altricial and precocial trends in
ontogeny. Such early maturation is the classic response of an altricial form.
There is little doubt that an earlier age of first reproduction will have the
greatest effect on the rate of population increase (Lewontin 1965; Wilson
and Bossert 1971; Emlen 1973; Southwood 1976; Horn 1978; Krebs 1978;
Pianka 1978). It is clearly a heterochronous shift towards a more altricial
form, as we would predict.
Tilapiine fishes are almost certainly derived from fluvial ancestors and still
retain (at least in some species) the ability to successfully invade newly-
created marginal aquatic habitats (Welcomme 1970; 1979a; Lowe-McConnell
1975, this volume). Stocking these fish in a pond or other aquaculture
facility under the usual conditions (Balarin and Hatton 1979 ; Lovshin, this
volume) is as close to a replication of those natural (ecological) phenomena
as one could imagine. A relatively small number of adults or juveniles is
introduced into a previously unpopulated pond, creating a low density,
non-competitive situation. Often supplemental food is also provided for the
fish (Hepher, this volume; Lovshin, this volume). A natural invasion into