a newly-created river floodplain pool or marginal lagoon (Welcomme 1970,
1979a) would be the ecological equivalent of this man-made event. The
response of the fish is identical in both situations. There is a shift towards a
more altricial life style, with a shorter interval of somatic growth (inferred
from smaller body size), an earlier onset of reproductive maturity (again
inferred from smaller body size) (Table 3), as well as production of more
numerous, smaller eggs (Lowe (McConnell) 1955b; Fryer and Iles 1972).
The apparent misinterpretation of this response in aquaculture conditions
as one of "stunting" has serious practical consequences (beyond any theoret-
ical implications). The fish clearly are stunted, in that they are physically
smaller than (large) adults known for the same species. But the real pheno-
menon is of course as we have described it. The fish are not "small for their
age", they are "old for their size". The difference is not only semantic, and
the consequences of the correct understanding are profound.
This also requires an understanding of the distinction between ultimate
and proximate factors regulating these responses of the fish. Our discussion
has centered on ultimate (i.e., evolutionary) factors. These must not be
confused with proximate (i.e., immediate) factors influencing the animals.
The latter might include food supply, water temperature, chemical signals
from conspecifics and so on (Guerrero, this volume; Mires, this volume). For
example, one result of the misunderstanding that the fish in ponds are
"stunted" has been a misguided effort to provide ever more food for the
animals. On the assumption that the fish are truly (somatically) stunted,
from lack of sufficient food, the solution would appear to lie in providing
more and more food. Ironically, this may worsen the problem. Not only may
such attempts lead to serious problems of oxygen depletion (Balarin and
Hatton 1979; Caulton, this volume; Hepher, this volume), but they may
exacerbate the basic problem. If we assume that the fish are responding to
what they perceive (by whatever means) as their invasion into a "vacant",
low-competition habitat, then providing ever more food may simply add
to that perception. Perhaps fish culturists should adopt the opposite strategy.
Some evidence for the success of this exists in the literature, but it does not
appear to have been fully appreciated or investigated (Hauser 1975; Balarin
and Hatton 1979).
We would predict that if one wanted to produce large fish, with late onset
of breeding (in ontogeny), and with a long interval of somatic growth, one
should do things to push the fish more towards a precocial life style. This
would mean that conditions should favor high intraspecific competition,
with relatively higher mortality (rate) for younger fish and a lower rate for
older individuals (see our previous discussion of the environmental conditions
associated with precocial life history styles). We predict, for example,
conditions such as restricted food, stable conditions over relatively long time
periods, and high population density should favor the precocial life style.
Some evidence from aquacultural practices supports this. For example, in
some cases, intensive stocking in aquaculture facilities has practically elimin-
ated reproduction and led to production of desirable (i.e., large body size)
fish in a relatively short time (Balarin and Hatton 1979). In fact, Allison et
al. (1979) found an inverse relationship between stocking density and
reproduction in S. aureus (but note the small tanks used by these authors
sean pound
(Sean Pound)
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