Size heterogeneity,
cannibalism and competition in cultured predatory fish
larvae: biotic and abiotic influences
P. Kestemont, S.
Jourdan, M. Houbart, Ch. Mélard, M. Paspatis, P. Fontaine, A. Cuvier, M.
Kentouri, E. Baras
Aquaculture, 227(1-4): 333-356
Abstract:
Growth heterogeneity is a central problem in
larviculture and especially in predatory species. It can be influenced by a
wide range of intrinsic and environmental factors, of which the respective
influences are largely unknown. The role of non-interactive (temperature,
day length, light intensity, food availability and composition) and
interactive factors (stocking density, initial size heterogeneity, hatching
time) on growth, survival and size heterogeneity was measured in larvae and
post-larvae of the European seabass Dicentrarchus labrax and Eurasian
perch Perca fluviatilis. Embryos hatching later than others were
found less competitive than those hatching earlier in both species, but to a
greater extent in perch. By contrast, the final size heterogeneity in both
species was independent from the initial size heterogeneity or recurrent
size sorting. High stocking density had a positive effect on perch larvae,
no effect on seabass larvae and a negative impact on the post-larvae of both
species, owing principally to density-dependent access to food. Day length
and light intensity produced contrasting results in larvae and post-larvae.
Larvae of both species performed better under bright light and continuous
day length. Post-larvae of seabass performed equally well at different light
levels but did better under short day lengths, whereas post-larvae of perch
were unaffected by day length but performed better under reduced light
levels. Increasing food availability resulted in increasing performance of
perch larvae, although cannibalism was higher for submaximal than for
maintenance rations. The similarity between the two species at the larval
stage, and differences at the post-larval stage can be accounted for by the
increasing specialisation towards specific environments and niches.
Regarding the impact of rearing factors on growth, survival and size
heterogeneity, interactive variables impacted essentially on growth and
survival, whereas size heterogeneity was chiefly influenced by
non-interactive variables, either directly or indirectly via interactive
mechanisms such as cannibalism and size-dependent mortality.
(The University of Namur, Unit of Research in
Organismic Biology, 61, rue de Bruxelles, B-5000, Namur, Belgium, e-mail: patrick.kestemont@fundp.ac.be)