SIBLING CANNIBALISM IN DORADA UNDER EXPERIMENTAL CONDITIONS. I. ONTOGENY, DYNAMICS, BIOENERGETICS OF CANNIBALISM AND PREY SIZE S

SIBLING CANNIBALISM IN DORADA UNDER EXPERIMENTAL CONDITIONS. I. ONTOGENY, DYNAMICS, BIOENERGETICS OF CANNIBALISM AND PREY SIZE SELECTIVITY

E. Baras, M. Ndao, M.Y.J. Maxi, D. Jeandrain, J.P. Thomé, P. Vandewalle, C. Mélard-2000

Journal of Fish Biology, 57 : 1001-1020

Abstract:

Cannibalism among sibling dorada Brycon moorei started before the yolk sac was completely absorbed, as soon as oral teeth were completely developed (1.2 mg fish, 21 h after hatching, 39 h after fertilization at 27.0 +/- 0.5°C under 12L:12N). Embryos attacked siblings of equivalent size or slightly larger than themselves, which were incompletely ingested, sucked up to the head and regurgitated (type Ia cannibalism). Two-day-old larvae performed complete ingestion but could not digest the head of their prey, which was regurgitated (type Ib cannibalism). One day later, all cannibals had turned to complete (type II) cannibalism. Type II cannibalism persisted during the larval period (ending c. 144 h after hatching, 26-38 mg fish) and the early juvenile stage (15-30-g fish). The logistics of type II cannibalism (maximum prey to cannibal weight ratio, W_p : W_c in percent) was modelled as 11.9607 W_c^-0.3429 (r²=0.974, P<0.0001), where W_c is the body weight of the cannibal (g), indicating that cannibals had to turn to increasingly smaller prey during their ontogeny. When being offered prey of different sizes, cannibals of all sizes (0.04-27 g) preferred the smallest prey available almost systematically. A shortage of prey of appropriate size caused them to turn to larger prey, and eventually to exert incomplete cannibalism over siblings exceeding the maximum W_p : W_c ratio. Cannibals could ingest extremely high food rations [R_max (% W_c)=47.4242 W_c^-0.4002; r²=0.906, P=0.0126], and showed extremely fast growth (G [% day-1]= -2.5895+0.5194 R-0.0007 R²; r²=0.974, P<0.0001). These traits caused cannibalism in dorada to be the earliest and most intensive ever reported in fish (95-98% fish cannibalized within the first week, of which c. 40% on the first day). The functional, adaptive and evolutionary implications of early predation and shifts between types of cannibalism in dorada are discussed.

(Aquaculture Research and Education Centre, University of Liège, 10 Chemin de la Justice, B-4500 Tihange, Belgium, Tel: +32 85 27 41 56, fax: +32 85 23 05 92, e-mail: E.Baras@ulg.ac.be)

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