Sibling cannibalism in dorada under experimental conditions. II. Effect ofinitial size heterogeneity, diet and light regime on early cannibalism

Cannibalism among embryos and larvae of Brycon moorei (Characidae) occurs d uring daytime and night-time, and persists under permanent darkness. Embryo s and larvae of dorada provisioned with formulated feed over the first week of exogenous feeding did not survive, except for those exerting cannibalis m. When offered alternative fish prey [embryos of Prochilodus magdalenae (0 .5-0.8 mg) and Oreochromis niloticus (9-10 mg)], I-day-old embryos of dorad a preferred preying on these, thereby reducing early cannibalism. However, this promoted depensatory growth and more intense cannibalism later in the larval stage. Dorada provisioned with Artemia nauplii in excess showed more homogeneous growth and higher survival, most cannibalistic acts being rest ricted to the first 24 h of exogenous feeding, just after oral teeth were f ully developed (21 h after hatching). Provisioning dorada with Artemia naup lii a few hours before their oral teeth were fully developed reduced early cannibalism from 41 to 15%. High proportions of deformed fish caused higher mortality, both directly and indirectly, as they promoted early cannibalis m, depensatory growth and more intense cannibalism among larvae. The initia l sorting of embryos, based on their occupation oh the water column improve d survival significantly during the first week of exogenous feeding, up to 52% in progenies containing <10% of deformed fish. Size-grading of larvae a nd young juveniles over the next 2 weeks reduced cannibalism to 2.6 and 1.9 % day(-1), in the first and second weeks, respectively. These results indic ate that cannibalism in dorada can be mitigated efficiently through appropr iate rearing procedures, and open promising perspectives for the intensive culture of this fast-growing tropical species. (C) 2000 The Fisheries Socie ty of the British Isles.