Agonistic behaviour and growth in the European eel,Anguilla anguilla L., in relation to warm-water aquaculture*

Agonistic behaviours were studied at high densities and in tournament experiments with pairs of small eels with and without prior isolation. Although innate differences probably exist, eels appear to learn their average positions in diffuse social and size hierarchies from the outcome of repeated agonistic encounters. Dominance or avoidance were most marked when the larger fingerling eels were about 1.5 times the body weight of the smaller. Larger eels tended to attack more readily, be dominant in threat encounters, be less active and spend less time swimming high in the water, consume more food, and show higher growth rates and lower mortality. Implications for warm-water aquaculture are discussed, and practical management techniques to minimize mortality and maximize productivity are suggested.