Two experiments (I wid 11) were performed in drainable ponds. Yellow eels Anguilla anguilla (L.) were stocked in early June a t three biomasses: 10,20 and 60 kg*ha-1 in experiment I; and 10, 20 and 40 kg-ha-1 in experiment 11. The mean body weights were 27.0 and 24.2 g respectively. Glass eels were stocked only in experiment I1 at equal densities of 1600.ha-1. I n both experiments each biomass of yellow eel was combined in a factorial design with three cyprinid cornmunities differing in biomass and in species-and size-composition. The ponds were drained in autumn. The final body weights a t draining ranged from 25.9 to 63.6 g for yellow eel and from 3.9 to 8.8 g for glass ecl. The final body weights of yellow eel and of glass eel decreased with increasing biomass of yellow eel. No significant relation was found between the bream Abra3mis brarna (L.) biomass iind t'he growth of eel. The growth rates uf yellow eel and glass eel were posit,ively correlated in experiment 11. At higher biomasses of yellow eel the percentage females dccreased slightly. The recaptiirr rates of yellow eel in experiments I and I1 amounted to 69.4 i9.8 and 92.2 i 4 . 9 yo (mean i sd) respectively. The lower recapture rates inexperiment 1 were caused by the inihppropriate drttining technique used. The glass eels were recaptured with 75.0 k5.6 : & efficiency. The mitximiiin net production of yellow eel occurred a t a biomass of 20-40 kg.ha-L and amounted t o 19 kg.hn-1.