One. ha38 1P3 Taggart, C. 8. 1984. Hypolimnetic aeration and zooplankton distribution: a possible limitation to the restoration of cold-water fish production. Can. I. Hypolimnetic aeration of a 1.23-ha eutrophic kettle lake during two consecutive summers increased [Qzl to more than 4m@L in the hypolimnion for extended periods. This improvement did not lead to the expected development of crustacean populations in the previously anoxic, zooplankton-deficient hypo. Bimnion. The rotifer Fdinia longiseta was the only zooplankter present, as isolated populations, in both the epilimnion and hypolimnion during summer. Eighty percent of the summer zooplankton community occurred exclusively in the epilimnion, and this was related to the development of an anoxic and toxic metalimnion that restricted migration from the epilimnion to the hypolimnion. Confinement of the zooplankton to the epilimnion coupled with predation by fathead minnows (Pirnephales promelas) appeared to be responsible for the change in the zooplankton community from large cladocerans and copepods to smaller species. This study suggests that hypolimnetic aeration as a means of restoring or enhancing the production of cold-water fish may be thwarted by the development of a stable anoxic and toxic metalimnion that precludes the development of the zooplankton food resource.L'aeration hypolimnetique d'une marmite eutrophe d'une superficie de I ,23ha durant deux etes consecutifs eut pour effet d'augmenter [Q2] a plus de 4mgL dans Ifhypolimnion pendant de longues periodes. Cette amelioration n'a pas cause le d6veloppement anticipe des populations d e crustaces dans un hypolimnion pauvre en zooplankton, precedemment anoxique. ke rotifere Filinia longiseta etait le seul zooplancton present, en populations isolees, a la fois dans I'epilimnion et l'hypolimnion en kte. Quatrevingt pour cent des communaut6s zooplanctoniques estivaies ont 6te trouvees exclusivement dans l'epilimnion, et ceci a ete attribue a la formation d'un m$ta%imnion anoxique et toxique, imposant des restrictions a la migration de I'epilimnion vers I'hypolimnion. k'emprisonnement du zooplancton dans !'epilirnnion, joint a la predation par le t6te-de-bouie (Pirnephalesprsrnelas), semble avoir ete responsable du changement qui s'est produit dans la communaute zooplanctonique, depuis de gros ciadoceres et copepodes a des especes plus petites. Cette etude donne a penser que l'aeration hypolimn6tique comme moyen d e retablir ou d'amkliorer 12% production d e poissons d'eau froide peut 6tre limitee par la formation d'un metalimnion anoxique et toxique stable empechant le developpement de B a ressokerce aiimentaire zooplanctonique.