A device for gradual breaking of stratification in deep fish culture reservoirs

Water bodies in the tropics and subtropics develop thermal stratification d uring the summer. The deeper water layers keep a lower temperature and do n ot mix with the upper layers, resulting in depleted oxygen and accumulation of toxic metabolites. In fish culture reservoirs this leaves a considerabl e volume of the water body unavailable for the fish and endangers them when stratification breaks up and the whole water column mixes. To gradually br eak seasonal stratification in a controlled way, a device based on an under water propeller which vertically transports oxygen rich warm water of the u pper layers down to the anoxic and relatively cold deep region was assemble d. The first results obtained in an Israeli fish culture and irrigation res ervoir are presented herein.