Abstract: An improved aquaculture system is provided which, in various embodiments, utilizes a single integrated unit to perform the biologic filtering, aeration and degassing functions; has a fish tank with an integrated multiphase drain for removal of fecal solids and uneaten feed with minimum water loss, for removing most of the water from the tank to be processed and returned to the tank and for segregating and for then selectively removing moribund and dead fish from the tank, preventing their cannibalization by other fish in the tank; and a single integrated unit for performing degassing, aeration, gas concentration and reaction/separation functions. An improved biologic filter is also discussed.