The invention relates to a collection device for collecting sludge such assunkenparticulate waste and dead fish from an aquaculture cultivation unit such as afishcage positioned in the sea. The collection device comprises a collection headat thebottom of the cage for collection of sunken sludge and sunken farmedorganisms,the collection head comprises a funnel formed top plate wherein the sunkensludgeand fish are collected in or in vicinity to the lowest point of the funnel. Itfurthercomprises a first removal system for sunken sludge, having a first inlet forsludgeand small particles at the lowest point of the funnel-formed top plate, thefirst inletbeing provided with a retaining system for holding back the farmed fish, andin thatthe first removal system further comprises a first pumping system for removalof saidsunken sludge from the first inlet. Dead fish accumulated on the top plate areremoved by a second removal system and a second pumping system.
