Abstract: Apparatus for segregating, collecting and removing fish from aquarium tanks comprising a divider engageable in a tank to divide said tank into compartments, a window opening in the divider through which fish can be herded from one compartment to another and a closure panel removably engageable in overlying relationship with the window opening, an upwardly opening box-like receiver engageable in the tank and having a gateway in one side through which fish can be herded, a gate removably engageable in the gateway, means to releasably couple the divider and receiver with the window opening and gateway in register, the divider and the upper portion of the receiver being perforated to permit the free flow of water through and into and out of the divider and the viewer, the lower portion of the receiver being imperforate and defining a catch basin to retain a portion of tank water and fish when the receiver is removed from the tank.