Abstract: A fish grader having a boxlike frame with at least one barred side with a net attached outside the frame. The grader is placed in water and fish to be sorted are put in it. The smaller fish swim through the bars into the net, leaving the larger fish in the grader box, from which they can be released into a rearing enclosure.

Abstract: A cylindrical fish culture tank adapted for a self-cleaning operation. Oxygenated water, whether fresh, recycled, or a mixture of fresh and recycled, enters a tangential inlet near the bottom of the tank and develops an upwardly flowing spiral action. The spiral action, assisted by swimming movements of fish, causes solids to gravitate towards the center of the tank. The bottom of the tank is shaped as an inverted obtuse cone with a screened, normally closed drain opening in the center. At the top of the tank is a screened overflow drain, from which water is normally withdrawn for discharge or for cleaning and filtering. About once a day, the fish culture tank may be cleaned by removing the solids through the screened drain. An airlift assembly may be connected to the drain for recovery of live fish when the screen is taken off the drain. At transfer or harvest time, the live fish may be drained from the bottom of the tank and recovered.

Abstract: A net-raising tool for use in raising fish nets, either empty or laden with fish. A series of dull, net-engaging hooks are located at one end of each of a series of several parallel tines. The tines all lie in substantially a common plane, and the hooks are all in line. The tines are joined together by at least one cross-member. A handle member is provided, preferably spaced from the cross-members, preferably taking the form of a bar parallel to the rearmost cross-member on the opposite side from the tines. The handle bar may be joined to the cross-member by members perpendicular to both of them, so as to provide a hand-receiving and hand-protecting opening in between the handle bar and the rearmost cross-member.