Abstract: A process for filleting unbeheaded fish, or beheaded fish with the collar bones still adhering to the body to be filleted conveyed tail forward comprises performing belly filleting cuts, back filleting cuts and rib cuts. The fillets are cut free by severing cuts, performed after the rib cuts, extending closely behind the collar bones, and inclined towards the roof or the skull, while leaving the collar bones and/or the head on the bone skeleton. An apparatus for filleting the fish comprises a conveyor for the fish, a pair of belly filleting knives, a pair of back filleting knives and a pair of rib knives. The axes of the rib knives are arranged almost parallel to each other and inclined in the feed direction of the conveyor. The rib knives are displaceable in the direction of their axes and connected with control means to raise them at least on the arrival of the abdominal cavity end of each fish.