The long-term survival of fin-clipped and unmarked rainbow trout was studied in Castle Lake, California. The results of this study confirmed the generally held belief among fishery workers that fin removal has a serious detrimental effect on fingerling salmonids. Moreover, the relative magnitude of this effect for each of the seven fins that could be removed was determined; viz.: (1) removal of the adipose fin may reduce survival by as much as 50%, (2) removal of a ventral fin may reduce survival by as much as 60 to 70%, (3) removal of a pectoral or dorsal fin may reduce survival by as much as 70 to 80%, and (4) removal of the anal fin may be no worse than removal of the pectoral or dorsal fins, but can have an inconsistent effect. The absence of a single fin did not reduce significantly the rate of growth of the members of a group possessing that mark.