Effects of Removal of Fins upon the Growth and Survival of Spiny-Rayed Fishes

fish for the purpose of identification has long been a standard practice in fishery investigations. There are two principal purposes for which it is employed. For one thing, the quantitative survival of young fish to catchable size has excited much interest, as only when this is known is it possible to estimate the benefits that will accrue from stocking a body of water with extra young. Quite commonly nowadays a part or all of the fingerling fish that are planted in the course of regular fish-cultural procedure are marked by removing one or more fins. The other important use of fin clipping is in studies designed to tell the annual survival rate, rate of exploitation, and actual abundance of natural populations of fishes of commercial or usable size. Technically, the most important difference between the two kinds of experiment just mentioned is that in the first case fish from an outside source are used, whereas in the second, native inhabitants of the body of water are employed. In addition, experiments designed to test the effectiveness of planting hatchery-reared fish usually have to deal with rather small specimens, whereas population studies are usually concerned chiefly with stock of moderate to large size. In either situation, any extra mortality caused by the marking procedure can have a distorting effect upon the results obtained. Such extra mortality can be divided into (1) mortality from infection, loss of blood, or rough handling involved in the marking process itself; and (2) continuing mortality which results from some disability which the fish suffer as a result of the absence of the fin, even after the wound is completely healed. In general it appears that removing a fin or fins usually has no immediately fatal effects upon either large or small fishes of the kinds that have been most used in marking experiments. (In North America salmonids and centrarchids have been used oftenest.) This has been found by keeping some of the marked stock under observation for a few days or weeks after marking and comparing their mortality with that of unmarked specimens. Usually n ither group suffers any significant loss.