Notes on Costia Necatrix

Costiasis, or the disease produced by the flagellated protozoan ectoparasite, Costia necatrix, is of considerable importance in the artificial propagation of both warm- and cold-water fishes. In spite of its importance, costiasis seldom is accurately diagnosed probably because of the extremely small size and sedentary nature of the causative organism. A general resume of the specific diagnostic characteristics, pathology, and recommended measures for the prevention and control of Costia necatrix are presented. The application of available information concerning the parasite may eliminate effectively the losses of fish in hatcheries occasioned by it.