Blood parasites of fishes are represented by eight species of Protozoa, one species of Trematoda (Sanquinicola) and one Nematode (Philometra). These are listed as representative of this major problem for fish biologists. Most are often overlooked due to the limiting effect most have on the host. Each example is discussed with the authors experience for the laboratory work on the parasite. Included is some of the recent research and studies relative to each sample.