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PROCEEDINGS OF THE DESERT FISHES COUNCIL Numbers of woundf i n at Dexter NFH&TC, 1987-1992 4 1992 - VOLUME XXIV 3.5 2.5 n N C C U) 2 3 O. L f 1.5 0.5 87 Be 89 90 91 92 ® Spring ® Fall Figure 1 Year Number Location 1979 240 Virgin River, AZ 1981 395 Virgin River, AZ 1983 460 Beaver Dam Wash area, AZ 1987 235 Beaver Dam Wash area, AZ 1988 28 St. George area, AZ 1988 415 St. George area, UT 1988 1600+ St. George area, UT 1989 1060 St. George area, UT Table 1 Numbers of wild woundfin Plagopterus argentissimus collected in the Virgin River, and brought to Dexter National Fish Hatchery and Technology Center. Ich Ichthyophthirius multif lis Fouquet is a protozoan with worldwide distribution. It is more commonly referred to as the tell-tale symptom which it causes in infected fish: "white spot." Host death occurs as a result of osmoregulatory imbalance, secondary infections, and finally malnutrition. Small-scaled or scaleless fish are more susceptible to Ich than those with large scales (Post, 1987). In fact, most Ich research is conducted on catfish. The woundfm, too is essentially scaleless, and therefore particularly at risk. It is the only species of 16 presently at Dexter which is chronically affected. The protozoan life cycle lasts from 4 to 40 days, and is temperature dependent: at 18°C/64°F it is completed in 10-12 days. The embedded stage is called the trophozoite, which burrows into the epithelium of the host, ingesting tissue fluids and epidermal cells (Amlacher, 1970). In response the host produces extra epithelial tissue, which is the source of the white spots. Only recently has there been evidence of reproduction at this stage (Ewing et al, 1988). In general, a mature adult leaves the host. At this free-swimming stage, it is called a trophont, and is positively identified by the horseshoe-shaped nucleus (Meyer and Bullock, 1990). It then becomes submergent 33