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ABSTRACTS OF PRESENTATIONS IN ORDER PRESENTED
<br />and secretes a cyst wall within 2-6 hours. While encysted, the tomont divides mitotically forming hundreds or
<br />thousands of new motile, infective units, called tomites. The tomite stage of this obligate parasite must encounter
<br />a fish host within 48 hours or die (Post, 1987). All ich treatments are directed at this free-living life stage, as both
<br />the encysted and the embedded stages are much more resistant.
<br />Woundfin at Dexter
<br />The hatchery water is supplied by a number of shallow wells, with pH of 8.5, 3500 mg/1 of total dissolved
<br />solids, and constant temperature of 18°C/64°F. Woundfim at Dexter NFH are typically maintained in 12 m
<br />raceways, and do not spawn until the water reaches above 21°C/70°F. To achieve that temperature during the
<br />spawning season (usually April-May), the raceway water is usually recirculated via pumps, and the inflow of cool
<br />well water is decreased. Prior to this year, when an Ich outbreak was noticed, the fish were treated with a Malachite
<br />Green/Formalin bath daily for 10-14 days (DNFH notes). Malachite has a very small margin of safety between host
<br />and parasite toxicity (Cross, 1972), and mortality does occur. Dosages were adjusted for woundfin, and each Ich
<br />outbreak was treated accordingly and eventually dissipated for a time. However, Ich seemed always to return. Either
<br />the fish continued to harbor the parasite through each successive treatment, or Ich reinfection occurs every year.
<br />In the fall of 1991, the Federal Drug Administration (FDA) banned the use of Malachite Green at federal
<br />hatcheries, citing its oncogenic, teratogenic, and mutagenic properties. The FDA also banned the use of formalin
<br />for all but a few species, for only a few specific uses. Since our chemical arsenal against Ich was now emptied, we
<br />had to find alternative treatment methods.
<br />Many non-chemical treatments have potential for treating Ich. These include filtration (with mesh size that must
<br />effectively screen out particles the size of Ich tomites, < 1 mm); radiation with ultraviolet light (at 100,000
<br />microwatts/second/cml); ozonation; pasteurization; and treatment with temperature extremes. The critical thermal
<br />maxima of woundfin is very high, even for a desert adapted fish (Deacon et al., 1987). As the temperature was
<br />quickly raised, it did not lose equilibrium (which would lead to death in the wild) until the water reached
<br />39.5°C/103°F. Ich dies at 32°C/89.5°F (Meyer, 1984), stops reproducing at 30°C/86°F (Dr. Nick St. Erne, DVM,
<br />pers. comm.), and does not infect new fish at 29.4°/85°F (Johnson, 1976). Based on these findings, it was decided
<br />to try heat as the non-chemical alternative with which to treat Ich.
<br />Methods
<br />Early this spring, in an effort to avoid Ich in the first place, none of the aforementioned techniques were used
<br />to warm the water. Instead of recirculating between raceways and decreasing the inflow, the inflow of cool water
<br />was left open. With flow-through well water, the temperature in the raceways does not get above 20'C/68 *F even
<br />in the summer. Ich was not observed by May, but neither was any spawning behavior. Lockhart (1980) suggested
<br />that woundfin live = 2.5 years in the wild. Since the majority of adults at Dexter are 3-4 years old, and this spring
<br />was possibly their last spawning season, it was decided then to increase the temperature, and the water inflow was
<br />cut down. This would allow spawning to occur, and enable us to try heat treatments as a prophylactic to the
<br />inevitable (Hamman, pers. comm.) spring Ich outbreak.
<br />From the raceways, most fish were brought into the holding house and held in 70-gallon aquaria; the remainder
<br />were left outside as a primary control for this stage of handling. The holding aquaria were maintained at
<br />23°C/73°F. The treatment tanks consisted of 10, 10-gallon aquaria, each with an airstone and a heater. Ten fish
<br />were placed in each tank and allowed to acclimate for 3 days. Temperature was then raised and lowered in each
<br />of the treatment tanks daily for 5 days (van Duijn, 1967; Amlacher, 1970). The temperature was gradually brought
<br />up from 23°C/73°F to at least 31°C/88°F during the course of a day, using 300-watt, thermostatically controlled
<br />Visitherm®* heaters, and monitored at two hour intervals. The water temperature was then lowered to the
<br />acclimation temperature during the course of 30-60 minutes by making a series of partial water changes. Cross
<br />(1972) suggested that changing water may in itself be a treatment (separating the host from the infective stage of
<br />the parasite). To test this possibility, two tanks in each trial were held at constant temperature and water changes
<br />were made daily. As an additional control, two tanks in each trial were not manipulated at all. Mortalities were
<br />recorded, and the maximum temperature tolerated by survivors was compared to that of those that died, using
<br />ANOVA. After the 5-day treatment, fish were transferred to 70-gallon aquaria. They were held there for
<br />observation before being released into a disinfected raceway. Eventually, all adults (except the primary raceway
<br />controls) and 10 juveniles were subjected to the treatments.
<br />Observations and Results
<br />Woundfin behavior changed when subjected to temperature increases. Dissolved oxygen also varied with
<br />temperature, from 83 to 75 % saturation at temperatures 23-31.5°C/73-89°F, respectively. When the water first
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