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7/14/2009 5:02:31 PM
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UCREFRP
UCREFRP Catalog Number
7774
Author
Desert Fishes Council, H., Dean A., ed.).
Title
Proceedings of the Desert Fishes Council Volume XXIV, 1992 Annual Symposium, 18 to 21 November, Mesa, Arizona.
USFW Year
1992.
USFW - Doc Type
November 18-21.
Copyright Material
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PROCEEDINGS OF THE DESERT FISHES COUNCIL 1992 - VOLUME MV <br />reached 31°C/87F°, fish would become very active, gilling faster, and taking forays to the surface where they <br />would skim their bodies along the surface. Perhaps this splashing cooled the water. After about 20 minutes at this <br />temperature the fish would calm down, but gilling rate would remain elevated. <br />First, I conducted a preliminary run by heating just one tank of 10 fish (see Table 2). Two fish died in control <br />tanks during this first week in aquaria. The average daily maximum temperature was 33°C/92°F. A total of three <br />fish died when the temperature reached its peak of 34°C/93°F, on the second and 4th days. Lockhart reported <br />similar results in 1980, when death occurred at 33.8°C/93F° for fish acclimated at 21.5°C/71°F. <br />The second run included all ten tanks and 100 fish, with tank treatment randomly assigned. Of the heated <br />tanks, the average daily maximum temperature was 32°C/90°F, and a total of 10 fish died. The highest overall <br />temperature reached during this run was 35°C/95°F, after which 5 of the 10 deaths occurred. <br />The third run included 4 adult tanks and one juvenile (or 1 year old). tank. The average daily maximum <br />temperature was 31°C/87.5°F, overall maximum for the run was 32/90°F, and no mortalities occurred during this <br />treatment. <br />There appears to be a direct relationship between average maximum temperature and mortality. Of the 13 fish <br />that died, the mean maximum temperature was 34°C/93 °F, while that of survivors was 31.5 °C/88.6°F, a significant <br />difference (t = -6.577, p < 0.01, df 53). <br />Mean <br />Trial Max Temp n Mort Max Temp <br />I 33.5°C 10 30% 34°C <br />II 32°C 60 16% 35°C <br />III 31°C 40 0% 32°C <br />Table 2 Results from experimental high temperature treatment for control of Ichthyophthiriasis, at <br />Dexter National Fish Hatchery and Technology Center during spring of 1992 (see text for further <br />explanation). <br />Discussion <br />No treated fish got Ich this year, however no control fish got Ich this year, either. Therefore, at best the results <br />of this experiment on the effectiveness of treating Ich-infected woundfm with heat are inconclusive. Some <br />explanations come to mind: It may be that the last malachite/formalin treatment finally did get rid of the parasite. <br />However, after so many unsuccessful trials, this is unlikely. Another possibility is that the usual procedure of <br />recirculating the raceway water gives the tomites a better chance of encountering a host. Continuous flushing (as <br />was done this year) may decrease the chance of such an encounter. Also, water quality would be enhanced by <br />continuous flushing, and therefore minimize that stress on the fish. <br />Although inconclusive about Ich, conducting this experiment did provide some additional insight into the <br />biology of these little-known fish. The woundfm's ability to withstand high temperature is surely an advantage in <br />the Virgin River system. Woundfin have been collected there at 36°C/97°F (Deacon, 1987). The maximum <br />temperature tolerated by woundfm in this experiment was 35'C/95 *F, while in Deacon's CTM experiment (1987) <br />it was 39.5°C/103°F. The difference in maximum temperatures obtained in these experiments may be explained <br />by the rate at which temperatures were raised. In this experiment, temperature was raised at an average rate of <br />0.03 °C per minute, while in Deacon's experiment it was raised 1 °C per minute. As woundfin can withstand higher <br />temperatures when raised quickly, this would imply a phsiological mechanism in place to buffer against the effects <br />of variable water temperatures. <br />Even with this thermal treatment and intensive handling this year, the fish still spawned. On the first days of <br />treatment I observed spawning behavior in the aquaria, and after all fish had been cycled through the primary <br />holding aquarium, I found fry. Since the last adults were removed from that aquarium on June 7, the fry were <br />spawned sometime prior to that. On July 7, fry were dipnetted from the raceway of treated fish. This continued until <br />Sept 23, for a total of 257 fry from treated fish. It is possible that some fry could have escaped our nets, making <br />this recruitment number a conservative one. Only 1 fry was observed in the raceway of untreated fish during the <br />same period. At Dexter National Fish Hatchery, fry are usually collected between May 18 and June 20 (DNFHTC <br />files), a period of 4 1/2 weeks. This year's experimentally delayed spawning season was at least 15 weeks long, <br />and therefore the longest recorded season of production at Dexter. Although Lockhart (1980) found peak gonad <br />35
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