8010 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I (Trichophyra sp.), columnaris (Flexibacter columnaris), black grubs (Neascus sp.) and myxosporean (Myxobolus sp.) take a heavy toll on fish held at Horsethief. The fish often suffer the additional stress of sunburn when they are ill and swimming near the surface. Prophylactic treatments of salt, formalin, or CWoramine T offer some benefits and are done regularly when handling fish, and at first sign of disease. Nitrogen supersaturation has also been a problem in the past, because the river water is supersaturated with nitrogen before it is pumped into the ponds. This becomes a major problem when the ponds ice over and the nitrogen is trapped in the water. Nitrogen supersaturation has been managed with the use of aerators and reducing the inflow rates to 1 00 gallons per minute or less. The reduced flow rate allows the aerators to release the nitrogen and oxygenate the water. Predation by herons, coyotes, and other birds and mammals is another problem that arises at Horsethief The predation is often dependant upon disease as predators would not normally have access to healthy fish. When the fish become ill and begin to succumb to a malady, they swim or float to the surface and eventually to the edges of the pond where predators have access to them. This often hides the severity of disease outbreaks as there are no dead or moribund fish to expose the problem. When this happens, no treatment is administered and the problem worsens. Problem animals have been removed from the area. Four of the ponds at Horsethiefhave been covered by nets to reduce avian predation. 24-ROAD HATCHERY 1996 In May of 1996, razorback brood stock from HorsethiefPonds were spawned and the eggs were transferred into the 24 Road Hatchery and acclimatated. The eggs received a 1,667 ppm formalin bath for fifteen minutes every day until hatch to avoid fungal growth. The razorbacks hatched and began feeding 3 to 5 days after spawning. A total of 13 family lots of fish hatched; 10 for brood stock and stocking and 3 for selenium studies. Hatching success varied from 3% to 95%. Over 29,500 fish were hatched from the 13 lots (Tables 2-3). Razorback suckers are thought to be able to imprint on synthetic chemicals (Scholtz et al1994), therefore different lots of eggs were subjected to two imprinting chemicals. Some eggs were placed in water treated with 0.056 ppm phenethyl alcohol and some in water with 0.000056 ppm morpholine (Table 3). After hatching the razorbacks were put in tanks without imprinting chemicals and the tanks with chemicals were drained. After hatching, the fish were fed a razorback diet prepared by Rick Barrows, USFWS, at the Bozeman Fish Technology Center. This razorback diet was produced in an effort to reduce -13-