Aquatic Invertebrates of Montana

Tubifex Likes it Cold

The evidence is mounting that in Montana Tubifex tubifex prefers cold water. This was unexpected to me, but it may be important in explaining some patterns in whirling disease across the country and within smaller areas. I guess it should not be too surprising that our marginal trout streams might be unfit for whirling disease, but it seems ironic!

What is the evidence

1. It is almost universally present in our cold springs (temperature below 60F all year).
2. It is so far universally absent in our warm springs (temperature above 70F all year). Warm springs often provide very good worm habitat and frequently harbor representatives of other tubificid species.
3. I could not find it anywhere in Montana's very warm prairie streams, ponds or lakes even though some of the habitats and communities looked very suitable for it.
4. In some of our warmest trout rivers, Tubifex may be very abundant during the winter and spring, but it largely disappears with high water and does not come back until the temperature drops in the autumn. This is long after the restoration of the mud habitat zone if it were washed out.
5. Within warmer areas of the state, Tubifex often become abundant in the cold tailwaters below tall dams. At 2 of these sites, the Bighorn River below the afterbay dam of Yellowtail Dam and the Missouri River below Holter Dam, it is also clear that Tubifex decreases going downstream into warmer water even though the mud habitat is abundant and the community is not so rich as to expect Tubifex exclusion.
6. From the literature, T. tubifex appears to be uncommon in the southern states and widespread and common in the northern states. It is also more common in the deeper parts of many lakes.

What might this explain

1. Why the disease varies so much across the country.
2. Why high water years often have higher infection rates in the young fish.
3. Why the disease does not spread quickly into downstream warmer areas.

Recommendations

1. The seasonality of Tubifex abundance should be correlated with temperature along the cool-to-warm transition zone in large trout rivers where the disease is present and simultaneously correlated with the fish infection rate.
2. At the same time, the effect of temperature on the production, release, survival and infective ability of the "Triactimomyxon" stage by the worm should be studied in the lab. If trout like it cold and Tubifex likes it cold, it seems reasonable that the parasite might also have some warm water limitations. These will be very important in modeling the disease in various habitats.

Management Implications

1. Some regulated rivers might have discharge options that might shorten the "Tubifex" season or the "Triactimomyxon" season and decrease fish infection rates once the details are understood.