It is a parasite of salmonid fish (salmon, trout and their allies) in the northern hemisphere and has mayflies as the alternate host.

The fish, mostly trout and juvenile salmon, acquire the worms by feeding on infected mayflies which are the alternate hosts of the parasite.

In the River Swincombe in England, the only mayfly in which the parasite develops is the sepia dun (Leptophlebia marginata).

[3] C. tenuissima is an annual parasite of fish, with the maturation of the nematode being correlated with the temperature of the water.

The eggs form part of the diet of many aqueous invertebrates but it is only when they are eaten by developing nymphs of mayflies that they can continue their life cycle.