Do fish move

[Chris Gearhart]

Does anyone know how trout behave in dirty water. Do they move to seek out clear water? How about feeding? Is it simply a matter of visibility?
Chris

[ptychocheilus]

A friend of mine at WVU was studying this in brook trout. There's a large body of scientific literature out there on the subject, that distills down to this...

Trout still feed at very high turbidity levels, but their ability to select food items decreases, and the distance at which they detect prey items decreases (duh!) as they switch over to olfaction and lateral-line. They can feed on even tiny chironomids in zero-vis turbidity or complete darkness, but with a correspondingly lower reaction time and detection distance. This drives a switch from drift feeding to active searching and/or feeding off the substrate as turbidity increases (the fact that part of the lateral-line canal system runs along each side of the lower jaw should make you think).

Local movement rates increase, but likely more as a result of the change in feeding strategy. That said, there's a lot of variation in behavior, both between species and between individuals of the same species. While fish may not be actually moving to clear water, fishing seams of clear water where tribs come in may be more productive just because it doesn't require you to bonk them on the nose...