I have a crowd simulation with a shark going through a shoal of fish.
However there is this undesirable effect of the fish agent getting bumped around by hundreds of little fish, and so it's motion becomes rather jerky with many sudden rotations.
Is there a way to make it stay on it's path and direction without the jerkiness?
Once again, it is impossible to google search what I'm looking for (google searches for specific houdini issues don't work at all for me) so I have to ask some intelligent people directly!

I don't think you even need the crowd system for that. Make the shark a collider for the fish, then their particle system will avoid the shark traveling on a path.