On Wed, 23 Feb 2005 20:07:24 -0500, "NetMax"
wrote:

"David" wrote in message
.. .
Has anyone had any experience with small fish swimming over, or being
swept over, weirs? Do they generally tend to stay away from
unexpected fast-moving currents "into the unknown abyss", or do they
instead tend to like to play with "weir roulette"? I am specifically
thinking right now of mosquito fish, but if anyone has experience with
larger fish, that would be of interest to me as well.


Without a doubt, they play weir roulette. The extent varies by the size
of the water body (smaller=more jumps), the water conditions (bad=more
jumps), food conditions and if they see-feel-sense water or movement on
the other side of the weir. Think about salmon making their way upriver.
It's natural.

Well, that gives me a pretty good perspective. And it also tells me
that there aren't going to be any shortcuts. Your suggestion of a
matrix of decreasing grid sizes, preceding the weir(s), will provide
more positive control anyway -- when it's time to lower the
mosquitofish population, just remove the last grid screen and let them
find their way over the weir, into the next lower pool, and, alas, the
predators.

Building a filter box with a matrix of removable grid screens,
installed in front of the weirs, (and subsequent waterfalls), seems
like a pretty straightforward solution.

Again, thanks,
David