So, I mentioned in the Oscar thread about stoning surgeonfish at the
aquarium.

We have a large number of surgeonfish, doctorfish and blue tangs
resident in the coral reef exhibit. We also have some groupers and a
lot of French and grey angelfish.

Some time ago, before I started diving at the aquarium in 2001,
someone discovered that these fish like to get stoned. I don't know
how this was discovered, though I can guess it came from observing
that some of them like to hover over places on the bottom where
incoming water creates a small fountain of the pebbles that line the
bottom. They lie close to the bottom and let the pebbles hit them. I
think it started with the groupers, specifically the red hinds, which
we currently don't have.

So probably someone wondered how they'd like having the pebbles
dropped on them from above.

Turns out they love it. The groupers would just lie on the bottom and
let you drop  the pebbles on them. Sometimes they would open their
mouths wide and flare their gill covers, just as they do on a cleaning
station in the wild. We deduced that the pebbles must have an effect
like cleaning, helping to slough off dead skin and possible micro-
parasites.

Pretty soon, the various surgeonfishes came round to investigate. A
bold few would swim under the stream of pebbles. Apparently liking the
sensation, they would turn on their sides to catch the pebbles and let
them run slowly off. Then the angelfish decided to join in the fun.
They would turn on their sides and catch the pebbles and channel them
to the base of their pectoral fin, which they would spin rapidly,
churning the pebbles before letting them fall off.

So stoning these fish has become one of our favorite jobs. Usually
it's after we've fed all the food, and there are enough people
scrubbing the decor to get the algae off. I like to just kneel on the
bottom and pick up handfuls of gravel, hold it up and let it cascade
from my hands. Within less than a minute, a dozen surgeons are
swirling around within the cascade, catching pebbles and then dropping
them to another fish below. They seem to get that they don't have to
be at the top of the pile and are happy to get "used" gravel.

I love doing that. It's totally relaxing, almost like meditating, and
it is one of many ways we get to interact with the animals in ways we
could never do in the wild (and wouldn't anyway). For some reason, the
visitors seem to enjoy it, too, though I'm sure it totally baffles
them unless an exhibit guide happens to be nearby to explain it. And
I'm not sure all the exhibit guides get it, either.

Of course, we can only guess why the fish are really doing it. The
cleaning theory makes sense, but who knows?

Whatever the reason, it's fun for us, and the fish seem to like it,
too.

gc