Question: Should a Clown Hang Vertically at the Top?

Answer:

In answer to the reader question:
"One of two recently acquired clowns is spending a lot of time in a vertical position at the surface of the aquarium. It does eat the flake food, but this behavior seems strange even for a clown loach. What would this indicate?"

Although it is not common to see a loach cruising the top surface of the aquarium, if any loach would be inclined to do so, it would be a Clown.

Clown loaches exhibit a wide range of behaviors, many of which aren't often seen in other fish. Lying on their side on the bottom of the tank is a common behavior, and frightens new owners into thinking they are sick or dying. Anyone who has owned a school of Clowns has seen them lounging about every which way in a giant pile, or seen them try to squeeze into impossibly small spaces.

Foods for Clowns
Despite their predisposition for unusual behavior, cruising vertically at the top surface of the water does seem rather odd. Are you providing sinking foods for your loaches? If you aren't, it's possible he's famished and is desperate to get at the food. Sinking carnivore pellets or shrimp pellets are great for clown loaches, as are frozen bloodworms and brine shrimp. They will even eat cooked peas (remove the skin) and zucchini.

As a precaution I'd test the water for ammonia. If you've recently added fish, you could have a small ammonia spike that is stressing the clown and causing the unusual behavior.

Loaches are particularly sensitive to water conditions.

Good luck with your clowns. They are one of my favorite fish, and I suspect they will quickly be at the top of your favorite list too.