Clams in general startle very easy. They are sensitive to changes in light and tactile stimulation, so the traditional methods of feeding (mostly perpetuated on the Internet) are generally too intrusive. For example, you may be familiar with the method of feeding clams that includes covering the clam with half of a 2-liter soda bottle and filling that isolated area with phytoplankton. Even more primitive techniques are still common, like using a baster or syringe to “shoot” food at a clam.
In theory, the idea is to isolate a food-rich area without spreading the food to the rest of the aquarium. In practice, though, this just bothers the clam by changing light levels and providing tactile stimulation, and most of the time the clam just closes up to avoid the new stimuli. By the time the clam opens again and begins to feed, the food has dissipated, and the clam has expended energy unnecessarily with a defensive response. Over time, this could weaken the clam and potentially cause it to starve.
There aren’t really a lot of visible signs of an “irritated” clam, other than that it won’t stay open fully, and the mouth opening of its siphon either isn’t open normally or is “gaping” really wide. Ideally, hobbyists should just add food into a high-flow area so that it will stay in suspension long enough for the clam to capture it. An established system should be able to process and accommodate that much food.
Want to read the full story? Pick up the September 2010 issue of Aquarium Fish International today.