Behavior

Most shrimp are omnivorous, but some are specialized for particular modes of feeding. Some are filter feeders, using their setose (bristly) legs as a sieve; some scrape algae from rocks. Cleaner shrimp feed on the parasites and necrotic tissue of the reef fish they groom. In turn, shrimp are eaten by various animals, particularly fish and seabirds, and frequently host bopyrid parasites. Shrimp behavior changes dramatically at night, and, as expected, the biggest changes take place at sunset and sunrise. During the day, juvenile shrimp move around in troops, packed solid, as many as 250 per square meter. They move together somewhat the way a school of fish moves, in unison. When threatened by a predator, they scatter the same way a school of fish scatters, confusing the predators and making it difficult for them to zero in on individual animals. The troops become much more compact as the number of light increases. At midday, you see the tightest troops. At night, when the predators can’t see them, juveniles scatter throughout their environment. During the day, the troops will break up and scatter about if there is substrate available, like mangrove roots or seagrass. When you look at how we do shrimp farming, it seems really odd. The only surface we provide is the bottom. Relative to the surface area that could be created in the pond, it’s a small fraction of what they would normally have in the wild. The same thing in the hatchery, we give them the bottom when they are looking for grass and roots.

Typically, juvenile shrimp are in shallow estuaries where the water is only five to fifteen feet deep, hanging under a root or on the backside of a seagrass blade. During the day, shrimp form troops and roam around the bottom of the pond looking for food. They move at a pretty good clip, especially the benthic species like stylirostris and vannamei, with the very largest shrimp at the head of the troop and the smallest shrimp at the back, or not really with the troop at all. The smallest shrimp are off in the shallows around the edge of the pond looking for food and protection. Within the troops, the competition for food is brutal. Obviously, the guys at the front of the troop get most of the feed. So if you don’t do a good job of dispersing your feed, those guys get most of it. When the sun comes up the troops are quite small, maybe only five or six shrimp in each, but as they start roaming around the bottom of the pond looking for food, they bump into other troops and unite. This process continues until you have some really big troops. At night, when the troop breaks up, and individuals move out on their own, the antennae are very active, sweeping forward like tentacles, searching for food. When the antennae lock on to a food source, they point directly at it and sometimes twitch. They can sense the extremely small electrical fields generated by the animals that live in the pond bottom. When they locate something, they move their antennae over the spot and then start digging. It’s tough to see what they pull out of the bottom because they tear it apart so quickly. They’re vicious little critters