Do you have tiny white "bugs" swimming in your saltwater aquarium? You are probably seeing copepods or amphipods. These tiny, shrimp-like crustaceans dwell in marine substrate as adults, but during their larval and juvenile stages, they swim freely through the water. Copepods and amphipods most often appear in aquariums after live rock or sand has been added. You can keep and cultivate them for fish food or remove them from your tank.
Benefits of Saltwater Copepods and Amphipods
Because these tiny organisms are endemic to the ocean, they are considered natural inhabitants of a saltwater aquarium environment and are not harmful. For many saltwater fish and other marine species, copepods and amphipods are preferred foods, both in nature and in captivity.
Your fish can benefit from the presence of copepods and amphipods as a supplemental source of nutrition, but you may not want to rely on the naturally occurring population of these crustaceans as your primary food source unless you're interested in culturing your own.
Fish that Feed on These Crustaceans
According to a breeder's registry database, copepods and amphipods are used as a food source when hatching and rearing gobies, seahorses, and octopus.
Some fish rely on these sea bugs as their primary food, such as mandarinfish (Synchiropus splendidus, S. ocellatus, S. picturatus, S. stellatus, and Dactylopus dactylopus), sand sifting gobies, and sleeper gobies (Valenciennea spp.).
There are quite a few species that actively pick at live rock and sift the substrate in search of these tasty little morsels, which in turn helps to naturally control their populations in a saltwater aquarium or reef tank system:
- Midas blenny (Ecsenius midas)
- Adult seahorses
- Most angel, butterfly, hawk, and wrasse fish species
- Carnivorous crustaceans
- Shrimp, true crabs, hermit crabs
- Many small polyp stony corals, gorgonians, and other soft corals that feed on plankton and plankton byproducts
Most of the saltwater fish that strictly require these crustaceans for food are challenging to keep. They require a well-established aquarium with a consistently high copepod and amphipod population. With an insufficient food population, they may starve.
So what do you do if your aquarium does not have a good crustacean population present to sustain fish that require them and you don't want to wait around until one develops?
There are a few suppliers where you can buy copepods and amphipods. These can be introduced directly into an aquarium or cultured in another system, such as a refugium, and then harvested for feeding.
Removing Copepods and Amphipods
Even though these sea creatures are considered a food source for some aquarium inhabitants, some aquarists consider them a nuisance.
When large populations of free-swimming larval and juvenile copepods and amphipods are present, you may see fish in the tank shaking or shuddering. This is because the crustaceans crawl on the fish and tickle them. Even though this isn't dangerous, it can become overwhelming and somewhat stressful.
If this happens, and you are concerned about your fish, you can add a hang-on-tank type power filter with a fine micron sleeve to the tank. A canister filter with a pleated cartridge will also work. These types of filters will sieve the crustaceans out of the water.