Saltwater Copepods and Amphipods

The Little White Bugs in Your Aquarium

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It is not unusual at one time or another when keeping a saltwater aquarium to find tiny microscopic-like white bugs swimming or crawling all over your tank. What you are most likely seeing are Copepods and/or Amphipods. These are shrimp-like crustaceans that dwell in the substrate as adults, but during their larval and juvenile stages are most often free-swimming.

Because of the complex number of families, genera, and thousands of species contained within the Phylum Arthropoda > Class Crustacea > Subclass Copepoda, and Subclass Malacostraca > Order Amphipoda / Order Amphipoda groups , we are not going into detail about the taxonomy of these organisms, but here are some basic facts about these tiny crustaceans.

Saltwater Copepods and Amphipod Basics

  • There are both pelagic (free-swimming), and benthic (bottom-dwelling) bugs.
  • Copepods occur in all types of aquatic ecosystems; freshwater, estuarine (brackish) and marine.
  • Amphipods are mostly found in marine ecosystems, but there are some freshwater and terrestrial species.
  • They are just a few of the tiny animal organisms that make up zooplankton, which contributes to the makeup of plankton.
  • These creatures eat phytoplankton (tiny plants and algae that also help make up plankton), small microzooplankton (the division of zooplankton that is smaller than 200 microns, or 1/127th of an inch in size), and detritus.
  • Only a few of the thousands of species of copepods and amphipods known are carnivorous or parasitic, and these are rarely found in a saltwater aquarium system.
  • For many saltwater fish and other marine species, copepods and amphipods are a primary food source, both in nature and in captivity.
  • Because these tiny organisms are a natural part of the plankton food chain in the ocean realm, they are naturally going to occur in a saltwater aquarium environment. They are also micro-cultured as food for various species of adult marine animals, as well as used and tested as a food source in the research of culturing and rearing all kinds of tank-raised fry.
  • Copepods and amphipods most often appear in closed aquarium systems after live sand and/or rock has been added.

Fish and Other Marine Animals That Eat Copepods and Amphipods

From the Breeder's Registry Database, here are just a few reports that show how copepods and amphipods were used as a food source when hatching and rearing the following species of marine fry.

Here are other 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.

  • Mandarinfishes: Synchiropus splendidus, ocellatus, picturatus, stellatus, and Dactylopus dactylopus species.*
  • Actually Dragonets, Mandarinfish are members of the Family Callionymidae.
  • Sand Sifting Gobies*
  • Sleeper Gobies (Valenciennea sp.)*
  • Signal/Crab Eye Goby (Signigobius biocellatus)
  • Midas Blenny (Ecsenius midas)
  • Unlike most of its close relatives, this species feeds mostly on zooplankton, rather than algae.
  • Seahorses

Amphipods (Grammarids) are one of the main live food sources of adult Seahorses, as well as newly hatched fry. They will wrap their tails around something stable and then feast on them as they swim or float by.

  • Most Firefishes are planktivores and feed mainly on prey suspended in the water column, but may occasionally pick these bugs or other food off the substrate.
  • Most Angel, Butterfly, Hawk and Wrasse fish species spend their days picking small crustaceous life forms from rocks, corals, and the sand. Since copepods and amphipods are shrimp-like crustaceans, these types of fish do not consider them to be a primary food source, but may opportunistically feed on them to some extent when they are present.
  • Carnivorous Crustaceans
  • Many species of Shrimps, True Crabs, Hermit Crabs, as well as other crustaceans that are carnivores.
  • Carnivorous Invertebrates
  • Many SPS corals and other animals such as Gorgonians and other soft corals feed on plankton, as well as get nutrition from plankton byproducts.

Now don't get us wrong.

We are not suggesting you immediately run out and buy some of these fish. The ones that are marked with the * are species that feed on these little bugs as their primary food source. They are challenging to keep, require a well-established aquarium with a heavy bug population present to live on, or they may starve, and should not be kept with aggressive fish where they have to compete for food. They are definitely not good fish for beginners, or for newly started aquariums. Do your research and learn all about any of these fish BEFORE you consider keeping one. Their survival depends on you knowing how to properly care for them, and besides, some are not compatible with each other or may be harmful to other ornamental inhabitants.

So what do you do if your aquarium does not have a good bug population present to sustain these types of fish and you don't want to wait around until one develops, or their numbers are taking over the aquarium and you want to control or remove them?

If you do not want to wait around until your aquarium develops a good copepod/amphipod population to keep fish species that require these tiny crustaceans as a primary food source to survive, here are a few suppliers where you can buy them. These can be introduced directly into an aquarium or micro-cultured in another system, such as a refugium, and then harvested for feeding. You can also check out any local saltwater fish stores in your area, or browse these other livestock and aquarium product supplier's online stores to see if they carry these types of live foods as well.

How To Control or Remove Copepods and Amphipods

Even though considered a food source to some tank inhabitants, these bugs are considered no more than a nuisance to others. Sometimes when very large populations of these bugs are present in the free-swimming larval and juvenile stages, you may see fish in the tank shaking or shuddering.

This is because the bugs crawl around on the bodies of the fish, causing what you might explain as a tickling sensation that is annoying to them. This can become overwhelming and exhausting for the fish because they find it difficult to get any rest as they constantly move or dart around to keep the bugs off of themselves.

If this happens and you are concerned about your fish, and you do not have any bug-eating animals present in the aquarium to help reduce their numbers naturally, it may be necessary for you to take steps to control or thin them out. This can easily be accomplished by simply running a hang-on-tank type canister filter (read reviews compare prices) with a fine micron sleeve or pleat cartridge on the aquarium for a short period of time to filter the bugs out of the water.

Remember, these tiny bugs are a beneficial and natural part of a well-balanced aquarium ecosystem, and an important food source required by some species to survive! They aren't really hurting anything, and unless they are causing a big problem for the fish or other tank inhabitants, you shouldn't have to do anything about them. Once they grow to maturity, they will retire into the rocks and substrate of the aquarium.