Reef aquarists frequently talk about copepods. They are generally viewed as a positive thing for a saltwater tank, and they are an important food source for many fish, most notably the mandarin fish, seahorses and some crabs.

Today we'll take a deep dive into the world of copepods, no pun intended.

Male tigger pod, a euryhaline and eurythermal copepod.
r2rTigriopus californicusMale.jpg

This photo is from the Reef2Reef archives courtesy of @Reef Nutrition ©2019, All Rights Reserved.

What are copepods?

Copepods are tiny crustaceans that inhabit wet environments. They can be found in freshwater lakes and rivers, brackish environments, saltwater environments at all ranges of salinities, and even on land in anything wet, boggy, or swampy.

They range in size from about 1mm to about 30mm, but most are in the 1-2mm range. They have a hard exoskeleton, but they're so small that the exoskeleton is typically very thin and clear. Like many other crustaceans, copepods regularly molt as they mature to adulthood.

Some have one eye in the middle of their...foreheads, and some are blind. Some live a pelagic or planktonic life in the water column and others are benthic, making their home on the substrate.

There are at the time of this writing about 14,000 known copepod species and about 20 percent of them are found in freshwater habitats.

Most are teardrop or torpedo-shaped and swim very well.

Next, let's take a look at taxonomy.


A brief look at copepod taxonomy.
maldives-island-with-gorgeous-turquoise-water_7kIyX4 (1).jpg

Image courtesy of @Seawitch ©2019, All Rights Reserved.

If we stop and look at the family tree, we see that copepods are distantly related to critters like spiders, that share the same phylum, Arthropoda, and more closely related to creatures like lobsters, that share the same subphylum, Crustacea. Barnacles, which share the class, Hexanauplia, would be like kissing cousins.


Copepods have been remarkably successful at adaptation. I don't dare use the word intelligent, but they are definitely well suited for their environments and have some pretty amazing characteristics.

They are dioecious, with males and females. How males and females find each other in the vast ocean to reproduce is awe-inspiring. They don't see that well, and they can't hear, yet they can sense movement near them of predators, prey, and potential mates.

Copepods have an incredible ability to evade predation and jump out of the way, fast and far, in the water, by being able to sense both physical/mechanical and chemical changes in the water column around them.

Some copepods are herbivores and eat algae, microscopic algae that is. Some are predators that will eat smaller copepods or other microscopic creatures, and some will eat waste and detritus. Some will eat a combination of the above food sources.

What I didn't know when I started writing this was that some copepods are parasitic and live off of other livestock such as fish or bivalves. Yes, they're not all beneficial for all involved.

We frequently refer to the Cirolanid isopods as the scourge of reef aquarists, but apparently not all copepods are your friends.

So, while some copepods can be used to control, for example, mosquito larvae, other copepods can even be vectors for disease transmission.

Sometimes efforts are made to control the copepods which might be carrying something that causes disease in humans or fish. e.g. dracunculiasis or Guinea worm disease (GWD) is controlled and monitored in Vietnam by treating drinking water to specifically eliminate copepods.

When drinking water isn't filtered (like in New York City) there can be copepods in the drinking water. At one point, this created a problem with the orthodox Jewish population in Manhattan, as it wasn't clear if the presence of copepods made the water unkosher. But I digress.

Copepods have several specific, discrete, and well-defined life forms as they mature to adulthood. Because of this--and because they are small, hardy, and have a relatively short lifespan--they are frequently studied to determine an environment's biodiversity and/or ecotoxicity.

Home-raised phytoplankton--good for feeding copepods.

This photo is from the Reef2Reef archives courtesy of @Tonii ©2019, All Rights Reserved.

The marine aquarium

Marine aquarists like copepods. It's possible to culture them separately as a food source for your tank (think mandarin fish), and if offered a place to reproduce without predation--like in a refugium--most copepods will be happy to oblige and give you a steady and sturdy population. Keep in mind that if you are trying to increase your population of copepods, then the addition of some phytoplankton is a good idea, as it's one their main food sources.

We will address amphipods and isopods separately in future articles.


Thomas Kiørboe, What makes pelagic copepods so successful?, Journal of Plankton Research, Volume 33, Issue 5, May 2011, Pages 677–685,

Geoff A. Boxshall, Terue C. Kihara, Rony Huys, Collecting and Processing Non-Planktonic Copepods, Journal of Crustacean Biology, Volume 36, Issue 4, 1 July 2016, Pages 576–583,

Josefin Titelman, Øystein Varpe, Sigrunn Eliassen, Øyvind Fiksen, Copepod mating: chance or choice?, Journal of Plankton Research, Volume 29, Issue 12, December 2007, Pages 1023–1030,

Qiao Hu, Colleen M. Petrik, Cabell S. Davis, Normal versus gamma: stochastic models of copepod molting rate, Journal of Plankton Research, Volume 29, Issue 11, November 2007, Pages 985–997,


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Author Profile: Cynthia White

Cynthia received her BA in English from NYU a long long time ago. She has been a freelance writer and editor for over 20 years. In 2018, she won the President's Award from the Professional Writers Association of Canada. Now she is a writer and editor on staff at R2R, where her forum nickname is @Seawitch.