I have just returned from the last International Marine Aquarium Conference and I thought it would be a good time to review the status of copepod products which are available to home hobbyists. While there are several varieties of copepods currently on the market, all of them fit into the two main orders of free swimming copepods found in the oceans: the orders Calanoida (or calanoid copepods) and the Harpacticoida (known as harpacticoid copepods).

Calanoid Copepods
Calanoid copepods are mainly planktonic with elongate bodies and often frilly appendages, and their antennae are generally longer than their body length, which is typically 1 to 2 mm. Calanoid copepods usually take a few weeks to mature, and either spawn by shedding eggs and sperm into the water or else brood their eggs in special brood sacs. Calanoids can release several dozen eggs a day, which sink to the bottom and hatch within approximately 24-48 hours.
Adult calanoids often have a taste for their own young, so most culture systems need to account for this by separating the adults from their young (known as nauplii).
Calanoid copepods are most useful to the hobbyist breeders as they remain in the water column at all times. However, in regular tank systems they can get flushed out and destroyed easily by the pump systems.

Harpacticoid Copepods
The other type of copepod found on the hobbyist market is the harpacticoid copepod. Harpacticoid copepods tend to be much smaller than calanoid copepods and usually have an “epibenthic” swimming pattern. This means that they are found in the water column, but close to the bottom, often resting to the glass or grazing on seaweed and detritus in the tank.
Harpacticoid copepods are torpedo-shaped and have very short antennae, so they are less likely to be disturbed by the flow of water in the tank, and can survive a trip through an pump’s impeller unscathed.

How Friendly is your System to Copepods?
The difficulty for your average consumer is how to decide which copepod product to choose for your system. The type and number of copepods depends on a few factors:

1. Size of the tank and amount of live rock
2. Is there a refugium?
3. Number and types of fish in the tank
4. The presence of adverse predators: bristle worms, sea stars, emerald crabs, ornamental shrimp, lined wrasse, etc
5. Whether you plan to breed your fish

First of all, the size of the tank can help to maintain/sustain the original pod population that came in with the live rock and live sand when the tank was originally started. Larger tanks with more live rock and a refugium are going to sustain copepod populations for a very long time. If you have had a large system set up for several months, it is easy to check for the copepods by shining a light on the tank at night and looking for the telltale movement of little white specks towards the light. Depending on the cleanliness of the tank, copepods can often be found grouped near the corners or in the quiet spots behind your live rock; they look like tiny little white specks.

Refugiums are a natural location to find copepods in your system. However, some other refugium residents may have eaten a substantial number of your pods. Basically, large crustaceans will eat small crustaceans when given the chance. Most copepod species are actually cannibalistic. Amphipods, emerald crabs, bristle worms, and ornamental shrimp may be snacking on your pod supply, so it may be a good idea to remove a few of these predators from the refugium before attempting to start a copepod population. If this proves to be too difficult, copepods can be reared outside of the tank system and occasionally placed back into the refugium as needed.

Because the copepods need to be able to reproduce and grow faster than they get eaten, there may be an upper limit on the number of fish that you should have in a system that require copepods as a sole source. This is the rational behind many of the recommended tank sizes for keeping Synchiropus species: mandarin dragonets and scooter blennies. Many other fish species love to snack on your copepods, and will even resort to chasing away the fish that require the copepods: Anthias, Chromis, Pseudochromis, clownfish and wrasse species (especially line wrasse) all exhibit these tendencies.

Selecting Copepods for Culture
So, where does that leave the home hobbyist who wants to make sure their tank has enough copepods to feed their pet “Mandy” or little “Scooter”? The good news is that there are now a variety of products that can help a fish through the difficult transition phase. Having copepods available allows the owner of a tank to continue to train their dragonets onto easy-to-manage live feeds such as brine shrimp, or even frozen feeds such as bloodworms.

The most common copepod species on the market is Tigriopus californicus. Tigriopus are found in the tide pools on the western coast of the United States. They tend to be able to handle high densities in the tide pools, so they can easily be transferred to a home culture system. However, depending on the origin of the strain of copepod, they may be more or less heat tolerant. Also, they tend to display a marked seasonality in their reproduction rates; so, if the temperature goes up or down a few degrees in the culture system, the copepods can mistake this for a seasonal cue and cease reproduction at a high rate. Many store bought species require a period of trial and error before the optimum temperature can be found.

Other harpacticoid species are supplied by more specialized retailers including Tisbe, Nitokra and Euterpina spp. These species are smaller and will be more numerous once introduced into the system. They tend to be more like the species that are found on tropical live rock and in live sand. Their importance can be underappreciated by the amateur hobbyist, because they are harder to find and their pink and white coloration makes them difficult to see against the live sand and live rock. Nitokra and Tisbe do well at many temperatures and salinities, and tend to have more offspring in a shorter amount of time than the larger Tigriopus.

However, upon examination, most hobbyists with established tanks will find these little white and pink gems everywhere – grazing on detritus, hanging to the macroalgae, crawling along the live rock, and in between the sand grains. If you have ever wondered why your mandarin had a grin after pecking through the sand grains, it is usually because they found something good to eat down there!
While these copepods may be smaller in size, they are actually more nutritious and easier to digest than many of the larger species that have more complex exoskeletons and will store their lipids as wax esters instead of free fatty acids. Also, the larger species, such as Tigriopus spp. have the ability to fight back and will actually be able to occasionally claw their way out of a fish gut using the same strong mouthparts that allow them to latch onto the rocks in their tide pools.

Care should be taken to observe the fish response to the larger copepods to avoid these adverse interactions. Tigriopus should never be used with delicate larval fish as they like to cling to the larvae, and this stresses the fish and can lead to death within a few hours.

Enhancing Copepod Populations in Your System
If your tank does not already have a thriving copepod population this could be for many reasons. Usually, a tank will not show detectable signs of copepods until it has had time to cycle and mature. In addition, some medical treatments have chemicals that are harmful to the copepods. For example, the products used to kill the “red bugs”, another small crustacean, will also kill the copepods in your system. Any trace metals introduced in excess tend to be harmful to copepod reproduction rates, so what feeds the corals can sometimes be detrimental to the copepods.
In other cases, the tank may just be kept too clean. While I haven’t heard this lately, I know that some hobbyists will vacuum their gravel to remove the detritus, also removing many of the smaller copepod species. Scraping the algae religiously off the glass also reduces the habitat for the copepods. This is why a refugium can be used to enhance a copepod population – the refugium will contain lots of unclean surface area for the copepods to graze upon and will usually have a healthy load of bacteria and detritus mixed in with the live sand or mud. Bio-filters also remove copepods; it is useful to occasionally inspect the filter socks to see if you can recollect the copepods crawling on its surface by simply shaking the filter sock out into a separate container of saltwater.

Whether you are setting up a new tank or just enhancing a separate system, most products can be added directly to the tank. Any of the harpacticoid species are suitable as a live feed.  Adult fish will consume the larger Tigriopus, while corals and other filter feeders consume the smaller Tisbe, Euterpina and Nitokra.  When adding these feeds directly to the tank, it is best to turn the pumps off for a few minutes to allow them to swim down to the surfaces so that a few will escape immediate predation and live to reproduce in the system.

While it is possible to culture harpacticoid species in the refugium and sump portions of a tank set-up, a separate culture system will improve results.  The smaller species such as Tisbe and Nitokra will reproduce more reliably and become more numerous in a shorter amount of time. Tigriopus is cannibalistic, and requires a high density of feed with the right level of light and nutrients to retain its red color and nutritional value. All of these species can be reared on live phytoplankton or any high quality fish food that has been pulverized to reduce the particle size. Any type of macroalgae is a good addition to a copepod culture system as well, because it increases the surface area available for the copepod nauplii to graze.

In summary, copepods are a great addition to the tank system. Most tanks will have a resident population that can be enhanced by dosing the refugium or main tank with a shot of live phytoplankton. The best copepods for the general hobbyist to use are the harpacticoid copepods. They are available in a range of sizes and behaviors, and more diversity will become available as the hobby develops.  Copepods are a hobby in themselves, and each marine tank system is unique, so have fun experimenting with this sustainable food supply – your mandarin will thank you for it.

• Good quality live rock is prime copepod habitat (© Neale Monks)
• Providing adequate copepods is fundamental to keeping reef-dwelling dragonets alive; this clearly underweight Synchiropus picturatus will not last for much longer without improvements to its diet (© Bob Fenner)
• This Synchiropus picturatus is in much better shape thanks to its maintenance in a mature aquarium with a healthy population of benthic copepods (© Bob Fenner)
• Dragonets will spend much of the day foraging for copepods among the live rock and corals in your tank, as here with a mated pair of Synchiropus splendidus (© Bob Fenner)
• Before you add Synchiropus splendidus to your tank, make sure you’ve thought about what it will eat! (© Bob Fenner)