Copepods and amphipods are microscopic crustaceans that form an essential link in the marine food chain. These tiny organisms are a natural part of the plankton food chain in the ocean (there are freshwater copepods, too). They graze on phytoplankton, rotifers (microscopic aquatic animals), and in some cases, detritus. They incorporate the protein and fatty acids from these food sources and concentrate it into a highly nutritious package for consumption by marine animals that then eat them.
You can culture (or raise) your own amphipods to feed your aquarium fish, since they are an important food source required by some fish species to survive in the wild. Many of these fish will starve to death in an aquarium if they can't be weaned onto other, more convenient foods such as frozen mysis shrimp, brine shrimp, or another finely-chopped meaty fare such as krill. Some fish, such as the Mandarin/dragonette and seahorses, are found by most aquarists to be extremely difficult to get to eat anything other than amphipods/copepods. Amphipods are also the main food for many sandsifting and sleeper gobies.
Before You Begin
Make sure you are prepared for a constant cycle of feeding, maintenance, and harvesting your amphipods. While the physical requirements aren't great, there are a lot of details involved and you must manage the filtration, light, salinity, and more.
What You Need
Copepods/amphipods can be cultured in almost any suitable container, and only a few elements are needed for a copepod tank:
- 5 or 10-gallon plastic bucket or aquarium
- Sufficient light
There are a lot of theories about filtering a copepod/amphipod grow tank. The natural biological filtration offered by live rock or a sand bed that contains nitrifying bacteria, and/or microalgae are excellent for maintaining water quality. Of the microalgae, Chaetomorpha, Caulerpa, and Halimeda are probably best, but not Ulva, which has little surface area for the mass. The downside to Halimeda is that it is calciferous and will require calcium additions. A simple airstone with a medium airflow should be enough to keep the water moving in the culture vessel. Avoid using a protein skimmer, as it will have a tendency to capture the free-floating copepods/amphipods and discharge them with the waste foam.
Culture Surface Area
Amphipods are both pelagic (free-swimming), and benthic (bottom-dwelling) creatures, but are primarily bottom dwellers. Amphipods have more of a tendency to rise from the bottom of the aquarium and enter the water column at night. If there are large quantities of amphipods in a tank, they can easily be seen with a flashlight a few hours after dark. Amphipods do best in an aquarium containing large surface areas to graze on, such as old bio balls, live rock, old filter pads, coarse sand, or crushed coral substrates. Amphipods/copepods grow very well in an inexpensive UGF with a coarse crushed coral substrate.
Amphipods/copepods don't really need a lot of light in order to grow or reproduce. Around 12 to 16 hours per day of minimal light (ambient daylight, small wattage incandescent, or LEDs) works well. A clamp on LED is perfect. If you are using macroalgae as a growth medium, you will want to supply the right amount of light for algae growth.
Fine Tune the Salinity
Maintain the salinity of your copepod/amphipod system at the level of the target tank you will be depositing them into. If you are using an in-line refugium with your main tank, you won't have to worry about it; the tank water cycles through the rearing system.
Adjust the Temperature
Maintain a stable temperature between 72 to 82 degrees Fahrenheit. Amphipods/copepods are cold-blooded, so the warmer the water, the more active (feeding and reproducing) they are, but don't "cook" them. Temperatures above 85 degrees Fahrenheit could be harmful.
Amphipods aren't necessarily predatory, but they do prefer meaty foods. They are omnivorous that tilt toward the role of carnivore much more than of herbivore. Feed meaty foods that break down fairly quickly in the water column. A good mixture of marine pellet and marine flake fish foods ground up in a mortar and pestle will yield terrific results. You can also culture phytoplankton in a 2-liter plastic bottle to feed your copepods. There are a number of complete phytoplankton culturing kits available online.
Don't overfeed them. They will consume what they need and no more. Putting more food in the tank will not make them eat more. Test the ammonia in the tank to see if you are feeding too much. If your ammonia readings start to spike, perform a water change to lower the level and cut back on the food. It may take a bit of experimenting, but you should be able to find the right amount of food to periodically introduce to the culturing tank.
Maintain the Tank
If an in-line refugium is being used, little maintenance will be needed. A stand-alone system will need a few water changes (once per month or replacing water after harvest will suffice), as long as feeding is not overdone. Some Amphipods, such as the Gammarids, are amazingly tolerant to varying water conditions and tend to thrive in higher nutrient systems.
Harvest the Crustaceans
Harvesting can usually be done by siphoning the critters into a fine mesh fish net. If you are using old filter pads for a growth medium, just remove them from the growth tank and place them in a bucket of tank water, then pour the water through a net. If you are using a crushed coral substrate, siphon the substrate the same as you would gravel vacuum your tank bottom, using a fine mesh on the water outflow to catch the copepods/amphipods.
Introduce Them Into the Aquarium
The amphipods and copepods that you collect in the fish net can then be fed to your fish by putting the net in the water and swishing the tiny organisms out. The fish should immediately respond and swim toward the net to consume them.
Copepods and amphipods are often naturally introduced into closed aquarium systems when live sand and or live rock has been added. They will begin to multiply and grow in the tank when the aquarium water temperature is slightly warmer and a food source is available. Live copepods are also available for purchase online (such as AlgaGen ReefPods) in a bottled form.
Once you have your amphipod/copepod culturing system set up and running and have worked the wrinkles out of feeding, maintenance, and harvesting, you will find that the system is an easy, low-cost method to provide a high nutrition food to your difficult to feed marine fish.
Preventing Problems During Culturing
If you find that your cultivating is not going as planned, don't worry. It can be hard to determine the exact cause. It may make the most sense (and save time and energy), to simply start again rather than tweak the cultivation setup you have. Another option is to work with a local fish store or another expert who may be able to help examine your set up and provide suggestions or problem-solving techniques.
Jagadeesan, L. et al. Feeding Preference And Daily Ration Of 12 Dominant Copepods On Mono And Mixed Diets Of Phytoplankton, Rotifers, And Detritus In A Tropical Coastal Water. Environmental Monitoring And Assessment, vol 189, no. 10, 2017. Springer Science And Business Media LLC, doi:10.1007/s10661-017-6215-9