Amphipods and copepods are natural foods for fish in the wild, so they are one of the healthiest options for pet fish, too. Some saltwater fish, such as mandarinfish and seahorses, prefer amphipods and copepods and may refuse to eat anything else. Amphipods are also a favorite food of sandsifting and sleeper gobies as well as freshwater beta fish. Culturing your own crustaceans for fish food in either a saltwater or freshwater tank is easier than it sounds and can be fun for dedicated DIY aquarists.
What Are Amphipods and Copepods?
Amphipods and copepods are microscopic crustaceans that form an essential link in the marine food chain. They graze on phytoplankton, rotifers (microscopic aquatic animals), and in some cases, detritus. They incorporate the protein and fatty acids from their food sources and concentrate them into a highly nutritious package for consumption by multiple marine animals.
Copepods naturally live in both saltwater and freshwater, making them a great choice for either type of aquarium system. Amphipods are primarily found in marine (saltwater) ecosystems, but there are freshwater species, too. Freshwater amphipods, commonly known as "scuds," belong to the Gammarus and Hyallela genera.
Culturing procedures are the same for both freshwater and saltwater micro-crustaceans, but make sure to purchase amphipods that are suited to freshwater environments, such as Hyalella azteca or any of the Gammarus species, if you have a freshwater tank.
Before You Begin
Make sure you are prepared for a constant cycle of feeding, maintaining, and harvesting your crustaceans. While the physical requirements aren't extensive, you must manage details like filtration, light, and salinity on an ongoing basis.
Copepods and amphipods can be cultured in almost any suitable container, and only a few elements are needed to create an operational cultivation tank:
- 5 or 10-gallon plastic bucket or aquarium
- Sufficient light
- The natural biological filtration offered by live rock, a sand bed containing nitrifying bacteria, and/or microalgae is excellent for maintaining water quality.
- The microalgae, Chaetomorpha, Caulerpa, and Halimeda are preferable (skip Ulva, which has a minimal surface area for its mass). Note that Halimeda is calciferous and will require calcium additions.
- A simple airstone with medium airflow should be sufficient to keep the water moving in the culture vessel.
- Avoid using a protein skimmer, as it will have a tendency to capture free-floating copepods and amphipods and discharge them with the waste foam.
- Both amphipods and copepods grow well with an inexpensive UGF (under-gravel filter) with a coarse crushed coral substrate.
Amphipods and copepods 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.)
These tiny crustaceans 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.
Neither amphipods nor copepods need a lot of light to grow or reproduce. Around 12 to 16 hours per day of minimal light (ambient daylight, small wattage incandescent, or LEDs) is sufficient. A clamp-on LED is perfect.
If you are using macroalgae as a growth medium, though, you will want to supply the right amount of light for algae growth.
It's essential to maintain the salinity of your culturing system at the aquarium level in which you will be depositing the amphipods and copepods.
Using an in-line refugium with your main tank, you won't have to worry about it because the tank water cycles through the rearing system.
Maintain a stable temperature between 72 and 82 degrees Fahrenheit. Amphipods and copepods are cold-blooded, so the warmer the water, the more active (feeding and reproducing) they are. Just don't "cook" them. Temperatures above 85 degrees Fahrenheit can be harmful.
Amphipods aren't necessarily predatory, but they do prefer meaty foods. They are omnivores 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 several complete phytoplankton culturing kits available online.
Don't overfeed your crustaceans. 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
An in-line refugium requires little maintenance, but a stand-alone system will need a water change once per month (or after harvest). If you're overfeeding, then you may need additional water changes until you determine the appropriate amount of food to maintain your crustaceans without excess.
Harvesting can usually be done by siphoning the tiny crustaceans into a fine mesh fishnet.
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 and amphipods.
Feeding Your Fish
The amphipods and copepods that you collect in the fishnet can be fed to your fish by putting the net in the water and swishing the tiny organisms. 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 have 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.
Once you have your crustacean 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 hard-to-please marine fish.
If you find that your cultivation 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 setup 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