How to Build a Self-Sustaining Amphipod Population

Amphipods are the bigger, less-talked-about cousins of copepods. They're shrimp-like crustaceans that live in rockwork, substrate, and macroalgae, where they eat detritus and breed steadily. They're also one of the best long-term live food sources you can have in a reef tank.

This guide covers what amphipods do, why they matter, and how to build a population that sustains itself for years.

What amphipods are

Amphipods are crustaceans in the order Amphipoda. The species you'll find in reef tanks are typically:

• Gammarid amphipods (the curled-shrimp-shaped ones, 3 to 15 mm)
• Caprellid amphipods (skeleton shrimp, weird-looking and rare)

For practical purposes, "amphipod" in the reef hobby means gammarids. They breed steadily, eat almost anything organic, and provide live food at a size larger than copepods.

What they actually do

An established amphipod population provides three things:

• Detritivore cleanup. Amphipods eat uneaten food, decaying algae, and detritus that would otherwise contribute to nitrate.
• Live food for predators. Larger reef fish (wrasses, basslets, dragonettes, dottybacks) eat amphipods enthusiastically. They're a substantial food item compared to copepods.
• Biodiversity. A reef with amphipods is a more complete ecosystem. The microfauna supports the broader food web.

What eats them

Amphipods are large enough to be on the menu for many reef fish:

• Adult mandarin dragonettes
• Wrasses (six-line, fairy, flasher)
• Most dottybacks
• Anthias
• Pipefish
• Larger seahorses (amphipods over mysids for some species)

This is good and bad. Predators control amphipod populations naturally, but a heavy predator load can wipe a population out faster than it can rebuild.

Building the population

The strategy is simple: give amphipods a safe place to breed where predators can't reach them, then let them spill into the display.

• Run a refugium. Same setup as for copepods, but with extra rock rubble. Amphipods need crevices.
• Add live rock rubble. Fist-sized pieces in the refugium. The more surface area and shelter, the more amphipods.
• Seed with a live amphipod culture. Or take a chunk of mature live rock from a friend's established tank.
• Feed the population. Phytoplankton supports detritivores indirectly. Some leftover food in the refugium also helps.
• Be patient. Amphipods breed slower than copepods. Expect 2 to 3 months before a population is truly established.

Why populations crash

Amphipod populations fail for predictable reasons:

• Too many predators in the display. If amphipods can't establish in the display, they're entirely dependent on the refugium population spilling over.
• No safe shelter. Without rock rubble, amphipods get eaten before they can breed.
• UV sterilizers. UV kills amphipod nauplii moving through. Run UV intermittently or skip it.
• Aggressive mechanical filtration. Filter socks and roller mats remove larvae before they settle.
• Massive water changes that strip detritus. Amphipods need some detritus to feed on.

Multi-pod stocking

Amphipods work best as part of a broader microfauna mix:

• Tisbe copepods on surfaces and rockwork
• Apocyclops in the water column
• Tigriopus for variety and carotenoids
• Amphipods in the refugium and rock rubble

This combination feeds different fish at different stages and keeps the food web stable across the whole tank.

Adding amphipods to a heavily-predated display

If your display has multiple pod-eaters and you're trying to build amphipod populations from scratch:

• Seed heavily into the refugium first. Wait 6 to 8 weeks before introducing any amphipods to the display.
• Add amphipods to the display at lights-out, in batches.
• Avoid disturbing rockwork for a few weeks after adding.
• Don't aim for visible amphipods in the display. The goal is a slow steady spillover from the refugium.

The bottom line

Amphipods take longer to establish than copepods but provide a more substantial live food base. A productive refugium with rock rubble and the right feed will give you a population that supports demanding fish for years.

If you keep wrasses, dragonettes, dottybacks, or any species that hunts substantial prey, amphipods belong in your tank. Build the population once, harvest sparingly, and it'll keep producing indefinitely.