Acropora Parasitic Copepods

What Are Acropora Parasitic Copepods?

Acropora “bugs” are tiny copepod-like crustaceans that live on or around the tissue and polyps of Acropora corals. The best-known example is the classic red bug, Tegastes acroporanus, but reef keepers also encounter darker “black bugs” and pale or white forms. These colour names are useful in the hobby, but they do not necessarily represent one single species in each group. Red and black bugs are associated with several harpacticoid copepod genera, while the identity of many so-called white bugs is still much less certain. Many are only around half a millimetre long; some spend much of their time around coral polyps or within the coral structure. Not every tiny copepod on Acropora is automatically harmful; identification matters. Concern starts with consistent coral association plus reduced extension, colour/vigour loss, poor growth, or progressive decline. White forms may be harmless or associated with stressed Acropora. This guide treats red, black, and white bugs together while separating differences in appearance, behaviour, or treatment response.

Identifying Acropora Parasitic Copepods

Red bugs, black bugs and white bugs can all produce very similar signs in Acropora: reduced polyp extension, duller colour, slower growth and a general loss of vigour.

A useful way to think of them is as tiny vampires feeding on the coral. They sap the Acropora over time, and affected tissue can start to look thin, faded or almost dusty, as though the colony has lost some of its richness and substance.

Because these pests are extremely small, magnification is essential if you suspect an infestation. A jeweller’s loupe or good magnifying lens will help you establish two things: whether parasitic bugs are actually present, and which type you are looking at.

• Red bugs - tiny yellow or tan copepods with a noticeable red eye or reddish marking.
• White bugs - tiny white, pale grey or translucent organisms, sometimes appearing almost kite-shaped or cross-shaped.
• Black bugs - very small dark or black moving specks on the tissue and around the corallites.

Not every copepod in a reef tank is harmful, so the important clue is the combination of bugs sitting directly on Acropora tissue together with that characteristic loss of extension, vigour and tissue quality.

Once you’ve confirmed what you’re dealing with, you can move on to the treatment regime below.

Sourcing Milbemycin Oxime

Milbemycin oxime is a veterinary antiparasitic medication commonly used in dogs for the prevention and treatment of worm infections, including heartworm prevention.

Depending on where you live, it may be sold under different veterinary brand names.

• United States: Interceptor Plus contains milbemycin oxime and praziquantel.
• United Kingdom: Milbemax contains milbemycin oxime and praziquantel.
• Europe: Milbemax and other authorised milbemycin-containing veterinary medicines may be available, although brand names and tablet strengths vary between countries.

In many regions these are prescription veterinary medicines, so they should be sourced legally through a veterinary professional or authorised supplier.

If you are struggling to obtain the medication, speak to an exotics or aquatic-animal veterinarian in your area. Explain that you are dealing with parasitic copepods affecting Acropora and that you are looking for a milbemycin-oxime-based treatment. A suitably experienced vet may be able to advise on the appropriate legal route for obtaining it.

When calculating an aquarium treatment, always work from the actual milligrams of milbemycin oxime in the product, rather than simply dosing by tablet count, because different brands and tablet sizes can contain very different amounts of the active ingredient.

System Preparation and Administration

• Calculate the actual system water volume rather than the nominal aquarium size.
• Remove shrimp, crabs and other vulnerable crustaceans wherever practical before treatment. Risk increases substantially at the higher white- and black-bug concentrations.
• At white-bug concentration, shrimp and crabs may become sluggish and small or delicate shrimp may be lost.
• At black-bug concentration, significant crustacean mortality is a realistic risk.
• Take activated carbon and other chemical filtration offline during treatment. Turn ozone and UV off.
• Maintain strong circulation, oxygenation and biological filtration. A skimmer may be used for aeration only if it is prevented from exporting the medication.
• Measure the required active milbemycin oxime accurately, crush or disperse the measured product into aquarium water, then add it into a high-flow area.
• After the treatment period, resume chemical filtration, use fresh activated carbon and perform an appropriate water change. Remove dead crustaceans and monitor ammonia, nutrients and oxygen demand.
• Re-examine Acropora under magnification before repeat treatments and again after the course.

What to Expect After Treatment

A successful response may include stronger polyp extension, improved lustre and vigour, improved feeding/growth behaviour and a recovery in major-element consumption as growth normalises.

Improvement is encouraging, but it is not proof that every pest has been eliminated. Continue magnified checks rather than judging clearance on colour alone.

Long-Term Monitoring

Particularly after white- or black-bug treatment, continue monitoring for up to six months. Periodically reassess suspect colonies under magnification. If symptoms recur, re-identify the organism rather than automatically escalating the dose.

Information for Your Veterinary Surgeon

This guide discusses treatment of Acropora-associated parasitic copepods using milbemycin oxime. The best-documented organism is the Acropora “red bug”, Tegastes acroporanus. Milbemycin oxime has published extra-label use in captive coral systems.

The higher white- and black-bug concentration frameworks in this guide are practitioner-derived Signature Frags / reef-keeping protocols rather than established veterinary standards. A veterinary surgeon should independently review the evidence, the legal prescribing route, the specific medicinal product and the risks to non-target crustaceans before making any prescribing decision.