Copper and medication toxicity in invertebrates

What you can and cannot establish yourself

Cause

Copper and other compounds toxic to invertebrates at low concentrations

Spread between fish

Not transmissible

Urgency

Act now

Affects

shrimp, snail, crayfish, crab, other-invertebrate

Confidence

moderate confidence

Signs

• Deaths beginning within hours to a couple of days of something being added to the tank
• Shrimp swimming erratically around the tank before dying, quite unlike their normal grazing behaviour
• Shrimp lying on their sides, unresponsive, with no external lesion
• Snails detaching from surfaces, extending from the shell and failing to retract
• Fish in the same tank behaving entirely normally — which is the observation that identifies this
• Losses across the whole invertebrate population rather than individuals over time

Do this first: the environmental response

Water quality is the cause, the contributing factor or the deciding variable in the great majority of aquarium health problems. These steps come before any treatment decision, and for several conditions they are the entire treatment.

1. Stop dosing anything, immediately.
2. Large water changes, repeated. Dilution is the only response available.
3. Run fresh activated carbon or a copper-specific resin to remove what remains in solution.
4. Establish what went in and when. This is diagnostic and preventive at the same time, and the answer is usually in the last week.
5. Where copper plumbing is suspected, run the tap for a while before drawing water for the tank.
6. Treat a tank that has held copper as unsuitable for ornamental invertebrates until proven otherwise.

What else it could be

Every entry names the observation that separates it from this record. Work through these before deciding what you are treating — the most expensive mistake in fish health is confident treatment of the wrong thing.

What makes it more likely

Each entry states the mechanism, not just the association — an association without a mechanism is not something you can act on.

• Treating a community tank in place rather than moving fish out. Most parasite treatments are dosed to the whole volume, and the invertebrates cannot be dosed around.
• Copper persistence in substrate and silicone. Copper adsorbs onto surfaces and re-enters the water over months, so a clear water test does not mean a tank is safe for invertebrates again.
• Small tank volume. Dosing errors that would be diluted in a large tank reach lethal concentrations in a small one.
• First-draw water from copper plumbing. Water standing in copper pipes overnight picks up measurably more copper than water drawn after running the tap.

Treatment categories

AquariumHQ names classes of response and never doses. Product concentrations differ between markets and formulations, several actives are temperature- and pH-dependent, and the invertebrate and plant tolerances that decide whether the rest of the tank survives are not printed on the label. Where a category puts a chemical in the water, what it can damage is stated with it.

Isolation and quarantine

• Move surviving invertebrates to clean, parameter-matched water immediately if any is available. This is one of the few cases where moving animals is clearly the right call, because the water is the problem.
• Do not return them to the affected tank until the source has been identified and dealt with — and understand that where copper has been used, the substrate and silicone may continue to release it.

When a vet is the right call

• Losses continuing after water changes and carbon, which suggests a continuing source
• A valuable breeding colony where identifying the source matters commercially

Prevention

• Read the full ingredient list of anything before it goes into a tank with invertebrates, and treat 'invertebrate safe' claims as a starting point for checking rather than an assurance.
• Keep a separate hospital tank so fish can be treated without dosing the invertebrates.
• Never use copper-based treatments in a tank you intend to keep invertebrates in again.
• Dose fertilisers by tank volume and err low.
• Run the tap before drawing water where the plumbing is copper.

What AquariumHQ does not know

Published rather than hidden. A health page that lists no limitations has not had its limitations looked for.

• Species-level sensitivity thresholds for ornamental dwarf shrimp are not established in the literature AquariumHQ has reviewed. The aquaculture work is on penaeid shrimp and crayfish, which are not the same animals.
• How long copper remains bioavailable in a treated aquarium is reported qualitatively and not quantified in a form useful to a keeper.

Evidence

Each claim is shown with what kind of support stands behind it and how strongly we hold it. Those are separate axes: a measurement held tentatively and an editorial position held firmly are different things.

Related

• shrimp dying
• snails dying
• source water
• water changes