SWAN MUSSELS - Fish or Wildlife Pond and bog Aquatic Plants (1 - 10)

Britain's largest native freshwater mussel

The swan mussel (Anodonta cygnea) is the biggest freshwater mussel found in British waters, reaching up to 20cm across a smooth, olive-to-brown oval shell. It spends its life half-buried in the silt at the bottom of the pond, drawing water in through one siphon and pushing it back out through the other — quietly working through suspended algae, phytoplankton and fine organic particles as it goes.

It is one of the few pond animals that genuinely earns its place through what it removes rather than what it eats off the surface. In a mature, silt-bottomed wildlife pond, a small group of swan mussels helps take the edge off green water and adds a piece of native aquatic life most ponds never get.

Please read the suitability section below before ordering. Swan mussels are not a substitute for a filter and they are not suitable for every pond. Sold to the wrong pond they will slowly starve, and we would rather sell you none than sell you five that die.

Why keep swan mussels

• Live filter feeders. Each adult mussel processes many litres of pond water a day, removing suspended algae and fine particulates that mechanical filters pass straight through.
• Host species for bitterling. European bitterling (Rhodeus amarus) lay their eggs inside a living mussel's gill chamber. Without swan or duck mussels, bitterling cannot breed. If you keep bitterling, this is the missing piece.
• Genuinely native. Anodonta cygnea is a British native in long-term decline. Established, silt-bottomed garden ponds are a real refuge for it.
• Long-lived and low maintenance. In the right pond a swan mussel needs no feeding and no intervention, and can live well over a decade.
• Fascinating to watch. They plough slow furrows through the silt with a muscular foot, leaving visible tracks along the pond bottom.

Is your pond suitable?

Yes, if your pond has:

• Been established and biologically mature for at least 12 months
• A soft bottom — at least 8–10cm of silt, mud, sand or fine gravel for the mussel to burrow into
• At least 1,000 litres (1m³) of water per mussel
• Some natural green water, algae or suspended organics — a slightly "living" pond, not gin-clear
• Gentle circulation and good dissolved oxygen

No, if your pond has:

• A bare liner or concrete base with nothing to burrow into
• A UV clarifier and heavy mechanical filtration keeping the water sterile and crystal clear — there will be nothing left in suspension for the mussel to eat, and it will starve over several months
• Been set up in the last year, or was recently drained and refilled
• Less than 1,000 litres, or is a preformed/patio pond
• Heavy predation pressure from herons or corvids in shallow margins

Blunt version: a swan mussel in a filtered, UV-clarified koi pond is a slow death sentence, and a large mussel dying unnoticed in a small pond can foul the water badly enough to kill fish. If you are buying these to clear a green pond, a barley straw treatment, more marginal planting or a proper UV unit will do that job — a mussel will not.

Care at a glance

Introducing your mussels

1. Float the sealed bag in the pond for 20–30 minutes to equalise temperature.
2. Open the bag and mix in pond water gradually over another 20 minutes.
3. Place each mussel by hand onto the pond floor, narrow hinged edge down, at a slight angle into the silt. Do not simply drop them in — a mussel landing flat on its side may not right itself.
4. Space them out rather than clustering them.
5. Leave them alone. They will bury themselves within a day or two, and you may see nothing of them for weeks. That is normal.

Check occasionally that a mussel has not been lifted into the shallows or left gaping open on the surface of the silt. A shell that stays wide open and does not close when handled has died and should be removed promptly.

Compatibility

Fine with goldfish, orfe, rudd, tench, native amphibians, snails and all pond plants. Ideal alongside bitterling. Not recommended with koi, which will dig them out of the substrate, or in ponds stocked heavily enough that oxygen is already under pressure.

A note on breeding: swan mussel larvae (glochidia) attach briefly to the gills and fins of passing fish before dropping off as juveniles. This is a natural part of the life cycle and healthy fish are unaffected, but it is worth knowing about if you keep valuable or already-stressed fish.