How Are Freshwater Pearls Farmed and Cultured?

A single freshwater mussel can carry dozens of pearls at once. An FAO field report from a Chinese fish culture centre described mussels yielding up to 40 to 50 cultured pearls each, two summers after grafting. A saltwater oyster typically produces one or two, which goes a long way towards explaining why freshwater pearls cost less.

The method keeps changing, too. Farmers once grew pearls from tissue alone, which takes years to reach a decent size. Newer operations increasingly add a bead, and GIA gemmologists have reported seeing larger bead-nucleated freshwater pearls as the process has improved.

Below is how a mussel becomes a pearl, step by step, and what that means for the pearl jewellery you actually wear.

How are freshwater pearls farmed? The short version

1. Healthy mussels are raised in ponds, lakes or reservoirs.

2. Small pieces of mantle tissue from a donor mussel are surgically placed inside a host mussel, sometimes along with a bead.

3. The tissue forms a pearl sac, which lays down nacre layer by layer.

4. The mussels hang in the water for years while the pearls grow, usually three to four years for the larger sizes.

5. Farmers open the shells, collect the pearls and sort them by lustre, shape, surface and colour.

A short history of freshwater pearl farming

Freshwater pearl culture is older than most people assume. GIA traces it in China back to the thirteenth century, when pearls bearing Buddhist images were produced in mussels. Japan began culturing freshwater pearls at Lake Biwa in 1935, and annual Japanese production peaked at seven tons a year between 1970 and 1980, just as Chinese freshwater pearls were reaching the market. China now supplies most of the freshwater pearls sold around the world.

The mussels doing the work

Freshwater pearls grow in mussels, not oysters. The FAO report lists three species reared in Chinese ponds: Hyriopsis cumingii, which it rates the best, plus Cristaria plicata and Anodonta woodiana. Japanese farmers at Lake Kasumigaura use a hybrid of H. cumingii and Hyriopsis schlegelii, according to GIA. Mussels are filter feeders, so they live on whatever the water supplies. That is why water quality matters so much on a pearl farm.

From graft to harvest

Grafting the mantle tissue

The mantle is the soft tissue that builds a mussel's shell. A technician cuts small pieces from a donor mussel and places them inside the host. The FAO report describes several dozen pieces going between the mantle and the shell of each host, with a skilled worker preparing about 30 mussels a day. The grafted tissue grows into a pearl sac, and the sac secretes nacre, the calcium carbonate that gives a pearl its glow. The donor mussels in that report were killed for their tissue.

Adding a bead for bigger, rounder pearls

Tissue-only pearls are nacre all the way through, but they grow slowly. Bead nucleation adds a small shell bead alongside the tissue, so more of the pearl's size comes from the bead. GIA notes that farmers at Lake Kasumigaura began chasing bead-cultured pearls over 10 mm to rival South Sea pearls, and they now cultivate them for around three and a half to four years.

Growing in ponds and lakes

After grafting, the mussels are hung in the water, often individually on a vertical thread, as the FAO report described. Pearls were harvested after two summers at water temperatures of 20 to 25°C, though FAO noted that quality varied widely from mussel to mussel.

Harvest and sorting

Bigger pearls take longer. GIA describes growing periods of three to four years in Chinese freshwater culture. Once the shells are opened, pearls are sorted by lustre, shape, surface, colour and matching. Our pearl grading chart shows what we look for.

Why pearl farming takes patience

Not every graft turns into a pearl. A graft is a foreign body, and the mussel can mount an immune response against it. Researchers have studied exactly that in Hyriopsis cumingii, as shown in a 2024 paper in Frontiers in Marine Science. Farmers also carry years of feeding and care before they see a result, and some mussels will not survive to harvest. It is slow, uncertain work, and that is worth remembering the next time a strand of pearls looks expensive.

Telling farmed pearls from imitations

Farmed freshwater pearls are real pearls, so they behave like them. Genuine pearls are rarely perfectly identical, and you will usually see tiny differences in surface and shape from one pearl to the next. Imitation beads tend to look uniform, feel too light or too smooth, and the coating can chip around the drill hole. Jewellers also suggest gently rubbing a pearl against the edge of a tooth, where a real pearl feels slightly gritty and a glass or plastic bead feels smooth. If you are in doubt, buy from a seller who can tell you where their pearls come from.

What farming means for the pearl you wear

Colour comes first. GIA notes that freshwater cultured pearls come in white, orange, pink and purple hues. Treatments such as dyeing and coating do exist, so ask your seller. Ours are sold without chemical or colour coatings, and we buy directly from pearl farmers.

Shape is next. A pearl grows inside a living animal, and it does not always grow evenly. That is why you see baroque, rice and potato shapes, and why plenty of shoppers prefer them. Our classic pearl necklaces, pearl stud earrings and freshwater pearl rings show the range.

Then price. Many pearls per mussel keeps the cost per pearl down. That is a farming outcome, not a quality compromise. A well-grown freshwater pearl can look far better than a poorly grown saltwater one.

How to spot a well-farmed pearl

Check lustre, surface, shape and how well pearls match each other. Be wary of labels. Grades such as A to AAA are trade terms rather than a universal standard, so ask what a seller's grade actually means. If you are comparing options, our pearl buying guide walks through the basics.

Which freshwater pearl suits you?

• A necklace for daily wear: round or near-round pearls in a classic necklace. They layer easily.

• Something that stands out: baroque pearls, such as those in our pearl rings.

• A subtle everyday piece: pearl stud earrings.

• A first pearl gift: browse gifts under $100.

• A wedding: see our pearl bridal jewellery.

• A wrist piece: our pearl bracelets suit anyone who dislikes rings and necklaces.

Frequently asked questions

How are freshwater pearls made?

A technician places small pieces of mantle tissue from a donor mussel into a host mussel, sometimes with a bead. The tissue forms a pearl sac that coats the pearl in nacre over several years.

How long does it take to grow a freshwater pearl?

It depends on the size. GIA reports growing periods of three to four years for larger Chinese freshwater pearls. Pearls grown for a shorter time are generally smaller.

Are freshwater pearls real pearls?

Yes. They are cultured, meaning people start the process, but the mussel still builds the pearl from nacre. Natural pearls form without human help and are very rare.

Where do freshwater pearls come from?

Mostly China today. Japan began freshwater pearl culturing at Lake Biwa in 1935, according to GIA.

Why are freshwater pearls cheaper than saltwater pearls?

One mussel can produce dozens of pearls, while an oyster typically makes one or two. Price also reflects size, shape and quality, so a fine freshwater pearl can still cost more than a poor saltwater one.

What is a baroque pearl?

A pearl with an irregular shape instead of a round one. It happens when the nacre does not build up evenly, and it gives each pearl a different character.

How should I care for freshwater pearl jewellery?

Pearl is soft, ranking 2.5 on the Mohs scale according to GIA, so wipe it with a soft cloth after wearing and keep it away from perfume, hair spray and harsh cleaners. Our care guidelines have the full detail.