why is there a price difference between a fresh water pearl and a salt water pearl?

Answer 1

Nearly 100% of the pearls found for sale today are cultured pearls, whether they are Freshwater pearls or Saltwater pearls.

Cultured Pearls are grown inside a mollusk when a foreign item has been surgically implanted by human means. Cultured pearls are grown on pearl farms where several thousand mollusks can be implanted and cared for over the 2-5 years required for a pearl to develop. Cultured pearls were generally thought of as expensive, high-end pearls, and the word is still used widely with that higher value in mind. But in a sense, all pearls grown on pearl farms are cultured – the word simply refers to those grown with human intervention rather than occurring randomly in nature.

Natural Pearls are formed more or less randomly in nature when some sort of irritant becomes lodged in the tissue of an oyster or mollusk. In response to the irritation, the oyster secretes nacre, which gradually builds up in layers around the irritant. Over a period of several years, this build-up of nacre forms a pearl. Very few Natural Pearls are harvested each year and even fewer ever make it into the jewelry markets outside of the local area where they are found.

SALTWATER PEARLS are pearls that come from mollusks that live in saltwater, the most well-known of which are oysters. Traditionally, pearls in past generations were almost all saltwater pearls. But these days, the majority of pearls are freshwater pearls. Saltwater pearls tend to be rounder and have richer tones, and thus still fetch a much higher price. The best pearls in upscale jewelry shops are usually saltwater pearls.

FRESHWATER PEARLS are pearls that come from freshwater mollusks (not oysters, which are in salt water only) and cultivated in lakes and rivers, not in the ocean. They are often somewhat less lustrous than their saltwater counterparts. However, they appear in a wide variety of shapes and colors, and they tend to be less expensive than saltwater pearls, making them quite popular. Freshwater pearls are also quite durable, resisting chipping, wear, and degeneration. A single mollusk can produce up to 50 pearls. The quality of freshwater pearls is improving each year, and it is getting more difficult to tell the difference between them and their saltwater cousins.

Answer 2

From reading articles below the price difference is primarily between cultured and natural pearls, whereas many cultured pearls are freshwater and "all" saltwater pearls are natural.
[This is my understanding from what I read below:

Wikipedia:
Pearls fit into two categories: freshwater and saltwater. As their name implies, freshwater pearls are formed in freshwater mussels that live in lakes, rivers, ponds and other bodies of fresh water. Most freshwater cultured pearls sold today come from China. By contrast, saltwater pearls grow in oysters that live in the ocean, usually in protected lagoons. Akoya, South Sea and Tahitian are the three main types of saltwater pearls.

In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. Freshwater pearls are characterized by the reflection of rainbow colors in the luster. Cultured pearls are also produced using abalone.

The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large, perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants. Irregular shaped pearls are often used in necklaces.

In general, cultivated pearls are less valuable than natural pearls, and imitation pearls are the least expensive. One way that jewellers can determine whether a pearl is cultivated or natural is by x-raying the pearl. If the grit in the centre of the pearl is a perfect sphere, then the jeweller knows it is cultivated.

Nova:
A great irony of pearl history is that the least expensive cultured pearl product in the market today rivals the quality of the most expensive natural pearls ever found. The price-value anomaly is obvious to consumers as they hasten to buy Chinese freshwater bargains. Indeed, pearls from freshwater mussels lie at the center of the liveliest activity in pearling today.

Natural freshwater pearls occur in mussels for the same reason that saltwater pearls occur in oysters. Foreign material, usually a sharp object or parasite, enters a mussel and cannot be expelled. To reduce irritation, the mollusk coats the intruder with the same secretion it uses for shell-building, nacre. To culture freshwater mussels, workers slightly open their shells, cut small slits into the mantle tissue inside both shells, and insert small pieces of live mantle tissue from another mussel into those slits. In freshwater mussels that insertion alone is sufficient to start nacre production. Most cultured freshwater pearls are composed entirely of nacre, just like their natural freshwater and natural saltwater counterparts.

Answer 3

its because one is easily produced while the other one is hard to be produced. I heard some fishermen built fish pools just to breed clams (just to produce pearl).