Pearls have been known to mankind since the beginning of civilization. They are highly esteemed as gems for their beauty and splendour. These structures are secreted by the mantle (i.e., the skin) of pearl oysters in response to irritations caused by external or internal stimuli such as sand grains, molluscs eggs, parasites, detritus, and other foreign particles. Many attempts have been made to culture pearls in freshwater mussels. In the 13th century the Chinese fixed small Buddha figures inside freshwater mussels which became covered with a pearly layer. After considerable perseverance and study on the mode of pearl formation, success was achieved early in this century in Japan on the production of spherical cultured pearls. The Japanese grafted a piece of mantle with a small bead in a pearl oyster and reared the oyster in protected coastal waters with favourable environmental conditions.
India has one of the highest demand for pearls for setting in jewellry, and is particularly famous for its pearl oyster resources which yield superb pearls. The pearl oyster fisheries are located in two main areas: 1) in the Gulf of Mannar off Tuticorin coast and 2) in the Gulf of Kutch on the northwest coast of the country. The pearl oysters are found in two different environments in the two localities, at depths up to 23 meters in the Gulf of Mannar, in the intertidal zone in the Gulf of Kutch. These bivalves form large beds on hard substrata in the Gulf of Mannar, while they are sparsely distributed in the Gulf of Kutch. The pearl oyster resources in the two areas have been fished for pearls until the early 1960's.
After surveying the pearl oyster resources and fisheries in the two Gulfs at the beginning of the century, Hornell (1916) recommended that in order to maintain pearl fisheries profitably it was necessary to develop techniques to induce the Indian pearl oysters to form pearls by artificial means. In response, the then Madras Government Fisheries Department carried out preliminary research at the Marine Biological Station in Krusdai Island, Gulf of Mannar. Research focused mainly on the biology and ecology of several species. The oysters were reared in cages and induced to form pearls. That work managed to produce only two poorly shaped pearls and a half-pearl attached to the shell. Efforts in Gujarat did not meet success either.
In October 1972 the Central Marine Fisheries Research Institute started a pearl culture research project at Tuticorin. Success came in July 1973 when a perfectly spherical pearl was produced. This breakthrough was achieved by introducing a graft of the oyster mantle in the gonad of an adult specimen together with a shell bead nucleus. This is a delicate operation.
Following this success an Ad-hoc Research Scheme on pearl culture under the Indian Council of Agricultural Research (ICAR) was implemented (from 1973–78) by the CMFRI in association with the Department of Fisheries, Government of Tamil Nadu. During this Research Scheme, production of cultured pearls by multiple implantation was successfully achieved. Several aspects of pearl formation and pearl oyster biology and ecology -- highly important for successful pearl culture -- were investigated.
The CMFRI also succeeded in artificially spawning Pinctada fucata, rearing of larvae, and producing seed in the laboratory by hatchery techniques. This breakthrough is very important in light of the difficulty in obtaining sustained supplies of oysters from natural banks for culture purposes. Recently the CMFRI also produced seed of the black-lip pearl oyster, Pinctada margaritifera which produces the highly valuable black pearl.
To follow-up on the development of pearl culture technology, the Tamil Nadu Fisheries Development Corporation and the Southern Petro-chemical Industries Corporation Ltd. established in 1983 a company to produce cultured pearls, with the farm at Krusadai and the nucleus implantation centre at nearby Mandapam. Since then other companies have became interested in taking up pearl culture on a commercial scale.
The CMFRI is making efforts to promote the pearl culture technology by conducting short- and long-term training programmes. Scientific and technical personnel from fisheries institutes in all of the maritime states as well as from the Fisheries Faculties of Agricultural Universities are given the opportunity to be trained in these programmes.
This manual covers various aspects of pearl oysters, such as taxonomy, morphology, anatomy, ecology and pearl oyster seed production through hatchery techniques, and pearl oyster framing.