Molluscan Culture: Clam

Molluscs contribute 18.1% to the total world aquaculture production, in which clams form 21.9%. China, Republic of Korea and Malaysia are the leading clam producing countries. In India, clams are the most important among the bivalve resources. They are distributed in the backwaters and estuaries along the Indian coast

Reproductive biology of the commercial sea cucumber Holothuria spinifera (Echinodermata: Holothuroidea) from Tuticorin, Tamil Nadu, India

The annual reproductive cycle of the commercial sea cucumber Holothuria spinifera was studied in Tuticorin, Tamil Nadu, India, from September 2000 to October 2001, by macroscopic and microscopic examination of gonad tubule, gonad index and histology of gametogenic stages, to determine the spawning pattern. The gonad consists of long tubules with uniform development. It does not confirm the progressive tubule recruitment model described for other holothurians. The maximum percentage of mature animals, gonad and fecundity indices, tubule length and diameter, with the observations on gonad histology, ascertained that H. spinifera had the peak gametogenic activity during September and October 2001 followed by a prolonged spawning period from November 2000–March 2001

Growth of the hatchery-produced juveniles of commercial sea cucumber Holothuria (Theelothuria) spinifera Theel

The present study was conducted to develop the hatchery technology for seed production of the widely exploited commercial sea cucumber Holothuria spinifera Theel 1886, to facilitate an e¡ective stock enhancement programme. Broodstock collected by skin divers were used for spawning trials. The embryonic and larval stages were similar to other aspidochirotes. The larval survival rate was 43.5% on day 9, which decreased to 18.3% nearing metamorphosis on day 13, the growth rate was 48 mmday_1and the settlement ratewas 3.5%. Algamacs used to induce settlement also served as the food source for the early settled juveniles, followed by Sargassum spp. extract (o40 mm) for the ¢rst month. Sargassum spp. powder along with ¢ne sand (1:1)was givento juveniles420mm. Addition of Spirulina spp. along with Sargassum spp. powder and ¢ne sand (0.5:1:2) enhanced the growth rate of the juveniles. In the hatchery, the juveniles attained an average size of 1, 30 and 48 on 20, 80 and 120 days respectivel

Effects of temperature, salinity and pH on larval growth, survival and development of the sea cucumber Holothuria spinifera Theel

For large-scale seed production of sea cucumbers through a hatchery system, it is imperative to know the effects of environmental parameters on larval rearing. Auricularia larvae (48 h post-fertilization) were obtained from induced spawning of Holothuria spinifera and used in experiments to ascertain the effects of temperature, salinity and pH on the growth and survivorship of the larvae. The larvae were reared for 12 days at temperatures of 20, 25, 28 and 32 °C; salinities of 15, 20, 25, 30, 35 and 40 ppt; and pH of 6.5, 7.0, 7.5, 7.8, 8.0, 8.5 and 9.0. The highest survivorship and growth rate and fastest development of auricularia indicated that water temperature of 28–32 °C, salinity of 35 ppt and pH of 7.8 were the most suitable conditions for rearing larvae of H. spinifera

The reproductive biology of the baby clam, Marcia opima, from two geographically separated areas of India

A study of the reproductive cycle of the baby clam, Marcia opima (Gmelin) was conducted at two sites along the southeast (Tuticorin Bay) and southwest (Ashtamudi estuary) coast of India from December 1998 to January 2000. Histological evidence showed that baby clam from both the sites showed two spawning seasons. First spawning season was recorded from May to July in the southeast coast. In the southwest coast, the first spawning season was observed through March to May. A second spawning season from September to December was recorded in both the coasts. In the southeast coast, minimum and maximum condition indices were obtained in January 2000 and April 1999 respectively and decreased from May to June and November to January, signifying the two spawning periods. Most of the animals were either in spent or indeterminate gonadal stage from May to August and November to January indicating the active spawning during that months in the southeast coast

Effect of temperature on the feeding rate of cymatiid Cymatium (Monoplex) pileare (Gastropoda:Prosobranchia)

Influence of temperature (24°, 28°, 31° or 34°C) was studied on the feeding rate of predatory cymatiid. Cymatium (Manop/ex) pileare fed with edible oyster.The rate of feeding increased from 2 to 5.3 oysters/gastropod/month as temperature increased from 24° to 31°C. Increase in temperature decreased the days of feeding interval from 6.3 days at 24°C to 3.7 days at 34°C. All test animals courted mortality at 34°C on 17th day suggesting it as the upper tolerable limit of temperature

Regeneration of the proboscis of cymatiid Cymatium pileare (Gastropoda: Proso branchia)

Cymatiids cause considerable damage to bivalve stock in molluscan culture. Bivalves are preyed upon by cymatiids with insertion of proboscis and interaction of radula and jaws. Rate of regeneration of proboscis in cymatiid was faster than predatory thiasid and muricid gastropods

Post-harvest technology

In recent years great interest is envinced in several countries in the culture of molluscan shellfish. In the tropics favourable conditions exist for rapid growth and marketable oysters are obtained with in vir^n to twelve months. Investigations have been conducted at the Central Marine Fisheries Research institute and success has been achieved in perfecting the techniques of oyster culture in coastal waters (Nayar and Mahadevan, 1983). The awareness that shellfish have to be purified and rendered harmless goes back to the time of the Roman Empire. During the first century B.C. the Romans consumed cockles and oysters after treating them in tanks known as cockle washery (Yonge, 1962)

Technology of edible oyster culture

Oysters, mussels, clams, scallops, cockles and abalones are major groups of molluscs which are cultured in different parts of the world. Edible oysters are the most important among them, as they are great delicacy and there is growing demand. There is an increasing interest in oyster culture in tropical countries in recent years. Apart from the edibility of meat, the shells have various industrial and agricultural use. Considering the oysters as a renewable resource of much needed animal protein and the employment potential, oyster culture offers to the rural communities, its culture has been taken up as an R & D programme of the Central Marine Fisheries Research Institute. The studies carried out since 1970, have resulted in developing simple culture methods suitable for Indian conditions

Biochemical changes during larval development in the short neck clam, Paphia malabarica Chemnitz

Biochemical compositions were determined for eggs, D-shaped larvae, umbo larvae and pediveliger of the short neck clam Paphia malabarica Chemnitz. Spawned eggs were composed of 63.2% protein, 25.4% lipid and 11.4% carbohydrate. After 48 h of embryogenesis, 2.6% of the protein, 11.8% of the lipid and 3.2% of carbohydrate mass had been lost, providing 20.5%,75.4% and 4.1% of the total energy expenditure of 0.2147mJ embryo�1. During 48h of metamorphosis, lipid was utilized ¢rst, followed by a heavy consumption of protein; protein, lipid and carbohydrate lost 23.8%, 50.2% and 32.5% of their mass respectively. Protein and lipid supplied a comparable amount of energy for metamorphosis,34.2% and 55.2%, respectively, whereas, carbohydrate contributed only10.6% to the 2.733mJ larva�l metamorphic energy expenditure