The reproductive biology of tumid venus clam Gafrarium tumidum (Roding) was studied in detail from the Southeast coast of India. Sample size ranged from 10.3 to 41.3 mm. Sexes are separate but not di¡eren-tiated externally. Annual sex ratio male:female (M:F) deviated signi¢cantly from the 1:1 ratio with females dominating. Based on ova diameter progression of gonad smear and histology, four and two maturity stages of gonads were di¡erentiated in female and male clams, respectively. Peak spawning was observed during November and a minor one in April. The monthly average condition index based on wet/ dry £esh weight ranged from 7.24 (November) and 14.14 (September) and 8.82 (October) and 14.38 (August), respectively. The condition index observed by both the methods is comparable and corresponds with the spawning season. Water content observed for male and female clams varied negligibly and showed positive correlation with spawning period. Size at ¢rst maturity was estimated to be 22.3 mm.
Spawning and successful rearing of larvae of honeycomb grouper Epinephelus merra Bloch 1793 upto juvenile stage was accomplished at the ¢n¢sh hatchery of Mandapam Regional Centre of Central Marine Fisheries Research Institute during 2004. The fertilized eggs were free, spherical and buoyant with size ranging from 710 to 730 mm. Complete early embryonic development took place within 24^27 h and hatching occurred. The hatchlings measured1.5 mm. Mouth opening (115 mm) appeared at 72 h when the larvae were 2.2 mm in size. Pectoral ¢n developed on the ¢fth day. Complete metamorphosis took place and by the 60th day the larvae transformed into juveniles (45 mm) and attained skin colouration and honeycomb pattern.
Research on marine gastropod breeding in India is in its infancy and scanty literature is only available. To fill the lacunae, marine gastropods of three ornamentally valued and conservation important groups such as Cyprids, Strombids and Muricids were held under captivity and studied for their broodstock maintenance, spawning behaviour, larval rearing and metamorphosis into juveniles at the Shellfish Hatchery of Central Marine Fisheries Research Institute, Tuticorin. Valuable information on the focal themes of the article was obtained for Strombids and Muricids leading to the successful life cycle closing for Lambis lambis and Chicoreus virgineus are reported earlier. In the present study, experiments were conducted on aspects such as post-metamorphosed juvenile rearing up to 76 days post hatch for L. lambis, spawning, larval development and life cycle closing and reasonable level of juvenile production (8.8%) for Chicoreus ramosus. In addition, the primary observations on the captive breeding of Cypraea tigris with reference to its egg mass, brooding habit and early development is reported. However, while studying these groups few unanswered questions and bottle necks in their breeding nature, larval rearing and metamorphosis arose. The following account details the experiments conducted and results obtained in each of the focal themes of the paper and the constraints faced.
Muricids are commercially important gastropods and are exploited primarily for shell craft industries. They also occupy a niche in ornamental keeping. Studies on the larval development of muricids in Indian waters are few. Hence, an attempt was made to study with a focus on the optimum requirements for captive brood maintenance; regional variation in egg laying, intracapsular development and to estimate production potential of individual brooder (the length/ weight ranged from 80 -110 mm/49 -169 g (average 94.875 ± 3.980 mm/111.625 ± 14.870 g) of Chicoreus virgineus var. ponderosa collected off Tuticorin coast, Gulf of Mannar. Experimental airlift water circulation system fitted in 1 t FRP tanks having an overturn of 300% water is found suitable for long term maintenance and maturation of brooders with near cent percent survival over a year. Spontaneous breeding commenced from June'09. Eggs cases were "vase" shaped and measured 1.2 -1.5 cm in height. Egg case numbers varied between 110 and 140 and got reduced to 10 -40 during October and increased in Nov & December. Number of eggs within the egg case was highly variable ranging from 100 -380. Eggs were spherical, embedded in jelly mass within the egg case and measured 510 -608 µ (578 µ). Intra capsular development is detailed and compared with the earlier report on this species from other areas of Indian coast. Development took nearly 20 days and only few free living juveniles measuring between 1.7 -1.9 mm emerged and the rest of the eggs have functioned as "Nurse eggs". Average net production potential of a single viable egg case was estimated to be 6.7 nos for Chicoreus virgineus var. ponderosa of Tuticorin coast of Gulf of Mannar.
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