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 8C; 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 8C, salinity of 35 ppt and pH of 7.8 were the most suitable conditions for rearing larvae of H. spinifera. D

The results of the study on the suitable algal feed for the mass rearing of holothurian larvae through hatchery system are presented. Auricularia larvae. after 48 h of fertilization, obtained from induced spawning of Holoth~iria spinifera, were fed with different algae Isochrysis galbana, Nanodlloropsis snlinn, Pavlava lutheri. Tetmselmis chllii and Chaetoceros cnlcitrans as well as I. galbana+C. calcitrans to ascertain the effect of single and combined microalgal diet. The rate of feeding was 2 x lo4 cells larvae-'.day-l for a period of 9-12 days. The growth rate of 59 pm day -' with 90% and 43 pmday with 100% occurrence of late auricularia in the larvae fed with C. calcitrans alone and I. galbnna+C, calcitrans, respectively, indicated that C.calcitrans itself or in combination with I. gnlbana is the effective feed for the larvae of H. spinijera.

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

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 mm day À1 and the settlement rate was 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 given to juveniles 420 mm. 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 respectively.

The performance of I and II meiotic triploids and control oysters (Crassostrea madrasensis) reared at Tuticorin Bay was compared to determine if the improvements in the growth of edible oysters were additive to faster growth in triploids. After a grow-out period of 12 months, both mean whole weights and shell heights were in order I meiotic triploid4II meiotic triploid4control. Mean whole weights and shell height of di¡erent oyster lines were all signi¢cantly di¡erent (Po0.05). On an average, larger morphological traits indicated that growth improvements from triploids were additive, and throughout the study triploid oysters maintained faster growth rate than their diploid siblings. Condition index and adductor muscle diameter of both triploids were higher than those of control.

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

The 'baby clam' Marcia opima (Gmelin) was spawned on seven occasions in the shellfish hatchery at the Tuticorin Research Centre, India. The fertilized eggs measured 47.8 Am in diameter and the straight hinged larvae attained at 20 h were 87 Am in length and 71 Am in height. Settlement occurred on day 9 at 273 Am. The percentage of settlement varied from 13.9% to 56.2%. The growth of post-set clam spat has been described by the equation of L=0.0086x1.4672 , where L is the length in mm and x is the number of days. The clam seed reached a size of 11.5 mm at 4 months. The significance of this study is to standardize the techniques for hatchery production of the seeds of M. opima. D

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