SETTLEMENT AND GROWTH OF EASTERN OYSTERS PRODUCED FROM CRYOPRESERVED LARVAE

Previous reports on viability of cryopreserved oyster larvae have been limited to evaluation of planktonic stages for less than 6 d after th awing. However, for hatchery and aquacultural purposes the performance of larvae through settlement is of primary importance. The present ex periments on production of oysters from cryopreserved larvae were cond ucted in two consecutive years. Observations through veliger larvae on ly were collected from the first year because of interruption by a hur ricane. In the second year, growth was observed for 4 months. A total of 3 x 10(6) trochophore larvae (12 h post-fertilization) were diluted in a cryoprotectant solution composed of artificial sea water and 15% propylene glycol. Larvae were placed in 5-mL straws, frozen at -2.5 d egrees C per min, and stored in liquid nitrogen. The frozen material w as transported to an oyster hatchery at Grand Isle, Louisiana. Larvae were thawed at 70 degrees C for 15 sec and were incubated in a 200-L t ank. For a control treatment, 6 x 10(6) eggs were fertilized and incub ated in the same conditions as the thawed larvae. After 24 h of incuba tion, 28% of the control group developed into D-stage larvae, while 24 % of the thawed larvae developed to this stage. Larvae were fed daily with 20 L of microalgae (Isocrysis glabana) for 10 d. After incubation , larvae were allowed to metamorphose and attach to substrate and were held for 8 d. Spat were placed in mesh plastic bags and suspended in Caminada Bay (29 degrees 15'12 '' N, 90 degrees 03'26 '' W) to evaluat e survival and growth. After 4 months, 1,000 oysters from the control group, 850 from the thawed larvae, and 57 from naturally spawned oyste rs were found. The results indicate that oysters produced from thawed larvae developed normally in the hatchery, opening opportunities for u se of cryopreserved larvae in oyster research and in commercial indust ry.