To quantify the effects of seasonal harvests on ploidy type, several spawns using tetraploid oysters held from the spring 2016 spawn were attempted in the fall at a participating commercial hatchery; however, viable gametes were not obtained. Since availability of triploid seed was limited, it was decided to purchase single-set seed with project funds from the Louisiana Sea Grant oyster hatchery and Auburn University shellfish hatchery. Disease certifications and ploidy verification required by the Department of Agriculture and Consumer Services for out-of-state oyster seed were obtained. These stocks were combined. A similar number of diploid seed was obtained from a Florida hatchery using a spawn that occurred at a similar timeframe as the triploid spawns (September/October). Both sets of seed were nursed over the winter at a commercial nursery facility in Cedar Key until they reached the size to be distributed to participating growers.
Distribution of Seed to Growers
Grower commitments were the same as those in the previous crop when seed were distributed in late July 2016 and harvested in March 2017 (see July 27, 2016 news article). Eight growers in four counties (Charlotte, Franklin, Levy, and Wakulla) agreed to participate again. Seed, 2500 diploids and 2500 triploids, were delivered to these growers between March 16 and April 5. In the land-based nursery phase, the triploid seed grew faster than the diploids. When the seed were distributed, the average size of triploids was 25 mm (1”) in shell height and 2.6 grams in total weight, while the average size of diploids was 21 mm and 1.5 grams. These oysters may be ready to harvest as early as October as most of the culture period will occur during the summer when water temperatures are the warmest, as opposed to the first crop in which most of the culture period occurred during the winter months.
Initiation of UF Field Trials
Seed oysters were also deployed at the UF experimental lease in Cedar Key on April 20. Both diploid and triploid seed were stocked into 9 mm mesh Vexar bags supported by bullet floats at a density of 700 per bag. By this time, triploid oysters had reached an average size of 34 mm (1.4”) and 5.1 grams, while diploid oysters were 29 mm (1.2”) and 3.3 grams. Within 4-6 weeks, the bags will be pulled and oysters graded and restocked into 14 mm mesh bags. This will initiate the next phase of the growout study and another set of replicated field trials in which float design and biocide-free antifouling coatings for biofouling control will be evaluated. Samples (n=50) of diploid and triploid seed were provided to Dr. Huiping Yang whose UF laboratory has a flow cytometer, which is used in counting the number of chromosomes in living organisms. The results confirmed the ploidy of oysters being used in this new crop.
Pictures of diploid seed (blue tag, left) and triploid seed (orange tag, right) distributed in March and April.