Performance of triploid Eastern oysters, Crassostrea virginica, in Mobile Bay, Alabama

A number of researchers have grown triploid oysters, however, the benefit of triploids may be site specific and some attributes remain to be determined. In May 1996, triploidy was induced by treating newly fertilized Eastern oyster, Crassostrea virginica, eggs with cytochalasin B (CB). In October 1996, approximately 2,000 oysters from each group (treatment and control) were transferred to plastic-mesh bags and suspended on a long-line culture system in Mobile Bay. The ploidy of CB-treated oysters was determined to be 77% (23/30), therefore, diploids and triploids were analyzed separately, thereby creating two groups among CB-treated oysters: triploids and treated diploids. Thirty oysters from the CB-treated and control groups were sampled monthly. In May 1997, after 12 months of culture, 83% (25/30) of the CB-treated group was found to be triploid. The mean shell height of the 12 month old oysters was 65.5 mm (n = 5) for CB-treated diploids, 69.1 mm (n = 25) for triploids, and 62.0 mm (n = 30) for untreated diploid (control) oysters. Mean whole weights for the same groups were 28.6 g, 32.9 g, and 26.7 g, respectively. Whole volumes were 19.0 ml, 20.9 ml, and 17.7 ml, respectively. The moisture content was 83.7%, 82.5%, and 84.3% for the treated diploids, triploids, and untreated control diploids, respectively.;In November 1997, after 18 months of culture, 87% (26/30) of the CB-treated group was found to be triploid. Mean shell height of the 18 month old oysters was 87.5 mm (n = 4) for CB-treated diploids, 90.2 mm (n = 26) for triploids, and 84.2 mm (n = 30) for untreated diploids. Mean whole weights for the same groups were 80.2 g, 80.9 g, and 69.7 g, respectively. Whole volumes for the same groups were 52.6 ml, 53.1 ml, and 46.1 ml, respectively. Moisture content was 77.9% for the treated diploids, 80.6% for the triploids, and 79.0% for the untreated control diploids. Shell cavity volumes were 31.6 ml, 32.3 ml, and 28.1 ml for the treated diploids, triploids, and untreated controls, respectively. Wet meat weights were 17.1 g, 16.8 g, and 14.3 g for the same groups. Condition index was 120.4, 102.2, and 107.3 for treated diploids, triploids, and untreated controls, respectively. Gonadal surface areas were 29.26%, 27.28%, and 25.59% for the same groups. Triploid oysters showed many improved growth characteristics over their diploid siblings when compared after 12 months and continuing until 18 months of growth. Triploids had a survival of 60% during the growout phase, while the treated diploids had 30% survival. The untreated controls had a survival of 72.2%.;Shelf life between the untreated controls and treated group were compared after 17 (October 1997) and 24 months (May 1998) of growth. Both groups followed similar patterns of mortality, on both occasions. In October, after the spawning season, diploids showed their first mortality one week before triploids. In May, just prior to the spawning season, triploids showed their first mortality two days before diploids. Three taste tests were given on different dates: May 1997, September 1997, and May 1998. Consumers generally chose triploids over diploids when evaluating flavor, texture, and overall preference. (Abstract shortened by UMI.).