The Production of Triploid Oyster Larvae (Crassostrea Virginica (Gmelin)) in Louisiana.

Gonadal recycling of oyster broodstock, salinity effects during induction, and cytochalasin B (CB) dosage were investigated as factors affecting the production of triploid oyster larvae in Louisiana. These factors were studied at an oyster hatchery on Grand Isle, LA during 1992-1994 to help transfer triploid oyster technology to the Gulf region. Oyster broodstock were held nearshore in Caminada Bay, Louisiana and histologically analyzed between induced spawnings and during the winter of 1992-1993. Gametogenesis was analyzed qualitatively by developmental staging and quantitatively using mean gonad/body ratios (GBR) per section. The monthly percent occurrence of the developmental stages, as well as histological evidence, showed that gonadal recycling was occurring. Significantly different mean GBR\u27s were found between developmental stages and between successful and unsuccessful spawning attempts (P $\u3c$ 0.05). Experiments were conducted by exposing fertilized oyster eggs to 10 ppt, 20 ppt and 30 ppt seawater after a one week broodstock acclimation period at 13 ppt, 20 ppt and 30 ppt. Resulting polar body extrusion data revealed significant differences between mean synchrony levels of broodstock salinity$\sp{\*}$treatment salinity interactions at mean development time (P $\u3c$ 0.00138). The rates of change in synchrony at each interaction were also plotted. Both analyses showed the highest levels and rates of synchrony were at broodstock salinity$\sp{\*}$treatment salinity interactions of 20$\vert$30 ppt, 20$\vert$20 ppt and 30$\vert$30 ppt. Low salinity was detrimental to obtaining synchronous meiotic development. Survival and ploidy of D-stage oyster larvae were estimated after exposing embryos to CB dosages of 0.5 mg/L, 0.25 mg/L, and 0.125 mg/L for 10-15 minutes, with 0.05% DMSO and ambient seawater as controls. No significant differences were found in survival and triploidy between CB dosages of 0.5 mg/L and 0.25 mg/L and between 0.125 mg/L and the controls (P $\u3c$ 0.05). Recommendations are provided to optimize triploid induction of Crassostrea virginica using CB