Influence of microalgae concentrate diet mixture on growth and survival of larval eastern oysters, Crassostrea virginica  

Previous studies and success of facilities producing commercial quantities of oyster seed have proven that rearing eastern oyster larvae, Crassostrea virginica, using solely microalgae concentrates is effective. Facilities using microalgae concentrates to rear oyster larvae typically feed solely Shellfish Diet 1800^® procured from Reed Mariculture Inc.. In an effort to optimize larval survival and growth, varying rations of concentrated Pavlova 1800 diet were added to the diet for the duration of larval culture.   Diet mixtures included: 100% Pavlova, 50% Pavlova/50% Shellfish Diet 1800^®, and, as a control, 100% Shellfish Diet 1800^®.  

Oysters were spawned at the Lady's Island Oysters hatchery in Seabrook, South Carolina, USA.  Eggs and sperm were collected from local wild broodstock and pooled prior to fertilization.  Fertilized eggs were equally distributed among eight, 113L tanks containing one micron filtered, ultraviolet sterilized aerated seawater at densities recommended by previous microalgae concentrate diet studies (Rikard & Walton, 2012).  Treatments were randomly assigned to the eight tanks, with three replicates per experimental treatment and two control replicates.  Larvae were fed every 8-10 hours at volumes, and using methods, recommended by Rikard and Walton (2012) for batch feeding.  Tanks were drained every other day to assess larval development and survival.

Preliminary analyses indicate larvae fed a diet consisting of 50% or 100% Shellfish Diet 1800^® experienced significantly better survival than oyster larvae fed a diet consisting of 100% Pavlova 1800.  While larvae fed a 100% Pavlova 1800 diet performed well initially, they experienced significantly higher mortality by Day 14 than our other treatments.  Interestingly, oyster larvae fed a diet consisting of a mixture of 50% Shellfish Diet 1800^® and 50% Pavlova 1800 performed the best with regards to survival, achieving 42% greater survival than the control group.  Final results of this study will be presented, along with effects of diet on larval growth.