Effects of controlled air exposure on the survival, growth, condition, pathogen loads and refrigerated shelf life of eastern oysters

Abstract

The benefits of exposing eastern oysters to air during commercial culture have not been well-characterized. An adjustable longline system (ALS) designed in Australia and recently adopted by the nascent aquaculture industry in the northern Gulf of Mexico, allows growing oysters at any position in the water column and is perfectly suited to study the benefits of air exposure. Four-month old diploid oysters were deployed in an ALS and divided into three groups: 1) oysters exposed to air daily for 8-12 hr during low tide, 2) oysters exposed to air weekly (~24 hr once a week), and 3) oysters kept subtidally. Oyster mortality and growth rates, Perkinsus marinus load and condition index were then determined every 3 months over 2 years, while refrigerated shelf life and Vibrio vulnificus load were determined in summer and early fall of the second year. Summer mortalities were delayed, P. marinus infection intensities tended to be lower and condition index was significantly higher in oysters exposed to air daily compared with oysters exposed to air weekly or held subtidally.Shell heights of oysters exposed to air daily were lower for most of the study due to a lower growth rate during the initial sampling interval following deployment. No consistent differences were found in V. vulnificus loads or refrigerated shelf lives between the groups. It is recommended that ALS be set so that oysters are kept subtidally fall through spring to promote growth, and exposed to air daily during summer to delay P. marinus proliferation.

Characterizing the Epigenetic and Transcriptomic Responses to Perkinsus marinus Infection in the Eastern Oyster Crassostrea virginica

“…The fact that these two datasets provide similar findings of a small number of genes being differentially expressed suggests two major takeaways; (1) that the individuals observed in this study were likely suffering from longterm infections of P. marinus; and, (2) that the shared differential expression of genes associated with tumor necrosis factors (complement system C1q) means these genes in particular are good candidates for further investigation as potential markers of disease resistance. Assuming that the individuals were suffering from long-term infections is consistent with other observed infection rates at this out-plant site (La Peyre et al, 2018). For the genes identified by both our study and the previous controlled exposure (complement C1q tumor necrosis factor-related protein 7-like and multimerin-2-like) we see an approximate sixfold increase in expression between the moderate-heavy and verylight infection categories.…”

“…Infection intensities were enumerated by adding 0.22 µm filtered seawater (20 ppt) at a concentration of ∼0.4 g ml −1 and homogenizing the oyster meat in each 50 ml test tube. One ml of the oyster homogenate was used to measure the number of P. marinus hypnospores g −1 oyster wet tissue using the wholeoyster procedure (La Peyre et al, 2018). Oyster infections were classified as either very-light (≤1,000 parasites g −1 wet tissue), light (1,001-10,000 parasites g −1 wet tissue), moderate (10,001-100,000 parasites g −1 wet tissue) or moderate-heavy (>100,000 parasites g −1 wet tissue).…”

Lack of genotype‐by‐environment interaction suggests limited potential for evolutionary changes in plasticity in the eastern oyster,Crassostrea virginica

“…Perkinsus marinus infection intensities were evaluated by adding 0.22 µm filtered seawater (20 psu) at a concentration of ~0.4 g ml −1 and homogenizing the oyster tissue in each 50-ml test tube. One millilitre of the oyster homogenate was used to measure the number of P. marinus parasites per gram of oyster wet tissue using the whole-oyster procedure (La Peyre et al, 2018).…”

Producing young, single and meaty oyster Crassostrea iredalei (Faustino, 1932) in grow‐out culture using pouches suspended from rafts

“…Also, using C. iredalei , Chueachat et al (2018) reported a significantly higher survival when they were cultured inside earthen ponds (99.8%), as compared to when they were reared in mangrove canals (66.7%). Compared with the other species of Crassostrea in grow‐out culture studies, survival was quite low than what was reported for C. virginica cultured for 9 months subtidally (97.6%) or exposed daily for 8–12 h (98.7%), but higher than those exposed for 24 h once a week (86.5%) (La Peyre et al, 2018). On the other hand, in a 14‐month culture of C. gigas , Brown and Hartwick (1988) reported a lower survival of 31.5%–57.3% for those initially stocked at 20–30 mm shell height while higher at 63.2%–89.7% for those with an initial height of 40–50 mm.…”