دانلود رایگان مقاله ارزیابی سهام برای تولید صدف خوراکی شرقی

Abstract

There is little information on the performance of oyster populations from Louisiana estuaries limiting the ability to choose stocks for hatchery seed production and field grow-out. The objectives of this study were therefore to compare the mortality, growth, dermo (Perkinsus marinus) infection intensity and condition index of the progeny of wild oysters collected from three Louisiana estuaries differing in salinity regime and oysters specifically selected for dermo resistance. Progeny were deployed in cages in the field, along a salinity gradient in coastal Louisiana. Overall, salinity and temperature had major impacts on the mortality, growth, dermo infection intensity and condition index of oysters of all four stocks and a few differences between stocks could be shown at some sites. At the lowest salinity site, the progeny of wild oysters from Sister Lake, a low salinity estuarine lake, had the lowest mortality suggesting enhanced tolerance to low salinity conditions compared to the other stocks. At the highest salinity site, the progeny of wild oysters from Lake Calcasieu, a high salinity estuarine lake, had the lowest mortality during summer concomitant with increasing dermo infection intensities suggesting a better resistance to dermo disease compared to the other wild stocks and confirming an earlier finding. This initial result suggests that the stocks used are genetically differentiated with respect to low salinity tolerance as well as dermo-related mortality at high salinity and that stock selection for aquaculture grow-out or restoration effort will benefit from being site-specific and dependent on the dominant environmental conditions. Statement of relevance: Assessment of eastern oyster stocks in Louisiana or other Gulf of Mexico estuaries for seed production and field grow-out is lacking.

5. Summary

The most significant differences between oyster stocks in our study were their mortalities. The differences in mortalities, however, varied depending on site or interval salinity suggesting genetic × environment interaction. While mortalities were highest at the low and high salinity sites and lowest at the intermediate salinity sites, a different stock had the lowest mortality at the low (i.e., Sister Lake) and high (i.e., Lake Calcasieu) salinity sites. This initial result suggests that the stocks used are genetically differentiated with respect to low salinity tolerance as well as dermo-related mortality at high salinity. Stock selection for aquaculture grow-out or restoration effort will therefore need to be site-specific and dependent on the dominant environmental conditions. The ability of oyster stocks to tolerate extended periods of low salinity will be critical in Louisiana estuaries where large freshwater diversions are planned. In contrast, the ability of a stock to rapidly grow off-bottom to market size in less than a year and be harvested before succumbing to dermo should be selected for in high salinity areas. Selection based on resistance to or tolerance of P. marinus infection will still be needed in estuaries where oysters require more than one growing season to reach market size. Differences in oyster responses to environmental conditions due to their genetic background will need to be addressed more thoroughly in future studies considering the diverse and varying environmental conditions encountered in Louisiana and other Gulf of Mexico estuaries.