Temporal variation in biodeposit organic content and sinking velocity in long-line shellfish culture

We measured the organic content and sinking velocities of biodeposits from two scallop species(Chlamys farreri,Patinopecten yessoensis) and abalone(Haliotis discus hannai) that were cultured on suspended long-lines.Measurements were conducted every two months from April 2010 to February 2011.The shellfish were divided into three size groups(small,middle,and big sizes).At each sample point,we assessedbiodeposit organic content,average sinking velocity,the frequency distribution of sinkingvelocities,and the correlation between organic content and sinking velocity.The organic content of biodeposits varied significantly among months(P<0.05) and the pattern of change varied among species.Sinking velocities varied significantly,ranging from <0.5 cm/s to >1.9 cm/s.The sinking velocities of biodeposits from C.farreri and P.yessoensis were 0.5-1.5 cm/s and from H.discus hannai were <0.7 cm/s.The organic content was significantly negatively correlated to the sinking velocity of biodeposits in C.farreri(P<0.001) and P.yessoensis(P<0.05).

Use of natural trophic resources by Eastern oysters and Pacific oysters of different ploidy

Ploidy manipulation,such as triploidy,in farmed oysters has been used as a tool to enhance oyster quality throughout all seasons because triploid oysters allocate less energy to gametogenesis,and therefore are deemed better performers than fertile diploids.Nevertheless,scientific reports describing no differences between ploidies and,in certain conditions,disadvantages of triploids are not uncommon.As the use of triploid oyster seed increases culture cost for growers,consistency in performance of triploids is considered to be an important goal.Thus,research to assess how ploidy affects physiological processes underlying oyster performance is fundamental for the aquaculture industry.This work was undertaken to assess if ploidy-based differences in performance in the two most commonly cultivated commercial species of oyster in the United States,Crassostrea virginica and Crassostrea gigas,are associated with filtration,feeding,and metabolism.To test this hypothesis,biodeposition measurements were made with oysters exposed to ambient water conditions at locations and seasons providing a variety of environmental conditions.Oysters did not show differences in filtration and feeding associated with ploidy,but physiological feeding variables fluctuated with environmental characteristics associated with spatial and seasonal differences.A preliminarily test of the hypothesis that differences in energy metabolism may account for differences in performance among ploidy levels indicates that basal metabolic rates of diploid,triploid,and tetraploid Eastern oysters are not different.