While shell movement and pumping rate serve as good indices of 

 immediate responses of oysters, they cannot at present be directly related to 

 growth. Four groups of West Bay oysters were used to study such relation*- 

 ships and to determine the effects on growth of various water treatments. 

 Three of these groups, containing 10 individuals each, were maintained in the 

 sea-water laboratory. These groups received untreated water, filtered water, 

 and filtered ultraviolet-irradiated water, respectively, at the rate of about 60 

 liters per hour. Filters (Aqua-Pure, Cuno) containing elements with a por- 

 osity of 5 microns were used. The fourth group was maintained in Offats 

 Bayou in a tray suspended from a pier. 



Growth rate of oysters main- 

 tained in sea-water laboratory 

 and Offats Bayou. The death 

 of the largest oyster in the 

 group receiving untreated 

 system water accounts for 

 the sharp decrease in the 

 mean immersed weight of 

 this group between May 16 

 and May Z3. 



Oyster growth was measured in terms of immersed weight, a method 

 that circumvents the inaccuracies of either weight-in-air or length measure- 

 ments. The range of the initial immersed weights for each group was about 

 5 to 20 gra} IS. The results are presented in the figure. 



The most striking result is the difference between growth rates of 

 the Offats Bayou and sea- water laboratory groups. The more rapid growth of 

 the former group probably stems from a greater abundance of food. Since 

 oyster food is generally considered to be particulate, unfiltered water contain- 

 ing such material should support better growth than filtered water. This was 

 not the case in this experiment. The growth rates of laboratory oysters in fil- 

 tered water were highly similar to those of the oysters in unfiltered water. 

 This similarity suggests that a shortage of particulate food is inherent to the 

 laboratory water. 



It is interesting that both immediate and long-term oyster responses 

 to an artificial environment provide similar indications. 



74 



