INDEXES OF CONDITION IN MARINE BIVALVE MOLLUSCS 491 



problems involved in comparing animals of differing sizes. Physiolog- 

 ical functions can be used to compare animals of differing sizes if we 

 know the allometric relationship of that function to size. Thus, if 



P=aW^ 



where P is the specific rate function, W is the weight, and a and b are 

 constants, animals of differing sizes can be compared by expressing 

 the rate function using the "physiological weight" (W^) rather than 

 the absolute weight (W). Thus comparisons of weight-specific 

 ammonia excretion rates change from 



Mg NH3 - N g dry W~ ^ hr~ ^ 



to 



Mg NH3 - N g dry (W'' )~ ' hr^ ^ 



The nature of the allometric relationship may also change with the 

 seasonal gametogenic cycle. Bayne and Scullard (1977a) described 

 this change for ammonia excretion in M. edulis. Ryther and Mann 

 (1977) described a similar increase in weight-specific ammonia 

 excretion rates and a change in the allometric relationship of this rate 

 to dry-meat weight after spawning in the oysters Crassostrea gigas 

 and Ostrea edulis. 



COMPARING GRAVIMETRIC AND BIOCHEMICAL INDEXES: 

 MATERIALS AND METHODS 



Literature Data 



Data from Masumoto, Masumoto, and Hibino (1934) for C. gigas 

 (Kusatsu stock grown at Kusatsu), from Dare and Edwards (1975) 

 for 65-mm-long M. edulis, and from Walne and Mann (1975) for 

 O. edulis were recalculated to obtain values for percentage carbohy- 

 drate, carbohydrate/N ratios, percentage organic content, and 

 dry-meat /dry-shell ratios for the shellfish stocks examined. Data for 

 each biochemical index for each species were compared to the 

 gravimetric condition index by linear regression analysis. 



Laboratory Studies 



An experiment was performed to delineate the effect of 

 temperature on growth, biochemical storage cycles, and gameto- 



