488 MANN 



in some species (e.g., M. edulis), by the initiation of gametogenic 

 processes before low metabolic activity is again evident in relation to 

 low water temperatures. 



During the late stages of gametogenesis, glycogen reserves are 

 rapidly depleted (Masumoto, Masumoto, and Hibino, 1934; Mann, 

 unpublished data). Thus a statement like that of Galtsoff (1964): 

 "Oysters of good quality have a relatively large amount of meat in 

 relation to their total volume. Their glycogen content is high, and the 

 meat has a creamy color ... ." can be misleading. The creamy color, 

 caused by developing gonadal material, is produced at the expense of 

 the glycogen reserves. Once gonad development is initiated and a 

 temperature stimulus is maintained, development continues at the 

 expense of stored reserves whatever the physiological state of the 

 animal. This was well demonstrated for M. edulis by Bayne, Gabbott, 

 and Widdows (1975). Also, Mann (unpublished data) observed gonad 

 proliferation in juvenile C. gigas starved for a period of 3 weeks at 

 14.5°C. 



A simple gross biochemical analysis for major components 

 (carbohydrate, protein, lipid, and ash) or calorie content during late 

 gametogenesis can also be misleading because the possibility exists 

 that a considerable proportion of the energy-rich lipid component is 

 stored in gametogenic products and is not generally available for 

 energy metabolism by the animal. 



Larval forms of oysters (and probably other bivalves) have a 

 lipid— protein-based respiratory metabolism, but there is a gradual 

 change to a carbohydrate— protein-based respiratory metabolism 

 after settlement (Holland and Hannant, 1974). In an ecological sense 

 this is a useful strategy since a high lipid content provides bouyancy 

 in a pelagic larval form. This is unnecessary in a sessile adult in which 

 the requirement for a readily mobilized reserve material is adequately 

 served by glycogen. If the initial effect of a temperature stress is a 

 drain of such reserve material, then, by definition, the quantity of 

 available reserves can be used as an index of condition: 



% Carbohydrate content = Biochemical index (5) 



As for the gravimetric and volumetric indexes (Ito 4), some 

 problems are evident when we apply this index to a wide size range 

 of animals. Metabolic functions, which will inevitably influence the 

 rate of utilization of reserves, are generally related allometrically to 

 the absolute size of the animal. Thus, when Holland and Hannant 

 (1976) examined the summer and winter glycogen contents of five 

 age groups of Ostrea edulis L., they found that, on a percentage 



