Relationship between possible available food and the composition, condition, and reproductive state of oysters from Galveston Bay, Texas.

Possible food for oysters was measured as a food index. The food index was defined as the percentage food (food= lipid + carbohydrate + protein) in the total seston. Highest condition index values (C.I.= dry weight/mantle volume X 100) of oysters were not related to the time of greatest available food. The food index was, however, correlated with the gonadal index (G.I.= gonadal thickness/adductor muscle diameter) of oysters. The greatest amount of available food was present during the time of presumed greatest demand, namely the period of gametogenesis. The concept of the storage cycle is applicable to Crassostrea virginica. Changes in the oysters' composition and in condition and gonadal indices support the hypothesis that stored glycogen is converted into the lipid reserves of the developing eggs. The percent carbohydrate and percent lipid content of oysters are positively correlated with the condition index. Increasing carbohydrate levels and condition indices are indicative of oysters in the fattening stage. The increase in lipid levels began in the early spring as carbohydrate levels began to decline. High lipid levels and high gonadal indices occur as a prelude to spawning. High percent protein values and low condition and gonadal indices are characteristics of oysters that have spawned. Changes in the condition and gonadal indices of oysters are temperature-related. Initial spawning apparently occurred at a temperature between 21 and 25 C.