Changes in tissue concentrations of the vitamins B1 and B2 during reproductive cycle of bivalves Part 2. The Pacific oyster Crassostrea gigas

Thiamin and riboflavin (vitamins B1 and B2) were measured in different orga ns of the Pacific oyster Crassostrea gigas over an annual cycle in Marennes Oleron (France), to study the natural accumulation and their possible tran sfer to gonads and eggs. We observed an annual cycle of vitamin concentrati on with low levels in winter and high levels in spring. The first increase was observed in the digestive gland (DG) in March with no change in the man tle plus gonad tissue or muscle, suggesting no immediate transfer to gonad tissue or a strong utilisation of these vitamins in the gonad in winter. A second peak was observed in the DG in spring, coinciding with an increase i n the gonad plus mantle and muscle, suggesting that vitamin transfer was im mediate in spring. The DG could be an intermediate compartment in vitamin t ransfer. Riboflavin was mainly concentrated in eggs and disappeared from th r: gonad during spawning. Thiamin was also concentrated in eggs but also in the gonad-mantle tissue. By artificial conditioning, it was possible to in crease the thiamin concentration 2.5-fold in eggs in spring, but riboflavin concentrations remained similar to those in nature. No difference was evid ent in D-larval production from natural or hatchery spawnings, nor in larva l growth rate in spring. Vitamins B1 and B2 in eggs were probably above D-l arval requirements in spring (9 and 20 fg/egg (dry weight) for thiamin and riboflavin, respectively). Low vitamin concentrations observed in winter co inciding with gonadal mitoses and glycogen metabolism, could be explained b y a high vitamin utilisation for these biological processes. These results may explain low levels of vitamins observed in eggs from winter conditionin g of oysters as natural vitamin concentration in this period is low. and tr ansfer to gonads seems limited. (C) 2001 Elsevier Science B.V. All rights r eserved.