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 organs of the Pacific oyster Crassostrea gigas over an annual cycle in Marennes Oleron (France), to study the natural accumulation and their possible transfer to gonads and eggs. We observed an annual cycle of vitamin concentration 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 mantle 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 in the gonad plus mantle and muscle, suggesting that vitamin transfer was immediate in spring. The DG could be an intermediate compartment in vitamin transfer. Riboflavin was mainly concentrated in eggs and disappeared from thr: gonad during spawning. Thiamin was also concentrated in eggs but also in the gonad-mantle tissue. By artificial conditioning, it was possible to increase the thiamin concentration 2.5-fold in eggs in spring, but riboflavin concentrations remained similar to those in nature. No difference was evident in D-larval production from natural or hatchery spawnings, nor in larval growth rate in spring. Vitamins B1 and B2 in eggs were probably above D-larval requirements in spring (9 and 20 fg/egg (dry weight) for thiamin and riboflavin, respectively). Low vitamin concentrations observed in winter coinciding with gonadal mitoses and glycogen metabolism, could be explained by a high vitamin utilisation for these biological processes. These results may explain low levels of vitamins observed in eggs from winter conditioning of oysters as natural vitamin concentration in this period is low. and transfer to gonads seems limited. (C) 2001 Elsevier Science B.V. All rights reserved.