Abstract

To understand the relationship between the nutritional status and the digestive gland structure, we investigated the evolution of the digestive gland of Strombus gigas during a starvation experiment. After the starvation period, conchs were fed again with algae and their digestive gland was also examined. Conchs collected in sea grass beds were kept in 5?mfiltered sea-water during starvation experiments. After seven, thirteen, and twenty one days of starvation (T0+7d, +13d, +21d), the digestive glands were dissected for histological study. Acini are constituted of three cell types: digestive, cryptic, and vacuolar cells. In wild juveniles, the digestive cells contain numerous, large proteoglycan granules (8 - 12 ?m) stained by Alcian blue. For starving conchs, the size of Alcian blue positive granules decrease to 5?m and their number strongly decrease until complete disappearance at T0+21d. After the starvation experiment, surviving conchs were relocated in a Thalassia testudinum environment and recollected after four days. The histological analysis of digestive glands showed again a normal supply of proteoglycan granules. In addition, the evolution of cellular activity was investigated by molecular hybridisation of ribosomes with a fluorescent probe (FISH). Similar cellular activity was detected before, during and after the starvation experiment in all conchs tested. Cryptic cells appear as positive, demonstrating their synthetic function. Research is in progress to investigate the nature and function of proteoglycan granules in digestive cells and to understand the function of vacuolar and cryptic cells in the kinetic of digestion, assimilation and secretion in the digestive gland of queen conch.

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