Introduction aux recherches sur la presence de substances hydro-carbonnées et lipo-proteiques dans les claires a huitres et sur leur relation éventuelle avec la pigmentation de Navicula Ostrearia B.

In an initial study, Moreau (1967) studied the role of the Navicula ostrearia B. pigment complex in the green colouration of oysters in finishing ponds. Subsequent studies explored the influence of various environmental factors on this mechanism of colouration. The greening process is not well understood and we wished to test the hypothesis by which N. ostrearia pigmentation is closely linked to the presence of oysters (Ranson, 1927). For Ranson, "oyster mucus is made up of mucin that undergoes bacterial-type acid hydrolysis resulting in reducing sugars". These sugars were thought to be the causal agent of N. ostrearia pigmentation. This point of view was greatly debated by Bachrach (1935) and Ranson himself cited several authors (Miquel, 1892; Chodat, 1913) for whom the presence of carbohydrates "causes diatoms to lose their colour". The present note presents research carried out on the presence, the nature and the relationship of these substances, in dissolved or particulate form, with green colouration and pigmentation in N. ostrearia. Carbohydrate production, although well understood particularly in lower plants, appears to be greater in diatoms that grow in unfavourable, nutrient-deficient conditions and in low light, according to Strickland (1960). Interestingly, these same factors seem to favour optimal pigmentation in N. ostrearia. Old cells, after several days of pigmentation, produce more oligosaccharides and polysaccharides, which are the main carbohydrate reserves in the Chlorophyceae, organisms which are made up of glucose polymers. Moreover, according to Parsons et al. (1961) the presence of hexuronic acid has not been detected in all protophyte species. (unverified OCR)