A study has been carried out on the acid soluble fraction (hydrosysis at pH 1.5, 3N HCl, 20 % KCl) of organic matter (OM) in the highly calcareous lacustrine sediments of the Jura region, France. Amino acids (AA's) were quantified and determined ninhydrin photometry and HPLC respectively. There was a high degree of interference by calcium in both procedures. The mechanism of interference is explained and methodology adopted to overcome it, by removal of calcium, are dealt with. The results of both methods are compared.

The spionid polychaete Polydora sp. can live and reproduce inside the oysters' shell, excavating a U-shaped burrow the central portion of which is filled with detritus and particles of dissolved shell. The oyster responds by secreting an organic layer, confining the worm, and later covering it with calcitostracum. This process creates a characteristic "mud blister". Crassostrea gigas were analysed for the organic matrix amino acid content and 14 metals of the whole shell of normal oysters and severely Polydora infested ones. Amino acid, DOPA and FT-Raman analyses were also performed on isolated membranes from the characteristic mud blister and on prismatic layer insoluble matrix (PLIM) of infested oysters, with the aim of detecting any differences between the two organic matrices. Membranes and PLIM composition differ from whole normal shell organic matrix by having lower aspartate and glycine and higher levels of virtually all hydrophobic amino acids, especially alanine. There are no significant differences between membranes and PLIM in the ratio of charged to non-polar amino acids, respectively 0.54 and 0.59. L-DOPA content is also similar in the two matrices with 0.45 (± 0.18) and 0.57 (± 0.30) ng.mg−1 protein for PLIM and membranes respectively. The FT-Raman spectra of membranes is very similar to that of PLIM, suggesting that they have identical composition. Zinc, iron and manganese are significantly higher in infested than in normal shells. Infested oysters can provide an excellent opportunity for investigating normal biological calcification processes.

Reliable data on tilapia nutrition and feeding are scarce. In the best documented field, that of protein requirement, current data show good agreement with available information on coldwater and warmwater fishes. Various feedstuffs have been used to satisfy the protein needs, but the effects of variations of their quality have not been sufficiently studied. The main problem lies in the assessment of the effects of natural food in open rearing structures; thus there are some discrepancies with the results obtained in laboratory. More insight on in situ nutrition of pond fish, as well as the management of the feedstuffs and feeding practices is needed.

Suitable winter wheat cultivars of different degree of resistance to cereal aphids, Sitobion avenae F. and Rhopalosiphum pali L. have been studied in the field conditions. The differences in the chemical composition of possible attractants and repellants have been analysed. The results confirm the inter-pendence between contents of yellow and orange plant pigments in the leaves of the studied varieties and their preference by the aphids. The leaves of the susceptible cultivars also had the highest level of sucrose. The number of the aphids was directly proportional to the total free amino acids content. The higher degree of resistance of the cultivars was related to the contents free phenols in their tissues and was also associated with a high value of ‘toxicity index’, which is the ratio of free phenols content to free amino acids content. Also the contents of structural polysaccharides (cellulose, hemicelluloses and pectins) of the investigated cultivars were inversely proportional to the degree of their infestation.