Henri Grizel

Separation of Crassostrea gigas hemocytes by density gradient centrifugation and counterflow centrifugal elutriation.

A protocol is described to separate several subpopulations of hemocytes in a unique medium which avoids cell aggregation and retains cell-viability. Isopycnic centrifugation in Percoll followed by counterflow centrifugal elutriation provides large quantities of separated granulocyte and hyalinocyte subpopulations.

Phylogeography of the green turtle, Chelonia mydas , in the Southwest Indian Ocean

Patterns of mitochondrial DNA (mtDNA) variation were used to analyse the population genetic structure of southwestern Indian Ocean green turtle (Chelonia mydas) populations. Analysis of sequence variation over 396 bp of the mtDNA control region revealed seven haplotypes among 288 individuals from 10 nesting sites in the Southwest Indian Ocean. This is the first time that Atlantic Ocean haplotypes have been recorded among any Indo‐Pacific nesting populations. Previous studies indicated that the Cape of Good Hope was a major biogeographical barrier between the Atlantic and Indian Oceans because evidence for gene flow in the last 1.5 million years has yet to emerge. This study, by sampling localities adjacent to this barrier, demonstrates that recent gene flow has occurred from the Atlantic Ocean into the Indian Ocean via the Cape of Good Hope. We also found compelling genetic evidence that green turtles nesting at the rookeries of the South Mozambique Channel (SMC) and those nesting in the North Mozambique Channel (NMC) belong to separate genetic stocks. Furthermore, the SMC could be subdivided in two different genetic stocks, one in Europa and the other one in Juan de Nova. We suggest that this particular genetic pattern along the Mozambique Channel is attributable to a recent colonization from the Atlantic Ocean and is maintained by oceanic conditions in the northern and southern Mozambique Channel that influence early stages in the green turtle life cycle.

Isolation and purification of the protozoan Bonamia ostreae (Pichot et al. 1980), a parasite affecting the flat oyster Ostrea edulis L.

The isolation and purification of Bonamia ostreae (Ascetospora), an intrahemocytic protozoan parasite of Ostrea edulis, have been achieved according to an original protocol. The purified cells showed good retention of infectivity and ultrastructural morphology. They could also be used to prepare specific immune sera for indirect immunofluorescence.

Interactions between Bonamia ostreae (Protozoa: Ascetospora) and hemocytes of Ostrea edulis and Crassostrea gigas (Mollusca: Bivalvia): Entry mechanisms

Entry mechanisms of the intrahemocytic parasite Bonamia ostreae (Ascetospora) into hemocytes of the sensitive (Ostrea edulis) and a resistant (Crassostrea gigas) oyster species have been analyzed. The study was based upon the development of a B. ostreae-hemocyte in vitro system. Ultrastructural features and Cytochalasin B sensitivity of the phenomenon demonstrate that B. ostreae enters into the two oyster species hemocytes by host-specified phagocytosis, although parasite contribution to entry into O. edulis hemocytes cannot be discarded. Possible receptors and the postphagocytic fate of the parasite are discussed.

Interactions between Bonamia ostreae (Protozoa: Ascetospora) and hemocytes of Ostrea edulis and Crassostrea gigas (Mollusca: Bivalvia): in vitro system establishment

Abstract Based on parasite purification and hemocyte primary culture, an in vitro system was established for studying early interactions between Bonamia ostreae and the hemocytes of sensitive Ostrea edulis and resistant Crassostrea gigas. Infections were observed whichever the hemocytic types and the oyster species. The advantages and disadvantages of the system are discussed with regard to the study of recognition, entry, and survival mechanisms of the parasite.

Histological study of a cellular reaction in Ruditapes decussatus infected by a protozoan

An infection caused by a Perkinsus -like parasite has been observed in Ruditapes decussatus from Portugal (Comps and Chagot, 1987). Following a pathological study carried out on clams affected by mortalities in the Algarve area, this parasite was found again, inducing a reaction process in the host. Histological examination reveals the parasite in the connective tissue of different organs. The adjoining tissues, particularly the epithelia, are not affected.

Ostrea angasi acclimatization to French coasts

Abstract Following losses of the European flat oyster Ostrea edulis due to epizootic diseases in France, an acclimatization experiment was conducted with hatched juveniles of O. angasi . Major mortalities were rapidly noted in the cultures and attributed to a haplosporidian ( Haplosporidium sp.) to which O. angasi was very sensitive. This species also contracted Bonamia and Marteilia parasites of O. edulis .

Evidence of neutralizing activity against T3 coliphage in oyster Crassostrea gigas hemolymph

To investigate defense reactions of bivalve molluscs against viruses, experimental in vitro assays have been developed using T3 coliphage as a test virus. A native neutralizing factor in oyster Crassostrea gigas serum showed high individual variability and was enhanced significantly by repeated sampling of hemolymph from the same oysters. The responsible factor is apparently thermolabile and sensitive to EDTA treatment. Because of an inhibitory effect by the enzymatic inhibitor, phenylmethylsulphonyl fluoride (PMSF), the T3-neutralizing factor may be related to serine protease.

Induced triploidy and tetraploidy in the European flat oyster, Ostrea edulis L.

Abstract Eggs of the European flat oyster, Ostrea edulis , were treated with cytochalasin B (1 mg/l, 20°C, 20 min), at different time intervals after in vitro fertilization. Ploidy levels were assessed by chromosome counting on 1- and 54-day-old specimens. Evidence for bimodal distribution was found to separate meiotic I and meiotic II triploids. Peaks were located at 30–35 min and 90–100 min post-fertilization, triploid rates reaching 70% and 68% respectively. Tetraploid embryos were induced in two major groups. The effective shocks were those applied at 5–25 min and 260–280 min after fertilization (respectively 40% and 53% tetraploid metaphases). Karyological examinations of embryos and spat, carried out 20 h and 54 days after fertilization, showed a differential mortality among triploids and diploids in all treated groups and no tetraploids among the spat.

Mussel (Mytilus edulis) treatment against the red copepod Mytilicola intestinalis

Abstract Mytilicola intestinalis , a copepod parasite of the gut of mussels, is endemic along European coasts. It has been responsible for heavy mortalities, especially in Mont Saint-Michels Bay (Northern Brittany) between 1982 and 1984. From laboratory screening of seven drugs, an organophosphorate Dichlorvos appears to be the most efficient. Dichlorvos treatment for 2 h at 30 mg/l concentration frees mussels from Mytilicola without any mortality. Later field trials showed an equal efficiency if the drug is used properly.