A deterministic, forecasting, equilibrium study has been conducted of the multispecies and multi-métier fisheries of the Celtic Sea, ICES divisions VIIf and g. Calculations have been made of the optimal fleet sizes and mesh sizes required to maximize objectives of joint relative sustainable yields, gross revenue and net revenue. The species modelled are the resident populations of cod (Gadus morhua), whiting (Merlangius merlangus), sole (Solea solea), plaice (Pleuronectes platessa) and Norway lobster (Nephropsnorvegicus), with additional consideration given to catches of hake (Merluccius merluccius), monkfish (Lophius sp.) and megrim (Lepidorhombus whiffiagonis). The fleet métiers modelled are the beam trawls, Nephrops otter trawls and non-Nephrops otter trawls. If mesh sizes can be calculated independently for each métier, then the yields and the gross revenue are maximized by increased effort and mesh sizes, especially in the non-Nephrops fleet. If a common mesh size is required for all fleets, then the yields and the gross revenue are maximized when (i) this mesh size is of 114 mm, (ii) the fishing effort in beam and Nephrops fleets is significantly increased, (iii) the non-Nephrops fleet is almost eliminated. Maximization of net revenue requires a mesh size similar to the current mesh of 80 mm, but with significant reductions of fishing effort in all fleets. Average profitability is increased by 50 millions EUROs per year for the Celtic Sea fishery. The model provides a basic structure for examining the management with a more realistic dynamic and stochastic description of the Celtic Sea fisheries.

Fish Farming enriches the water column in dissolved organic and inorganic material. These materials excreed by the fish, elutriate from uneaten food and derive from other polluting substances. Ratios of the organic/inorganic forms of substances (for example N and P) are thus modified. Such perturbations in turn affect phytoplankton development. From in vitro analyses and tests of water taken from a turbot rearing tank, we show the changes in seawater chemical composition produced as well as the way growth was modified in three phytoplankton species: the diatom, Chaetoceros gracile, and the dinoflagellates, Gymnodinium cf. nagasakiense and Alexandrium minutum. Elutriates from the granules used for feed (0.1 to 100 mg.l−1) were found to be stimulating, particularly for Gymnodinium. Alexandrium was strongly inhibited both by turbot-tank water diluted 10-fold with coastal seawater and by diluted faeces elutriates. Urea added at low concentrations (1 to 2.5 µmol.l−1) inhibited growth in Alexandrium and Chaetoceros, but at 1 µmol.l−1 it stimulated growth in Gymnodinium. The antibiotic, Oxytetracycline was complex in its effects, with growth inhibition being observed in Chaetoceros and Gymnodinium, but stimulation in Alexandrium (at 0.2 mg.l−1). In general, we found fish farming to allow phytoplankton growth, except for Alexandrium in a few cases. Additions to the water from fish farming may regulate growth in some species. As such additions act differently on growth in different species, fish farming is likely to markedly modify species composition in its vicinity.

Mussel (Mytilus galloprovincialis) plasma contains cytotoxic activity against both vertebrate (erythrocytes and mouse tumour) and protozoan cells. Procaryotes (Escherichia coli and Vibrio alginolyticus) were not sensitive to the cytotoxicity. The activity was still present in dialyzed samples but was inhibited by heating at 45 °C. Large individual variability which was not correlated with protein concentration and an increasing number of reactive specimens following injection, suggested that naive mussels were in various stages of immune response. Purification by anion exchange chromatography followed by gel filtration revealed a 320 kDa cytotoxic polymeric protein that acts through a polymerization process after binding onto target cell membranes as revealed by ultrastructural observation.

European and Pacific oysters (Ostrea edulis and Crassostrea gigas) expressed antibacterial activity against both Gram negative and Gram positive bacteria which was most probably due to small proteins. When tested against the marine pathogenic Vibrio alginolyticus, hemocyte lysates of both species were more active than cell-free plasma. Antibacterial activity showed significant individual variability that was dramatically reduced by stimulation through mechanical stress or injection. The number of spontaneously active Pacific oysters increased from 50 to 100% following a single injection of bacteria.

These results strongly support the view that bivalve molluscs possess sensitive immuno-defense mechanisms that will greatly aid the development of aquaculture systems by employing refined techniques of transgenesis.

Several virulence factors involved in the potential pathogenic capacity of Vibrio P1, the causative agent of brown ring disease (BRD) affecting cultured Manila clam adults (Ruditapes philippinarum), have been evaluated in comparison with other strains of several Vibrio species isolated from diseased clams. The importance of bacterial cell surface associated properties as virulence factors has been studied considering both non-specific and specific bacterial adhesion to clams. Vibrio P1 showed moderate hydrophobicity, but high affinity to bind to Congo Red dye and the presence of appendages, characterized as fimbriae or pili. All the strains of Vibrio P1 secreted haemolysis and cytotoxins, and were also strong exotoxin producers. The presence of a large 49.2-MDa plasmid in all the strains of Vibrio P1 may be used as an epidemiological marker, but its involvement in pathogenic mechanisms has not yet been established. Although in some Vibrio strains, iron-acquisition systems play an essential role in their pathogenicity, they do not seem to be an important factor in Vibrio P1, since this pathogen lacks siderophore-mediated iron transport mechanisms.

Adult, healthy Manila clams, Ruditapes philippinarum, were inoculated in the laboratory with different, possibly pathogenic bacteria species to study the cellular immune responses. Challenging the clams with Vibrio P1, the causative agent of brown ring disease, induced significant increased total hemocyte counts three days post-challenge. The triggering role of the number of bacteria in the inoculum suggested a threshold for inducing the host response. In addition, a significant decrease of hyalinocytes and an increase of granulocytes revealed a modification in hemocyte population balance. No response was observed in individuals that received either heat killed-Vibrio P1, V. anguillarum or V. pelagius. These experiments demonstrate in R. philippinarum the influence of bacterial parameters on the selective induction of host immunodefence mechanisms. The biological processes by which intra-pallial inoculation of Vibrio P1 stimulates the internal defence system of the host has not yet been identified but the role of some bacterial factors (toxins, adherence capacity) is discussed.

Juvenile oyster disease (JOD) in the eastern oyster, Crassostrea virginica, is characterized by a conchiolin deposit on the inner surface of the valves. Similarities to pathological syndromes affecting other oysters (pearl oyster mortality) and clams (brown ring disease), has suggested an infectious origin and a possible bacterial etiology. Bacteriological analysis (Total Heterotrophic Bacteria, THB and Total Vibrio sp., TVS) of oyster soft tissues, shell fluid and inner shell surfaces were monitored during the course of JOD onset and development. A significant increase in THB (but not TVS) occurred in shell fluid and at the surface of the inner shell of JOD affected oysters. At the same time, changes in cytometric parameters (Total Hemocyte Counts, THC; Differential Hemocyte Counts, DHC) in hemolymph and shell fluid were documented in symptomatic oysters. THC in the shell fluid showed a decrease in late-stage JOD oysters. The disease was also correlated with altered cell ratios in both hemolymph and shell fluid, resulting in an increase in the percentage of the granulocytes in both locations. Our results have showed that main pathological changes associated with JOD occurred in extrapallial region rather than in the soft tissues. The disease was transmitted in the laboratory by extracts from diseased oysters: anomalous conchiolin developed within 4 weeks and the prevalence was higher when two inoculations were performed rather than one. A number of bacterial strains were found at high levels in diseased oysters and isolated. However, none produced the JOD deposit when injected into asymptomatic oysters. The bacterial etiology hypothesis for JOD should be explored further, expanded beyond the family Vibrionaceae, and should include consideration of a multiple etiology.

A description is provided of the anomalous conchiolin deposits which are formed by Pinctada maxima and which are associated with unusual mortalities. Comparisons are made with brown ring disease found in Ruditapes philippinarum and juvenile Crassostrea virginica. In P. maxima, the deposits are not organized into a ring but rather are broad-based and result in retraction of the mantle with the deposits lying outside the edge of the mantle. Vibrio sp. have been implicated in causing the diseases of P. maxima and R. philippinarum whereas the etiological agent of the disease in C. virginica is unknown. It is suggested that the coccoid bodies formed in the mantle of C. virginica, but not in affected P. maxima and R. philippinarum, are sequestered portions of cytoplasm formed as a result autophagocytosis. Stimuli which could be responsible for inducing sequestration are discussed. The ultrastructure of the presumptive autophagosomes is described and compared to similar bodies found in C. gigas infected with a herpes-like virus.

In the late 1980's juvenile oysters, Crassostrea virginica, spawned and cultured in New England and New York, began experiencing up to nearly 100% mortalities in some batches of juveniles. The cause of these mortalities was not ascertained immediately, but examination of dead and dying oysters did not reveal a previously recognized disease syndrome. Early studies showed that it was not an environmental or genetic problem, thus we hypothesized that a new, transmissible disease agent caused the observed mortality. This was verified under laboratory conditions where the disease was readily transmissible. Transmission was enhanced by warm water temperatures, 22–26 °C, and salinities of 18–30 ppt. Also, the infectious agent was filterable and sensitive to erythromycin, supporting the hypothesis that the causative agent may be a protistan parasite in the 2–6 μm size range. No evidence to support a viral or bacterial etiology was found.

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.