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The occurrence of brown ring disease (BRD) in farmed Manila clams Ruditapes philippinarum is seasonal. Development of the disease is believed to require the presence of the infective agent Vibrio tapetis and particular environmental conditions. This paper studies the effect of salinity (20 to 40 ‰) on measurable immune parameters of Manila clams, and the progression of BRD in experimentally infected individuals. At 20 ‰ salinity, the total haemocyte count was reduced and disease prevalence was highest. At 40 ‰ salinity significantly fewer clams presented signs of BRD, and this was correlated with increases in the total haemocyte count, hyalinocyte count, phenoloxidase levels and phagocytic activity of haemocytes. Inoculation of clams with V. tapetis did not have a significant effect on the immune parameters measured. Thus, this laboratory-based study relates environmental stress to disease development.KEY WORDS: Vibrio tapetis · Brown ring disease · Aquaculture · Salinity · Immune response Resale or republication not permitted without written consent of the publisherDis Aquat Org 56: [249][250][251][252][253][254][255][256][257][258] 2003 To ascertain salinity tolerance, Strains CECT 4600 T and IS1 of Vibrio tapetis were cultured at a range of salinities from 5 to 60 ‰ in TSB; salinity was adjusted by addition of appropriate amounts of a stock solution of 20% (w/v) NaCl in TSB. The medium was dispensed in 200 µl vol in a 96-well microtitre plate, and at each salinity triplicate wells were inoculated with 10 µl of a standard suspension of V. tapetis to a final concentration of 10 6 bacteria ml -1. The plates were incubated at 20°C with gentle shaking, and growth was measured as the mean optical density at 600 nm.For the inoculation of clams, bacteria were cultured in 100 ml TSB at salinities of 20, 30 and 40 ‰, at 20°C with gentle shaking in an orbital incubator.Inoculation of clams. Adult Manila clams (35 to 40 mm) were obtained from Marennes, France. The clams were maintained in twelve 50 l aquaria with under-gravel filters containing aerated artificial seawater (ASW) at 20, 30 and 40 ‰. Clams were held at a density of 1 individual l -1 water and at a temperature of 15.5 ± 1.5°C. Upon arrival at the laboratory, the clams were initially held in ASW at 30 ‰ salinity for 2 d, after which time the salinity was adjusted as necessary over a 6 d period (3.3 ‰ every 2 d) from 30 ‰ to 20 or 40 ‰ (4 aquaria per salinity, each containing 50 clams). Clams were held for a further week before inoculation to allow acclimatisation.A third of the volume of water was exchanged with fresh ASW of the appropriate salinity 3 times a week. Water was removed from the tanks with a siphon, and faecal waste was removed from the bottom of the tanks during this procedure. It was established by measuring levels of nitrite and ammonia (TetraTests, TetraWerke) that this cleaning/water-replacement regime maintained low concentrations of these toxic compounds.For the duration of the experiment, clams were fed daily on a mixed alg...

International audienceJuvenile clams were distributed in four rearing sites selected for their varied ecological characteristics to assess the effects of environmental conditions on the physiological and immunological parameters, and Brown Ring Disease (BRD) status. Clams were sampled every 3 months for 15 months at each site. Brittany rearing sites, especially the Bay of Brest, showed the worst performances in terms of immunological and physiological indices and disease status, while the best were obtained in Marennes ponds. When the health of the clams was compared to assess seasonal effects, the winter clearly was a stressful period. A combination of bad rearing site and winter conditions led to major mortalities in the Bay of Brest in February. In other sites, winter mortalities were low. Condition index, total haemocyte count and haemocyte size were greatly affected by seasonal variation whereas haemocyte complexity and lysozyme content were more affected by the location of the site. Growth and haemolymph protein content were affected by both season and sites. Linear regressions between and within the physiological and immunological parameters indicated that large haemocyte size was related to low total haemocyte count (THC) and low haemocyte mortality. This relationship suggests a reduction in the cell division rate. Total haemocyte count and protein and lysozyme concentrations were positively correlated to the condition index. Seeded clams showed very low BRD prevalence in all sites and for all seasons; however, high prevalence was observed in natural stocks from one of the studied sites (Gulf of Morbihan), suggesting that hatchery-seeded clams may be more resistant to BRD and may be worthy of further studies

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Piscirickettsia salmonis was grown in established insect, frog, and fish tissue culture cells. The yield of P. salmonis in Sf21 cells was up to 100 times that obtained in CHSE-214 cells, and virulence for Atlantic salmon was retained. The ceiling temperature for growth of P. salmonis in Sf21 cells was 24°C