Search

Experimental bath challenge of juvenile and sub-adult Atlantic halibut with Vibrio anguillarum induced severe mortalities of 47 and 80%, respectively. However, animals vaccinated with a commercial V. anguillarum vaccine demonstrated excellent protection against the disease (100% RPS). This study also describes the gross pathology and histological changes associated with this infection. A loss of coordination, haemorrhage at the fin base and splenomegaly were frequent findings. Serum agglutinating activity demonstrated a rise following vaccination, the mean log2 titre rising from 3.8 to 8.4. This was associated with a significant rise in antibody-mediated complement killing ability of immune serum when compared to non-immune serum.

We have studied the early inflammatory response induced by Vibrio anguillarum and by its extracellular products (ECPs) in rainbow trout after intraperitoneal injection. The results showed a very similar inflammatory response which included leucopenia, mainly due to lymphopenia, neutrophilia and an increase in the number of circulating monocytes. Melanomacrophages as well as immature leucocytes were frequently observed circulating in the blood of injected rainbow trout. Monocytes often contain phagocytosed bacteria and other, altered cells including erythrocytes and leucocytes. However, neutrophils only occasionally phagocytosed bacteria. Many circulating leucocytes showed important structural alterations. Neutrophils of trout injected with bacteria and ECPs also showed stronger PAS‐staining than those of control trout as well as Dohle bodies and swollen granules. A marked vasodilatation was observed in the kidney and spleen which was coincidental with a mobilization of eosinophilic granular cells and an hypertrophy of sinusoidal endothelial cells showing an increase in the number of cytoplasmic granules. An increase in the number of macrophages and melanomacrophages in the kidney and spleen as well as oedema and leucocyte infiltration in the liver and gills were also noted. Copyright © 1994, Wiley Blackwell. All rights reserved

Atlantic salmon (Salmo salar) post-smolts exposed to 1.23‰ hydrogen peroxide for 20 min at 13.5 ‡C suffered an acute toxicity resulting in a 35% mortality within 2 h. Under similar conditions at 10 ‡C no mortalities were observed with Atlantic salmon or goldsinny wrasse (Ctenolabrus rupestris). No histological changes were noted in tissues from exposed fish. Thirty-three per cent of adult and pre-adult sea lice (Lepeophtheirus salmonis) were immobilized or killed following exposure to 0.5‰ hydrogen peroxide at 10 ‡C, rising to 98% at 2‰. Some lice were able to recover and regained normal swimming movements. Gas bubbles within the haemolymph caused affected lice to float on the water surface. A delay in the toxicity of hydrogen peroxide to copepodites occurred, with a 10% mortality following a 20 min exposure to 1.25‰ at 10 ‡C rising to 100% mortality at 19 h post treatment.

Evaluation in vivo and in vitro of the extracellular products (ECP) of a group of Renibacterium salmoninarum strains from different geographic origins revealed a low production of extracellular proteins in all strains and confirmed that most of the isolates were poor producers of proteolytic enzymes. The ECP displayed neither haemolytic activity nor capacity to alter the osmotic equilibrium of fish erythrocytes. In addition, none of the ECP samples displayed cytotoxic activities regardless of the origin of the cell line employed and did not contain substances lethal for fish, since no mortalities were recorded when doses ranging from 10 to 20 μg protein/g fish were administered. Although the present work failed to demonstrate toxicity in vivo of the ECP, it is possible that some extracellular enzymes contribute to the weakening of fish during the disease process and allow bacterial survival.

Seven (0.039%) and five (0·028%) of 18 163 common dab from the east coast of Scotland were definitive hosts to Lernaeocera branchialis and to Haemobaphes cyclopterina, respectively. Both represent new host records. Muscle necrosis and localized haemorrhage were associated with H. cyclopterina infestation and as described from other definitive hosts.

Summary The treatment of sea lice, Lepeophtheirus salmonis infestations on farmed Atlantic salmon, Salmo salar requires regular bathing of the fish in diachlorvos (DDVP), 2,2-dichlorovinyl dimethyl phosphate, with subsequent release to the marine environment of spent pesticide. The toxicity of a possible alternative compound, carbaryl, l-naphthyl N-methylcarbamate) to kill sea lice and Atlantic salmon was examined. Preliminary studies with carbaryl indicate the potential advantage of a reduced treatment dose was outweighed by the greater persistence of both the parent compound and of its toxic degradation product. Hence this carbamate insecticide is unlikely to be considered by regulatory authorities as an alternative treatment for sea lice infestations.

Overview of cage cutlure marine and brackish water - coldwater fishes freshwater - coldwater fishes marine and brackish water - warmwater fishes fresh water - warmwater fishes noninfectious disorders emerging infectious diseases.

Cranial nodules are described from Atlantic salmon, Salmo salar fry hatched from certain egg batches. Conspicuous, smooth, mostly unilateral nodules were recorded on the cranium. Histologically, the cerebellum appeared normal, but was displaced dorsally. Karyorhectic malpighian cells were absent from the epidermis and the meninges appeared normal. There was no apparent contact of the cerebellum with the water, or evidence of fungal, bacterial or parasitic infection. Mortality of up to 15% as recorded. The aetiology of this condition is currently unknown.

Bacterial kidney disease was induced experimentally in rainbow trout, Salmo gairdneri Richardson, and Atlantic salmon, S. salar L., and selected serum parameters measured over a 35-day period. In those fish which became infected a significant increase in the erythrocyte sedimentation rate and in the serum levels of bilirubin, blood urea nitrogen and potassium were recorded. A significant decrease in total serum protein, cholesterol and sodium also occurred in these fish. Electrophore-tic analysis of serum proteins showed the fast migrating fraction was reduced before the slower migrating material in infected fish.

Disease levels in common dab were found to be significantly lower in an area receiving sewage sludge in comparison to an adjacent control area; a ‘rested’ dump area with its adjacent control area; and a control area in a region well separated from sources of pollution. The pattern of serum lysozyme levels reflected the different prevalance of disease but kidney bacterial levels showed no discernible pattern between areas. Single pathological conditions examined in cod and haddock showed no trend. Until more information is available on the distribution and causes of natural variations in fish disease levels caution should be exercised in the interpretation of positive or negative correlations found between fish disease levels and pollution.

The first outbreak of bacterial kidney disease in farmed salmonids in Scotland was recorded in 1976, The number of individual outbreaks has now risen to at least 37. Disease outbreaks are seasonal, reaching a peak during May. In many cases infection has spread following the movement of juvenile fish. Mortalities are variable; in extreme cases 20% per annum occurs. Both gross signs and mortalities are reduced in fish reared in sea water.

Direct connections (abdominal pores) between the peritoneal cavity and the external environment of elasmobranch fishes and some teleost species including the Salmonidae were recognized almost 100 years ago but over this period their existence in these teleost species has been omitted from anatomical texts. In this report, the abdominal pores of rainbow trout, Salmo gairdneri, Atlantic salmon, Salmo salar, and the cisco, Coregonus artedii, were examined in relationship to ip injected particulate material. Both carbon particles and suspensions of the bacterial kidney disease organism were found to be extruded within masses of macrophages and as free particles through the abdominal pores in fish injected ip 72 h previously. The pores were patent in male and female, mature and immature fish. The role and significance of the abdominal pores in rainbow trout in the clearance from the body of material, including material likely to be used for vaccinating fish, is discussed.

An outbreak of clinical furunculosis in commercially reared Atlantic salmon, Salmo salar L., broodfish in fresh water was successfully treated with a single intraperitoneal injection of oxytetracycline. The mean serum oxytetracycline residue in these fully mature fish did not decline and, at 8 weeks post-injection, was 3·7 μg/ml. In contrast, the mean serum residues in other fully mature but healthy fish declined during an 8-week experimental period to 1·3 μg/ml. The mean concentration of oxytetracycline in the liver of healthy mature fish was approximately two-fold that of similar aged but non-mature fish, and approximately four-fold the concentration found in post-smolts. Oxytetracycline residues 8 weeks after injection exceeded the minimum inhibitory concentration required for oxytetracycline sensitive Aeromonas salmonicida isolates in all groups, therefore under these circumstances, this antibiotic may be effective at a lower dose than that currently recommended. The histology of the liver from the furunculosis-surviving broodfish showed an increase in tissue lesions when compared with the other mature and non-mature fish in fresh water. The combination of prior infection and the physiological status of fasting broodfish may have influenced the rate at which this antibiotic is removed, and, in cases where these residues persist, there may be further damage to the liver.

Culex pipiens fatigans females were offered a choice of oviposition sites, and a significant response was recorded to the presence of egg rafts at various densities. Further experiments indicated that this response was due to the presence of the apical droplet material located on each egg. A larger amount of apical droplet material produced a more highly significant response. The attractant properties associated with the apical droplets decreased with time. Cx. p. fatigans responded in an idenical manner to 1 egg raft of Cx. p. fatigans, Cx. p. molestus or Cx. tarsalis , thus establishing the nonspecific nature of the attractant. Cx. tarsalis required the presence of larger numbers of egg rafts before showing a response. The male mosquito played no role in the formation of the apical droplet or its attractant properties. Simulated egg rafts were not attractive. Oviposition by Cx. p. fatigans was not influenced by the presence of larvae or pupae at 2 different densities, by the presence of trapped adults at the water surface or by a 5% sucrose solution.