A survey of viral diseases in farmed and feral salmonids in Switzerland

A field survey was carried out to study the occurrence and distribution of viruses causing diseases of major impact in fish farming, namely viral haemorrhagic septicaemia (VHS), infectious haematopoietic necrosis (IHN) and infectious pancreatic necrosis (IPN) in farmed and wild fish in Switzerland. The presence of VHS virus (VHSV), IHN virus (IHNV) and IPN virus (IPNV) in the tissue samples was tested by virus isolation in cell cultures, and subsequent virus identification by immunofluorescence. The sera were screened for anti-VHSV antibodies (VHSV-AB) using a serum plaque neutralization test with complement addition. These data were then compared with results of a similar survey performed in 1984/85, and with data from routine diagnostic work completed at the Centre for Fish and Wildlife Health (FIWI) of the University of Bern from 1978 to 2001. Sampling sites included private and government fish farms as well as natural habitats from all major river catchments in Switzerland. In 2000/01, 522 tissue samples and 1910 sera were collected from 3400 fish. In 1984/85 1239 tissue samples and 694 sera were collected from 1628 fish. During the last 24 years of routine diagnostics at the FIWI, 1776 tissue samples were examined for presence of viruses. The results of the tissue analysis from the surveys in 1984/85 and 2000/01 showed low numbers of sites with virus-positive fish (five VHSV, three IPNV and three VHSV, one IPNV, respectively) in Swiss fish farms and rivers. The sites with virus-positive fish were located throughout the country. The decline in virus-positive cases observed between the two surveys agrees with data from the routine diagnostic work of the FIWI which show a decrease in total virus isolations from approximately 35 cases per year in the late 1970s, to approximately 10 cases per year during the last 10 years. However, in 1984/85 8.3% (58 of 694 serum samples) and in 2000/01 6.3% (121 of 1910 serum samples) proved to be positive for VHSV-AB. The 58 positive samples in 1984/85 originated from 40 of 175 sites (23%) and the 121 positive samples in 2000/01 were from 84 of 217 (29%) sites. These results are indicative of a wider distribution of VHSV than expected from the results of the virus isolations.     

Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review

Osmoregulatory actions of growth hormone (GH) and its mode of action in salmonids are reviewed. We present evidence suggesting that insulin-like growth factor I (IGF-I) mediates some of the actions of GH on seawater acclimation. Plasma concentration and turnover of GH rise following exposure to seawater. Exogenous GH (in vivo) increases gill Na⁺,K⁺-ATPase activity and the number of gill chloride cells, and inhibits an increase in plasma osmolarity and ions following transfer of fish to seawater. A single class of high affinity GH receptors is present in the liver, gill, intestine, and kidney. The levels of IGF-I mRNA in the liver, gill and kidney increased after GH-injection. After transfer to seawater, IGF-I mRNA increased in the gill and kidney following the rise in plasma GH, although no significant change was seen in the liver. Injection of IGF-I improved the ability of the fish to maintain plasma sodium levels after transfer to seawater. GH treatment also sensitizes the interrenal to adrenocorticotropin (ACTH), increasing cortisol secretion. Both cortisol and IGF-I may be involved in mediating the action of GH in seawater adaptation, although studies on the effect of GH on osmoregulatory physiology of non-salmonid species are limited. An integrated model of the osmoregulatory actions of GH is presented, and areas in need of research are outlined.

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Résumé Cet article est une revue des effets osmorégulateurs de l'hormone de croissance et de son mode d'action. Nous présentons des résultats qui suggèrent que le facteur de croissance de type insuline (IGF-I) est un médiateur de certaines des actions de la GH sur l'adaptation à l'eau de mer. Les concentrations plasmatiques et le renouvellement de la GH augmentent après transfert en eau de mer. La GH exogène stimule (in vivo) l'activité Na⁺,K⁺-ATPase et le nombre de cellules à chlorure branchialeset inhibe les augmentations de l'osmolarité et des concentrations ioniques du plasma observées après transfert en eau de mer. Une seule classe de récepteurs à haute affinité pour la GH est présent dans le foie, les branchies, l'intestin et le rein. Les niveaux d'ARNm d'IGF dans le foie, les branchies et le rein augmentent après injection de la GH. Après transfert en eau de mer, les ARNm de l'IGF augmentent dans les branchies et dans le rein en suivant l'augmentation de GH plasmatique, bien qu'aucune modification ne soit observée au niveau du foie. L'injection d'IGF augmente la capacité du poisson à maintenir ses niveaux de sodium plasmatique après transfert en eau de mer. Le traitement à la GH augmente la sensibilité à l'adrenocorticotropine (ACTH) et stimule donc les niveaux de cortisol. A la fois le cortisol et l'IGF-I semblent impliqués comme médiateurs des effets de la GH dans l'adaptation à l'eau de mer, bien que les études sur les effets de la GH sur la physiologie de l'osmorégulation chez les espèces non-salmonidés restent encore limitées. Un modèle intégré des actions de la GH sur l'osmorégulation est présenté et les domaines de recherche à développer sont soulignés.

     

Diversity of Flavobacterium psychrophilum and the potential use of its phages for protection against bacterial cold water disease in salmonids

Flavobacterium psychrophilum causes rainbow trout fry syndrome (RTFS) and cold water disease (CWD) in salmonid aquaculture. We report characterization of F. psychrophilum strains and their bacteriophages isolated in Chilean salmonid aquaculture. Results suggest that under laboratory conditions phages can decrease mortality of salmonids from infection by their F. psychrophilum host strain. Twelve F. psychrophilum isolates were characterized, with DNA restriction patterns showing low diversity between strains despite their being obtained from different salmonid production sites and from different tissues. We isolated 15 bacteriophages able to infect some of the F. psychrophilum isolates and characterized six of them in detail. DNA genome sizes were close to 50 Kbp and corresponded to the Siphoviridae and Podoviridae families. One isolate, 6H, probably contains lipids as an essential virion component, based on its chloroform sensitivity and low buoyant density in CsCl. Each phage isolate rarely infected F. psychrophilum strains other than the strain used for its enrichment and isolation. Some bacteriophages could decrease mortality from intraperitoneal injection of its host strain when added together with the bacteria in a ratio of 10 plaque-forming units per colony-forming unit. While we recognize the artificial laboratory conditions used for these protection assays, this work is the first to demonstrate that phages might be able protect salmonids from RTFS or CWD.     

海洋鱼类的转换效率及其影响因子

转换效率(conversion efficiency)是指单位时间内生物的生产量占食物消耗量的比例,一般从能量的角度来考量,称之为生长效率(growth efficiency),或者能量转换效率;当从生物量的角度来考量时,多称之为食物转换效率。中国学者也将食物转换效率称为生态生长效率,并将能量转换效率和食物转换效率统称为生态     

Polyaromatic hydrocarbons in aquafeeds,source, effects and potential implications for vitamin status of farmed fish species: a review

Access to marine feed ingredients is considered a limiting factor for the rapidly growing aquaculture industry. With increasing inclusion of vegetable feed ingredients in aquafeeds, new challenges have arisen. Substituting marine oils and meals with vegetable ingredients has decreased the level of persistent organic pollutants (POPs) in marine farmed fish such as Atlantic salmon. Consequently, this shift in feed ingredients has led to increased levels of polyaromatic hydrocarbons (PAHs) in aquafeeds. Several of the PAHs listed are on EFSAs and EPAs list of priority substances. Not only are the carcinogenic and genotoxic properties of PAHs of concern, but also their ability to interact with and disrupt metabolic pathways such as vitamin metabolism and signalling. The interactions, and the potential depletion of vitamin stores that follows, are of particular interest as marine ingredients are naturally rich in micronutrients such as vitamins A and D. This study has summarized the current knowledge on the effect of PAHs commonly found in vegetable feed ingredients on vitamin metabolism/signalling and their possible implications in fish.     

Multilocus sequence analysis of Vibrionaceae isolated from farmed amberjack and the development of a multiplex PCR assay for the detection of pathogenic species

Since 2011, high mortality rates and symptoms consistent with vibriosis have been observed in farmed amberjack (Seriola dumerili) in Japan. To identify 41 strains isolated from diseased amberjack, a multilocus sequence analysis using nine concatenated genes (ftsZ, gapA, gyrB, mreB, pyrH, recA, rpoA, topA and 16S rRNA) was conducted. Twenty‐seven strains were identified as Vibrio harveyi, suggesting an epidemic of V. harveyi infection in amberjack farms. Other strains were identified as Vibrio anguillarum, Vibrio owensii and Photobacterium damselae subsp. damselae. To develop an efficient diagnostic method for vibriosis in amberjack, a multiplex PCR system was developed to identify V. anguillarum, V. harveyi and P. damselae subsp. damselae. The method successfully discriminated between these three bacterial species, with amplification products of 350 bp for V. anguillarum, 545 bp for V. harveyi and 887 bp for P. damselae subsp. damselae and can be used for diagnosis in aquaculture farms.     

Evaluation of head-only and head-to-tail electrical stunning of farmed eels (Anguilla anguilla, L.) for the development of a humane slaughter method

The overall objective was to evaluate the suitability of electronarcosis as a stunning method for farmed eels. In the first experiment the minimum electrical current needed to induce a general epileptiform insult by head‐only stunning was assessed. The individual eels (n = 40) with a live weight of 700–800 g were fixed in a specially designed re‐strainer. The EEG (electroencephalogram) and ECG (electrocardiogram) recordings, observation of behaviour and responses to pain stimuli were used to assess unconsciousness, insensibility and cardiac function. The applied current of 150, 200 or 250 V, 50 Hz, AC was delivered via scissor‐model stunning tongs for approximately 1 s. A general epileptiform insult was observed in 31 eels for which a successful EEG recording was obtained, using 255 ± 4 V, 545 ± 32 mA, for 1.2 ± 0.2 s. The general epileptiform insult as measured on the EEG was characterized by a tonic/clonic phase and an exhaustion phase. The behaviour showed one phase: tonic cramps alternated by clonic ones. The heart rate was 22 ± 8 beats min^?1 (n = 23) prior to stunning. After stunning the ECG revealed fibrillation. In the second experiment the behaviour of seven individual eels able to move freely in water was observed after head‐only stunning (250 V). Two phases were distinguished. Limited tonic and clonic cramps combined with backward swimming were followed by heavy clonic cramps combined with unco‐ordinated movements such as jumping out of the water. A distinct exhaustion phase was not observed in all animals. In the third experiment a head‐to‐tail electrical method was examined in 15 eels for rendering the eels unconscious and insensitive prior to slaughter. They were stunned by applying 253 V for 3 s followed by 50 V for 5 min. In the fourth experiment nine eels were head‐only stunned with 260 V for 1 s immediately followed by 50 V for 5 min applied from head to tail. Results obtained in these two experiments were similar. After stunning no brain activity and no responses to pain stimuli on the EEG were observed and the ECG showed ventricular extra systolae. It was observed that it might take 60 ± 25 min or longer for a complete recovery. It can be concluded that for effective electrical stunning of eels with a weight of 700–800 g an average current of 545 ± 32 mA (at approximate 250 V, 50 Hz AC) is needed. In this case, within a confidence level of 95% at least 91% of the eels are effectively stunned (n = 31). Therefore, it is recommended to increase the minimum current for an effective stun in practice to 600 mA. Further research is needed to determine the conditions to induce permanent unconsciousness and insensibility of the eels to protect the animals at slaughter.     

Effect of feed and feeding in the culture of salmonids on the marine aquatic environment: a synthesis for European aquaculture

While marine aquaculture has grown rapidly, so have concerns regarding the environmental impacts caused by the industry. In particular, increasing discharges of solid and dissolved fish excretions, nutrients and therapeutic chemicals have coincided with greater public awareness of the possibility of environmental damage. This has stimulated a number of criticisms, drawn from a wide spectrum of interests, ranging from the use of natural fish stocks to produce fish meal for aqua feeds to the effects of enhanced nutrient input on the coastal marine environment. The present study reviews available information on the environmental effects of feeding practices in salmonid aquaculture in Europe. Accumulation of waste food and fish faecal material results in changes in the sediment under fish cages, characterized by a low redox potential, high content of organic material and accumulation of nitrogenous and phosphorous compounds. Although significant environmental impacts have been reported in the literature at distances of up to 100 m from the cages, in general such impacts are reported to be localized to within 20–50 m around the cages. For farmed salmon and trout, mass balance models have been developed for nitrogen and phosphorus, indicating that 50% of the nitrogen and 28% of the phosphorus supplied with the food is wasted in dissolved form. The maximum nutrient release can be estimated from the hydrographic conditions in the immediate vicinity of the farm, such as water volume, tidal water exchange and currents. At present production levels, improvements in the feeding efficiency and feed quality of aquafeeds could reduce waste and consequent environmental impacts.     

泉州市渔船历史沿革及今后发展方向

渔船是渔民出海捕鱼的主要工具。从古至今,泉州海洋捕捞渔船的发展历程经历了三个阶段：木帆渔船时期、机帆渔船时期、钢质渔船时期。本文在对三种类型渔船发展历史沿革进行回顾的同时,重点对近20年来钢质渔船的发展变化进行总结,并对渔船目前存在的问题及今后的发展方向进行探讨。     

A review of potential factors promoting fish movement in inter-basin water transfers,with emergent patterns from a trait-based risk analysis for a large-scale project in china

Inter-basin water transfers create new pathways between previously disjunct systems and communities. If fish movement occurs, it can lead to invasion or altered regional connectivity patterns, which could induce biotic/genetic homogenisation or synchronisation. Understanding ecological factors promoting movement is critical for predicting potential impacts during project planning, to assess ongoing effects, and to develop mediation strategies. Potential characteristics influencing movement rates were reviewed, including intrinsic traits that increase passive entrainment or active dispersal rates, extrinsic traits of the connected environments and their interactions. In order to examine patterns among these potentially influencing characteristics, a trait-based screening method for movement and invasion risk was developed to analyse linked communities in a database from a large-scale inter-basin water diversion in China. Groups of fishes that scored high in the risk assessment were compared with worldwide examples of entrainment in inter-basin water transfer systems or smaller-scale diversions to examine emergent patterns of shared ecological characteristics. Specific traits that were most often shared in these groups, indicating a higher likelihood of movement in water diversions, include the following: a smaller body size, high adult or larval abundance, migratory behaviour, generalist and pelagic habitat preferences, and a high reproductive output. The synthesis of factors identified in this research can be used to guide future empirical studies to fill knowledge gaps regarding ecological impacts of inter-basin water transfers or other smaller-scale diversions on local communities and ecosystems.     

A review of the use of ivermectin as a treatment for sea lice [Lepeophtheirus salmonis (Krøyer) and Caligus elongatus Nordmann] infestation in farmed Atlantic salmon (Salmo salar L.)

Ectoparasitic sea lice, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus (Nordmann) browse on the skin of farmed Atlantic salmon, Salmo salar L.. The resulting lesions cause stress and increase the susceptibility of the fish to secondary infections. In extreme infestations, fish can suffer from osmoregulatory failure and death. The most immediate treatment for the relief of sea lice infestations at fish farms is the use of chemotherapeutants, either by bath or oral administration. One compound which has been investigated for use as a chemotherapeutant is ivermectin. Ivermectin is a member of the avermectin group of macrocyclic lactones. The avermectins are neurotoxins, which have been used successfully in the treatment of helminthic parasitic infections in a number of terrestrial farm animals and also in the treatment of river blindness in humans. Owing to the low solubility of the compound, ivermectin has been administered as an oral treatment with the feed and has been found to be effective for the treatment of sea lice on Atlantic salmon. Ivermectin is poorly absorbed by fish with a high percentage of the administered dose being excreted in the faeces. The highest concentrations of the absorbed ivermectin were found in lipid‐rich organs. The ivermectin remained in the tissues of the treated fish for a prolonged period of time and was excreted mainly in the unchanged form. Ivermectin can reach the marine environment via excretion from the bile, unabsorbed via the fish faeces and by uneaten food pellets and has a strong affinity to lipid, soil and organic matter. Risk assessments have shown that ivermectin is likely to accumulate in the sediments and that the species therein would be more at risk than the species in the pelagic environment. Ivermectin has been shown to be toxic to some benthic infaunal species in single species tests, but there is no evidence that treatment of fish with ivermectin has affected multispecies benthic communities in the field situation. This review paper ends with details of the development and the status of the use of ivermectin in the treatment of sea lice infestations at Scottish fish farms.     

Variability and stability in predation landscapes: A cross‐ecosystem comparison on the potential for predator control in temperate marine ecosystems

Predation can play an important role in population, community and ecosystem processes. When predator guilds are diverse, fluctuations in individual predator populations may have small influences on the guild at large, suggesting that predator diversity stabilizes the amount of predation prey experience. The strength of this phenomenon depends on how synchronously populations within predator assemblages vary and whether all predators are equally important consumers. We utilized a database of biomasses of fish species across ten temperate marine ecosystems paired with diet composition and feeding rate information from mass‐balance food web models to develop a predation index that weights the importance of predators on a prey based on predator feeding habits. Using the index, we asked how diverse sources of predation in these ecosystems are and how much diversity stabilizes variability in predation. Predator assemblages displayed a wide range of diversity; in one‐third of assemblages, a single predator group accounted for over half of all predation. Abundances of predator populations within assemblages generally varied independently of one another (neither synchronously nor asynchronously), implying an intermediate stabilization on predation intensity by predator diversity. Accounting for interaction strength (versus mere presence) is critical for interpreting the predator landscape; doing so led to a wider range in predator assemblage diversity and less synchronous assemblages. This work challenges conventional notions that marine food webs are diverse and therefore less susceptible to predator control. Future work should consider the temporal variability of the predator assemblages and account for differences in mortality induced by each predator population.     

A review of the development and application of soybean‐based diets for Pacific white shrimp Litopenaeus vannamei

The production of the Pacific white shrimp (Litopenaeus vannamei) has expanded to the point of being the most widely cultured species of shrimp. One of the advantages of this species is its acceptance of a wide variety of feed formulations including plant‐based feeds. Given the increases in ingredient costs, particularly fish meal, there is considerable interest in the use of alternative feed formulations for cultured species. Given that soybean meal is one of the most widely available protein sources for which production can be expanded, the move to soy‐based diets is inevitable. The successful use of alternative feed ingredients for shrimp production depends on a number of factors. This paper summarizes studies regarding the move towards high soy diets concerning manipulation of ingredients and nutrient profiles to maintain balanced feed formulations.     

The effectiveness of management interventions for the control of Spartina species: a systematic review and meta‐analysis

• 1. Spartina species (cordgrasses) have been introduced to the estuaries around Europe, USA, Australia, New Zealand and Asia as a coastal management tool to stabilise mud banks, and through accidental introductions. These mainly non‐native species are highly aggressive in their new environment, and frequently become the dominant plant species, displacing native flora and fauna.
• 2. The majority of organisations managing estuarine environments within the USA and UK have established integrated control programmes to eradicate Spartina spp. These plans can be expensive to deliver and take many years. For example, the Willapa Bay, WA control programme in 2003 had been implemented for over 3 years, but with an annual cost of approximate $2 m year^?1 (～£1.2 m year^?1).
• 3. Through the use of the systematic review process and meta‐analysis, the effectiveness of management interventions (chemical, mechanical and biological) used to control or eradicate invasive Spartina spp. were investigated.
• 4. The effectiveness of glyphosate and imazapyr herbicides at reducing S. alterniflora differ greatly depending upon application method and whether surfactant or wetting agents are used. Cutting combined with smothering is highly effective at reducing S. anglica densities, but its efficacy has not been established for other Spartina spp. Cutting alone increases densities of S. anglica and S. townsendii, while reducing S. alterniflora densities. Biological control, while in its infancy, has the potential to significantly reduce S. anglica densities, while against S. alterniflora it might be of benefit as part of an integrated programme.
• 5. The results highlight the need to establish targeted control programmes, dependent upon the Spartina spp., the underlying site characteristics and the available budget. Where the evidence base is limited or absent, recommendations of further experiments are presented, including a call for improved reporting of site characteristics and experimental methodology, allowing managers to establish whether trial results are applicable to their own sites and therefore limiting the implementation of ineffective management interventions.

Copyright © 2007 John Wiley & Sons, Ltd.     

Social control of growth in Macrobrachium rosenbergii (De Man): a review and prospects for future research

The wide range of sizes of sexually mature prawn populations and particularly of the males is very typical of Macrobrachium rosenbergii (De Man) and a major obstacle to increased profitability of prawn culture. Prawn size variation reflects a complex population structure composed of three major male morphotypes – the small males, the orange‐claw males and the blue‐claw males – which differ in their morphology, physiology and behaviour. Social interactions among juveniles and among sexually mature males affect their growth. Four different social mechanisms have been suggested to control growth in crustaceans: direct competition for food, appetite suppression, altered food‐conversion efficiency and increased energy expenditure on motor activity. Since all growth‐controlling mechanisms involve an aggressive behavioural component, our knowledge of prawn agonistic behaviour and prawn social organization has been reviewed. Present knowledge of the social mechanisms regulating growth among juveniles and among sexually mature male morphotypes as well as the sensory modalities involved was evaluated. The possible evolution of social growth‐controlling mechanisms is discussed. Various ways for implementing our knowledge on social control of growth into prawn culture to increase profitability are suggested.     

Estimation of the period sensitive for the development of abnormal morphology in brown sole <Emphasis Type="Italic">Pseudopleuronectes herzensteini</Emphasis> fed live food enriched with docosahexaenoic acid

The aim of the present study was to clarify the effect of a feeding regimen of live food enriched with docosahexaenoic acid (DHA) on the rates of abnormal morphology in larval brown sole Pseudopleuronectes herzensteini. Live foods were enriched with oil emulsion to produce both high-DHA and low-DHA content. Larvae in group 1 (control) were fed low-DHA-content live foods throughout the experiment. Conversely, larvae in group 2 were fed high-DHA live foods from 15 days post-hatching (dph), when larvae were D stage. Larvae in group 3 were fed high-DHA live foods from 25 dph, when larvae consisted mainly of E stage. The occurrence of normal morphology development in group 2 was significantly higher (P < 0.05) than those of groups 1 and 3, suggesting that normal morphology of brown sole is determined during the critical larval period (D–E stages).     

Research with a farming systems perspective needed for the development of small-scale aquaculture in non-industrialized countries

The global rise in the production of farmed fish and shellfish in non-industrialized countries has been supported by aquaculture research aiming most often to solve problems for factory-like production of highly valued aquatic species. It can be observed however, that research at the small-scale aquafarmers' level is lagging behind. Research with the holistic farming systems perspective and farmers' participation offers a chance to support aquaculture production at the small-scale farmers' level in non-industrialized countries.     

Bacteriocins and their applications for the treatment of bacterial diseases in aquaculture: a review

Aquaculture is one of the fastest growing food producing sectors in the world. The increase in the world population requires faster growth in aquaculture for better food availability and to overcome malnutrition. But this worldwide growth of aquaculture is overwhelmed by catastrophic fish diseases and spoilage during cultivation and preservation problems caused by pathogenic bacteria. Various remedies are available for food preservation and also from the bacterial diseases in the fish production. Due to the emergence of antibiotic resistance and adverse effects, an alternative to antibiotic is the need of the hour. The proteins such as bacteriocins, i.e. ribosomally synthesized antimicrobial peptides (AMPs) and possess antagonistic against closely related and other bacteria. These proteins are produced by most lineages of bacteria which are playing key roles in recognition and possess a cognate immunity system for self‐protection as well as host protection from infections. These proteins are potent immunomodulators with broad spectrum inhibition properties which are further used as novel therapeutic agents. In this review, we have tried to summarize the bacteriocins on the basis of their classifications, structural and functional attributes, mode of actions, bacteriocins isolated from fish and gut microbiota and presence of beneficiary bacteria in the fish gut. Further, this study highlighted where further research is a prerequisite to increase our basic understanding and search for novel bacteriocins to elucidate the proteins/peptides having antimicrobial properties for disease control in aquaculture as an alternative to antibiotics.     

Clinical and aetiological aspects of a summer enteritic syndrome associated with the sporulating segmented filamentous bacterium 'Candidatus Arthromitus' in farmed rainbow trout, Oncorhynchus mykiss (Walbaum)

An enteritic syndrome affecting farmed rainbow trout and occurring predominantly in summer has recently been described and related to the massive accumulation of a segmented filamentous bacterium (SFB), ‘Candidatus Arthromitus’, in the digestive tract of fish. Details of the clinical manifestations, the characteristics of the bacterium and the possible aetiology of the disease are presented in this paper. No other bacterial pathogen than ‘Candidatus Arthromitus’ was characterized in trout undergoing the enteritic syndrome. From clinical and histopathological observations, a toxin or toxic product accumulation was suspected in affected trout, and could account for the massive destruction of the intestinal mucosa. However, the origin and aetiological role of the SFB could not be clearly elucidated, although most of the filaments appeared to beviable and to produce and release strings of endospores in the lumen of the gut. The organism could not be cultured in the conditions tested, shared several morphological and structural characteristics with related bacteria described in the intestinal microflora of different vertebrate species, but no attachment structure was definitively recognized. All attempts to detect similar SFB in the fish diet orin the environment of affected fish farms were unsuccessful. It is unclear whether this organism represents a normal and not previously detected inhabitant of the intestine of trout stressed after environmental perturbation, or whether it results directly from external sources of contamination.