The population ecology of the diseases of the common dab (<I>Limanda limanda</I> L.) has been studied and the use of fish disease as a monitor of pollution in the marine environment reassessed. The diseases included in this study were lymphocystis disease, hyperplasia/papilloma, ulcer disease, inflammatory fat-cell necrosis, and X-cell disease. The interactions responsible for determining disease abundance were assessed by carrying out a detailed longitudinal field survey and interpreting the observed changes in abundance by reference to the population biology of the common dab, the abiotic environment, and the known biology of the diseases. The diseases were not evenly distributed within the host population. Significant differences in prevalence occurred between sexes, ages, and fish of differing maturity status. These were interpreted in terms of varying susceptibility of the host, the response of the host to infection and the dynamics of the diseases. Analysis of the age-prevalence relationships suggests that although some diseases have the potential for their abundance to be regulated this is not fulfilled. The temporal distribution of the diseases consisted of long-term trends, seasonal cycles, and short-term fluctuations. A variety of potential causal factors were highlighted including the spawning behaviour of the dab, temperature, and bacterial abundance related to environmental productivity. The patterns in the spatial distribution of the diseases were reflected in variation in prevalence on both large (˜100nml) and small scales (˜1nml). In this case the causal factors highlighted were salinity, host population density, and again bacterial abundance related to productivity. No effect of pollution on disease prevalence was demonstrated. Neither could the occurrence of lymphocystis disease be related to the concentration of chemical contaminants in the livers of dab.

Crosses were made between a stock of summer steelhead (Salmo gairdneri) known to be resistant to infection by Ceratomyxa shasta and stocks of summer steelhead known to be susceptible. Ceratomyxosis, the disease caused by C. shasta was initiated by exposure to Willamette River water. I found that the crosses were intermediate in susceptibility to ceratomyxosis relative to the parental stocks. There was no difference in susceptibility to ceratomyxosis between reciprocal crosses of the same stocks. Persistence of moderate susceptibility in the F₂ generation of experimental stock crosses and examples from both wild and hatchery stocks of mixed ancestry indicate long term disease problems may result from introductions of less adapted, foreign stocks. / Graduation date: 1987

Rainbow trout macrophages were stimulated with PMA to produce 02- and H2O2 as detected by the reduction of nitroblue tetrazolium (NBT) and the oxidation of phenol red respectively. Addition of DDC or nitroprusside, inhibitors of superoxide dismutase (SOD) increased O2-levels and decreased H2O2 levels, whereas addition of exogenous SOD had the reverse effect. Such data are indicative of a respiratory burst pathway in teleost macrophages comparable with that of mammals. Respiratory burst activity, acid phosphatase activity and RNA synthesis in rainbow trout macrophages which have been stimulated in vitro with the mitogen Concanavalin A (Con A) or in vivo by injection of formalin-fixed Aeromonas salmonicida in Freund's incomplete adjuvant (FIA) was analysed. With Con A, in vitro stimulated head kidney (HK) or elicited macrophages had increased O2-production and RNA synthesis but no significant increases in H2O2 or acid phosphatase activity after 72h post-stimulation with Con A. In contrast, all functions were increased in in vivo stimulated macrophages compared with FIA-elicited peritoneal macrophages. In a bactericidal assay, Con A stimulated macrophages did not show an increase in killing of an avirulent strain of A. salmonicida (004) above control levels whereas in vivo stimulated macrophages not only displayed increased killing of the avirulent strain of bacteria but also acquired the ability to kill a virulent strain (048). Thus, Con A stimulated macrophages only possessed some of the features of activation whereas in vivo stimulated macrophages were activated as defined by the increased bactericidal activity. Peritoneal washes obtained in the collection of activated macrophages were able to increase NBT reduction in normal HK macrophages suggesting the presence of a soluble activating factor. Lymphokine (LK)-containing supernatants produced using either HK or blood derived leucocytes, by pulsing with 10ug/ml Con and 5ng/ml PMA, were able to increase O2- and H2O2 production, to enhance the killing of an avirulent strain of A. Salmonicida and conferred the ability to kill a virulent strain of A. salmonicida. The LK present in these supernatants was therefore designated a macrophage activating factor (MAF). The use of potential second signals to enhance the killing of bacteria by LK-treated macrophages, met with limited success. Only A. salmonicida (strain 004) LPS was able to produce a small increase in killing above LK-treatment. The MAF produced in this study was tested for antiviral/interferon (IFN) activity. The results showed that the supernatants did contain IFN activity. Attempts to semi-purify the MAF from antiviral activity showed the two activities to co-purify, indicating that both activities may be due to the same molecular species. The retention time of the MAF/IFN, coupled with the results of SDS-PAGE analysis showed the molecular weight of the moiety to be approximately 19K daltons. Both activities were sensitive to low pH (pH 2), high temperature (60oC) and trypsin, providing further evidence that the MAF and IFN activity produced in these studies may be due to the same molecular species, possibly akin to IFN- of higher vertebrates.

No description available.

Prior to 1989 the total number of Gyrodactylus species recorded for all British freshwater fish numbered 20. The fauna present on the British Salmonidae was poorly documented and frequently not identified to species level. The European free market, created in 1992, resulted in legislative changes allowing the movement of live fish stocks, albeit under strict disease monitoring conditions, into the UK. One stipulation maintains that the fish stock be free of the ectoparasitic monogenean Gyrodactylus salaris Malmberg, 1957, a parasite made notifiable in the UK in 1987 (Diseases of Fish Act, 1937) owing to its pathogenicity and damage to Norwegian salmon populations in 38 rivers. Although this parasite has been reported since 1957 throughout mainland Europe, its occurrence in the UK was unknown. This project set out to make a national survey of British salmon ids and investigated 250 sample sites, examined four salmonid hosts, Atlantic salmon Salmo safar, brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss and Arctic charr Salvelinus alpinus. Seventy of the sites were found to be positive for Gyrodactylus. Distinctions were made between wild and farmed fish and prevalence, abundance and intensity data collected for comparison. Species determination within the genus Gyrodactylus is based upon subtle differences in hook morphology and has long posed a taxonomic problem. The discrimination of collected specimens was based on two platforms. The initial approach used classical morphometrics from the light microscope, the results being processed using multivariate analyses to separate species. The second approach analysed morphometric data collected from scanning electron micrographs. This was made possible by the development of a sclerite release technique utilising a source of ultrasound to liberate hooks from surrounding tissue and a subsequent flotation stage which permitted flat preparations. Sonication of fresh and frozen material retained the structures that would be lost by enzymatic digestion. The description of new morphometric parameters using digital image analysis allowed the subtle differences in hamuli and marginal hook shape to be discriminated when analysed using principal components analysis (PCA). Four species were identified following multivariate and morphological analyses of opisthaptoral sclerites. G. truttae Glaser, 1975 was found to occur on S. trutta and G. derjav;ni Mikailov, 1975 was found to occur on S. trllfta, S. salar and O. mykiss. Two hitheno undescribed forms, one on S. salar and one on S. alpinus which may be a new species are desclibed. In addition, two forms of G. derjavilli from S. salar and S. alpinlls and one form of G. truttae from S. tnltta are described. Sub-populations of Gyrodactylus sp. were found to be determined by the pattern of distribution of the host; S. salar. The two sub-populations were divided into a southern celtic population (Morph 1) and a nonhern boreal population (Morph 2). Water temperature, was found to be an important environmental parameter influencing sclerite size. The principal component analyses identified key characters which could discriminate G. salaris from the native British species using novel parameters based upon both single elements and the full complement of sclerites. Of these new parameters, the hamulus angle and the size of the marginal hook sickle aperture were the most discriminating. Electronmicrographs of hamuli were traced using a digitising tablet and prepared for image processing. The hamulus angle was measured on original hook images and on enhanced (skeletonised) images using an image analyser. Skeletonisation investigated the reliability of the hook angle as a taxonomic criterion by the removal of possible age-related sclerotisation of the hamulus. Statistical analysis of the data revealed that there are significant differences in hook angle between some species. The isolation of sclerites by sonication enabled their elemental composition to be investigated. The hamuli and marginal hooks were found to have a high sulphur content, indicative of a keratin-like substance. The ventral bar composed of sulphur and calcium is weakly keratinised. The hamulus and the ventral bar were also found to contain vanadium. the significance of which is unknown. The detailed morphology and composition of the individual sclerites is discussed in relation to the functional mechanics of the entire haptoral complex. The protein profiles of G. salaris. G. truttae and G. derjvani were investigated using SDS-PAGE gel electrophoresis, with four proteins common to the three species. Two antibodies raised against G. salaris were found using Western blots. The chaetotaxy of argentophilic structures on three species of the genus Gyrodactyllis was investigated to ascertain the usefulness of this technique in distinguishing species of this genus. Chaetotaxy maps were prepared for G. salaris from Scandinavia and compared to native species of Gyrodactylus parasitizing salmonids in Britain. A formula for the arrangement of the sensilla analogues and the evolutionary position of the genus Gyrodactylus is commented upon.

Streptococcus agalactiae infection is one of the major disease problems affecting farmed tilapia (Oreochromis niloticus) worldwide. Tilapia are highly susceptible to this disease which results in mortality of up to 70% over a period of around 7 days and significant economic losses for farmers. Affected tilapia commonly present with an irregular behaviour associated with meningoencephalitis and septicaemia. Currently, factors affecting the virulence and transmission of S. agalactiae in fish including tilapia are poorly understood. Reports from natural outbreaks of S. agalactiae infection on tilapia farms have suggested larvae and juvenile or fish smaller than 20 g are not susceptible. In addition, there is variability in individual response to experimental inflammatory challenge associated with coping styles (bold, shy) in common carp (Cyprinus carpio). The central hypotheses of this thesis were that weight, age and coping style might affect the development and progression of this bacterial disease. This study investigated these three factors with experimental S. agalactiae infection in Nile tilapia. A range of bacterial isolates recovered from farmed tilapia, presenting with clinical sign of streptococcosis during natural disease outbreaks were identified and characterised as S. agalactiae by standard conventional methods, biochemical characteristic tests, Lancefield serogrouping and species-specific PCR assay. These isolates were Gram-positive cocci, either β- or non-haemolytic (γ), non-motile, oxidase negative and all of serogroup B. In addition, they were able to grow on Edwards medium (modified) agar as blue colonies and growth was observed in broth from 22 to 37 oC and with 0.5-5% NaCl. The biochemical profiles showed some differences in reactions while all the PCR samples showed similarities to the S. agalactiae type strain. These data confirmed that these strains were identified as group B S. agalactiae. A challenge model for S. agalactiae in Nile tilapia was developed and the LD50 estimated prior to performing subsequent experimental challenge studies. Two exposure routes, immersion and intraperitoneal injection (i.p.), were tested with various concentrations of S. agalactiae. Only i.p. injection produced significant mortalities (9 × 108 CFU/ml = 48% mortality, 9 × 107 = 48% and 8 × 106 = 26%). Streptococcus agalactiae was recovered and identified from all the dead and moribund fish during these experiments, where affected fish showed similar clinical signs and pathology to those reported from natural S. agalactiae infections. The study results showed that an experimental i.p. challenge model for S. agalactiae infection had successfully infected healthy Nile tilapia. In the immersion challenges, only 1 fish died despite testing a range of bacterial concentrations, exposure times, stocking density, water system and bacterial preparations. The experimental studies were conducted to investigate the association between weight or age of fish and susceptibility to S. agalactiae infection in Nile tilapia. This was performed under experimental conditions including control groups and a single population of 8 months old fish from one set of parents divided into 7 weight categories. These fish received a single i.p. injection of 6 × 107 CFU/ml of S. agalactiae. Controls and fish of 4 or 8 months old with a mean weight of 5 g received an i.p. injection of 7 × 107 CFU/ml of S. agalactiae. Clinical signs, lesions and histopathological changes in the affected fish were consistent with those reported in natural infection. Streptococcus agalactiae was recovered and identified from all moribund or dead fish. The mortality in the study of different weights varied from 0 to 33% between the groups but the association with weight was weak (R2 = 0.02). In the study of different ages the 4 months old fish group had a total mortality of 24%, and the 8 months old fish group a total mortality of 4%. This study produced no evidence for an association between the weight and susceptibility to S. agalactiae infection but suggested an association between the age or growth rate of fish and this disease. Different coping styles and susceptibility to S. agalactiae infection in Nile tilapia was examined. Fish were screened and scored depending on their risk-taking behavioural responses to a range of different environmental conditions. Individual differences in behavioural responses were evident but only consistent across behavioural trials for some individuals. A selection of fish with consistent responses across trials was exposed to the 6 × 107 CFU/ml of S. agalactiae by i.p. injection. Fewer bold than shy fish died suggesting that the bold fish might be less susceptible to the infection than shy fish. In conclusion, this study characterised a number of S. agalactiae isolates and developed an experimental bacterial challenge model. Subsequent experiments suggested that age (or growth rate) and coping style in fish but not the fish weight may affect susceptibility to S. agalactiae infection in Nile tilapia.

The use of wrasse (Pisces: Labridae) as cleaner fish to combat infections with the parasitic copepods Lepeophtheirus salmonis (Kroyer) and Caligus elongatus (Nordmann) (sea-lice) in the culture of Salmo salar L. (Atlantic salmon) is now common. Infections with these parasites has caused considerable losses in the industry since its formative years. The use of the wrasse species Ctenolabrus rupestris (L. ) (goldsinny), Centrolabrus exoletus (L. ) (rockcook), Symphodus melops (= Crenilabrus melops) (L. ) (corkwing) and Labrus mixtus L. (cuckoo) as cleaner fish was first suggested in 1988. The use of these species in the industry is now widespread in Scotland, Ireland and Norway. The fish used are normally caught from the wild before being stocked with S. salar smolts during their first year at sea. The fish are routinely collected from waters close to the farm sites to be stocked. As most of the S. salar sea production sites in Scotland are located on the west coast of the country, the wrasse to be used in these sites are normally collected from these waters. The movement of wild fish into farm pens presents a risk of disease transfer from wrasse to S. salar and vice versa. Prior to their use as cleaner fish, these four species of wrasse had received little attention as subjects of scientific study. As a result, there was very little information available in the literature regarding their diseases. The present study was undertaken to investigate the potential pathogens present in wild populations in Scottish coastal waters, and, in particular, which of these pathogens, if any, could be transmitted to the S. salar. The study also investigated the susceptibility of wrasse to the two major viral diseases of S. salar to which they would be exposed in pens. In order to fully assess the pathogenicity of the potential disease agents under farm conditions, it was first necessary to establish the normal morphology of the wrasse species. Hence, a study of the morphological features of wrasse, with particular emphasis on those features important in the health of the fish was undertaken. Wrasse were shown to differ in many aspects from salmonids but shared many morphological features with other perciforme fish. Major differences from salmonids were evident in the skin, fins, pancreas, intestine, gonads and heart. There were also aspects of their morphology which differed from other perciforme fish, notably the structure of the heart. These features were regarded to be adaptations to the specific demands of their feeding strategies and habitats. This study was the first of its kind undertaken for wrasse and showed some early contraindications for the use of wrasse in culture; most notable was the marked lipid accumulation in, and resultant degeneration of, the liver resulting from the consumption of high energy S. salar feeds. Once the normal morphological features were established, it was possible to examine the disease status of wrasse. Wild fish were sampled from three different locations on the west coast of Scotland. These sites were all geographically distinct and were all used as sources of wrasse for the S. salar farming industry. Samples of wrasse were also obtained from farm sites supplied with wrasse from these wild sites, and an additional number of other geographically distinct farm locations. As a comparison wrasse were also obtained from a wrasse captive breeding facility and another captive location unrelated to the S. salar industry, a public aquarium. The fish from all of these sampling sites were examined fully for the presence of parasites, bacteria and, in some cases, viruses. Histological examination was also carried out on all of the fish studied. A total of 24 new parasite host records, and two tentative ones, were recorded from the four wrasse species studied. These new parasite records included protozoa, digeneans, nematodes and crustacea. Parasite infections were found to vary in prevalence, abundance and intensity in respect to the geographical characteristics of sampling sites and also the length of time spent in S. salar pens. It was concluded that the separation of wrasse from their natural diet and habitat influenced the degree of parasitism. None of the parasites found to infect wrasse were observed to cause any significant pathology in their hosts other than localised tissue responses. The possibility of transfer of wrasse parasites to S. salar was also investigated experimentally in a series of infections in which parasites dissected from wrasse were introduced to S. salar smolts by means of a novel gavage method. None of the parasites used established in the S. salar, indicating that there is little risk of transfaunation of parasites between wrasse and S. salar. However, this aspect requires further work due to the low number of parasites available and the subsequent low numbers of S. salar infected. Bacterial isolates were obtained from wrasse held in S. salar pens but were not found in any of the fish collected from the wild. Most of the bacterial strains isolated would normally be considered as opportunistic pathogens of fish. It was concluded that the relatively high levels of stress, both environmental and physical, that wrasse are subjected to under farm conditions were instrumental in the number of bacterial infections seen in wrasse. Only one pathogenic bacterial infection was seen in any of the fish sampled. This was an isolate of Aeromonas salmonicida, the agent known to cause the disease furunculosis, isolated from a wrasse obtained from one of the farm samples. Other authors have reported that this bacterium has already caused substantial losses of wrasse under farm conditions. It was concluded that Aeromonas salmonicida will prove to be a major pathogen of wrasse held in S. salar pens. No viruses wereI isolated from any of the wrasse studied. The susceptibility of wrasse to the most significant pathogens of S. salar under farm conditions was also subjected to investigation. In addition to sea-lice infection, the industry lists Infectious Pancreatic Necrosis (IPN) and Pancreas Disease (PD) as of primary importance for further research. Both of these diseases cause substantial losses in the industry. The susceptibility of wrasse to both of these disease conditions was investigated by means of experimental infections. In the case of IPN wrasse were infected by bathing with two different infective doses, a low dose which would be expected to induce the disease in S. salar parr and a second dose substantially higher than the first. The C. rupestris used were found to be susceptible to IPN. The wrasse developed some of the pathological characteristics typical of the disease in S. salar, however, other pathological signs were peculiar to wrasse. The recovery rate from the disease seen in wrasse was far more rapid than that recorded from S. salar. Shedding of the virus in the faeces of infected C. rupestris was also demonstrated. This study has illustrated for the first time the susceptibility of wrasse to IPN and that they can shed the virus in their faeces. This suggests that infected wrasse could be a source of continual reinfection in an affected sea site. Experimental infections of C. rupestris with PD followed a standard protocol for the reproduction of the disease in S. salar. Infection was by means of intraperitoneal injection with putatively infective material obtained from S. salar affected with PD. Two infection doses were used, the lowest dose used had been proven to be effective in inducing the disease in S. salar parr while the second dose, ten times higher than the first, had been shown to be effective in reproducing PD in S. salar smolts. The C. rupestris infected did not develop any of the typical signs of the disease seen in S. salar. It was, therefore, concluded that wrasse were not susceptible to PD.

In aquaculture worldwide, diseases are a significant constraint to economic expansion. The Scottish salmonid industry has experienced many cycles of development, with episodes of little or negative profitability caused by excess of production, and times of crisis due to different disease problems. In Scotland, the early implementation of regulation largely contributed to the control of infectious disease outbreaks. The recent Chilean outbreak of infectious salmon anaemia (ISA) illustrated the threats and the impacts of disease in the aquaculture industry and the importance of implementing good regulation and husbandry practices to reduce the impact of the spread of infectious disease. Databases of site production data have an important role to play in the investigation and understanding of diseases. They store valuable data collected during the time of production, which are essential for the identification of potential health and production problems during the production cycle of farmed fish. Mortality records are one of the most important sources of information on a farm, especially if it includes the cause of death as deformities, predators and diseases. Any deviation from the expected levels of mortality may indicate production problems, infectious diseases, or inadequate welfare. The investigation of increased rates of mortality must include examining farm records, determining the influence of death rate on production and the potential risk factors of diseases in a farm. This project demonstrated the importance of mortality records for setting industry standards of “expected” mortality losses and for investigating the value of recorded mortalities as a tool for aiding in surveillance and control of infectious diseases. It also aimed to determine the utility of reported mortality in supporting and assisting management-strategy decisions at the farm and industry level. In this project, we developed a baseline benchmark curve for expected mortality losses for Atlantic salmon in seawater. This novel approach constitutes a first attempt to establish a baseline curve for normal mortality, which allows detection of potential production problems based on deviations of mortality from the baseline curve of normal mortality. The results of this study also indicated that mortality levels may vary across production cycles, which can again be identified by using the baseline. We found that site was the factor with the highest contribution to variance in mortality. This site-to-site variation in mortality may have resulted from epidemics and environmental incidents, or other local event/effects. Temperature, and/or geographical area were also characteristics that contribute to variation in mortality. The regulator, Marine Scotland Science, with the backing and support of the salmonid industry has suggested potential mortality thresholds as an indicator of presence of infectious diseases, which could be used as alerts for inspection by the official authority. In this study, high mortality rates on fish farms were investigated as an indicator of the presence of infectious disease. The analysis was performed using several analytical approaches: receiver operating characteristic (ROC) curve analysis, measures of sensitivity and specificity, and bootstrap methods. The study was performed by splitting the production cycle into small fish with mean weight below 750 g and large fish with mean weight over 750 g. In the small fish, the results did not suggest reported mortality as a strong indicator of the presence of infectious disease, which may be caused by the lack of records of infectious disease at this stage of the production cycle. In the larger fish, high mortality rates were found to be a strong potential indicator of the presence of infectious diseases, including the suggested mortality threshold. In a survey, the role of traditional diagnosis in the prevention and control of disease outbreaks was assessed. For that, key informant interviews were performed with open questions to the health or farm manager of several trout and Atlantic salmon farms and we also used the diagnostic reports of the Veterinary Diagnostic Services (VDS) from Stirling University to triangulate the data. We showed that disease diagnoses are of great importance for disease identification and control of actual diseases. Farmer’s experience was also indicated as essential in the identification of the first signs of disease, which was principally through the daily monitoring of fish. This study suggested that disease diagnosis starts at the farm level with the daily monitoring of fish and the records of different parameters by the farmer, including mortality. Those records were showed to be vital to identify problems within the production. This thesis illustrated a novel approach to investigate and interpret recorded mortality at the farm level. The results presented in this thesis indicated reported mortality as a vital on-farm tool for identification of diseases and production problems. This thesis suggested priority areas where further investigation is required.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

The aim of the present study was to assess an influence of two different therapeutical concentrations of peracetic acid on selected haematological and biochemical parameters in grass carp (Ctenopharyngodon idella). Fish were radomly distributed to aquaria and exposed to concentrations of 0 mg.l-1 PAA (control group), 1.0 mg.l-1 PAA (P1 group), 3.0 mg.l-1 PAA (P2 group). Almost total mortality of fish was observed in the concentration 3.0 mg.l-1 PAA during the treatment comparing with the P1 group and untreated control where no mortality was observed. After the end of the experimental exposure of fish to peracetic acid, the sampling of blood has been realised. The samples of the blood were examined in order to determine haematological and biochemical parameters. Consequently, there were no significant differences (p<0.05) in a haematological profile of fish exposed to concentration of 1.0 mg.l-1 PAA. Goblet cells count and size have risen, that caused exposure of fish to peracetic acid. In the biochemical profile of fish, significant changes (p<0.01) in three parameters were found after exposure of fish to peracetic acid in concentration 1.0 mg.l-1. Changed parameters were: aspartate aminotransferase, creatine kinase and lactate dehydrogenase. The changes were moderate and it can be supposed that these changes are reversible. No significant change (p<0.05) in haematological parameters points out to the minimum negative influence of recommended therapeutical concntration (1.0 mg.l-1 PAA) to the health of C. idella.