Studies on dorsal fin rot in farmed Atlantic salmon (Salmo salar L.) parr

Aspects of dorsal fin rot in farmed Atlantic salmon parr were investigated and the associated pathology described. Substantial evidence was obtained which suggested that the condition was caused and maintained by repeated bites from other parr. The gross histological and scanning electron microscopic appearance of the lesions were consistent with bite wounds and the typical pathology was reproduced by repeated simulated bites. During behavioural experiments the parr were observed to both bite and damage each others dorsal fins. The typical nodular lesions were more prevalent and took longer to heal at lower temperatures. Dorsal fin rot was found to occur in the absence of damage to the other fins and was more severe in smaller fish. The bacteria associated with the natural lesions and following controlled damage were studied, but not found to play a significant role in the aetiology. They were capable of neither initiating nor maintaining the lesions. The main site of bacterial colonisation appeared to be on exposed fin rays. It was demonstrated that the natural lesions started to resolve as soon as the fish were placed in isolation. A limited study failed to demonstrate a definite relationship between dorsal fin rot and increased susceptibility to Aeromonas salmonicida infection. The implications of all these findings for control of the condition are discussed

The Complex Influences on How We Care for Farmed Fish

As a veterinarian and academic in aquaculture, in my personal experience, most farmers are concerned for their animals and want to take good care of them. There has been substantial improvement in the welfare of farmed fish in recent decades, but improvements have been inconsistent across culture systems and species. Where there has been a lack of progress, it is not simply due to the more obvious barriers, for example, lack of clear messages, lack of effective dissemination, or cost of implementation. Why have the good intentions of farmers and research by academics failed to improve the care of many farmed fish? The reasons would appear to be complex; however, human behavioral theory (this term is used to differentiate from animal ethology) offers both a conceptual framework and practical guidelines for improving the care of fish by influencing the behavior of farmers. Here, I present some background context and apply human behavioral theory to examples of on-farm care of fish

Searching for a signal: Environmental DNA (eDNA) for the detection of invasive signal crayfish, Pacifastacus leniusculus (Dana, 1852)

Environmental DNA (eDNA) is a rapid, non-invasive method for species detection and distribution using DNA deposited in the environment by target organisms. eDNA has become a recognised and powerful tool for detecting invasive species in a broad range of aquatic ecosystems. We examined the use of eDNA as a tool for detecting the invasive American signal crayfish Pacifastacus leniusculus in Scotland. Species-specific TaqMan probe and primers were designed for P. leniusculus and a robust quantitative PCR (qPCR) assay and DNA extraction protocol were developed. We investigated the detection capability for P. leniusculus from water samples in a controlled laboratory experiment and determined whether crayfish density (low = 1 crayfish 5.5 L-1 or high = 3 crayfish 5.5 L-1) or length of time in tanks (samples taken at 1, 3 and 7 days) influenced DNA detectability. Additionally, the persistence of DNA was investigated after P. leniusculus removal (samples taken at 1, 3 and 7 days post removal). P. leniusculus DNA was consistently detected during the entire 7-day period and higher density tanks yielded stronger positive results with lower Ct values. After removal of P. leniusculus, there was a rapid and continuous decrease in the detectability of DNA. P. leniusculus DNA could only be detected in high density tanks by the end of the 7-day period, while DNA was no longer detectable in low density tanks after 72 hours. Preliminary field experiments sampled water from three sites in winter and five sites in summer. P. leniusculus was known to be present at two of these sites. P. leniusculus was not detected at any site in winter. However, in summer, positive signals were observed at sites with known P. leniusculus, and at sites where P. leniusculus was believed to be present anecdotally, but not confirmed. All sites where crayfish were believed to be absent were negative for eDNA. Therefore, eDNA represents a promising technique to detect and monitor invasive P. leniusculus, although the presence of detectable amounts of eDNA may be season and location dependent, even where invasive crayfish are known to be present

Qualitative Behavioural Assessment (QBA) as a welfare indicator for farmed Atlantic salmon (Salmo salar) in response to a stressful challenge

Animal welfare assessments have struggled to investigate the emotional states of animals while focusing solely on available empirical evidence. Qualitative Behavioural Assessment (QBA) may provide insights into an animal’s subjective experiences without compromising scientific rigor. Rather than assessing explicit, physical behaviours (i.e., what animals are doing, such as swimming or feeding), QBA describes and quantifies the overall expressive manner in which animals execute those behaviours (i.e., how relaxed or agitated they appear). While QBA has been successfully applied to scientific welfare assessments in a variety of species, its application within aquaculture remains largely unexplored. This study aimed to assess QBA’s effectiveness in capturing changes in the emotional behaviour of Atlantic salmon following exposure to a stressful challenge. Nine tanks of juvenile Atlantic salmon were video-recorded every morning for 15 min over a 7-day period, in the middle of which a stressful challenge (intrusive sampling) was conducted on the salmon. The resultant 1-min, 63 video clips were then semi-randomised to avoid predictability and treatment bias for QBA scorers. Twelve salmon-industry professionals generated a list of 16 qualitative descriptors (e.g., relaxed, agitated, stressed) after viewing unrelated video-recordings depicting varying expressive characteristics of salmon in different contexts. A different group of 5 observers, with varied experience of salmon farming, subsequently scored the 16 descriptors for each clip using a Visual Analogue Scale (VAS). Principal Components Analysis (correlation matrix, no rotation) was used to identify perceived patterns of expressive characteristics across the video-clips, which revealed 4 dimensions explaining 74.5% of the variation between clips. PC1, ranging from ‘relaxed/content/positive active’ to ‘unsettled/stressed/spooked/skittish’ explained the highest percentage of variation (37%). QBA scores for video-clips on PC1, PC2, and PC4 achieved good inter- and intra-observer reliability. Linear Mixed Effects Models, controlled for observer variation in PC1 scores, showed a significant difference between PC1 scores before and after sampling (p = 0.03), with salmon being perceived as more stressed afterwards. PC1 scores also correlated positively with darting behaviours (r = 0.42, p < 0.001). These results are the first to report QBA’s sensitivity to changes in expressive characteristics of salmon following a putatively stressful challenge, demonstrating QBA’s potential as a welfare indicator within aquaculture

Crystal Growth Kinetics of Boron Oxide Under Pressure

We have measured the crystal growth rate u of B2O3-I in the amorphous phase, as it varied over five orders of magnitude with changes in temperature and pressure. We eliminated the crystal nucleation barrier by seeding the surface of boron oxide glass with crystals. u became measurable only when the pressure exceeded a threshold level near 10 kbar. Using the published thermodynamic information on the B2O3 system and a crude free-energy model for the crystal and glass phases, we account qualitatively for our results with the theory of crystal growth limited by the rate of two-dimensional nucleation of monolayers. The constants for the prefactor, activation energy, activation volume, and ledge tension are determined by fitting. By adjusting the thermodynamic parameters to a set of values that are well within the ranges delineated by their experimental uncertainties, we account quantitatively for the measured growth rates from 300 to 500 °C and from 0 to 30 kbar with the following relation: u(T,P)=(785 m/s)[||DeltaGm||/(RT)]1/6 ×exp[pi×3 Å(420 erg/cm2)2(28 cm3/mole)/(3 kTDeltaGm)]exp[−10 366 cal/mole/(RT)] ×exp[−P×16 cm3/mole/(RT)]×{1−exp[DeltaGm/(RT)]}2/3, with the driving free energy given by DeltaGm(T,P)=(13 cm3/mole) [PM(T)−P] and the melting curve given by PM(T)=(T−450 °C)/(42.6 K/kbar). The "B2O3 crystallization anomaly", that crystals have never been observed to grow at atmospheric pressure, is explained, since according to our model, the frequency of two-dimensional nucleation is negligible at all temperatures at pressures less than 10 kbarEngineering and Applied Science

Investigating the Effect of an Oxytetracycline Treatment on the Gut Microbiome and Antimicrobial Resistance Gene Dynamics in Nile Tilapia (Oreochromis niloticus)

Antibiotics play a vital role in aquaculture where they are commonly used to treat bacterial diseases. However, the impact of antibiotic treatment on the gut microbiome and the development of antimicrobial resistance in Nile tilapia (Oreochromis niloticus) over time remains to be fully understood. In this study, fish were fed a single treatment of oxytetracycline (100 mg/kg/day) for eight days, followed by a 14-day withdrawal period. Changes in the distal gut microbiome were measured using 16S rRNA sequencing. In addition, the abundance of antimicrobial resistance genes was quantified using real-time qPCR methods. Overall, the gut microbiome community diversity and structure of Nile tilapia was resilient to oxytetracycline treatment. However, antibiotic treatment was associated with an enrichment in Plesiomonas, accompanied by a decline in other bacteria taxa. Oxytetracycline treatment increased the proportion of tetA in the distal gut of fish and tank biofilms of the treated group. Furthermore, the abundance of tetA along with other tetracycline resistance genes was strongly correlated with a number of microbiome members, including Plesiomonas. The findings from this study demonstrate that antibiotic treatment can exert selective pressures on the gut microbiome of fish in favour of resistant populations, which may have long-term impacts on fish health

A study of the aetiology and control of rainbow trout gastroenteritis

Disease has been identified as a major problem in the aquaculture industry for the welfare of the fish stocked as well as for its economic impact. The number of diseases affecting cultured fish has increased significantly during recent years with the emergence of several conditions that have added to the overall impact of disease on the industry. Frequently, a lack of scientific knowledge about these diseases is compounded by an absence of effective treatment and control strategies. This has been the case with rainbow trout gastroenteritis (RTGE), an emerging disease of rainbow trout (Oncorhynchus mykiss Walbaum). This study investigated several aspects related to its aetiology and control. A retrospective survey of UK rainbow trout farmers was undertaken to ascertain the extent and severity of RTGE in the UK as well as to identify RTGE risk factors at the site level. Participants in this study accounted for over 85% of UK rainbow trout production in 2004. It was found that the total number of RTGE-affected sites had risen from 2 in the year 2000 to 7 in 2005. The disease was only reported from sites producing more than 200 tonnes of trout/year for the table market. Analysis of risk factors associated with RTGE at the site level showed that this syndrome was associated with large tonnage and rapid production of rainbow trout for the table market. The data collected during this study enabled the identification of those sites that were most likely to present with RTGE the following year and this information was used to study the epidemiology of RTGE at the unit level. A prospective longitudinal study was undertaken in 12 RTGE-affected UK sites. It described in detail the impact, presentation, current control strategies and spread pattern of RTGE within affected UK sites. The risk factors associated with RTGE presence and severity were also investigated. Data were collected for each productive unit (i.e. cage, pond, raceway or tank) on the mortalities, fish origin, site management and environmental factors. RTGE was identified using a case definition based on gross pathological lesions. Analysis of these data revealed that RTGE behaved in an infectious manner. This conclusion was supported by the presence of a pattern typical of a propagating epidemic within affected units. Also, the risk of an unaffected unit becoming RTGE positive was increased if it had received fish from or was contiguous to a RTGE-affected unit. The presentation also suggested an incubation period of 20-25 days. Risk factor analysis identified management and environmental risk factors for RTGE, including high feed input and stressful events, which could be used to generate a list of control strategies. A study of the histopathological and ultrastructural presentation of RTGE was conducted. The location of segmented filamentous bacteria (SFB) and pathological changes found in affected fish were examined. Pyloric caeca were the digestive organ where SFB were found more frequently and in higher numbers, suggesting that this was the best location to detect SFB in RTGE-affected trout. Scanning and transmission electron microscopy revealed a previously undescribed interaction of SFB with the mucosa of distal intestine and pyloric caeca and this included the presence of attachment sites and SFB engulfment by enterocytes, as previously described in other host species. The SFB were not always adjacent to the pathological changes observed in the digestive tract of RTGE-affected trout. Such changes included cytoskeletal damage and osmotic imbalance of enterocytes, with frequent detachment. These observations suggested that if SFB are indeed the cause of RTGE their pathogenesis must involve the production of extracellular products. Analysis of the gross presentation and blood biochemistry in RTGE-affected fish was used to examine the patho-physiologic mechanisms of RTGE. To enable identification of positive RTGE cases for this study, a case definition was created from the information available on RTGE gross presentation in the literature. This case definition was assessed in a sample including 152 fish cases and 152 fish controls from 11 RTGE-affected UK sites, matched by unit of origin. The analysis of these fish using bacteriology, packed cell volume (PCV) and histopathology revealed that RTGE occurred simultaneously with other parasitic and bacterial diseases in a percentage of fish identified with this case definition. With the information gained after analysing the gross presentation, RTGE-affected fish without concurrent disease were selected for the study of the pathogenesis, which included blood biochemical analyses. These analyses revealed a severe osmotic imbalance, and a reduced albumin/globulin ratio suggesting selective loss of albumin, typical for a protein losing enteropathy. The role of the SFB “Candidatus arthromitus” in the aetiology of RTGE was assessed using a newly developed “C. arthromitus”-specific polymerase chain reaction assay (PCR) in conjunction with histological detection. This technique was applied to eight different groups of trout, including an RTGE-affected group and seven negative control groups. This analysis was conducted on DNA extracted from paraffin wax-embedded tissues as well as fresh intestinal contents. The results revealed the presence of “C. arthromitus” DNA in apparently healthy fish from sites where RTGE had never been reported. Additionally, SFB were observed histologically in two trout from an RTGE-free hatchery. These findings do not permit the exclusion of “C. arthromitus” as the aetiological agent for RTGE, although they suggest that the presence of these organisms in the digestive system of healthy trout is not sufficient to cause clinical disease, and therefore other factors are necessary. In conclusion, this study has used a multidisciplinary approach to the study of RTGE which has generated scientific information related to the epidemiology, pathogenesis and aetiology of this syndrome. The results of this project have suggested priority areas where further work is required, including experimental transmission of RTGE, field assessment of the control strategies proposed and further investigation into the aetiology of RTGE.EThOS - Electronic Theses Online ServiceBritish Trout Association (BTA) : Department of Environmental, Food and Rural Affairs (DEFRA) : Scottish Aquaculture Research Forum (SARF)GBUnited Kingdo

A baseline method for benchmarking mortality losses in Atlantic salmon (Salmo salar) production

On-farm databases provide a large diversity of information regarding fish health and stock performance. Mortality records held in on-farm database are indicators of fish health status and of great interest for studying fish health, such as patterns of diseases. Mortality records from a Scottish Atlantic salmon production database of one company were used to develop a method of benchmarking production losses due to mortality. The records used concerned mortality loss numbers of Atlantic salmon in the seawater phase. The median, 10th and 90th percentiles of mortality were calculated for each week of production from 88 production recorded cycles. These values were used to delimit the range of a standard mortality curve through the production cycle. The effects of the different mortality losses from each cycle on production in terms of costs and time consumed were also described. Likewise, substantial interannual variation in mortality time series is described as well as the mortality variation associated with three diseases (Pancreas Disease, Cardiomyopathy Syndrome and Infectious Pancreatic Necrosis)

Prevalence of zoonotic trematodes in fish from a Vietnamese fish-farming community

The prevalence of fish-borne zoonotic trematode (FZT) metacercariae was investigated in fish farmed by rural households in Nghe An Province, located in northern Vietnam. In total, 716 fish, including tilapia (Oreochromis niloticus) and 6 carp species, i.e., grass carp (Ctenopharyngodon idellus), bighead carp (Aristichthys nobilis), mrigal (Cirrhinus mrigala), common carp (Cyprinus carpio), silver carp (Hypophthalmychthys molitrix), and roha (Labeo rohita), collected from 53 fish farms were examined. The overall prevalence of FZT metacercariae was 44.6%, ranging from 12.5% to 61.0% in fish species collected from grow-out ponds, which are the production system for growing fish from fingerling size to market size. The overall prevalence was 43.6% in fingerlings cultured in nurseries, ranging from 7.4% to 62.8% for different fish species. The FZT species recovered were heterophyids and echinostomatids and included Haplorchis pumilio, H. taichui, H. yokogawai, Centrocestus formosanus, Stellantchasmus falcatus, and Echinochasmus japonicus, all of which are intestinal flukes in humans, other mammals, and birds. This is the first report of H. yokogawai and E. japonicus in fish in Vietnam, and the first record for S. falcatus in northern Vietnam. Although a previous cross-sectional survey of the people living in these fish farm households revealed a very low prevalence of FZTs (<1%), our results demonstrate that intestinal flukes are common in farmed fish in this area, suggesting that reservoir hosts such as dogs, cats, and pigs are more important in sustaining the life cycles of these flukes in fish farms than human hosts. This has implications for the effectiveness of control programs focused mainly on treatment of humans