Atlantic salmon aquaculture is undergoing an expansion of land-based recirculating aquaculture systems (RAS), especially for freshwater (FW) stages of production. Juvenile salmon undergo parr-smolt transformation, also known as smoltification and become pre-adapted to tolerate seawater (SW). One aspect requiring study is the development of microbial communities during this time, especially in RAS systems. Here we analyzed temporal changes in microbiome associated with the intestine in Atlantic salmon during smolt production in a commercial RAS production facility and followed the same cohort of fish post-seawater transfer (SWT), using 16S rRNA gene sequencing. Microbial diversity and richness showed an increase over time across FW production, but declined sharply and significantly 1-week post-SWT before re-establishing itself with a completely different community structure after 4 weeks. Core microbial taxa could be assigned to three distinct categories; (1) omnipresent, (2) salinity specific, or (3) transient. By including diet and water samples in the analyses, we classified true core taxa associated with the host, those associated with the diet, and transient cores associated with microbial communities in tank water. The rising trend observed in microbial richness in the water may be a consequence of a temporal increase in organic load while dominance of Vibrionaceae may be attributed to the higher temperatures maintained during RAS production and above average natural water temperatures post-SWT. Functional analysis suggests modulation of metabolic pathways post-SWT, but downstream impacts on fish growth and health in a commercial setting remain to be elucidated. A deeper understanding of the interplay between microbial composition and functionality can play a role in optimizing fish performance in tightly regulated RAS production.
SUMMARYFew studies have focussed on the health and immunity of triploid Atlantic salmon and therefore much is still unknown about their response to commercially significant pathogens. This is important if triploid stocks are to be considered for full-scale commercial production. This study aimed to investigate and compare the response of triploid and diploid Atlantic salmon to an experimental challenge with Neoparamoeba perurans, causative agent of amoebic gill disease (AGD). This disease is economically significant for the aquaculture industry. The results indicated that ploidy had no significant effect on gross gill score or gill filaments affected, while infection and time had significant effects. Ploidy, infection and time did not affect complement or anti-protease activities. Ploidy had a significant effect on lysozyme activity at 21 days post-infection (while infection and time did not), although activity was within the ranges previously recorded for salmonids. Stock did not significantly affect any of the parameters measured. Based on the study results, it can be suggested that ploidy does not affect the manifestation or severity of AGD pathology or the serum innate immune response. Additionally, the serum immune response of diploid and triploid Atlantic salmon may not be significantly affected by amoebic gill disease.
Sterile triploid fish represent a solution to the problems associated with sexual maturation and escapees in aquaculture. However, as disease outbreaks continue to cause significant economic losses to the industry, it is essential that the response of triploids to disease and disease treatments be characterised. The aim of this study was to compare the response of triploid Atlantic salmon to a commercial furunculosis vaccine with that of diploid fish, and to assess the vaccine efficacy in the two ploidies through an experimental infection with Aeromonas salmonicida. Diploid and triploid Atlantic salmon were injected intraperitoneally with either phosphate buffered saline, liquid paraffin adjuvant or a commercial furunculosis vaccine. Following vaccination, growth, adhesion scores and a variety of assays to assess immune function, such as respiratory burst and antibody response, were measured. Vaccination did not have a significant effect on the weight of either ploidy prior to challenge at 750° days. Adhesion scores were significantly higher in vaccinated fish compared to unvaccinated fish, although no effect of ploidy was observed. Ploidy significantly affected respiratory burst activity following vaccination, however, with triploids exhibiting higher activity than diploids. Combined with lower white blood cell numbers observed in the triploids, it may be that this low cell number is compensated for by increased cellular activity. Ploidy however, did not have a significant effect on complement activity or antibody response, with significantly higher antibody levels detected in all vaccinated fish compared to unvaccinated controls. In addition, both ploidy groups were well protected following challenge with no difference in the relative percentage survival. Based on these results, it appears that ploidy does not affect the severity of adhesions that result post-vaccinate or in the fish's immune response following vaccination, and the furunculosis vaccine performs equally well in both diploid and triploid Atlantic salmon.
Amoebic gill disease (AGD) is emerging as one of the most significant health challenges affecting farmed Atlantic salmon in the marine environment. It is caused by the amphizoic amoeba Neoparamoeba perurans, with infestation of gills causing severe hyperplastic lesions, compromising overall gill integrity and function. This study used histology, transmission electron microscopy (TEM), immunohistochemistry and transcript expression to relate AGD‐associated pathological changes to changes in the morphology and distribution of chloride cells (CCs) in the gills of Atlantic salmon (Salmo salar L.) showing the progression of an AGD infection. A marked reduction in numbers of immunolabelled CCs was detected, and a changing pattern in distribution and morphology was closely linked with the level of basal epithelial hyperplasia in the gill. In addition, acute degenerative ultrastructural changes to CCs at the lesion site were observed with TEM. These findings were supported by the early‐onset downregulation of Na+/K+‐ATPase transcript expression. This study provides supportive evidence that histological AGD lesion assessment was a good qualitative tool for AGD scoring and corresponded well with qPCR genomic Paramoeba perurans quantification. Ultrastructural changes induced in salmon CCs as a result of AGD are reported here for the first time.
Background: To date, evidence on whether sexualized drug use (SDU) and chemsex occur less frequently in rural compared to urban areas in Britain has been conflicting. This study aimed to better measure and understand whether attending urban versus rural sexual health clinics in the United Kingdom was associated with a difference in men who have sex with men’s (MSM) experience of SDU or their access to SDU support. Methods: Men from 29 sexual health services across England and Scotland were recruited by self-completing a waiting room survey. Results: A total of 2655 men (864 MSM) took part. There was no statistically significant difference in recent SDU or chemsex identified in MSM attending rural compared to urban clinics. Gamma-Hydroxybutyrate/Gamma-Butyrolactone (GHB/GBL) was the most commonly reported chemsex drug used in a sexual setting, with equal prevalence of use in urban and rural MSM attendees. Distance travelled for SDU was not significantly different for rural compared to urban MSM. Rural MSM reported a higher rate of unmet need for SDU specific services, although this difference was not statistically significant. Conclusion: Within this sample of MSM, there were no significant differences in sexualized drug use behaviours between those attending rural compared to urban sexual health settings.
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