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Yersiniosis of cultured Atlantic salmon is a recurrent fish health management challenge in many continents. The causative organism, Yersinia ruckeri, can reside latently in the gut and lead to acute infection and disease during hatchery and sea-transfer stages. One potential prevention approach is the administration of probiotic bacteria to suppress gut colonization of Y. ruckeri. Our study aimed to isolate and identify anti-Yersinia activity among lactic acid bacteria (LAB) isolated from the gastrointestinal tract (GIT) of aquatic animals. Of the 186 aquatic GIT isolates examined, three strains showed diffusible antimicrobial activity towards Y. ruckeri O1b. Analysis of 16 s rRNA gene sequences indicated the three bacterial strains were Enterococci, related to Enterococcus sp. (99%), Enterococcus thailandicus (99%), and Enterococcus durans (99%). Anti-Yersinia activity was maintained at neutral pH (~6.5-7.0), and in-vitro environmental tolerance assays showed the three strains could withstand simulated salmonids gastrointestinal tract conditions of: low pH (3.4) and 3% bile salt content. All three Enterococci strains showed higher adhesion to the intestinal mucus of Atlantic salmon than Y. ruckeri O1b (E. durans 24%, E. enterococcus sp. 25% and E. thailandicus 98%, compared to Y. ruckeri O1b 5%). However, only Enterococcus sp. and E. thailandicus were able to grow in the salmon intestinal mucus broth while E. durans showed no growth. Anti-Yersinia activity was completely inactivated by proteinase-K treatment, suggesting that the active compound/s are proteinaceous and may be bacteriocin-like inhibitory substances (BLIS). Our data indicate that Enterococcus sp. MA176 and E. thailandicus MA122 are potential probionts for the prevention of yersiniosis in salmonids. Further in-vivo studies are required to determine whether these bacteria reduce the incidence of yersiniosis in Atlantic salmon.

Aims Assess bacterial diversity and richness in mucus samples from the gills of Atlantic salmon in comparison to preserved or fixed gill filament tissues. Ascertain whether bacterial diversity and richness are homogeneous upon different arches of the gill basket. Methods and Results Bacterial communities contained within gill mucus were profiled using 16S rRNA gene sequencing. No significant difference in taxa richness, alpha (P > 0·05) or beta diversity indices (P > 0·05) were found between the bacterial communities of RNAlater preserved gill tissues and swab‐bound mucus. A trend of lower richness and diversity indices were observed in bacterial communities from posterior hemibranchs. Conclusions Non‐lethal swab sampling of gill mucus provides a robust representation of bacterial communities externally upon the gills. Bacterial communities from the fourth arch appeared to be the least representative overall. Significance and Impact of the Study The external mucosal barriers of teleost fish (e.g. gill surface) play a vital role as a primary defence line against infection. While research effort on the role of microbial communities on health and immunity of aquaculture species continues, the collection and sampling processes to obtain these data require evaluation so methodologies are consistently applied across future studies that aim to evaluate the composition of branchial microbiomes.

Amoebic gill disease (AGD) is one of the main health issues impacting farmed Atlantic salmon. Neoparamoeba perurans causes AGD; however, a diversity of other amoeba species colonizes the gills and there is little understanding of whether they are commensal or potentially involved in different stages of gill disease development. Here, we conduct in vivo challenges of naive Atlantic salmon with cultured Nolandella sp. and Pseudoparamoeba sp. to investigate their pathogenicity to Atlantic salmon gills. Additionally, we assessed whether the presence of Nolandella sp. and Pseudoparamoeba sp. influences the onset and/or severity of N. perurans-induced AGD. All three strains attached and multiplied on the gills according to qPCR analysis. Furthermore, minor gross gill lesions and histological changes were observed post-exposure. While N. perurans was found associated with classical AGD lesions, Nolandella sp. and Pseudoparamoeba sp. were not found associated with lesion sites and these lesions did not meet the expected composite of histopathological changes for AGD. Moreover, the presence of these non-N. perurans species did not significantly increase the severity of AGD. This trial provides evidence that cultured Nolandella sp. and Pseudoparamoeba sp. do not induce AGD and do not influence the severity of AGD during the early stages of development.

Amoebic gill disease, caused by the protozoan ectoparasite Neoparamoeba perurans, remains a significant threat to commercial Atlantic salmon aquaculture operations worldwide, despite partial control afforded by selective breeding and therapeutic intervention. Anecdotal reports from commercial producers suggest that historically, smaller Atlantic salmon smolts are more susceptible to AGD than larger smolts. Here, large (350 g) and small (200 g) commercially sourced, AGD-naïve Atlantic salmon cohorts were experimentally exposed to 50 N. perurans trophozoites L

The use of probionts has been considered to be an effective technology in enhancing growth performances and survival rate of aquaculture species. This study examined the effect of three probiotic candidates (Bacillus amyloliquefaciens MA228, Enterobacter ludwigii MA208, and Pediococcus acidilactici MA160) on the growth and survival rates of juvenile abalone, Haliotis asinina L). The three probionts were incorporated as a mixture of two or three onto Gracilaria sp. and fed to juvenile abalone for 62 days. Then, specific growth rate (SGR), feed conversion ratio (FCR), and survival rate (SR) were measured. The results showed that the increments in weight and length were significantly higher (P 72% among the treatments and control. Our study shows that the growth of juvenile abalone could be improved through probiotic supplementation. Thus, E. ludwigii MA208 and B. amyloliquefaciens MA228 are considered potential probionts which can be used to shorten culture period of abalone aquaculture.

Branchial surfaces of finfish species contain a microbial layer rich in commensal bacteria which can provide protection through competitive colonization and production of antimicrobial products. Upon disturbance or compromise, pathogenic microbiota may opportunistically infiltrate this protective barrier and initiate disease. Amoebic gill disease (AGD) is a globally significant health condition affecting salmonid mariculture. The current study examined whether altering the diversity and/or abundance of branchial bacteria could influence the development of experimentally induced AGD. Here, we challenged Atlantic salmon (Salmo salar) with Neoparamoeba perurans in a number of scenarios where the bacterial community on the gill was altered or in a state of instability. Administration of oxytetracycline (in-feed) and chloramine-T (immersion bath) significantly altered the bacterial load and diversity of bacterial taxa upon the gill surface, and shifted the community profile appreciably. AGD severity was marginally higher in fish previously subjected to chloramine-T treatment following 21 days post-challenge. This research suggests that AGD progression and severity was not clearly linked to specific bacterial taxa present in these systems. However, we identified AGD associated taxa including known pathogenic genus (Aliivibrio, Tenacibaculum and Pseudomonas) which increased in abundance as AGD progressed. Elucidation of a potential role for these bacterial taxa in AGD development is warranted.

This chapter explores the history of the “micro-/macroevolution” distinction and its significance for the history of Darwinism, its “eclipse,” and the “evolutionary synthesis.” By noting how Darwin, Galton, DeVries, Fisher, Wright, Haldane, Chetverikov, Severtsov, Filipchenko, Dobzhansky, Goldschmidt, J. Huxley, Mayr, Simpson, Guyenot, Rensch, and others understood the distinction, and the language and arguments they used, the article chronicles the problems it posed for “synthesizing” diverse biological disciplines, and documents how the fundamental disagreements among them were successfully finessed by synthesis advocates. These findings force us to rethink the history of Darwinism, population genetics, and the evolutionary synthesis and their political, methodological, and national dimensions.

Amoebic gill disease (AGD) is one of the main health issues impacting farmed Atlantic salmon. Neoparamoeba perurans causes AGD; however, a diversity of other amoeba species colonizes the gills and there is little understanding of whether they are commensal or potentially involved in different stages of gill disease development. Here, we conduct in vivo challenges of naïve Atlantic salmon with cultured Nolandella sp. and Pseudoparamoeba sp. to investigate their pathogenicity to Atlantic salmon gills. Additionally, we assessed whether the presence of Nolandella sp. and Pseudoparamoeba sp. influences the onset and/or severity of N. perurans-induced AGD. All three strains attached and multiplied on the gills according to qPCR analysis. Furthermore, minor gross gill lesions and histological changes were observed post-exposure. While N. perurans was found associated with classical AGD lesions, Nolandella sp. and Pseudoparamoeba sp. were not found associated with lesion sites and these lesions did not meet the expected composite of histopathological changes for AGD. Moreover, the presence of these non-N. perurans species did not significantly increase the severity of AGD. This trial provides evidence that cultured Nolandella sp. and Pseudoparamoeba sp. do not induce AGD and do not influence the severity of AGD during the early stages of development.

Amoebic gill disease is a parasitic condition that commonly affects marine farmed Atlantic salmon. The causative agent, Neoparamoeba perurans, induces a marked proliferation of the gill mucosa and focal superficial necrosis upon branchial lesions. The effect that amoebic branchialitis has upon gill associated commensal bacteria is unknown. A 16S rRNA sequencing approach was employed to profile changes in bacterial community composition, within amoebic gill disease (AGD)-affected and non-affected gill tissue. The bacterial diversity of biopsies with and without diseased tissue was significantly lower in the AGD-affected fish compared to uninfected fish. Furthermore, within the AGD-affected tissue, lesions appeared to contain a significantly higher abundance of the Flavobacterium, Tenacibaculum dicentrarchi compared to adjunct unaffected tissues. Quantitative PCR specific to both N. perurans and T. dicentrarchi was used to further examine the co-abundance of these known fish pathogens. A moderate positive correlation between these pathogens was observed. Taken together, the present study sheds new light on the complex interaction between the host, parasite and bacterial communities during AGD progression. The role that T. dicentrarchi may play in this complex relationship requires further investigation.

This study is aimed at the isolation and screening of alginate lyase-producing bacteria from the gastrointestinal tracts of hybrid abalone, Haliotis rubra x H. laevigata, as probiotic candidates. Six bacterial isolates were detected to produce alginate lyase. Of these, the isolate with the highest alginate-lyase activity was identified as Enterobacter ludwigii strain EN-119, displaying 99% similarity of 16S rDNA sequence. Further assays indicated that E. ludwigii showed good viability and stability when it was incorporated into manufactured pellets and stored at 4°C for 7 days. The isolate also had high tolerance of high salinity (35 mg/L), low pH in simulated stomach juice (5) and to simulated intestinal juice containing surfactants such as bile salts and gastric enzymes (pepsin and trypsin). Additionally, a short, preliminary study indicated that supplementation of E. ludwigii via manufactured pellets improved the total weight gain and specific growth rate of hybrid abalone. These results suggest that E. ludwigii is a potential probiont for shortening the culture period of hybrid abalone.

Amoebic gill disease (AGD) is caused by Neoparamoeba perurans and represents a significant threat to Atlantic salmon marine farming in several countries worldwide. Sequential natural reinfection with N. perurans after treatment occurs after the first AGD outbreak during the grow-out phase of Atlantic salmon culture. Little is known about the immune response of Atlantic salmon following reinfection with N. perurans. In a previous single exposure study, using gill biopsies with various severity of AGD-lesion, we reported that the immune signalling in AGD-affected gills was highly dependent on the ratio of normal to hyperplastic gill tissues. Here, following experimental reinfection we investigated the transcriptional immune response in the gills of AGD-affected Atlantic salmon. Furthermore, we reported the inflammatory and immune response following a single exposure to N. perurans during late infection and compared it to the reinfected fish. Fish groups were selected based on the gross gill scores carried out during the trial. Two gill biopsies were collected from each AGD-affected individual, one with no lesion and one partly including AGD-lesion. Furthermore, gill biopsies were collected from uninfected controls. Pro-inflammatory and immune-related genes were characterised at the mRNA level by using a quantitative RT-PCR. Targeted immune genes included IL-1β, TCR-α chain, CD8, CD4, MHC-IIα, MHC-I, IgM and IgT. Histopathology and image analysis were used to assess the severity and to verify the reliability of the gross gill score as AGD severity assessment method to select fish groups for gene expression studies. Overall the expression at the mRNA level of the immune and pro-inflammatory genes analysed showed little change in AGD-affected gills of experimentally reinfected fish and of fish exposed once to N. perurans.

Oil extracted from cloves, Syzygium aromaticum, consists mainly of eugenol, which has been documented to affect protozoa attachment, viability and growth. Isoeugenol (sold under the trade name AQUI-S®) is a commercially available fish anaesthetic produced by isomerisation of eugenol. Both are anaesthetics commonly employed during the husbandry and euthanasia of Atlantic salmon, Salmo salar L., used for amoebic gill disease (AGD) research. Neoparamoeba perurans (the causative agent of AGD) trophozoites were exposed to clove oil at 10, 20, 40 and 80 μL L− 1 for 10 min and 5, 10, 20 and 40 μL L− 1 for 120 min; AQUI-S® at 5, 10, 20 and 40 μL L− 1 for 10 min and 2.5, 5, 10 and 20 μL L− 1 for 120 min There were no significant differences in viability and survival of trophozoites after exposure to the anaesthetics. When trophozoites were exposed to clove oil at 80 μL L− 1 for 10 min there was significantly (P Statement of relevance We believe that the study has relevance because it establishes that there were no anti-amoeba properties of eugenol observed at concentrations commonly used and therefore interpretation of previous in vitro and in vivo work unlikely to be affected as will future work.

A total of 20 lactic acid bacteria (LAB) were isolated from the gastrointestinal tracts of Atlantic salmon (Salmo salar) and screened for antimicrobial activity against six fish pathogens using either a microtiter plate assay or a well diffusion assay. The results indicated that three LAB exhibited antimicrobial activity against at least two pathogens. Based on their partial 16S ribosomal deoxyribonucleic acid (16S rDNA) sequences, these isolates were identified as Lactobacillus farraginis, Pediococcus acidilactici, and P. pentosaceus. In addition, these LAB were able to tolerate the simulated gastrointestinal tract conditions (stomach and intestine), had a good adhesion capacity to intestinal mucus as well as were able to grow in intestinal mucus of Atlantic salmon. These results suggest that these LAB are potential probionts in aquaculture. However, further studies are required to evaluate probiotic properties in aquatic animals.