Diseases of Aquatic Organisms

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ISSN / EISSN : 0177-5103 / 1616-1580
Published by: Inter-Research Science Center (10.3354)
Total articles ≅ 4,152
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M Bennion, P Ross, J Howells, Ir McDonald, H Lane
Diseases of Aquatic Organisms, Volume 146, pp 91-105; https://doi.org/10.3354/dao03626

Abstract:
The toheroa Paphies ventricosa is a large Aotearoa New Zealand (ANZ) endemic surf clam of cultural importance to many Māori, the Indigenous people of ANZ. Extensive commercial and recreational harvesting in the 20th century dramatically reduced populations, leading to the collapse and closure of the fishery. Despite being protected for >40 yr, toheroa have inexplicably failed to recover. In 2017, intracellular microcolonies (IMCs) of bacteria were detected in ‘sick’ toheroa in northern ANZ. Numerous mass mortality events (MMEs) have recently been recorded in ANZ shellfish, with many events linked by the presence of IMCs resembling Rickettsia-like organisms (RLOs). While similar IMCs have been implicated in MMEs in surf clams elsewhere, the impact of these IMCs on the health or recovery of toheroa is unknown. A critical first step towards understanding the significance of a pathogen in a host population is pathogen identification and characterisation. To begin this process, we examined 16S rRNA gene sequences of the putative IMCs from 4 toheroa populations that showed 97% homology to Endozoicomonas spp. sequences held in GenBank. Phylogenetic analysis identified closely related Endozoicomonas strains from the North and South Island, ANZ, and in situ hybridization, using 16S rRNA gene probes, confirmed the presence of the sequenced IMC gene in the gill and digestive gland tissues of toheroa. Quantitative PCR revealed site-specific and seasonal abundance patterns of Endozoicomonas spp. in toheroa populations. Although implicated in disease outbreaks elsewhere, the role of Endozoicomonas spp. within the ANZ shellfish mortality landscape remains uncertain.
, Bc LaBumbard, Eh Le Sage, Dc Woodhams
Diseases of Aquatic Organisms, Volume 146, pp 81-89; https://doi.org/10.3354/dao03621

Abstract:
Detecting and quantifying pathogens with quick, cost-efficient and sensitive methods is needed across disease systems for addressing pertinent epidemiological questions. Typical methods rely on extracting DNA from collected samples. Here we develop and test an extraction-free method from water bath samples that is both sensitive and efficient for 2 major amphibian pathogens—Batrachochytrium dendrobatidis and B. salamandrivorans. We tested mock samples with known pathogen quantities as well as comparatively assessed detection from skin swabs and water baths from field sampled amphibians. Quantitative PCR (qPCR) directly on lyophilized water baths was able to reliably detect low loads of 10 and 1 zoospores for both pathogens, and detection rates were greater than those of swabs from field samples. Further concentration of samples did not improve detection, and collection container type did not influence pathogen load estimates. This method of lyophilization (i.e. freeze-drying) followed by direct qPCR offers an effective and efficient tool from detecting amphibian pathogens, which is crucial for surveillance efforts and estimating shedding rates for robust epidemiological understanding of transmission dynamics. Furthermore, water bath samples have multiple functions and can be used to evaluate mucosal function against pathogens and characterize mucosal components. The multifunctionality of water bath samples and reduced monetary costs and time expenditures make this method an optimal tool for amphibian disease research and may also prove to be useful in other wildlife disease systems.
Cl Nordheim, Jm Grim,
Diseases of Aquatic Organisms, Volume 146, pp 67-73; https://doi.org/10.3354/dao03623

Abstract:
Batrachochytrium dendrobatidis (Bd) is a pathogenic fungus known to infect amphibians and crayfish. In crayfish, Bd causes gill tissue damage, and in some cases, mortality. Most research has focused on the amphibian-Bd system, so to date, little is known about the effects of Bd on the crayfish host. Here, we studied the effects of sublethal exposure to Bd and the metabolites produced by Bd on crayfish Procambarus alleni survival, gill damage, and oxygen consumption (as a proxy for mass-specific metabolic rate). Oxygen consumption increased 24 h post-exposure to live Bd, indicative of a stress response, followed by a decrease in oxygen consumption over time (χ2 1 = 6.39, p = 0.012). There was no difference in response when comparing the crayfish exposure to live Bd and Bd-metabolites alone (χ2 1 = 2.70, p = 0.101), indicating that the metabolites may have been the causative agent responsible for the response. Additionally, oxygen consumption decreased with gill damage (tissue recession) in Bd-exposed individuals. We found that high doses of Bd cause outright mortality in crayfish, and we show here that sublethal Bd-induced inhibition of oxygen consumption could negatively impact crayfish in the field, possibly reducing their overall fitness. More research is needed to understand this understudied host-parasite system. It is essential that we incorporate the disease dynamics associated with Bd and crayfish in conservation disease models, as this is the only way to develop comprehensive community-based models.
, V Jung-Schroers, F Teitge, M Adamek, D Steinhagen
Diseases of Aquatic Organisms, Volume 146, pp 107-115; https://doi.org/10.3354/dao03625

Abstract:
This study outlines a multifactorial disease outbreak in a population of the freshwater shrimp Neocaridina davidi, with the focus on a rarely described parasitic alga. Within this multifactorial disease outbreak, low but consistent mortality was observed. During microscopic examination, an infection of the shrimp with bacterial and fungal-like agents was diagnosed. Furthermore, the green alga Cladogonium sp. was found in pleopodal regions. The alga compromised the body surface of the shrimp, and its rhizoids penetrated the chitin shell and reached into the subcutaneous tissue. This might be a first indication of a parasitic lifestyle. In addition to a morphological description, sequencing data are presented which allow the taxonomic classification of the organism within the order Trentepohliales.
D Mugetti, E Colombino, , C Salogni, P Pastorino, L Chiappino, A Sereno, M Prearo, F Guarda
Diseases of Aquatic Organisms, Volume 146, pp 75-79; https://doi.org/10.3354/dao03620

Abstract:
Lambl’s excrescences (LE) are fibrous strands typically occurring at coaptation lines of cardiac valves. Although they have been widely reported in human medicine, information on LE occurrence in veterinary medicine is still scarce. The present study aimed to investigate the presence of LE in different freshwater fish and in swordfish. A total of 185 hearts were collected from different fish species, and samples of different cardiac areas (sinus venosus, atrial wall with sinoatrial valves, ventricular wall with atrioventricular valves and bulb with bulboventricular valves) were submitted to histopathological evaluation. LE were detected in 6 of 103 freshwater fish (5.8%) and 19 of 82 swordfish (23.2%). LE developed in atrioventricular, sinoatrial and bulboventricular valves. All affected valves also showed endocardiosis. Based on the results of the present work, teleost fish, specifically swordfish, could be proposed as a novel spontaneous model for the study of LE pathogenesis.
, Vn Sreejith, Tc Joseph, V Murugadas, Kv Lalitha
Diseases of Aquatic Organisms, Volume 146, pp 117-128; https://doi.org/10.3354/dao03619

Abstract:
Quorum sensing (QS) is a type of cell to cell communication in bacteria that can also regulate the virulence potential in pathogenic strains. Hence, QS disruption, i.e. the quorum quenching (QQ) mechanism, is presently being explored as a novel bio-control strategy to counter bacterial infections. In the present study, we characterized the QQ ability of Bacillus spp. strains to reduce the expression of some virulence factors of a shrimp pathogen, Vibrio harveyi. We screened a total of 118 spore-forming bacterial isolates from aquaculture ponds and mangrove soil for their ability to degrade the synthetic N-acyl-homoserine lactones (AHLs) C4-HSL, C6-HSL, C8-HSL, and C10-HSL. We then selected the top 17 isolates with high AHL-degradation ability for further study. Among them, B. subtilis MFB10, B. lentus MFB2, and B. firmus MFB7 had the highest ability for degradation. These 3 isolates suppressed the expression of virulence genes encoding protease, lipase, phospholipase, caseinase, chitinase, and gelatinase, and potentially inhibited the biofilm formation of V. harveyi MFB32. The reduction in expression of virulence genes like those coding for metalloprotease, serine protease, and haemolysin were confirmed by real-time PCR analysis. Moreover, in an in vivo challenge experiment, these Bacillus spp. protected Penaeus monodon post-larvae against V. harveyi MFB3 infection. Our results demonstrate the potential application of AHL-degrading Bacillus spp. as an alternative to antibiotics in shrimp hatcheries to control luminescent vibriosis. This novel bio-therapeutic method is a promising approach towards disease control in shrimp aquaculture.
, Mette Myrmel, Atle Lillehaug, Lars Qviller, Simon Chioma Weli
Diseases of Aquatic Organisms, Volume 144, pp 61-73; https://doi.org/10.3354/dao03572_c

Abstract:
Currently, the prevalence of salmonid alphavirus (SAV) in Norwegian Atlantic salmon farms is largely surveyed via sacrificing fish and sampling of organ tissue on a monthly basis. However, a more cost-efficient, straightforward, rapid, reliable, reproducible and animal welfare friendly method based on the detection of SAV in water could be considered as an alternative method. In the present study, such a method was developed and optimized through a 6 wk cohabitant challenge trial, using post-smolt Atlantic salmon Salmo salar L challenged with high or low doses of SAV subtype 3 (SAV3). Tank water and tissue samples from cohabitant fish were collected at 16 time points. SAV3 was concentrated from the water by filtration, using either electronegative or electropositive membrane filters, which were subsequently rinsed with one of 4 different buffer solutions. SAV3 was detected first in tank water (7 d post-challenge, DPC), and later in cohabitant fish organ tissue samples (12 DPC). The electronegative filter (MF-Millipore™) and rinsing with NucliSENS® easyMAG® Lysis Buffer presented the best SAV3 recovery. A significant positive correlation was found between SAV3 in the tank water concentrates and the mid-kidney samples. Based on these results, detection of SAV3 in filtrated seawater is believed to have the potential to serve as an alternative method for surveillance of SAV in Atlantic salmon farms.
, M Myrmel, A Lillehaug, L Qviller, S Chioma Weli
Diseases of Aquatic Organisms, Volume 144, pp 61-73; https://doi.org/10.3354/dao03572

Abstract:
Currently, the prevalence of salmonid alphavirus (SAV) in Norwegian Atlantic salmon farms is largely surveyed via sacrificing fish and sampling of organ tissue on a monthly basis. However, a more cost-efficient, straightforward, rapid, reliable, reproducible and animal welfare friendly method based on the detection of SAV in water could be considered as an alternative method. In the present study, such a method was developed and optimized through a 6 wk cohabitant challenge trial, using post-smolt Atlantic salmon Salmo salar L challenged with high or low doses of SAV subtype 3 (SAV3). Tank water and tissue samples from cohabitant fish were collected at 16 time points. SAV3 was concentrated from the water by filtration, using either electronegative or electropositive membrane filters, which were subsequently rinsed with one of 4 different buffer solutions. SAV3 was detected first in tank water (7 d post-challenge, DPC), and later in cohabitant fish organ tissue samples (12 DPC). The electronegative filter (MF-Millipore™) and rinsing with NucliSENS® easyMAG® Lysis Buffer presented the best SAV3 recovery. A significant positive correlation was found between SAV3 in the tank water concentrates and the mid-kidney samples. Based on these results, detection of SAV3 in filtrated seawater is believed to have the potential to serve as an alternative method for surveillance of SAV in Atlantic salmon farms.
, R El Jeni, F Amdouni, S Zreilli, H Djabou, S Khemiri, I Tliba, B Bouhaouala-Zahar, K Maatoug, S Zaafran, et al.
Diseases of Aquatic Organisms, Volume 146, pp 53-63; https://doi.org/10.3354/dao03614

Abstract:
The purpose of this study was to determine the phylogenetic relationships among the primary betanodavirus strains circulating in Tunisian coastal waters. A survey was conducted to investigate nodavirus infections at 15 European sea bass Dicentrarchus labrax and gilthead sea bream Sparus aurata farming sites located along the northern and eastern coasts of Tunisia. The primary objective of the study was to create epidemiological awareness of these infections by determining phylogenetic relationships between the main betanodavirus strains circulating during the period 2012-2019, using RNA1 and/or RNA2 genome segments. Approximately 40% (118 of 294) tissue pools tested were positive for betanodavirus. Positive pools were distributed across all of the sampling sites. While fish mortalities were always correlated with the presence of virus in sea bass, a severe outbreak was also identified in sea bream larvae in 2019. Phylogenetic analysis revealed that almost all Tunisian strains from both sea bass and sea bream irrespective of outbreaks clustered within the RGNNV genotype. It is noteworthy that samples collected during the 2019 outbreak from sea bream contained both RNA1 and RNA2 fragments belonging to the RGNNV and SJNNV genotype, respectively, an indication of viral genome reassortment. To our knowledge, this is the first report of reassortant betanodavirus in Tunisia.
S Correia, R Freitas, X de Montaudouin,
Diseases of Aquatic Organisms, Volume 146, pp 23-28; https://doi.org/10.3354/dao03616

Abstract:
The cockle Cerastoderma edule, a socioeconomically important bivalve of the northeast Atlantic, is host to several trematodes, including Himasthla elongata. In the life cycle of this trematode, cercariae (free-living stages) emerge from the first intermediate host, a snail, to infect cockles as second intermediate hosts. During their lifespan (less than 2 d), cercariae must ensure successful host-to-host transmission via the surrounding water and therefore are exposed to and impacted by different environmental conditions, including abiotic factors. Given that the light:dark cycle is one of the major drivers of behaviour in aquatic habitats, we aimed to determine the influence of light on cercariae and host behaviour based on 3 hypotheses. First, by having a benthic second intermediate host, these cercariae will display a photonegative orientation; second, and conversely, host behaviour will not be influenced by light; and third, cercariae infection success will be light-dependent. Results showed that cercariae display a photopositive orientation (first hypothesis rejected), displaying movements towards light. Host activity (evaluated by oxygen consumption) was similar among conditions, i.e. dark vs. light (second hypothesis accepted), but hosts acquired more parasites when experimentally infected in the dark (third hypothesis accepted). This light-dependent infection of the host is explained by a change of cercarial behaviour when exposed to light, decreasing their infection success. This study highlights that trematode responses to external conditions may be linked to successful life cycle completion rather than being altered by the host habitat. Light influence on cercarial behaviour resulted in increased infection success that may affect trematode population dynamics and their distributional range.
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