Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L

Diversity of fungus-like stramenopilous organisms (Oomycota) in Lithuanian freshwater aquaculture: Morphological and molecular analysis, risk to fish health

The present work is the first comprehensive study of fungus-like stramenopilous organisms (Oomycota) diversity in Lithuanian fish farms aimed at proper identification of saprolegniasis pathogens, which is important for water quality control, monitoring infection levels and choosing more effective treatments for this disease in aquaculture. Pathogenic to fish, Saprolegnia and other potentially pathogenic water moulds were isolated from adult fish, their eggs, fry and from water samples. All detected isolates were examined morphologically and confirmed by sequence-based molecular methods. A total of eight species belonging to the genera Saprolegnia, Achlya, Newbya and Pythium were identified. Four species (S. parasitica, S. ferax, S. australis and S. diclina) were found to be the main causative agents of saprolegniasis in Lithuania. S. parasitica and S. ferax dominated both in hatcheries and open fishponds, accounting for 66.2% of all isolates. S. parasitica was isolated from all farmed salmonid fish species as well as from the skin of Cyprinus carpio, Carassius carassius and Perca fluviatilis. S. australis was isolated from water and once from the skin of Oncorhynchus mykiss, and S. diclina was detected only once on the skin of Salmo salar fish. In addition, Achlya ambisexualis, Saprolegnia anisospora and Newbia oligocantha isolated during this study are noted as a possible source of saprolegniasis. The results of this study are relevant for assessing the risk of potential outbreaks of saprolegniasis or other saprolegnia-like infection in Lithuanian freshwater aquaculture.

Specific Phylotypes of Saprolegnia parasitica Associated with Atlantic Salmon Freshwater Aquaculture

Saprolegniosis is a major destructive disease in freshwater aquaculture. The destructive economic impact of saprolegniosis on freshwater aquaculture necessitates further study on the range of Saprolegnia species within Atlantic salmon fish farms. This study undertook a thorough analysis of a total of 412 oomycete and fungal isolates that were successfully cultured and sequenced from 14 aquaculture sites in Scotland across a two-year sampling period. An ITS phylogenetic analysis of all isolates was performed according to whether they were isolated from fish or water samples and during enzootic or epizootic periods. Several genera of oomycetes were isolated from sampling sites, including Achlya, Leptolegnia, Phytophthora, and Pythium, but by far the most prevalent was Saprolegnia, accounting for 66% of all oomycetes isolated. An analysis of the ITS region of Saprolegnia parasitica showed five distinct phylotypes (S2-S6); S1 was not isolated from any site. Phylotype S2 was the most common and most widely distributed phylotype, being found at 12 of the 14 sampling sites. S2 was overwhelmingly sampled from fish (93.5%) and made up 91.1% of all S. parasitica phylotypes sampled during epizootics, as well as 67.2% of all Saprolegnia. This study indicates that a single phylotype may be responsible for Saprolegnia outbreaks in Atlantic salmon fish farms, and that water sampling and spore counts alone may be insufficient to predict Saprolegnia outbreaks in freshwater aquaculture.

Saprolegniosis in Amphibians: An Integrated Overview of a Fluffy Killer Disease

Amphibians constitute the class of vertebrates with the highest proportion of threatened species, with infectious diseases being considered among the greatest causes for their worldwide decline. Aquatic oomycetes, known as “water molds,” are fungus-like microorganisms that are ubiquitous in freshwater ecosystems and are capable of causing disease in a broad range of amphibian hosts. Various species of Achlya sp., Leptolegnia sp., Aphanomyces sp., and mainly, Saprolegnia sp., are responsible for mass die-offs in the early developmental stages of a wide range of amphibian populations through a disease known as saprolegniosis, aka, molding or a “Saprolegnia-like infection.” In this context, the main objective of the present review was to bring together updated information about saprolegniosis in amphibians to integrate existing knowledge, identify current knowledge gaps, and suggest future directions within the saprolegniosis–amphibian research field. Based on the available literature and data, an integrated and critical interpretation of the results is discussed. Furthermore, the occurrence of saprolegniosis in natural and laboratory contexts and the factors that influence both pathogen incidence and host susceptibility are also addressed. The focus of this work was the species Saprolegnia sp., due to its ecological importance on amphibian population dynamics and due to the fact that this is the most reported genera to be associated with saprolegniosis in amphibians. In addition, integrated emerging therapies, and their potential application to treat saprolegniosis in amphibians, were evaluated, and future actions are suggested.

Toxic effects in Aphanomyces brasiliensis and zebrafish embryos caused by oomyceticides

In fish farming, high losses occur during egg incubation and larviculture due to diseases caused by oomycetes. This study aimed to identify the oomycete species that occurs in zebrafish Danio rerio eggs and to evaluate the oomyceticidal effect of copper sulfate, bronopol and methylene blue on the mycelial growth of this organism, as well as to determine the lethal and sublethal toxicity of these compounds in embryos of D. rerio. The isolates were cultivated in yeast-starch medium to determine the concentration necessary to inhibit mycelial growth by 50% (IC50) and 100% (minimum oomyceticidal concentration) after a 96 h exposure to these compounds. In addition, tests with D. rerio eggs were conducted to determine the lethal concentrations for 50% of the organisms (96h-LC50), and the concentrations that inhibited 17% of the eggs hatching (96h-IC17) after 96 h. The organism responsible for the mortality of D. rerio eggs was classified by classical and molecular methods as Aphanomyces brasiliensis, representing the first report of this pathogen in zebrafish eggs. IC50 values could be determined for both bronopol and copper sulfate, whereas methylene blue had low effectiveness against the oomycete. Copper showed high toxicity to D. rerio eggs at low concentrations, while methylene blue and bronopol toxicity was low and similar to each other. The use of bronopol at a concentration of 4.8 mg l-1 for the treatment of zebrafish eggs allows controlling the pathology without causing deleterious effects to the treated organisms.

Study on pathogenicity and characterization of disease causing fungal community associated with cultured fish of Kashmir valley, India

Cultured fisheries of developing countries are continously challenged by a number of pathogenic microbes. Among microbial diseases, fungal and fungal like pathogen outbreaks lead to negative social and economic impacts on stakeholders. The cultured fisheries of Kashmir valley are also facing challenge from fungal pathogens, leading to tremendous socio-economic lossess to the fish farmer community hence, yearns to boost the sector with efficient management strategy. Our study was aimed at investigating the diversity of fungal communities infecting cultured rainbow trout and carp fish species. We employed classical microbiology, macro and micro morphological characteristics, and molecular analysis (multilocus typing) for fungal identification. Also histopathological approach was used to examine the pathogenicity patterns of diverse fungal groups. The study revealed that the infection in fish was predisposed to both superficial as well as visceral organs. However, skin, gills and head were predominantly infected compared to internal organs. The microbiological investigation of infected fish by culture dependent approach helped us to obtain the total of 250 fungal isolates. Out of these isolates, 21 different species were identified belonging to three diverse fungal groups which mostly included 14 species among Ascomycetes, 03 species of Oomycetes and 04 species of Zygomycetes. The majority of fungi which were infectious to cultured fish of valley are biotrophic or opportunistic soil fungi, and some of them being exclusive pathogens of fish.

Isolation, molecular identification, and pathological lesions of Saprolegnia spp. isolated from common carp, Cyprinus carpio in floating cages in Mosul, Iraq

Background and Aim:

Saprolegniasis is a fungal disease that infects freshwater fish. The condition is characterized by a cotton-like appearance in the gills and body. This study aimed to isolate Saprolegnia from common carp, Cyprinus carpio, raised in a floating cage in Wana district, Mosul, Iraq.

Materials and Methods:

Samples were collected from 15 infected fish and examined microbiologically, molecularly, and histopathologically. Saprolegnia DNA was extracted which was amplified using universal primers give a 540 bp DNA fragment, and gill and muscle tissue were also examined for histopathological changes.

Results:

Isolated colonies of Saprolegnia were characterized by a circular, white cottony appearance with long hair. Lactophenol staining demonstrated hyphae as branched non-septate, transparent masses. The genomic DNA of isolates was consistent with Saprolegnia spp. The infected tissue samples showed variable pathology in gills. Severe hemorrhage and edema were observed in primary gill filaments with hyperplasia in epithelial cells and infusion in secondary gill filaments. Hyphae of Saprolegnia were seen between necrotic and edematous myofiber with inflammatory cells infiltration.

Conclusion:

Saprolegnia can cause economic impacts through lethal infection of fish. Clinical signs of Saprolegnia infection were confirmed molecularly and microscopically, and these findings were supported by histopathological lesions in gill and muscle tissues.

Anti-saprolegnia potency of some plant extracts against Saprolegnia diclina, the causative agent of saprolengiasis

Saprolegnosis of fresh water fishes caused by Saprolegnia diclina often results in serious economic losses to fish hatcheries. Despite the proven efficiency of malachite green as a potential fungicide in prevention and control of fish saprolegnosis, there is a strong debate about its safety aspects in use since it was documented to be responsible for many carcinogenic and teratogenic attributes. Bioactivity of four ethanolic plant extracts were assessed to attain a natural alternative to the traditional fungicide currently used in saprolegnosis control. Ethanolic extracts of Punica granatum and Thymus vulgaris exhibited a potential efficacy in suppressing mycelial growth of S. diclina at concentration of 0.5 mg/ml while extracts of Nigella sativa and Zingiber officinales were not effective respectively. The extract of pomegranate showed the highest antifungal potency with minimum inhibitory concentration (MIC) of 200 ppm while thyme extract was less effective and recorded MIC of 400 ppm against S. diclina. The acute fish toxicity of the plant extracts indicated the low toxicity of P. granatum and T. vulgaris extracts as no fish mortalities were detected at aquaria containing 200, 400 and 800 ppm of plant extracts respectively. Considering the low toxicity of these plant extracts, it may be concluded that 200 and 400 ppm of pomegranate and thyme extracts which suppressed the mycelial growth of the S. diclina could be safely used for saprolegniasis control.

Both of pomegranate and thyme extracts which proved to possess a potential antifungal activity can be considered as a natural alternative fungicides to control saprolegniasis avoiding carcinogenic malachite green application.

Interaction of carboxylated CdSe/ZnS quantum dots with fish embryos: Towards understanding of nanoparticles toxicity

Due to colloidal instability even with protective coatings, nanoparticles tend to aggregate in complex environments and possibly interact with biota. In this study, visualization of quantum dots (QDs) interaction with rainbow trout (Oncorhynchus mykiss) embryos was performed. Studies on zebrafish (Danio rerio) and pearl gourami (Trichogaster leerii) embryos have shown that QDs interact with embryos in a general manner and their affects are independent on the type of the embryo. It was demonstrated that carboxylated CdSe/ZnS QDs (4 nM) were aggregating in accumulation media and formed agglomerates on the surface of fish embryos under 1-12 days incubation in deep-well water. Detailed analysis of QDs distribution on fish embryos surface and investigation of the penetration of QDs through embryo's membrane showed that the chorion protects embryos from the penetration through the chorion and the accumulation of nanoparticles inside the embryos. Confocal microscopy and spectroscopy studies on rainbow trout embryos demonstrated that QDs cause chorion damage, due to QDs aggregation on the surface of chorion, even the formation of the agglomerates at the outer part of the embryos and/or with the mucus were detected. Aggregation of QDs and formation of agglomerates on the outer part of the embryo's membrane caused the intervention of the aggregates to the chorion and even partially destroyed the embryo's chorion. The incorporation of QDs in chorion was confirmed by two methods: in living embryos from a 3D reconstruction view, and in slices of embryos from a histology view. The damage of chorion integrity might have adverse effects on embryonic development. Moreover, for the first time the toxic effect of QDs was separated from the heavy metal toxicity, which is most commonly discussed in the literature to the toxicity of the QDs.

A thicker chorion gives ova of Atlantic salmon (Salmo salar L.) the upper hand against Saprolegnia infections

Since the ban of malachite green in the fish farming industry, finding alternative ways of controlling Saprolegnia infections has become of utmost importance. Much effort has been made to elucidate the mechanisms by which Saprolegnia invades fish eggs. Little is known about the defence mechanisms of the hosts, making some eggs more prone to infection than others. One clue might lie in the composition of the eggs. As the immune system in the embryos is not developed yet, the difference in infection levels could be explained by factors influenced by the mother herself, by either transferring passive immunity, influencing the physical aspects of the eggs or both. One of the physical aspects that could be influenced by the female is the chorion, the extracellular coat surrounding the fish egg, which is in fact the first major barrier to be overcome by Saprolegnia spp. Our results suggest that a thicker chorion in eggs from Atlantic salmon gives a better protection against Saprolegnia spp. In addition to the identification of differences in sensitivity of eggs in a fish farm set-up, we were able to confirm these results in a laboratory-controlled challenge experiment.

Factors influencing Saprolegnia spp. spore numbers in Norwegian salmon hatcheries

A quantitative survey of Saprolegnia spp. in the water systems of Norwegian salmon hatcheries was performed. Water samples from 14 salmon hatcheries distributed along the Norwegian coastline were collected during final incubation in the hatcheries. Samples of inlet and effluent water were analyzed to estimate Saprolegnia propagule numbers. Saprolegnia spores were found in all samples at variable abundance. Number of spores retrieved varied from 50 to 3200 L(-1) in inlet water and from 30 to >5000 L(-1) in effluent water. A significant elevation of spore levels in effluent water compared to inlet water was detected. The estimated spore levels were related to recorded managerial and environmental parameters, and the number of spores in inlet water and temperature was the factor having most influence on the spore concentration in the incubation units (effluent water). Further, the relative impact of spore concentration on hatching rates was investigated by correlation analysis. From this was found that even high spore counts did not impact significantly on hatching success.