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The production of river catfish Pangasius hypophthalmus trade has increased significantly over the past decade. Concerning the high demand for river catfish, P. hypophthalmus, these freshwater fish are susceptible to fungi infection that can cause mortality to individual and fish eggs. This study has been conducted to identify the morphology of isolated fungi and their extracellular- enzymes for virulent screening. Three fishes with apparent signs of infection such as ulcerative, haemorrhages and dermal lesions were collected from the fish cage culture at Kampung Serada, Kuala Terengganu. Fungi were isolated from the fish externally (fin, skin, mouth, gill) and internal organs (kidney and liver). The fungal morphology was characterised macroscopically by observing the colony features such as margin, pigmentation (colour), elevation, texture and shape of fungi on an agar plate. Meanwhile, for micromorphology observation were characterised the fungi structure includes the spore, hyphae, and conidiaphore. Based on the identification using a general key to characteristics moulds, two fungi have been classified into two genera: Rhizopus-like sp and Geomyces-like sp. These fungi proceeded with extracellular enzyme tests such as the proteolysis assay, amylases test and lipases test. The reaction enzymes of fungi from the amylases test showed the clearing zone around the radial colony growth of fungi. The test strain of fungi screened during the present investigation proved to be an efficient producer of protein and polysaccharide degrading enzymes. Rhizopus-like sp and Geomyces-like sp to produce extracellular amylase enzyme indicated the virulent characteristic of the isolate and the ability of those fungi to initiate infection or resist harsh environments and treatments.

Oomycetes are fungal-like eukaryotes and many of them are pathogens that threaten natural ecosystems and cause huge financial losses for the aqua- and agriculture industry. Amongst them, Aphanomyces invadans causes Epizootic Ulcerative Syndrome (EUS) in fish which can be responsible for up to 100% mortality in aquaculture. As other eukaryotic pathogens, in order to establish and promote an infection, A. invadans secretes proteins, which are predicted to overcome host defence mechanisms and interfere with other processes inside the host. We investigated the role of Lhs1 which is part of an ER-resident complex that generally promotes the translocation of proteins from the cytoplasm into the ER for further processing and secretion. Interestingly, proteomic studies reveal that only a subset of virulence factors are affected by the silencing of AiLhs1 in A. invadans indicating various secretion pathways for different proteins. Importantly, changes in the secretome upon silencing of AiLhs1 significantly reduces the virulence of A. invadans in the infection model Galleriamellonella. Furthermore, we show that AiLhs1 is important for the production of zoospores and their cluster formation. This renders proteins required for protein ER translocation as interesting targets for the potential development of alternative disease control strategies in agri- and aquaculture.

Aphanomyces invadans is a eukaryotic pathogen and the causative agent of Epizootic Ulcerative Syndrome (EUS) in fish and is responsible for mortalities of up to 100% in aquaculture. A. invadans was first discovered in Japan in 1971, and since then it has been found in Australia, North America, Southern African countries and Asia. Methods for the correct identification of A. invadans are well established now and involve PCR-based detection and microscopy. However, the pathogenesis of A. invadans is poorly understood. Environmental stress (mainly temperature) and the associated immunocompromised fish seem to induce infections of A. invadans and outbreaks of EUS. Understanding the process of infection in more depth is fundamental for the discovery of novel effective treatments to combat the disease. In this review, we discuss morphological characteristics of A. invadans and its pathogenicity as well as various approaches of treatment.

Oomycetes are eukaryotic pathogens infecting animals and plants. Amongst them Saprolegnia parasitica is a fish pathogenic oomycete causing devastating losses in the aquaculture industry. To secure fish supply, new drugs are in high demand and since fish experiments are time consuming, expensive and involve animal welfare issues the search for adequate model systems is essential. Galleria mellonella serves as a heterologous host model for bacterial and fungal infections. This study extends the use of G. mellonella for studying infections with oomycetes. Saprolegniales are highly pathogenic to the insects while in contrast, the plant pathogen Phytophthora infestans showed no pathogenicity. Melanisation of hyphae below the cuticle allowed direct macroscopic monitoring of disease progression. However, the melanin response is not systemic as for other pathogens but instead is very local. The mortality of the larvae is dose-dependent and can be induced by cysts or regenerating protoplasts as an alternative source of inoculation., Graphical abstract, Highlights • Galleria mellonella serves as a heterologous host model system for Saprolegniales. • The melanisation of the larvae is local around the growing hyphae. • Regenerating protoplasts can be used as an alternative inoculum to cysts.

Outbreaks of edwardsiellosis have severe impact on the aquaculture production of African catfish Clarias gariepinus. In this study, feed supplemented with apple mangrove Sonneratia caseolaris extract was evaluated for its protective effect against Edwardsiella tarda infection in African catfish. Results showed an increase in growth performance and higher survival rate in the treatment groups in a dose dependent manner. Haematological analyses showed an increase in white blood cell count in the treatment groups. Histopathological analysis revealed degenerative changes and regeneration of liver tissue architecture in both the control and treatment groups. However, the presence of inflammatory cells was found exclusively in the kidney of T3 treatment group that was supplemented with the highest dose of extract at 3.17 mg/ml, which inferred the activation of immune response in the fish. Contrast to the deteriorative alteration observed in the kidney of the control group due to E. tarda infection, treatment group exhibited tissue regeneration and well-defined kidney tissue architecture at 3 dpi. Taken together, these results demonstrated that supplementation with the methanol extract of S. caseolaris possesses protective effect in African catfish against the infection of E. tarda.