Immunohistochemistry of Atlantic cod larvae Gadus morhua experimentally challenged with Vibrio anguillarum

Abstract

Farming of Atlantic cod Gadus morhua is one of the most rapidly growing sectors of Norwegian aquaculture. Classical vibriosis caused by Vibrio anguillarum is a problem in cod aquaculture. To prevent disease outbreaks, a thorough understanding of the infection route and the impact of the bacteria on the host is important. The intestinal tract, skin and gills have all been proposed as routes of entry for bacterial infections such as vibriosis. We aimed to further develop understanding of V. anguillarum serotype O2α infections in cod larvae by elucidation of a possible route of entry, the pattern of infection and its histopathology. Cod eggs were transferred to a 24-well polystyrene multi-dish with 2 ml of sterile aerated 80% (28 ‰ salinity) seawater. Challenge doses were 10 4 and 10 6 CFU ml -1. Unchallenged larvae were used as controls. Larvae for immunohistochemical examination were sampled daily from each group. In most of the larvae, either no or very few bacteria were observed. Typical findings were clusters of bacteria in the spaces between the primary gill lamellae. None of these bacteria seemed to have adhered to the gills. Intestines of 3 out of 161 larvae examined contained positively immunostained bacteria. Some bacteria appeared attached to the microvilli, but none was observed inside epithelial cells. Only 2 larvae from the low-challenge dose group showed clear signs of histopathology, which occurred in the intestine. It is not possible to draw any conclusions regarding the portal of entry. KEY WORDS: Vibrio anguillarum · Cod larvae · Immunohistochemical studies · Challenge experimentResale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS

Differentially expressed proteins in the skin mucus of Atlantic cod (Gadus morhua) upon natural infection with Vibrio anguillarum

“…The observations were made only during early stages of infection. The V. anguillarum H610 challenge protocol at Institute of Marine Research (IMR), Bergen is robust and well established as reported in different studies [7,54]. …”

“…The ubiquitous distribution of V. anguillarum in various marine habitats, their opportunistic nature, and the sporadic recurrences of vibriosis caused by deviating serotypes make the complete eradication of this disease in fish farms infeasible [7,8]. …”

“…Other studies have shown that establishment of bacteria in the gut is facilitated by chemotaxis, induced by mucosal components such as amino acids, carbohydrate moieties on proteins like high molecular weight mucins, and bile components [11]. Skin is also considered as a potential infection route for V. anguillarum , besides gills and gut [7]. Bath challenge experiments have shown that the primary site of attachment and colonization of V. anguillarum is the skin and intestine of zebrafish ( Danio rerio ) [12], and skin and fins of juvenile rainbow trout [13].…”

Screening and characterisation of potentially pathogenic bacteria associated with Atlantic codGadus morhualarvae: bath challenge trials using a multidish system

“…Reisolation of bacteria from larvae is difficult, particularly due to the small size of the larvae; the need for exterior washing or disinfection results in a decreased number of viable bacteria. Concerning this matter we chose immunochemistry methods to verify the presence of Vibrio anguillarum (Engelsen et al 2008). Given that sterile water and a high concentration of bacteria were added to each well, it is reasonable to believe that the dominant bacteria inside the wells were the bacteria used for challenge.…”

Characterization of GP21 and GP12: Two Potential Probiotic Bacteria Isolated from the Gastrointestinal Tract of Atlantic Cod

“…Such outbreaks are not unfamiliar in Atlantic cod, Gadus morhua L., a cold-water fish that is being intensively farmed [21]. Two of the most prominent bacterial diseases of cod are vibriosis caused by Vibrio anguillarum and furunculosis caused by Aeromonas salmonicida [9,30]. Cod affected by vibriosis mainly show fin erosion and hemorrhages in the head region, especially in and around the eye, while those affected by furunculosis will have widespread granuloma formation as well as necrotic changes in several of their organs [30].…”