| Summary: | In November 2020, a mortality episode in juvenile sturgeons occurred in a hatchery in Northern Italy, associated with severe abdomen dilatation and peculiar behavioral alteration, characterized by upside-down surface swimming. Juveniles (4-5 months old, average weight ± 25g) of Siberian and Russian sturgeons (Acipenser baerii and A. gueldenstaedtii) and hybrid sturgeons GUBA (A. gueldenstaedtii x A. baerii), were promiscuously maintained in concrete hatchery tanks supplied by well water (15 °C, O2 7 ppm, CO2 12 ppm), and fed at 0.4% of body weight per day. The outbreak resulted in cumulative mortality of 25%. Thirty moribund sturgeons were collected, euthanized with an overdose of MS-222, and underwent necropsy followed by histological, bacteriological, and virological investigations. Main macroscopic findings included diffuse and severe bloating of gastrointestinal tracts due to foamy contents, with severe thinning and stretching of the intestinal wall, absence of visceral fat, and small size of the hepatopancreas. Histology revealed variable degrees of attenuation, sloughing, and necrosis of the intestinal epithelium, associated with bacterial aggregates, and hepatocellular degeneration. All specimens were negative for Herpesviruses by WSSK-1 cell culture, and Iridovirus (AcIV-E) and Betanodavirus by molecular methods. Bacteriological examination revealed Plesiomonas shigelloides and Cetobacterium somerae in a subset of intestines, while other organs yielded negative results. Based on recent literature, an intestinal dysmicrobism was suspected, and anaerobic gram+ bacteria were investigated. Clostridium perfringens was isolated from the intestines, and specific PCRs identified the toxinotype A and the β2 toxin gene. The quantity of food was raised to 1.5% of body weight, and after 5 days the abnormal behavior and mortality ceased. The analyses were repeated after 12 weeks from the food increase and showed no alterations including negative results for C. perfringens isolation. Therefore, we hypothesize that ...
|
|---|