ABSTRACT
This study aimed to investigate outbreak with high mortality in cultured juvenile cobiaoccurred in Southeast Brazil in 2011. Fish displayed retarded growth rates, lethargy, fin ulceration, skin depigmentation, corneal opacity, and physical deformities. Internally, livers were increased in volume and pale in different degrees. Firm whitish nodules were disseminated in the liver, kidney and spleen. A moderate number of parasites identified as Neobenedenia melleni were recovered from the body surface. Microscopically, severe hepatic steatosis and extensive granulomatous lesion were identified in all fish sampled. Microbiological analysis of moribund fish revealed the presence in pure culture of a Gram-negative bacterium identified as Photobacterium damselae subsp. piscicida using biochemical and molecular characteristics. Analysis of the partial 16S rRNA sequences confirmed the results demonstrating high identity (98%). The isolates were sensitive to chloramphenicol and enrofloxacin and resistant to ciprofloxacin, florfenicol, doxycycline hydrochloride, norfloxacin, oxytetracycline, and tetracycline. Chronic pasteurellosis was considered as the main problem in the farm, while hepatic steatosis and parasitic infestation may have contributed to the development of the process.
Este estudo objetivou investigar um surto com alta mortalidade em cobia juvenis cultivadas na região Sudeste do Brasil em 2011. Os peixes apresentavam baixa taxa de crescimento, letargia, ulceração nas nadadeiras, despigmentação da pele, opacidade da córnea e deformidades físicas. Internamente o fígado apresentava aumentado e pálido em diferentes graus, com nódulos esbranquiçados e firmes disseminados no fígado, rins e baço. Na superfície corporal dos peixes foram observados moderado número de parasitas identificados como Neobenedenia melleni. Microscopicamente verificou-se esteatose hepática grave e extensa lesão granulomatosa em todos os peixes amostrados. A análise microbiológica dos peixes moribundos revelou a presença, em cultura pura de uma bactéria Gram-negativa identificada como Photobacterium damselae subsp. piscicida usando características bioquímicas e moleculares. A análise das sequências parciais de 16S rRNA confirmou os resultados demonstrando alta identidade (98%). Os isolados foram sensíveis a cloranfenicol e enrofloxacina e resistente a ciprofloxacina, florfenicol, cloridrato de doxiciclina, norfloxacina, oxitetraciclina e tetraciclina. A pasteurelose crônica foi considerada como o principal problema na maricultura, enquanto a esteatose hepática e a infestação parasitária podem ter contribuído para o desenvolvimento do processo.
Subject(s)
Yersinia pseudotuberculosis Infections , Fishes , GranulomaABSTRACT
Aeromonas bacteria can cause an infection characterized by septicemia and is one of the most common pathogens in tropical fish. This disease is responsible for high morbidity and mortality rates, causing considerable losses in aquaculture. Thus, the understanding of its pathophysiology is crucial to develop control strategies of this bacterial infection in farmed fish. This study aimed to characterize early pathological aspects of acute sepsis in pacu (Piaractus mesopotamicus) experimentally infected with Aeromonas hydrophila. A total of 160 juvenile pacus were inoculated intraperitoneally with A. hydrophila (1.78 x 109 CFU/mL) and at 0 (control), 1, 3, 6, and 9 hours post-inoculation (hpi), animals were anesthetized and samples were collected for microbiological, light microscopy and transmission electron microscopy (TEM) analyzes. The results showed the occurrence of hemodynamic alterations, such as hemorrhage and congestion, which were observed mainly after 6 and 9 hpi. It was possible to re-isolate Aeromonas at all sampling times except in control group. However, just after 9 hpi it was possible to find the bacteria in all fish and tissues. Light microscopy analyses revealed a degenerative process, necrosis and vascular damage mainly at 6 and 9 hpi. According to the ultrastructural examination, areas of cellular death were identified in all examined tissues, especially at 6 and 9 hpi. However, the most severe, related to necrosis, were observed after 6 and 9 hpi. The findings suggested that this bacterium spreads in the first hpi through the fish organs, mainly affecting spleen, liver and kidney, causing irreversible lesions at the molecular level.
