Isolation and characterization of pathology in case of massive mortality by Photobacterium damselae subsp. piscicida in Rachycentron canadum / Isolamento e caracterização da patologia em caso de mortalidade maciça por Photobacterium damselae subsp. piscicida em Rachycentron canadum

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.

The Chelating Mineral on Organic Acid Salts Modulates the Dynamics and Richness of the Intestinal Microbiota of a Silver Catfish Rhamdia quelen.

The aim of this study was to evaluate the influence of the chelating mineral on propionic acid, calcium or sodium on the composition, dynamics and richness of the intestinal microbiota of a native silver catfish Rhamdia quelen through high-throughput sequencing (HTS). A total of 225 fish (8.43 ± 0.18 g) were distributed in tanks, 15 fish per tank in five groups with three replicates each: Control, Ca-propionate 0.25% (Ca0.25%) Ca-propionate 1% (Ca1%), Na-propionate 0.25% (Na0.25%) and Na-propionate 1% (Na1%). The feed was provided four times a day for 60 days. After experimental period, the fish were fasted for 24 h and the intestine was aseptically collected, pooled by treatment, and fixed in pure absolute ethanol for subsequent DNA extraction and HTS. The HTS showed that the supplementation of the propionic acid chelated to the mineral calcium or sodium in the different concentrations increased the operational taxonomic units and richness in comparison to control group. The main phyla found were Fusobacteria, Firmicutes, Proteobacteria and Bacteroides. Both the fusobacteria and the genus Cetobacterium, especially C. somerae, were positively modulated with Ca0.25% and Na1% supplementation. It can be emphasized that supplementation with calcium or sodium propionate at different concentrations changed the natural microbiota of R. quelen.

Leukocyte response and phagocytic activity in Nile tilapia experimentally infected with Enterococcus sp.

This study evaluated the total and differential leukocyte counting and the phagocytic activity in Nile tilapia Oreochromis niloticus experimentally injected with Enterococcus sp. in the swim bladder. Fish were distributed in four treatments in triplicates of non-injected fish, fish injected with 1 ml of sterile saline solution 0.65%, and fish injected with 1 x 10(3) and 1 x 10(6) colony-forming units (CFU) of Enterococcus diluted in 1 ml sterile saline. Twenty-four hours after injection, the fish were anesthetized and the blood collected for white blood cell (WBC) counts, differential counting of WBC, and phagocytic activity of blood leukocytes. The increased numbers of WBC and lymphocytes were followed by decreased number of monocyte after infection. The percentages of phagocytic activities in the blood were 55.3 and 55.9%, respectively, in tilapia injected with 1 x 10(3) and 1 x 10(6) CFU/ml.