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Background: Fish production in Brazil is growing strongly. This growth is being mainly driven by mainland aquaculture, which in 2017 produced 691.700 tons of fish. To improve production levels, fish farms have become increasingly intensive, but in these systems, the high fish densities in the ponds, the high feeding rate, and the high organic matter levels in the water can lead the fish becoming stressed. This can cause bacterial proliferation and an increase in mortality. Most species of fish-causing bacteria are saprophytes. They are found naturally in the environment and are usually responsible for secondary or opportunistic infections. This study reports on an outbreak of Pacus (Piaractus mesopotamicus) mortality at an intensive fish farm, in the municipality of Campo Grande, MS, Brazil, that used excavated tanks. Cases: The outbreak occurred at a fish farm in the municipality of Campo Grande, MS, during August, 2015. A total of 200 pacus in two tanks died after they showed the following symptoms: lethargy, anorexia, increased mucus production, and disordered swimming and water surface searching. The temperature and dissolved oxygen were measured using a digital thermometer and an oximeter, respectively, and water transparency was measured with a Secchi disc. The pH was measured using a portable digital potentiometer. The values for the water quality parameters analyzed during the mortality period were temperature, 22.5°C; transparency, 20 cm; oxygen dissolved in the early morning 3 mg/L and at the end of the afternoon, 4.5 mg/L; pH 8.3; and toxic ammonia, 0.002 ppm. Five fishes were collected from the tank, immediately cooled to 4°C, and sent to the Microbiology and Pathology Laboratories to perform the microbiological and pathological laboratory procedures. After the replication process, the slow glucose fermentation characteristics in MacConkey Agar and other biochemical tests showed that the lactose non-fermenter bacterium was Pseudomonas aeruginosa and the fermenting bacterium was Pantoea agglomerans. A necroscopic examination revealed congestion of viscera in general and thickening of the gills; the histopathological examination showed an intense inflammatory reaction in the gills; and the liver showed congestion and dilation of the central, hepatoportal, and sinusoidal veins, marked cytoplasmic vacuolization, the presence of hemosiderin and leukocytosis, and coagulation necrosis and cholestasis foci. Discussion: The water temperature in the tanks (22.5°C) was lower than what is considered ideal for tropical fish. It ranged from 25 to 32°C. Furthermore, the pH (8.3) was close to the limit of what is considered appropriate. The mean tank flow rate at the time of death was 15 L/min, corresponding to a daily renewal rate of 1.2%, which was lower than the 10% per day recommended as the ideal rate for excavated ponds in a semi-intensive production system. The decreased water flow in the tank during the period when mortality was recorded caused an increase in the amount of accumulated organic matter. This rise is commonly referred to as eutrophication, which is characterized by an increase in the rate of decomposition and release of nutrients into the water. The excess nutrients, mainly nitrogen and phosphorus, cause excessive phytoplankton and aquatic macrophyte growth, which results in a significant reduction in the amount of dissolved oxygen, particularly during periods of low photosynthetic activity. In this case study, the cause of the fish mortality was attributed to opportunistic infection by Pantoea agglomerans and Pseudomonas aeruginosa caused by imbalances in water quality. [ABSTRACT FROM AUTHOR]

The occurrence of Trypanosoma spp. in wild carnivore populations has been intensively investigated during the last decades. However, the impact of these parasites on the health of free-living infected animals has been largely neglected. The Pantanal biome is the world's largest seasonal wetland, harboring a great diversity of species and habitats. This includes 174 species of mammals, of which 20 belong to the order Carnivora. The present study aimed to investigate the effect of Trypanosoma evansi and Trypanosoma cruzi infections and coinfections on the health of the most abundant carnivores in the Pantanal: coati (Nasua nasua), crab-eating fox (Cerdocyon thous), and ocelot (Leopardus pardalis). We captured 39 coatis, 48 crab-eating foxes, and 19 ocelots. Diagnostic tests showed T. cruzi infection in 7 crab-eating foxes and 5 coatis. Additionally, 7 crab-eating foxes, 10 coatis, and 12 ocelots were positive for T. evansi. We observed coinfections in 9 crab-eating foxes, 8 coatis, and 2 ocelots. This is the first report of T. evansi and T. cruzi infection on the health of free-living ocelots and crab-eating foxes. We showed that single T. evansi or T. cruzi infection, as well as coinfection, caused some degree of anemia in all animals, as well as an indirect negative effect on body condition in coatis and crab-eating foxes via anemia indicators and immune investment, respectively. Furthermore, the vigorous immune investment observed in sampled coatis, crab-eating foxes and ocelots infected by T. evansi, T. cruzi and coinfected can be highly harmful to their health. Overall, our results indicate that single and combined infection with T. evansi and T. cruzi represent a severe risk to the health of wild carnivores in the Pantanal region., Competing Interests: The authors have declared that no competing interests exist.