Resumo Doenças parasitárias causam problemas significativos a produção mundial de peixes. Esse estudo aprofundará nosso conhecimento neste complexo problema e ajudará implementar estratégias de prevenção e controle. O objetivo deste trabalho foi analisar os parasitas encontrados em Megaleporinus obtusidens de piscicultura extensiva e descrever as relações epidemiológicas e patológicas entre eles. Cinco peixes moribundos foram enviados para análise parasitológica. O tegumento e as brânquias foram raspados com lâminas de vidro e examinados em microscópio óptico. Os crustáceos parasitas foram processados para análises histologicas e de microscopia eletrônica de varredura. Todos os peixes analisados foram infestados pelos crustáceos Dolops carvalhoi, Lernaea cyprinacea e pelo Epistylis spp. Epistylis spp. foram também encontrados na superfície de todo tegumento dos crustáceos parasitas. As brânquias parasitadas apresentaram hiperplasia e hipertrofia do epitélio lamelar, infiltrado inflamatório, telangectasia, focos hemorrágicos e necróticos, extensas áreas com fusão de lamelas secundárias e desprendimento de epitélio lamelar. Os crustáceos parasitas são vetores mecânicos importantes da epistilíase, disseminando o microorganismo nas criações de peixes. A infestação por Epistylis spp. afeta a saúde dos peixes e tem impacto ecológico e econômico significativo na aquacultura.

Abstract Parasitic diseases have caused significant problems to global aquaculture production. These studies will further our knowledge of this complex problem and help implement adequate prevention measures and control strategies. The present study aimed to investigate the presence of parasites in Megaleporinus obtusidens and to describe the epidemiology and pathology of parasitic infections in these fish. Five moribund fish were sent for parasitological examination. The integument and gills were scrapped off with a glass slide, and samples were examined under a light microscope. Parasitic crustaceans found in these specimens were submitted for scanning electron microscopy and histological analyses. The crustaceans Dolops carvalhoi and Lernaea cyprinacea and the Epistylis spp. were present in all fish examined. Epistylis spp. were also seen on the entire surface of the crustacean integument. Microscopic lesions observed in the parasitized gills included hyperplasia and hypertrophy of the lamellar epithelium, an inflammatory infiltrate, telangiectasia, foci of hemorrhage and necrosis, fusion of the secondary lamellae, and detachment of the lamellar epithelium. Crustacean parasites are important mechanical vectors of Epistylis infection and disseminate the disease in fish farming operations. Epistylis spp. infection affects the health of fish and has significant ecological and economical impact on aquaculture.

ABSTRACT In this experiment, the beneficial effects of mannan-oligosaccharide (MOS) on immunology and intestinal microbiology of Nile tilapia juveniles was demonstrated. Prior to this, three levels of MOS in Nile tilapia diets (1, 8, and 15 g.kg−1) were tested, and hematological parameters, serum lysozyme, and intestinal microbiology were analyzed. The fish blood was sampled at day zero (basal sample) and after 45 days of trial, and the intestinal microbiota was evaluated at the end of the experiment. After 45 days of trial, fish fed 8 and 15 g.kg−1 of MOS presented an increase in both aerobic and lactic acid bacteria numbers in their guts. The MOS feeding also increased the counts of total leukocytes, monocytes, and lymphocytes of fish, but a decrease in neutrophils was also observed. Additionally, the serum lysozyme was higher in all fish fed MOS. The dietary MOS is able to modulate the intestinal microbiota, increasing the number of beneficial bacteria, and immunostimulates the Nile tilapia juvenile, giving rise to white blood cells and serum lysozyme.