Chilodonelids are small ciliated protozoans found worldwide and can be dangerous in culture conditions. This study presents morphometric data on the ciliate Chilodonella that is found in cultured Nile tilapia (Oreochromis niloticus), native bait fish tuvira (Gymnotus aff. inaequilabiatus) and native pacu (Piaractus mesopotamicus) and includes a histopathological assessment of the changes that occur in the pacu. For parasitic diagnosis, skin and gill samples were scraped onto slides, dried at room temperature, stained with Giemsa or impregnated with silver nitrate, and the measurements were obtained from photomicrographs. In the diseased pacu, the first gill arch was collected and fixed in a 10% buffered formalin solution for histopathological analysis. Parasite specimens from the different collection sites were identified morphologically as C. hexasticha Kiernik (1909). Diseased fish exhibited depigmentation, skin ulceration, scale loss, excessive mucus production and gill lesions. Histopathological analysis of pacu gills displayed epithelial proliferation with mononuclear inflammatory infiltrate, hemorrhages, and scattering necrosis. In Brazilian-farmed fish this is the first record of C. hexasticha, which has great pathogenic potential in cultured freshwater species. In addition, two new hosts are presented.

Trichodinids are ciliated protozoa that are widely known as one of the main groups of fish parasites. The genus Trichodina presents the greatest species diversity. However, records of Paratrichodina species are scarce, and little is known about their pathogenicity in hosts. The present study provides new records of Paratrichodina africana Kazubski and El-Tantawy (1986) in Nile tilapia from South America and descriptions of pathological changes and seasonality. A total of 304 farmed fish were examined. From gill scraping, parasites were identified using Klein's nitrate impregnation method. Gill samples were fixed for histopathological analysis. Small trichodinid found in this study have a prominent blade apophysis and narrow central part and blade shape that corresponds to the characteristics of P. africana Kazubski and El-Tantawy (1986). Gill lesions were proportional to parasite intensity, in which the gill tissue was compromised in heavy infestation. Proliferative disturbances were found, including epithelial hyperplasia, desquamation, and mononuclear and eosinophilic infiltrate that culminated in necrosis. We did not observe a seasonality effect on the occurrence of P. africana. This ciliated protozoan causes compromised respiratory capacity that leads to severe gill lesions and currently is an important pathogen that afflicts intensive tilapia cultures in Brazil.

Intensive fish farming systems in Brazil have increased the disease incidence, mainly of bacterial origin, due to higher stocking density, high organic matter levels and poor quality of the aquatic environment that causes high mortality rates during outbreaks. The identification of pathogenic species using a fast and reliable method of diagnosis is essential for successful epidemiological studies and disease control. The present study evaluated the use of direct colony PCR in combination with 16S rRNA gene sequencing to diagnose fish bacterial diseases, with the goal of reducing the costs and time necessary for bacterial identification. The method was successful for all 178 isolates tested and produced bands with the same intensity as the standard PCR performed using pure DNA. In conclusion, the genetics methods allowed detecting the most common and important pathogens in Aquaculture, including 12 species of occurrence in Brazilian fish farms. The results of the present study constitute an advance in the available diagnostic methods for bacterial pathogens in fish farms.

The role of glucan as a biologically active immunomodulator has been well documented for more than 40 years. However, the wide diversity of β-glucan forms and the extraction process has implications for the benefits of these compounds. Biorigin developed two samples of β-glucans using different biotechnological processes. Thus, in the present study, we fed Nile tilapia (Oreochromis niloticus) diets containing these two β-glucan molecules (BG01 and BG02) for 30 days prior to bacterial infection with Streptococcus agalactiae. The results showed that the different β-glucan samples exhibited biologically differently behaviors, but both increased the resistance against bacterial infection. Specifically, BG01 increased immunostimulation, while BG02 improved growth performance. In summary, these findings confirm the benefits of β-glucans in aquaculture and also provide further evidence of the growth promotion of these compounds.

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The utilization of probiotic bacteria have been widely tested and applied in intestinal microflora modulation, through competitive exclusion of the pathogenic bacteria. Aeromonas hydrophila is a gram-negative bacterium, responsible for fish outbreaks in farms around the world, and is one of the major loss causes for neotropical fish farmers. 660 pacus (67 ± 7 g) were distributed in 20 tanks (n = 33), constituting five groups (four tanks for each treatment): four groups were fed with different levels (2, 4, 8 and 16 g kg −1) of Bacillus cereus and Bacillus subtilis (1:1, 10 8 CFU g −1), and the fifth group was fed with a control diet (without probiotic). Pacus fed with probiotic showed increment in the ROS production associated to elevated neutrophil and monocyte counts and increased phagocytic activity without affecting the growth parameters. Probiotic fed fish presented higher survival rates, subjected to an i.p. challenge with 10 8 CFU mL −1 of A. hydrophila. The results demonstrated a dose response effect and the ideal level of the probiotic (Bacillus cereus and Bacillus subtilis, 1:1, 10 8 CFU g −1) in P. mesopotamicus diets was around 8 g kg −1 , as the highest survival rates and immunological responses were found in groups of fish fed with this diet. In addition, too much probiotic should be avoided, as pacus fed diet with 16 g kg −1 showed partial suppression of these responses.

No abstract

Anthelmintic drugs are successfully used in aquaculture to control parasitic infections or infestations. This study analyzed the effectiveness of levamisole as an antiparasitic and its effect on the liver of juvenile pacu (Piaractus mesopotamicus). A total of 300 fish (180 ± 1.27 g; 16 ± 0.4 cm) were fed a diet containing levamisole hydrochloride (LHC) for fifteen days. A control group (T0) and four treatments were tested: T1 (100), T2 (150), T3 (300) and T4 (500) mg kg −1 LHC in quadruplicate (15 fish per repetition). Four fish per treatment (n = 20) were euthanized by sectioning the spinal cord; the sample was forwarded for parasitological analysis. The gill arches and intestines were removed and preserved in formaldehyde 10% for identification and quantification of the parasites. For evaluation of the liver histology, four fish per treatment (n = 20) were euthanized with benzocaine (100 mg L −1 ) for liver removal. In intestines and gills, we identified the parasites Rondonia rondoni (Nematoda, Atractinae) and Anacanthorus penilabiatus (Monogenoidea, Dactylogyridae), respectively. Both were at high prevalence and intensity of infection and infestation, respectively. The 300 mg kg −1 LHC treatment reduced the infection by R. rondoni but not the infestation by A. penilabiatus. Concentrations of 150 and 300 mg kg −1 LHC caused moderate liver changes, and no changes were observed in fish treated with 100 mg kg −1 LHC. The highest concentration of LHC (500 mg kg −1 ) induced a high occurrence of sinusoid dilation, blood congestion and leukocyte infiltration in fish liver. Our results indicate that LHC (300 mg kg −1 ) was effective in controlling the infection by R. rondoni and caused moderate histological changes in pacu liver.