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Sulfadimethoxine (SDM) and ormetoprim (OMP) are antimicrobials used in combination to treat bacterial infections in fish farming. The use of this drug combination is not yet regulated in some countries, such as Brazil. Due to the lack of regulated drugs for aquaculture in Brazil, this study investigated the residue depletion profile of SDM and OMP in Nile tilapia ( Oreochromis sp.) after oral administration. Fish were treated with medicated feed containing a 5:1 ratio of SDM:OMP at the dose of 50 mg kg BW -1 for five consecutive days with an average water temperature of 28 °C. The drugs were incorporated into the feed by using a gelatin coating process which promoted homogeneity in drug concentration and prevented the drug leaching into the water during medication. The SDM and OMP determination in fish fillets (muscle plus skin in natural proportions) was performed using the QuEChERS approach followed by LC-MS/MS quantification. The analytical method was validated according to Brazilian and selected international guidelines. A withdrawal period of 9 days (or 252 °C days) was estimated for the sum of SDM and OMP residues at concentration levels below the maximum residue level of 100 µg kg -1 .

An analytical method for the determination of erythromycin A (ERY) residues in fish fillet was developed, optimized, and validated employing a modified QuEChERS procedure associated to DLLME technique as a preconcentration step. The obtained LOD and the LOQ were 0.1 µg kg -1 and 1 µg kg -1 , respectively. The validated method provides linearity in the range of 1 to 20 µg kg -1 , precision (CV < 6.3 %) and accuracy (recovery ranging from 103 to 110 %). The procedure was applied in an experimental study to evaluate the residual depletion profile of ERY in fish (Piaractus mesopotamicus) after oral administration. The treatment was carried out at a daily dose of 100 mg (kg BW) -1 of ERY, for 7 consecutive days and with an average water temperature of 30 °C. A withdrawal time of 240°-day was estimated for eliminating ERY residues at concentration levels below the maximum residue limit considered (MRL 100 µg kg -1 )., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Monogenean infection of the internal organs is extremely rare when compared to external infections. This study describes mass mortality of Nile tilapia (Oreochromis niloticus L.) originating from co-infection with Enterogyrus spp. and Aeromonas jandaei following transport stress. The first fish deaths occurred on day 1 post-transport, while cumulative mortality reached approximately 90% by day 10 post-stocking. An atypical amount of pale (whitish) faeces floating on the surface of the water as well as typical clinical signs of motile Aeromonas septicemia, were reported. Adult monogeneans and countless eggs of monogeneans were found in the stomachs and the intestines of both moribund and dead fish, respectively. Two strains of A. jandaei were isolated from the kidneys. Scanning electron microscope microphotographs of the stomach revealed the presence of numerous monogeneans penetrating deep into the gastric tissue, and diffuse lesions filled with bacilliform bacteria. Histopathological examination showed multifocal eosinophilic infiltrate, gastric gland and epithelial necrosis with sloughed necrotic debris in the lumen. This is the first report of co-infection by Enterogyrus spp. and A. jandaei in Nile tilapia and the first report of Enterogyrus coronatus, Enterogyrus foratus, and Enterogyrus malbergi parasitizing tilapia in Brazil. These findings indicate that synergic co-infection by Monogenean stomach parasites (E. coronatus, E. foratus, and E. malbergi) and A. jandaei may induce high mortalities in tilapia following transport stress., (© 2021 Wiley-VCH GmbH.)

Tambaqui Colossoma macropomum is the most produced native fish in South America. Besides the lack of knowledge regarding bacteria-stricken diseases, the unappropriated using of off-label therapies are common. In this study, Aeromonas hydrophila pathogenicity for tambaqui was first established by Koch's Postulate. Lethal doses (LD) were settled for investigation of clinical signs and mortality. The antimicrobial activities were investigated by disk-diffusion test against 11 antibiotics and by broth microdilution methods against 3 antibiotics, 7 disinfectants and 11 herbal medicines. LD experiment showed up to 80% of fish mortality, skin darkness, ulcers, hemorrhage, lethargy and hypo/anorexia in all groups, with exception of control. The LD 10 , 50 , 90 and 99 were established in 4.1 × 10 7 , 8.8 × 10 7 , 1.9 × 10 8 e 3.6 × 10 8  CFU/mL, respectively. Ceftriaxone, florfenicol, oxytetracycline and thiamphenicol were considered promising against A. hydrophila. All herbal medicines were classified as bactericides, but clove Eugenia caryophyllata and cinnamon Cinnamomum zeylanicum displayed strongest activities. Among disinfectants, malachite green was the only that did not present acceptable values, discouraging its use. In conclusion, Koch's postulate was fulfilled and tambaqui entered to the vast list of A. hydrophila hosts and promising results of chemical substances were provided, contributing to motile Aeromonas septicemia (MAS) control., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Massive occurrence of trichodinids is frequently accompanied by serious disease in fish farms. In this study, trichodinid species from the gills and skin of Nile tilapia (Oreochromis niloticus) farmed in the central-western region of Brazil (state of Goiás) were morphologically characterized. Dried slides were prepared from the parasites and were impregnated with silver nitrate (2%). Morphometric characteristics were determined and schematic drawings of the denticles were made using photomicrographs produced from the slides. Seven species of trichodinid ectoparasites (Protozoa: Ciliophora: Trichodinidae) were found parasitizing the gills: four of the genus Trichodina Ehrenberg, 1838; one of Tripartiella Lom, 1959; one of Paratrichodina Lom, 1963; and one of Trichodinella Ṧrámek-Huṧek, 1953. On the body surface, three specimens of the genus Trichodina were identified. This study presents new geographical records of trichodinids in Brazil, thus confirming that Trichodina centrostrigeata, Trichodina compacta, Trichodina heterodentata, Paratrichodina africana and Tripartiella orthodens are widely distributed worldwide. Additionally, the first record of the genus Trichodinella in Brazil is presented.