ABSTRACT. Propolis can be used as growth enhancer due to its antimicrobial, antioxidant, and immune-stimulant properties, but its effects on morphometry and muscle gene expression are largely unknown. The present study evaluates the influence of propolis on muscle morphometry and myostatin gene expression in Nile tilapia (Oreochromis niloticus) bred in net cages. Reversed males (GIFT strain) with an initial weight of 170 ± 25 g were distributed in a (2 x 4) factorial 2 E.L. Buck et al.Genetics and Molecular Research 16 (1): gmr16019404 scheme, with two diets (DPRO, commercial diet with 4% propolis ethanol extract and DCON, commercial diet without propolis, control) and four assessment periods (0, 35, 70, and 105 experimental days). Muscles were evaluated at each assessment period. Histomorphometric analysis classified the fiber diameters into four groups: <20 mm; 20-30 mm; 30-50 mm; and > 50 mm. RT-qPCR was performed to assess myostatin gene expression. Fibers < 20 µm diameter were more frequent in DPRO than in DCON at all times. Fiber percentages >30 µm (30-50 and > 50 µm) at 70 days were 25.39% and 40.07% for DPRO and DCON, respectively. There was greater myostatin gene expression at 105 days, averaging 1.93 and 1.89 for DCON and DPRO, respectively, with no significant difference in any of the analyzed periods. Propolis ethanol extract did not affect the diameter of muscle fibers or the gene expression of myostatin. Future studies should describe the mechanisms of natural products' effects on muscle growth and development since these factors are highly relevant for fish production performance.

Due to increase in demand for healthy and chemical residue-free products, natural therapeutic substances are being enhanced in fish cultivation. Current study evaluates in an unprecedented way (Tesearchoxygen), the species is he effect of propolis on the parasite charge of the Nile tilapia (Oreochromis niloticus) reared in fish cages. Six hundred male Nile tilapia (200g) conditioned in ten 1 m 3 cages were used. Two treatments with five replications each were provided: TCON: control (extruded meal without propolis) and TPRO: extruded meal with 4% propolis extract. Parasite collection occurred on 0, 35, 70 and 105 days. At the same time, fillet was weighed and fish standard length measured. Temperature was kept within the comfort range for the species during the experimental period (> 25ºC). Trichodinids and Monogenoids (Dactylogyridae) were detected in the two treatments. There was no statistical difference (p > 0.05) in mean parasite intensity (total parasites/specimens with parasites) and abundance (total parasites/examined specimens) among treatments in the four evaluation periods. Lowest parasite prevalence occurred after 70 days in TPRO (26.66%). There was no statistical difference (p > 0.05) among treatments with regard to fillet weight and standard length of fish. Results show that propolis extract 4% did not significantly affect parasite load, fillet weight and standard length of Nile tilapia. Key words: Aquaculture. Oreochromis niloticus. Fish parasites. Natural products. ResumoDevido ao aumento da demanda por produtos saudáveis e livres de resíduos químicos, a utilização de terapêuticos naturais na criação de peixes tem sido cada vez mais estimulada. O objetivo do presente trabalho foi avaliar de forma inédita o efeito do extrato de própolis sobre a carga parasitária de tilápias-do-Nilo (Oreochromis niloticus) criadas em tanque-rede. Foram utilizados 600 machos revertidos de tilápia-do-Nilo (200g) contendo extrato de própolis a 4%. As coletas de parasitas foram realizadas nos dias 0, 35, 70 e 105 dias. Paralelamente, foi realizado a mensuração do peso do filé e comprimento padrão. A temperatura durante o período experimental se manteve dentro da faixa de conforto para a espécie. Foi verificada a presença de tricodinídeos e Monogenoides (Dactylogyridae) em ambos os tratamentos. Não houve diferença estatística (p > 0,05) nos valores de intensidade (total de parasitas/número de indivíduos parasitados) e abundância (total de parasitas/total de indivíduos examinados) média parasitária entre os tratamentos nos quatro períodos de avaliação. A menor prevalência parasitária foi aos 70 dias em TPRO (26,66%). Não foi constatada diferença estatística (p > 0,05) entre os tratamentos na mensuração do peso do filé e comprimento padrão. Conclui-se que o extrato de própolis a 4% não influenciou significativamente a carga parasitária, no peso do filé e no comprimento padrão em tilápias-do-Nilo. Palavras-chave: Aquicultura. Oreochromis niloticus. Parasitas de peixe. Produtos naturais.

The thermodimorphic fungus Paracoccidioides brasiliensis is the etiological agent of paracoccidioidomycosis (PCM), a deep mycosis endemic in Latin American countries that affects mainly male rural workers. Infection by P. brasiliensis has also been reported in several species of terrestrial animals; however, the capacity of the fungus to infect aquatic organisms is poorly known. The aim of this study was to detect P. brasiliensis in a fish species, Nile tilapia (Oreochromis niloticus), the most farmed and widely distributed fish in endemic areas for human PCM in Brazil. As a first step, the humoral immune response against the fungus was evaluated in an experimental group of three fish immunized with inactivated P. brasiliensis yeast cells. For the seroepidemiological study, serum samples of Nile tilapia raised in cages (n = 109) and in ponds (n = 105), collected from a fish slaughterhouse, were analyzed for P. brasiliensis antibodies by ELISA using gp43 as antigen. All the inoculated fish produced antibodies against the fungus. The seropositivity observed in fish raised in cages and ponds was 17.4 and 5.7%, respectively. Due to the higher seropositivity observed in caged fish, 100 tissue samples (encephalon, liver, and kidney), from another group of tilapia raised in cages, were analyzed by polymerase chain reaction (PCR; Pb-ITSR and Pb-ITSE). Three tissue samples (liver n = 1, kidney n = 1, and enchepahlon n = 1) from three different fish resulted positive to PCR. This is the first report to show serological and molecular evidence of P. brasiliensis infection in a fish species.