RESUMO
Streptococcosis caused by Streptococcus agalactiae (S. agalactiae) is a major bacterial disease affecting the production of Nile tilapia (Oreochromis niloticus L.), causing significant economic losses due to mortality in the growing phase. Vaccination is the most effective method for preventing streptococcosis on Nile tilapia farms. In Brazil, the major tilapia-producing regions have long production cycles (6-10 months) and harvest tilapias weighing over 900 g for fillet production. Thus, data on the duration of the humoral immune response and protection in farmed tilapia have not been reported or are poorly described. Furthermore, the efficiency of serological testing for the long-term monitoring of immune responses induced by vaccination against S. agalactiae has never been addressed. This study evaluated the duration of protection and humoral immune response induced in Nile tilapia vaccinated against S. agalactiae until 300 days post-vaccination (dpv). The immunization trial was composed of two groups: vaccinated (Vac), vaccinated intraperitoneally with a commercial vaccine, and unvaccinated (NonVac) group, injected fish with sterile saline solution. At 15, 30, 150, 180, 210, and 300 dpv, blood sampling was conducted to detect anti-S. agalactiae IgM antibodies using indirect Enzyme-Linked Immunosorbent Assay (ELISA), and the fish were challenged with pathogenic S. agalactiae to determine the duration of vaccine protection through relative percentage survival (RPS). Spearman's rank correlation was performed between the ELISA optical density (OD) of vaccinated tilapia and the duration of vaccine protection (RPS). The mean cumulative mortality in NonVac and Vac groups ranged from 65 to 90% and less than 35%, respectively. The average RPS was 71, 93, 94, 70, 86, and 67% at 15, 30, 150, 180, 210, and 300 dpv, respectively. RPS revealed that the vaccine provided protection from 15 to 300 dpv. The specific anti-S. agalactiae IgM antibody levels were significantly higher in the Vac group than that non-Vac group up to 180 dpv. The vaccinated fish exhibited significant protection for up to 10 months after vaccination. There was a positive correlation between the antibody response and RPS. This study revealed that a single dose of commercial vaccine administered to Nile tilapia can confer long-term protection against S. agalactiae and that indirect ELISA can monitor the duration of the humoral immune response for up to six months following vaccination. Finally, vaccine protection over six months can be associated with other components of the fish immune system beyond the humoral immune response by IgM antibodies.
RESUMO
RESUMO Objetivou-se realizar uma avaliação físico-química de amostras de água, sedimento e mata ciliar em uma piscicultura localizada próxima às margens do Ribeirão da Mata, Minas Gerais. As coletas de água foram semanais em quatro pontos assim denominados: (1) nascente; (2) entrada do sistema; (3) efluente concentrado e (4) ponto de lançamento. Foram monitorados os seguintes parâmetros físico-químicos: temperatura (ºC), pH, oxigênio dissolvido, demanda bioquímica de oxigênio, fósforo total, alcalinidade, sólidos dissolvidos totais, fosfato, nitrato, nitrito, sulfato, amônia e fenol das amostras de água. Foram pesquisados metais pesados (chumbo, cádmio, mercúrio e zinco) e agrotóxicos (organoclorados, organofosforados, clorofosforados, carbamatos, piretroides e rodenticidas anticoagulantes) nas amostras de água, sedimento e mata ciliar. Alcalinidade e sólidos totais apresentaram as maiores concentrações, provavelmente devido às características geológicas,por se tratar de região cárstica. Fenol, em todos os pontos, e fosfato, nos pontos 3 e 4, apresentaram valores acima dos limites permitidos para a classe II de água doce, segundo a Resolução CONAMA nº 357. Os outros parâmetros (amônia, nitrato, nitrito e sulfato), em todos os pontos de coleta, apresentaram baixos valores. Nas amostras de água não foram detectados chumbo e mercúrio; zinco apresentou valores abaixo de 0,007 mg.L-1. As amostras de sedimento apresentaram valores de chumbo entre 11,1566 e 37,0438 mg.L-1, estando 12 dessas acima do valor de referência de qualidade. Também em todas as amostras de sedimento foi detectado mercúrio, que variou de 0,35 a 0,82 mg.L-1. Em relação ao cádmio, esse não foi detectado nas amostras de sedimento e plantas. Também não foram detectados agrotóxicos em nenhuma das amostras estudadas.
ABSTRACT The aim of this study was to carry out a physicochemical analysis of water, sediment and riparian vegetation in a fish farm located near the Ribeirão da Mata basin in Minas Gerais State (Brazil). The water samples were collected weekly at four points: (1) source, (2) system entry, (3) discharge point, (4) and point release. The monitored physicochemical parameters in the water samples were: temperature (ºC), pH, dissolved oxygen, biochemical oxygen demand, total phosphorus, alkalinity, total dissolved solids, phosphate, nitrate, nitrite, sulfate, ammonia and phenol. Heavy metals (lead, cadmium, mercury and zinc) and pesticides (organochlorine, organophosphates, clorofosforados, carbamates, pyrethroids and anticoagulant rodenticides) were searched in the samples of water, sediment and riparian vegetation. Alkalinity and total solids presented the highest concentration, probably due to geological features of a carstic area. Phenol, at all points, and phosphate, at points 3 and 4, showed values above the limits allowed for class II freshwater, according to the CONAMA Resolution n. 357. The other parameters (ammonia, nitrate, nitrite and sulfate) in all sampling sites showed low values. It was not detected lead and mercury in the water samples; and zinc values were below 0.007 mg.L-1. However, the sediment samples showed lead values from 11.1566 to 37.0438 mg.L-1, with 12 of those samples above the quality reference value. In addition, it was detected mercury in all sediment samples, which ranged from 0.35 to 0.82 mg.L-1. It was not detected cadmium in samples of sediment neither plants. No pesticides were detected in the samples.
