The use of nitazoxanide against the pathogens Ichthyophthirius multifiliis and Aeromonas hydrophila in silver catfish (Rhamdia quelen)
Introduction
In aquaculture systems fish are sometimes concomitantly infected by multiple disease agents and co-infections by parasite and bacteria contribute to the severity of some diseases. Ichthyophthirius multifiliis and Aeromonas hydrophila are two common pathogens of cultured fish (Xu et al., 2012a). The protozoan I. multifiliis is a parasitic ciliate (commonly referred to as Ich) that infects a range of freshwater fish species and causes the disease known as ichthyophthiriasis. It is one of the most important pathogenic parasites of cultured fish, causing significant economic losses to the aquaculture industry. The life cycle of Ich consists of three stages: an infective theront, a parasitic trophont, and a reproductive tomont (Matthews, 2005). Outbreaks of bacteria of the genus Aeromonas in fish are associated with changes in environmental conditions and/or stress factors like parasitic infections (Barcellos et al., 2008). Infections caused by Ich enhance potential of invasion by A. hydrophila in fish causing outbreaks in fish farms with high mortality (Xu et al., 2012a).
Silver catfish (Rhamdia quelen) is a fast-growing species native to South Brazil which is well-adapted to cultivation. The use of salt, copper sulphate, and temperature rise are reported as alternatives to Ich control in silver catfish, but these treatments are limited by factors such as toxicity, as in the case of copper sulfate or are uneconomical in most fish culture conditions (Carneiro et al., 2005). Various antimicrobial drugs have been used against A. hydrophila, but the undue use of these drugs in silver catfish culture resulted in the emergence of resistant strains (Barcellos et al., 2008).
Nitazoxanide [2-[(5-nitro-1,3-thiazol-2-yl)carbamoyl]phenyl] acetate (NTZ) has broad-spectrum antiparasitic activity, acting in a wide spectrum of protozoa parasites in humans, such as amoebas, flagellates, sporozoans and ciliates (Abaza et al., 1998), as well as bacteria (Dubreuil et al., 1996, de Carvalho et al., 2011). Therefore, based on the needs of a therapy against ichthyophthiriasis and infections by A. hydrophila, the antiparasitic and antibacterial potential of NTZ was analyzed for the first time in fish infected by these pathogens.
Section snippets
Animals and water quality
Juvenile silver catfish (9.86 ± 0.40 g; 10.61 ± 0.18 cm) were purchased from a local fish culture and transported to the Laboratório de Fisiologia de Peixes at the Universidade Federal de Santa Maria, where they were acclimated for seven days in continuously aerated 250 L fresh water tanks with controlled water parameters (20.8 ± 0.04 °C, pH: 7.67 ± 0.04, dissolved oxygen levels: 7.34 ± 0.27 mg L−1). Dissolved oxygen and temperature were measured with an YSI oxygen meter (Model Y5512). The pH was determined
Water quality
The parameters of water quality were: temperature 20.0 ± 0.04 °C, dissolved oxygen levels 7.69 ± 0.12 mg L−1, pH 7.34 ± 0.05, maximum total ammonia 2.4 ± 0.9 mg L−1 and maximum non-ionized ammonia 0.02 ± 0.007 mg L−1.
Toxicity test
Fish mortality (20%) was observed only at the highest concentration (3.0 mg L−1).
Experiment 1
The survival in the control group was 40% after 144 h of experiment. In groups treated with 1.0 and 1.5 mg L−1 survival was 97% and 90% respectively, but in the groups treated with 2.0 and 3.0 mg L−1 of NTZ, despite a
Discussion
Several drugs such as formaldehyde, sodium chloride (salt), copper sulphate and potassium permanganate are currently administered in the form of baths against Ich infections (see review of Picón-Camacho et al., 2011). In many countries it is no longer allowed to treat fish for human consumption with malachite green, due to its carcinogenic potential (Wohllebe et al., 2012). Formaldehyde was reclassified by the World Health Organization – International Agency for Cancer Research as “carcinogenic
Conflict of interest statement
None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.
Acknowledgments
The authors acknowledge support from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), process 470964/2009-0. B. Baldisserotto received a CNPq research fellowship, and F. J. Sutili and M.A. Cunha received a CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) Msc and Postdoctoral fellowship's, respectively.
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