ABSTRACT Nile tilapia Oreochromis niloticus is one of the most economically important freshwater fish cultivated worldwide. Despite its importance and being one of the cichlid fish most studied from a parasitological point of view in Mexico, there are few studies about the ectoparasite protozoa that infect them. In this study, a total of 240 juvenile individuals of O. niloticus from an experimental culture (in Tabasco, Mexico) were examined to detect the presence of trichodinid parasites. Trichodinid parasites were impregnated with silver nitrate and stained with Harris’ hematoxylin solution for taxonomic evaluation. A disc-shaped trichodinid with a body diameter of 38 ± 3.3 μm adhesive disc diameter of 34 ± 3.3 μm and a denticulate ring diameter of 19 ± 2.1 μm was found. Trichodina centrostrigeata has been previously reported having specificity for cypriniform species, but in the present study, the Nile tilapia was reported as a new fish host and southeastern Mexico as a new geographical distribution for this parasite.

ABSTRACT Trichodiniasis is one of the major diseases found in fish aquaculture worldwide causing massive fish mortality and costly effects. In this study, fresh smears of gills and skin were prepared and analyzed for the presence of trichodinids under light microscopy, revealing the presence of Trichodina pediculus Ehrenberg, 1831, T. compacta Van As & Basson, 1989, and T. nigra Lom, 1960 and T. centrostrigeata (Basson, Van As & Paperna, 1983). The effectiveness of treatment with sodium chloride and formaldehyde was evaluated for controlling infection caused by these parasites in tilapia Oreochromis niloticus Linnaeus, 1758 in aquaculture facilities in southeastern Mexico. A total of 240 fish were examined. The results showed that all doses using sodium were effective for controlling trichodinids and eliminated the parasites (100%) however, fish exposed to doses of formalin showed a higher level of stress than those exposed to sodium chloride. Bathing in formalin 0.250 mL L−1 for 10 min and 30 g L−1 of sodium chloride for 10 min, significantly reduced parasitic infection in tilapia under captive conditions (P < 0.05). This is the first record of a trichodinids species for native wild freshwater fish in a culture environment in southeastern Mexico since all previous records were from exotic cultured fish. The species found were Trichodina pediculus, T. compacta, T. nigra and T. centrostrigeata are new records of host and geographic location.

ABSTRACT: The current study aimed to describe the massive mortality of farmed Nile tilapia Oreochromis niloticus associated with the monogenean Gyrodactylus cichlidarum from the northwestern Mexican Pacific coast. The ectoparasite was identified using measurements of the hard parts and compared with previous literature. Approximately 20,000 tilapias were subjected to subsequent losses over a three day period, a total of 2% of the initial seed stocked died due to the presence of this gyrodactylid parasite. The presence of the monogenean was the principal cause for chemical treatments. There is no doubt that infections by parasites have major consequences for species of small fish in culture and must consequently be considered as a fundamental factor within any system of aquaculture. A histo-pathological examination of the gills of fish showed the presence of the monogenean attached to the fi laments was causing hyperplasia. The fish showed no signs of bacteria or virus infection. This study reports for the first time the occurrence of massive mortality caused by this monogenean in a tilapia fish farm in the Mexican Pacific and also extends their known geographical distribution.

ABSTRACT Currently many species of Amazon sailfin catfishes (Loricariidae) have been introduced to wild environments outside their native range. There is, however, little knowledge about their role as vectors of parasites that can infect native fish or even humans through its consumption. The aim of the present study was to determine the parasitic fauna of the invasive sailfin catfish species Pterygoplichthys pardalis (leopard pleco) and P. disjunctivus (vermiculated pleco) from freshwater systems in the southeast of Mexico. Four ectoparasite species were found in P. pardalis (1 protozoan: Ichthyophthirius multifiliis ; 2 monogeneans: Urocleidoides vaginoclastrum and Heteropriapulus heterotylus ; 1 digenean: Clinostomum sp.), and only one in Heteropriapulus disjunctivus (H. heterotylus ). No endoparasites were found. Ichthyophthirius multifiliis , U. vaginoclaustrum and Clinostomum sp. , were considered as rare species (prevalence <5%) since they were found in a single individual of P. pardalis . H. heterotylus was the only species shared among both host species and it occurs throughout the year. This monogenean species represents 96% of total parasites recorded in P. pardalis and 100% in P. disjunctivus. Monthly values of prevalence, intensity and abundance of H. heterotylus in both host species showed important intra-annual variations, but not differ significantly between both hosts.

RESUMEN Actualmente muchas especies de peces conocidos como plecos o peces diablo (Loricariidae) han sido introducidas en ambientes silvestres fuera de su área de distribución natural. Sin embargo, hay poco conocimiento acerca de su papel como vectores de parásitos que puedan infectar a los peces nativos o incluso los seres humanos a través de su consumo. El objetivo del presente estudio fue determinar la fauna parasitaria de las especies de plecos Pterygoplichthys pardalis (pleco leopardo) y P. disjunctivus (pleco vermiculado) en sistemas de agua dulce del sureste de México. Fueron encontradas cuatro especies de ectoparásitos en P. pardalis (1 protozoario: Ichthyophthirius multifiliis ; 2 monogeneos: Urocleidoides vaginoclastrum y Heteropriapulus heterotylus ; 1 digeneo: Clinostomum sp.) y una en P. disjunctivus (H. heterotylus ). No se encontraron endoparásitos. Ichthyophthirius multifiliis, U. vaginoclaustrum y Clinostomum sp. fueron consideradas como especies raras (prevalencia <5%), ya que estuvieron en un solo individuo de P. pardalis . Heteropriapulus heterotylus fue la única especie compartida entre ambas especies de peces y que estuvo presente durante todo el año, y representó el 96% del total de parásitos registrados en P. pardalis y el 100% en P. disjunctivus. La prevalencia, intensidad media y abundancia media de H. heterotylus mostraron importantes variaciones intra-anuales en ambas especies de peces, pero no difirió significativamente entre ambos hospederos.