Anthelmintic drugs are successfully used in aquaculture to control parasitic infections or infestations. This study analyzed the effectiveness of levamisole as an antiparasitic and its effect on the liver of juvenile pacu (Piaractus mesopotamicus). A total of 300 fish (180 ± 1.27 g; 16 ± 0.4 cm) were fed a diet containing levamisole hydrochloride (LHC) for fifteen days. A control group (T0) and four treatments were tested: T1 (100), T2 (150), T3 (300) and T4 (500) mg kg −1 LHC in quadruplicate (15 fish per repetition). Four fish per treatment (n = 20) were euthanized by sectioning the spinal cord; the sample was forwarded for parasitological analysis. The gill arches and intestines were removed and preserved in formaldehyde 10% for identification and quantification of the parasites. For evaluation of the liver histology, four fish per treatment (n = 20) were euthanized with benzocaine (100 mg L −1 ) for liver removal. In intestines and gills, we identified the parasites Rondonia rondoni (Nematoda, Atractinae) and Anacanthorus penilabiatus (Monogenoidea, Dactylogyridae), respectively. Both were at high prevalence and intensity of infection and infestation, respectively. The 300 mg kg −1 LHC treatment reduced the infection by R. rondoni but not the infestation by A. penilabiatus. Concentrations of 150 and 300 mg kg −1 LHC caused moderate liver changes, and no changes were observed in fish treated with 100 mg kg −1 LHC. The highest concentration of LHC (500 mg kg −1 ) induced a high occurrence of sinusoid dilation, blood congestion and leukocyte infiltration in fish liver. Our results indicate that LHC (300 mg kg −1 ) was effective in controlling the infection by R. rondoni and caused moderate histological changes in pacu liver.

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We analyzed the effects of levamisole on stress and the innate immune responses of pacu (Piaractus mesopotamicus). A total of 300 fish (180 ± 1.27 g) were fed a diet containing levamisole hydrochloride (LHC) for 15 days, then distributed into the following groups: T0 (control group); T1 (100), T2 (150), T3 (300) and T4 (500) mg kg LHC (15 fish per group and four replicates per treatment). After this, fish (n = 8 per treatment) were exposed to air for three minutes to simulate stress conditions and were then challenged with the bacterium Aeromonas hydrophila to stimulate the immune system. Fish were sampled at 1, 3 and 24 h after bacterial inoculation to measure plasma cortisol and glucose concentrations, the leukocyte respiratory burst (LRB), hemolytic activity of the complement system (HAC) and serum lysozyme activity (SLA). LHC attenuated the increase in plasma cortisol at 1 h (500 mg kg) and 3 h (300 mg kg) after air exposure and bacterial inoculation compared to control fish. The highest glucose concentrations were observed at 1 and 3 h after stress, which then returned to initial levels after 24 h, without any effect of LHC. The LHC 100 mg kg dose increased LRB 1 h after inoculation and activated the HAC 3 h later. At 24 h, all LHC concentrations increased the HAC. SLA was reduced after inoculation, throughout the experimental period, without an effect of levamisole. Our results indicate that the oral administration of levamisole for 15 days modulated circulating cortisol levels during the stress response and improved the innate immune response against A. hydrophila infection in pacu.

Considerable losses may be related to diseases caused by parasites in aquaculture. Formaldehyde (37% gas dissolved in water) is an effective chemotherapeutic, widely used to control ectoparasites in fish. However, for many species of fish used in aquaculture, the control of external parasites and the deleterious effects of formaldehyde in shortterm baths are still uncertain. In order to clarify some gaps, 1 h-prophylactic baths (67.5, 135, 270, 405 and 540 mg L À1 formaldehyde in triplicate) were performed in juvenile mullet, Mugil liza (Valenciennes). Results showed that prophylactic baths of 135 mg L À1 formaldehyde by 1 h did not cause death in tested mullets. At this concentration, histopathologies were mild and fish survival was high. However, fish exposed to increasing concentrations of formaldehyde presented severe histopathologies in the gills besides behavioural and morphological alterations. The histopathological and behavioural implications of formaldehyde use in aquaculture are discussed.

Monogenoidea pathogenic activity can elicit various histological responses in fish. Species of Ligophorus are specific parasites of mullets, and its relationship with host fish may result in a moderate pathogenic action. In order to ascertain this relationship, estuarine mullets (Mugil liza) were collected in an estuary, reared in laboratory, for three weeks, and forwarded for histological and parasitological analyses. Ligophorus uruguayense (Monogenoidea) infestation in the gills of the mullets was identified. The severe infestation by only one species of Monogenoidea may result from the specificity of these parasites to mullets. Mullets submitted to histological analysis exhibited respiratory epithelium detachment; mild, moderate and severe hyperplasia of the respiratory epithelium; atrophy; and telangiectasia of the gills. This is the first study reporting that mullets highly infested by Monogenoidea can show mild (100%) to severe (20%) gill changes with a distinct frequency of occurrence. Because of the high prevalence of mild alterations observed, it is possible to accept that L. uruguayense is moderately pathogenic to M. liza, even during high prevalence and intensity of infestation, as a result of its specificity.

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a b s t r a c tStudies have developed techniques for bullfrog feeding in which movement of the food stimulates food intake in the absence of housefly larvae. We analyze a completely randomized design with two treatments (vibrating tray and linear feeder) in triplicate. A total of 1800 bullfrog froglets (Lithobates catesbeianus) (7.60 ± 0.59 g) were divided in six pens of 12 m 2 and density 25/m 2 . Three fattening pens contained linear cement feeders (3.0 × 0.50 m) with a V-shaped bottom that crossed the pen longitudinally at each side of the pool containing commercial diet (40% crude protein) with added 5% housefly larvae. In the other three pens, six vibrating feeders trays (80 × 34 cm) per pen were arranged linearly, three at each side of the pool with commercial ration without housefly larvae. The productive performance of frogs was assessed by weight gain, feed intake, feed conversion, specific growth rate and survival by 90 days. We observed that bullfrog froglets receiving food in a vibrating feeder tray present better productive performance (weight gain, feed conversion and specific growth rate) than animals fed ration and housefly larvae in a linear feeder. This response can be related to the greater visual stimulus of the food by frogs fed in vibrating feeder trays, in which food had greater movement.