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.
Myxobolus platanus n. sp. infecting the spleen of Mugil platanus Günther, 1880 (Osteichthyes, Mugilidae) from Lagoa dos Patos, Brazil is described The parasites formed round or slightly oval whitish plasmodia (about 0.05-0.1mm in diameter) on the surface of the organ. The spores were round in frontal view and oval in lateral view, 10.7µm (10-11) long, 10.8µm (10-11) wide and 5µm thick, and presented four sutural marks along the sutural edge. The polar capsules, equal in size, were prominent, surpassing the mid-length of the spore, and were oval with the posterior extremity rounded, and converging with their anteriorly tapered ends. They were 7.7µm (7-8) long and 3.8µm (3.5-4) wide. A small intercapsular appendix was present. The polar filament formed five to six coils obliquely placed to the axis of the polar capsule. No mucous envelope or distinct iodinophilous vacuole were found.
Macroecological variables of Anuran species found in a local assemblage from Central Brazil (Silvânia, Goiás State) were linked to population dyamics statistics of these species. Geographical range size (GRS), body size, and species' midpoints were the macroecological variables investigated for those species found in the local assemblage and for all other species (105 in the total) found in the Cerrado biome. For each species found in the local assemblage, data on abundance was obtained. Using this data, local population variability as expressed by the coefficient of variation was estimated. Distribution of means, medians, maximum, variances, and skewness (g1), for both GRS and body size, estimated in the local assemblage were compared, using null models, with the data extracted from the overall Cerrado species pool. The results indicated a clear macroecological relationship between GRS and body size and a decrease in local abundance when distance between the locality analyzed and species midpoint increased. According to null models, both body size and GRS values measured in the local assemblage can be considered a random sample from the regional species pool (Cerrado region). Finally, a three-dimensional analysis using body size, GRS, and local population estimates (abundance and variability), indicated that less abundant and more fluctuating species fell near the lower boundary of the polygonal relationship between GRS and body size. Thus, macroecological results linked with local data on population dynamics supported the minimum viable population model.
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