Parasitic and infectious diseases are common in finfish, but are difficult to accurately estimate the economic impacts on the production in a country with large dimensions like Brazil. The aim of this study was to estimate the costs caused by economic losses of finfish due to mortality by diseases in Brazil. A model for estimating the costs related to parasitic and bacterial diseases in farmed fish and an estimative of these economic impacts are presented. We used official data of production and mortality of finfish for rough estimation of economic losses. The losses herein presented are related to direct and indirect economic costs for freshwater farmed fish, which were estimated in US$ 84 million per year. Finally, it was possible to establish by the first time an estimative of overall losses in finfish production in Brazil using data available from production. Therefore, this current estimative must help researchers and policy makers to approximate the economic costs of diseases for fish farming industry, as well as for developing of public policies on the control measures of diseases and priority research lines.

Aeromonas hydrophila is causing substantial economic losses in world aquaculture. This study determined the tolerance limit (LD50-96h) of A. hydrophila in Arapaima gigas, and also investigated the clinical signs after intradermal inoculation. Arapaima gigas fingerlings were inoculated intraperitoneally with 0 (control), 1.0×10(5), 1.0×10(6), 1.0×10(7), 1.0×10(9) and 1.0×10(10)CFU/mL of A. hydrophila for the determination of LD50-96h, which was 1.8×10(8)CFU/mL. In another trial with intradermal inoculation of 1.8×10(8)CFU/mL A. hydrophila, there was a 91.6% of mortality between 8 and 23h, and several clinical signs were found. As follows: depigmentation in the tegument, lesions in the tail and fins, loss of balance, reduction of respiratory movements, hemorrhagic foci, necrotic hemorrhages in the kidney, liver and swim bladder, splenomegaly, ascites in the abdominal cavity and hyperemia, enlargement of the gall bladder, among other clinical signs observed. The results showed that A. gigas has a relative tolerance to A. hydrophila when compared to other Neotropical fish species.

This review article focuses on current knowledge about in vitro and in vivo experimentation relating to use of essential oils (EOs) to combat fish parasites. In addition, we discuss the existing methodologies used in studies to determine the antiparasitic activity of EOs, along with their toxicity and major compounds. The methodological approaches used to describe the anthelmintic properties of EOs were demonstrated. The consistency of their activity and thus their potential use for fish ectoparasites (in vitro and in vivo) and endoparasites (in vitro) control was reviewed. There is a clear need to find EOs and active agents of EOs to treatment in vivo against endoparasites of fish. Thus, progress may be achieved through considering the beneficial aspects of EOs when their complementarity and potentiality are exploited. EOs are therefore viable alternative sources of therapeutic products against fish parasites. On the other hand, use of chemotherapeutics has been increasingly questioned, such that constant environmental and consumer concerns regarding them now exist. The synergistic functions of EOs, in comparison with the action of one or two major compounds of these oils, seems unquestionable. It is possible that their activity is modulated by several molecules of the major compounds. Lastly, EOs are bioactive products that are viable sources of therapy against fish parasites. Although more than 3000 EOs are known, less than 0.4% of them have been tested on fish parasites. Thus, it has become clear that more studies testing these therapeutic alternatives are required, in order to evaluate the antiparasitic potential of other EOs for controlling fish parasites and to maximize their benefits to hosts.

This study evaluated the efficacy of albendazole, ivermectin, levamisole, mebendazole and praziquantel on monogeneans of Colossoma macropomum, based on in vitro and in vivo assays. In vitro assays indicated that albendazole (500, 100, 1,500 and 2,000 mg/L), ivermectin (200, 250, 300 and 350 mg/L) and levamisole (50, 75, 100 and 125 mg/L) were 100% effective against Anacanthorus spatulatus, Notozothecium janauachensis, Mymarothecium boegeri and Linguadactyloides brinkmanni, while mebendazole (125, 150, 175 and 200 mg/L) and praziquantel (5, 10, 15 and 20 mg/L) were ineffective. Fish mortality in 24 hr therapeutic baths with 500 mg/L of albendazole was 6.6%, but the behaviour of the animals remained unchanged, while 200 mg/L of ivermectin caused lethargy, signs of hypoxia and 100% mortality within 2 hr, and 125 mg/L of levamisole caused no mortality. The efficacy of 500 mg/L of albendazole was 48.6% in the 24 hr baths, while that of 125 mg/L levamisole was 88.2%. Although ivermectin showed in vitro efficacy, the lowest concentration used in baths was highly toxic to fish. Therefore, we recommend the use of 125 mg/L of levamisole to control and treat monogenean infestations on C. macropomum in fish farming.

The purpose of this study was to use the informations relating to parasite crustaceans species that was published over the course of one century (1913 to 2013), in order to search for infestation and distribution patterns among these ectoparasites in Brazilian freshwater fish species. This search was carried out on 445 samples of 119 host fish of 27 families within the orders Characiformes, Perciformes, Clupeiformes, Mugiliformes, Osteoglossiformes, Symbranchiformes, Tetraodontiformes and Siluriformes from various regions of Brazil. We organized different host-parasite systems into matrices grouping species at different taxonomic and infestation levels and according to host parameters. Five families of parasites (Ergasilidae, Argulidae, Lernaeidae, Lernaeopodidae and Cymothoidae) distributed into 76 species of 27 genera were analyzed in the host samples, which presented dominance of Ergasilidae species, mainly from the genus Ergasilus. Some crustaceans are host and site-specific, especially in relation to fish in particular habitats and lifestyles (e.g. Perulernaea gamitanae, Anphira branchialis and Riggia paranensis), while other parasites frequently have no preference (e.g. Lernaea cyprinacea and Braga patagonica). We found broadly similar distribution patterns for some crustacean species among the different localities, whereas other species showed well-defined geographical patterns, and these findings were discussed.