The South American continent is known for its high production and exports in fisheries and aquaculture, but has not reached its full potential in fish farming. The latest data on fish production in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, Uruguay and Venezuela were explored in this review. Aspects of biology, production, market and health of the species most produced in South America are described in detail. These species include the round fish (Colossoma spp., Piaractus spp. and hybrids) and catfish (Pseudoplatystoma spp. and hybrids), in addition to the promising pirarucu Arapaima gigas, yellowtail tetra Astyanax altiparanae and silver catfish Rhamdia quelen. Among the countries mentioned, Chile and Brazil are two of the largest intensive fish producers in the world. Chile relies primarily on marine fish, whereas Brazil is prominent for continental production. Special emphasis is given to the black pacu Colossoma macropomum because it is a commonly farmed fish in South American countries and offers several desirable productive characteristics (domesticated, omnivorous and easy to reproduce). Furthermore, this fish has the greatest potential to compete economically with tilapia production in South America. The production of native fish is currently overtaking the production of exotic species in some countries, which is considered a milestone for South American aquaculture. Regarding diseases, the main pathogens are similar to those observed throughout the world, such as Ichthyophthirius multifiliis, different species of monogeneans and trichodinids, and the bacteria Aeromonas hydrophila. Local pathogens, such as the parasites Perulernaea gamitanae and Goezia spinulosa, are also concerning.

Intensification of livestock rearing often promotes an increase in inappropriate practices that disregard care for the environment, animal health, and workers' health. Intensive fish farming systems are often associated with higher stocking density and massive use of artificial feed. Currently, outbreaks of parasitic, bacterial, and fungal diseases act as major limiting factors for fish farming, meaning that producers have to make use of massive amounts of antibiotics, disinfectants, and pesticides in order to control mortality and avoid huge economic losses. Because of adverse effects on the aquatic environment, terrestrial organisms, and human health (both fish handlers and consumers), this therapy has been criticized. Use of herbal medicines within animal production has shown promise, in that it is natural and biodegradable and has antimicrobial activity against various pathogens, including those relating to fish. Recently, researchers have reported promising effects from many herbal medicines for treating parasitic diseases caused by protozoa and metazoa, and broad activity against bacteria and fungi. This review addresses the current issues regarding indiscriminate use of chemicals and antibiotics in aquaculture and discusses the main findings and methodologies of the latest research on herbal medicines to stimulate and accelerate research in this field, especially in developing countries.

Trichodinids are ciliated protozoa that are widely known as one of the main groups of fish parasites. The genus Trichodina presents the greatest species diversity. However, records of Paratrichodina species are scarce, and little is known about their pathogenicity in hosts. The present study provides new records of Paratrichodina africana Kazubski and El-Tantawy (1986) in Nile tilapia from South America and descriptions of pathological changes and seasonality. A total of 304 farmed fish were examined. From gill scraping, parasites were identified using Klein's nitrate impregnation method. Gill samples were fixed for histopathological analysis. Small trichodinid found in this study have a prominent blade apophysis and narrow central part and blade shape that corresponds to the characteristics of P. africana Kazubski and El-Tantawy (1986). Gill lesions were proportional to parasite intensity, in which the gill tissue was compromised in heavy infestation. Proliferative disturbances were found, including epithelial hyperplasia, desquamation, and mononuclear and eosinophilic infiltrate that culminated in necrosis. We did not observe a seasonality effect on the occurrence of P. africana. This ciliated protozoan causes compromised respiratory capacity that leads to severe gill lesions and currently is an important pathogen that afflicts intensive tilapia cultures in Brazil.

Prochilodus lineatus is a freshwater fish species found in South America. It is common in aquaculture, but few studies regarding diseases of this fish have been performed. This study presents data of the occurrence of Trichodina heterodentata Duncan, 1977, as well as the pathological alterations detected by light and scanning electron microscopy (SEM). Twenty 20-day-old larvae were harvested from an earth pond and examined. Larvae showed erratic swimming on the pond edges and some had a whitish tegument. Larval smears were either impregnated with silver nitrate or stained with Giemsa stain to observe the taxonomic features of the ciliates. Five larvae were fixed in formalin solution for histopathological analysis, and another five specimens were fixed in glutaraldehyde for SEM. All larvae were diagnosed with a severe infestation by trichodinid T. heterodentata. Histological sections showed discrete hyperplasia of the gill filaments with subepithelial oedema of the secondary lamellae. In the SEM, suction areas were observed on the skin, gill and eye; corrosion and ulceration of the fins were associated with the bacterial presence of cocci on the lesions. This is the first report of T. heterodentata in P. lineatus that is responsible for an acute disease that culminates in larval mortality.

Monogeneans are major parasites of fish and cause large economic losses in aquaculture. Treatment for this parasitic infection is done with products that are mostly toxic to fish and the environment. Essential oils (EOs) of Melaleuca alternifolia and Mentha piperita and the oleoresin (OR) of Copaifera duckei were tested for their in vitro anthelmintic activity against the monogenean parasites (Anacanthorus penilabiatus and Mymarothecium viatorum) of pacu Piaractus mesopotamicus. Naturally infected gills were bathed with the herbal solutions (100, 200, 400, 800, and 1600 mg/L) and monitored every 15 min for 4 h. Because of its greater efficacy in vitro (p b 0.05) compared to the other herbal medicines, C. duckei OR was selected for in vivo testing. The in vivo treatment consisted of 10 and 50 mg/L baths of C. duckei OR for 10 min. Parasitological, hematological, and histological analyses were conducted post-bath and seven days after treatment. Parasite loads decreased by approximately 45% in fish treated with 50 mg/L of C. duckei OR. No hematological changes caused by treatment with C. duckei OR at 10 and 50 mg/L were observed. Histology revealed branchial and hepatic alterations in fish from all groups, whereas spleen and kidney tissues were not affected. Histopathological alterations observed in all fish were due to parasitism or nutritional/farming conditions. Hematological and histological results showed that short baths were safe for fish. Based on the strong anthelmintic activity observed, C. duckei OR offers a promising alternative treatment against monogenean parasites.

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In vitro effect of the Melaleuca alternifolia, Lavandula angustifolia and Mentha piperita essential oils (EOs) against Ichthyophthirius multifiliis and in vivo effect of M. alternifolia for treating ichthyophthiriasis in one of the most important South American fish, Piaractus mesopotamicus (Holmberg), were evaluated. The in vitro test consisted of three EOs, each at concentrations of 57 μL L(-1) , 114 μL L (-1) , 227 μL L(-1) and 455 μL L (-1) , which were assessed once an hour for 4 h in microtitre plates (96 wells). The in vitro results demonstrated that all tested EOs showed a cytotoxic effect against I. multifiliis compared to control groups (P < 0.05). The in vivo treatment for white spot disease was performed in a bath for 2 h day(-1) for 5 days using the M. alternifolia EO (50 μL L (-1) ). In this study, 53.33% of the fish severely infected by I. multifiliis survived after the treatment with M. alternifolia (50 μL L (-1) ) and the parasitological analysis has shown an efficacy of nearly 100% in the skin and gills, while all the fish in the control group died. Furthermore, the potential positive effect of M. alternifolia EO against two emergent opportunistic bacteria in South America Edwardsiella tarda and Citrobacter freundii was discussed.

Acanthocephalans are endoparasites of several vertebrate species. These parasites are able to attach the host intestine, which culminates in low nutrient utilization and severe economic losses. This review discusses the impact of acanthocephalosis for aquaculture and demonstrates promising control and treatment measures against this parasitosis. Echinorhynchus truttae was considered one of the main parasites affecting salmonids; however, there are currently no scientific data on relevant outbreaks of this parasitosis. It is emphasized that, currently, the disease caused by Neoechinorhynchus buttnerae in tambaqui Colossoma macropomum is the fish acanthocephalosis with the strongest impact, besides being one of the most important acanthocephalosis affecting animal production worldwide. It has been noted that this disease has direct correlation with an environment replete with contaminated zooplankton and biosafety failures. Amongst revised synthetic chemotherapeutics, carbon tetrachloride and loperamide are described as being strongly efficient against E. truttae, and levamisole has been the most studied molecule for N. buttnerae. Considering the demand for alternative molecules, studies have shown that thyme, garlic and peppermint are promising against acanthocephalans. It must be emphasized a great need for standardization of in vitro and in vivo tests, as well as the need for studies on pharmacokinetics and pharmacodynamics. As prospects to control acanthocephalosis, we highlight the need for development of innovative aquaculture environments (biofloc and recirculation systems) that can prevent or extinguish the intermediate host, new methods of drug inclusion in the diet and genetic studies aiming improvement of resistant fish lineage and even the genome description of the parasite.