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.

The effect of the essential oils (EOs) of peppermint, Mentha piperita L., and tea tree, Melaleuca alternifolia (Maiden & Betche) Cheel, on the haematological, biochemical, and immunological parameters and intestinal morphology of Nile tilapia, Oreochromis niloticus L., was evaluated. Fish (58.09 ± 5.87 g) were fed 100 mg/kg and 250 mg/kg of each EO and sampled on days 7, 14, 30 and 60 after starting supplementation. The haematological and biochemical parameters were not altered by the supplementation of EOs compared to the control (p > .05). With regard to the immunological parameters, the activation of the complement system of fish fed 250 mg/kg peppermint and 100 mg/kg and 250 mg/kg tea tree EOs were significantly higher compared to the control after 60 days of feeding (p < .05). The complement system plays an essential role in innate immunity and contributes significantly to the acquired immune response; thus, its activation through supplementation with EOs is promising for the formulation of nutritional additives in aquaculture. Regarding intestinal morphology, fish fed 250 mg/kg tea tree EO presented higher villus size compared to all other groups (p < .05), which represents a healthier gut. These fish present a larger intestinal surface, which can result in better absorption and utilization of the nutrients. Based on the responses found in this study, both EOs were considered promising for the formulation of feed additives for Nile tilapia.

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Trypanosomes are flagellated parasite protozoans that prey especially on wild fish and have recently been described affecting fish in aquaculture. The present study was carried out during a mortality outbreak of Nile tilapia Oreochromis niloticus reared in net cages. Samples of 10 fish in the finishing phase showing unspecific signs, such as anorexia, skin darkening and gill paleness, were analyzed using hemogram, parasitology, microbiology, histopathology, electron microscopy and molecular identification. For microbiological analysis, the kidney was collected aseptically and cultured on tryptone soy agar for 48 h at 30°C. For parasitological analysis, skin, gills, intestinal contents and blood scrapings were examined. Photomicrographs of the parasite were measured. For molecular identification, blood samples were processed and sequenced for amplification of the 18S rDNA gene. Gills, liver, spleen, kidney, heart and intestine were sampled for histopathological processing. The microbiological results indicated that the fish were not infected with bacteria. Scrapings of the skin and gills revealed the massive presence of kinetoplastids, which were also observed in greater numbers than erythrocytes in the blood. Intestines were not affected by endoparasites. The morphometric characteristics indicated the presence of the Trypanosoma genus, which was confirmed in the sequenced samples, where 95% and 98% of the identity were Trypanosoma sp. In histopathology, all organs presented different levels of alteration, accompanied by large numbers of the parasite in small and large vessels. The main findings were the description of mast cell infiltrates in the gill and intestine, as well as multifocal aggregates of melanomacrophages in the liver, pancreas, spleen and kidney. Furthermore, the study addresses the newest features of clinical signs of infected fish and possible causes of infestations and compares the diagnosis of this hemoparasite with other hemoflagellates. To our knowledge, this study represents the first outbreak of Trypanosoma in Nile tilapia in South America. The authors warn of possible new cases of trypanosomiasis in aquaculture, recommending possible forms of containment and biosecurity measures.

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO2 are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO2 changes in combination with parasite infection would interfere with the host’s physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO2 above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na+/K+-ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na+/K+-ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security.

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Parasites represent a serious obstacle in Brazilian intensive fish farming, and then, monitoring parasitic infestations in aquaculture is a duty of every tilapia producer. The objective of this study was to identify the branchial ectoparasites of Nile tilapia, evaluate the correlation between parasitic intensity, host biometrics, and limnological variables, as well as to identify gill histological changes in fish. Thus, fish representing the three phases (I, II, and III) of production were collected in two commercial fish farms - 1 and 2, necropsied, and their parasites quantified and identified. The gill alterations were processed for histological analysis.  Cichlidogyrus sclerosus and Scutogyrus longicornis (Monogenoidea), and Lamproglena monodi (Lernaeidae) have been identified in the tilapia gills. The highest intensities of Monogenoidea infestation were in summer and autumn in both fish farms, with a positive correlation between parasites and water temperature. Infestation by L. monodi occurred only in Fish farm 2, with greater infestations in winter and spring, with a negative correlation between water temperature and parasitism. There was also an increase in parasitism according to the weight and length of the fish in the two fish farms. Histological changes such as hyperplasia, lamellar hypertrophy, and the presence of basophilic cysts on the secondary lamellae were detected in tilapia. Thus, water quality parameters and season of the year, which are closely related, can affect communities of parasites that infest Nile tilapia grown in cages. These findings are important to assist in planning disease control and prevention strategies for Nile tilapia fish farming, to reduce economic losses resulting from fish diseases and death.