Osmoregulatory disturbances in Atlantic salmon, Salmo salar L., caused by the monogenean Gyrodactylus salaris

Anthelmintic Efficacy of Palmarosa Oil and Curcuma Oil against the Fish Ectoparasite Gyrodactylus kobayashii (monogenean)

Monogeneans are a serious threat to the development of aquaculture due to the severe economic losses they cause. The prevention and treatment of this disease are increasingly difficult because of the environmental and health concerns caused by the use of chemical anthelmintics and the emergence of drug resistance. It is thus necessary to search for effective alternatives for the treatment of monogenean infections. In the current study, anthelmintic efficacy of 16 selected essential oils (EOs) was investigated using the goldfish (Carassius auratus)–Gyrodactylus kobayashii model. The screening experiment indicated that palmarosa oil and curcuma oil had satisfactory anthelmintic activity against G. kobayashii with EC100 values of 10 and 12 mg/L after 24-h exposure, respectively. The in vivo and in vitro assays indicated anthelmintic efficacy of palmarosa oil against G. kobayashii was in a time and dose-dependent manner. Interestingly, curcuma oil showed an anesthetic effect on G. kobayashii, and its anthelmintic activity was dose-dependent rather than time-dependent in the concentration range tested in this study. Additionally, the 24-h LC50 (50% lethal concentration) against goldfish of these two EOs was 8.19-fold and 5.54-fold higher than their corresponding EC50 (50% effective concentration) against G. kobayashii, respectively. Moreover, exposure to these two EOs at 100% effective concentration against G. kobayashii had no serious physiological and histopathological influence on goldfish. These results demonstrated a high safety for goldfish of these two EOs. Overall, palmarosa oil and curcuma oil could be potential candidates for the treatment of G. kobayashii infections in aquaculture.

Climate change affects the parasitism rate and impairs the regulation of genes related to oxidative stress and ionoregulation of Colossoma macropomum

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.

Phylogeography and demographic history of Gyrodactylus konovalovi (Monogenoidea: Gyrodactylidae), an ectoparasite on the East Asia Amur minnow (Cyprinidae) in Central China

Gyrodactylus konovalovi is an ectoparasite on the Amur minnow (Rhynchocypris lagowskii) that is widely distributed in the cold fresh waters of East Asia. In the present study, the phylogeography and demographic history of G. konovalovi and the distribution of its host in the Qinling Mountains are examined. A total of 79 individual parasites was sequenced for a 528 bp region of the mitochondrial NADH dehydrogenase subunit 5 (ND5) gene, and 25 haplotypes were obtained. The substitution rate (dN/dS) was 0.068 and indicated purifying selection. Haplotype diversity (h) and nucleotide diversity (π) varied widely in the Qinling Mountains. Phylogenetic trees based on Bayesian inference (BI), maximum likelihood (ML), and maximum parsimony (MP) methods and network analysis revealed that all haplotypes were consistently well-supported in three different lineages, indicating a significant geographic distribution pattern. There was a significant positive correlation between genetic differentiation (F st) and geographic distance. The results of mismatch distribution, neutrality test and Bayesian skyline plot analyses showed that whole populations underwent population contraction during the Pleistocene. Based on the molecular clock calibration, the most common ancestor was estimated to have emerged in the middle Pleistocene. Our study suggests for the first time that a clearly phylogeography of G. konovalovi was shaped by geological events and climate fluctuations, such as orogenesis, drainage capture changes, and vicariance, during the Pleistocene in the Qinling Mountains.

Gyrodactylus lilianae n. sp. (Polyonchoinea: Gyrodactylidae) from Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil: a potential nuisance for aquaculture

Species of Monogenoidea (Platyhelminthes) are in its majority ectoparasites of marine and freshwater fishes. Many species of the group can promote great economic losses to fish production systems worldwide. The present study describes a new species, Gyrodactylus lilianae n. sp., from the body surface, fins and barbels of a captive South American catfish, Rhamdia quelen (Quoy & Gaimard) (Siluriformes: Heptapteridae) from southern Brazil. The new species is morphologically similar to Neotropical species of Gyrodactylus von Nordmann, 1832 from Siluriformes from which it differs most conspicuously by the morphology of the hook with a pronounced convex heel, somewhat depressed, slightly pointed toe, and a small distal bulb. The identity of the new species is also strongly supported by phylogenetic analysis based on cytochrome c oxidase subunit 2 mitochondrial gene (cox2) sequences and the rDNA fragment ITS1-5.8-ITS2. Infections with the new species in captive R. quelen juveniles were considered the main causative agent of observed mortalities. Tissue damage caused by G. lilianae n. sp. apparently facilitated the occurrence of secondary infections by protists (Ichthyophthirius multifiliis) and bacteria (Aeromonas hydrophila).

Are hybrids between Atlantic salmon and brown trout suitable long-term hosts of Gyrodactylus salaris during winter?

The monogenean parasite Gyrodactylus salaris poses serious threats to many Atlantic salmon populations and presents many conservation and management questions/foci and challenges. It is therefore critical to identify potential vectors for infection. To test whether hybrids of native Atlantic salmon (Salmo salar) × brown trout (Salmo trutta) are suitable as reservoir hosts for G. salaris during winter, infected hybrid parr were released into a natural subarctic brook in the autumn. Six months later, 23.9% of the pit-tagged fish were recaptured. During the experimental period, the hybrids had a sixfold increase in mean intensity of G. salaris, while the prevalence decreased from 81% to 35%. There was high interindividual hybrid variability in susceptibility to infections. The maximum infrapopulation growth rate (0.018 day^-1 ) of G. salaris throughout the winter was comparable to earlier laboratory experiments at similar temperatures. The results confirm that infrapopulations of G. salaris may reproduce on a hybrid population for several generations at low water temperatures (~1 °C). Wild salmon-trout hybrids are undoubtedly susceptible to G. salaris and represent an important reservoir host for the parasite independent of other co-occurring susceptible hosts. Consequently, these hybrids may pose a serious risk for G. salaris transmission to nearby, uninfected rivers by migratory individuals.