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Gyrodactylus spp. are common monogenean ectoparasites that may lead to significant fish mortality. To find effective anthelmintic agents with lower toxicity, a series of natural saponins were obtained and evaluated for their anthelmintic activity against Gyrodactylus kobayashii and acute toxicity to goldfish (Carassius auratus). Among all tested compounds, six compounds (1, 2, 3, 8, 10, and 13) shown higher anthelmintic activity and safety than widely used formaldehyde-based parasiticides, especially compound 1 having 100% anthelmintic efficacy against G. kobayashii at 0.3 mg/L and a therapeutic index of 16.6. Also, the three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of these saponins have been performed to explore the structural features reasonable for the anthelmintic activity against G. kobayashii. These models demonstrated that the hydroxyl group at C-17 position and the sugar moieties at C-3 position, especially the hydroxyl groups of the sugar moieties, were critical to the anthelmintic activity. The QSAR studies could provide useful information for further rational design and optimization of novel saponins for the control of gyrodactylosis.

Water-soluble chlorophyll (chlorophyllin) was used in a phototoxic reaction against a number of fish ectoparasites such as Ichtyobodo, Dactylogyrus, Trichodina, and Argulus. Chlorophyllin is applied to the water at concentrations of several micrograms per milliliter for a predefined incubation time, and afterwards, the parasites are exposed to simulated solar radiation. Application in the dark caused only little damage to the parasites; likewise, light exposure without the addition of the photosensitizer was ineffective. In Ichthyobodo, 2 μg/mL proved sufficient with subsequent simulated solar radiation to almost quantitatively kill the parasites, while in Dactylogyrus, a concentration of about 6 μg/mL was necessary. The LD50 value for this parasite was 1.02 μg/mL. Trichodina could be almost completely eliminated at 2 μg/mL. Only in the parasitic crustacean Argulus, no killing could be achieved by a photodynamic reaction using chlorophyllin. Chlorophyllin is non-toxic, biodegradable, and can be produced at low cost. Therefore, we propose that chlorophyllin (or other photodynamic substances) are a possible effective countermeasure against several ectoparasites in ponds and aquaculture since chemical remedies are either forbidden and/or ineffective.

In the present study, methanol extracts of 42 traditional medicinal plants with potent anthelmintic activity against Dactylogyrus intermedius (Monogenea) in goldfish (Carassius auratus) were investigated. Cinnamomum cassia, Lindera aggregata, and Pseudolarix kaempferi exhibited 100% activity and were selected for further evaluation by applying five solvents (petroleum ether, chloroform, ethyl acetate, methanol, and water) for the extraction of the samples, followed by the in vivo bioassay. Among the extracts tested, water and methanol extracts of C. cassia showed the highest efficacies with EC(50) values of 13.2 and 12.3 mg L(-1), showing 100% efficacy against D. intermedius at 30.0 and 40.0 mg L(-1), followed by methanol extract of L. aggregata which demonstrated 100% efficacy at 60.0 mg L(-1) with EC(50) value of 17.1 mg L(-1) after 48 h of exposure. Methanol and ethyl acetate extract of P. kaempferi, which exhibited a 100% efficacy against D. intermedius at 60.0 and 50.0 mg L(-1), revealed similar activity with EC(50) values of 23.5 and 23.3 mg L(-1), respectively. Acute toxicity of these active extracts was investigated on goldfish for 48 h and the corresponding median lethal concentrations (LC(50)) of 56.9, 31.3, 88.7, 168.2, and 165.7 mg L(-1), respectively. These findings indicated that these extracts of the three plants can be developed as preferred natural antiparasitic agents for the treatment of D. intermedius.

Dactylogyrus intermedius is one of the most common and serious cause of parasitic diseases of freshwater fish in aquaculture, and can cause morbidity and high mortality in most species of freshwater fish worldwide. To attempt controlling this parasite and explore novel potential antiparasitic agents, the present study was designed to ascertain the anthelmintic activity of Chelidonium majus L. whole plant and to isolate and characterize the active constituents against D. intermedius. The ethanol extract from C. majus whole plant showed significant anthelmintic activity against D. intermedius [EC(50) (median effective concentration) value = 71.5 mg L(-1)] and therefore subjected to further isolation and purification using various chromatographic techniques. A quaternary benzo[c]phenanthridine alkaloid exhibited significant activity against D. intermedius was obtained and identified as chelidonine. In vivo anthelmintic efficacy tests exhibited that chelidonine was 100% effective against D. intermedius at a concentration of 0.9 mg L(-1), with EC(50) value of 0.48 mg L(-1) after 48 h of exposure, which is more effective than the positive control, mebendazole (EC(50) value = 1.3 mg L(-1)). In addition, the 48-h median lethal concentration (LC(50)) for chelidonine against the host (Carassius auratus) was 4.54 mg L(-1). The resulting therapeutic index for chelidonine was 9.46. These results provided evidence that chelidonine might be potential sources of new antiparasitic drugs for the control of Dactylogyrus.

Dactylogyrus intermedius is a significant monogenean parasite on the gills of cyprinid fishes and can cause severe economic losses in aquaculture and ornamental fish breeding. In the present study, bioactivity-guide fractionation was employed to identify active compound from Chelidonium majus L. against D. intermedius. In vivo anthelmintic activity of petroleum ether, ethyl acetate, chloroform, and n-butanol extracts of C. majus were tested. Among them, only the n-butanol extract exhibited promising anthelmintic efficacy, and therefore subjected to the further isolation and purification using various chromatographic techniques. A compound showing potent activity was obtained and identified by hydrogen, carbon-13 nuclear magnetic resonance spectrum and electron ionization mass spectrometry as chelerythrine. In vivo anthelmintic efficacy tests exhibited that chelerythrine was 100% effective against D. intermedius at a concentration of 1.60 mg L(-1), with LC(50) values of 0.68 mg L(-1) after 48 h of exposure. The 48-h LC(50) value (acute toxicity tests) of chelerythrine was found to be 3.59 mg L(-1) for grass carp. These results provided evidence that chelerythrine can be selected as a lead compound for the development of new drugs against D. intermedius.

In the present study, an attempt has been made to petroleum ether, chloroform, ethyl acetate, methanol, and water extracts of Prunus amygdalus Batsch seeds (Semen amygdali), Cimicifuga foetida L. rhizomes (Rhizoma Cimicifugae), Peucedanum decursivum (Miq.) Maxim roots (Radix Peucedani), Momordica cochinchinensis Spreng. seeds (Semen Momordicae), and Bupleurum chinense DC. roots (Radix Bupleuri chinensis) for their in vivo anthelmintic activity against monogenean Dactylogyrus intermedius in goldfish (Carassius auratus). The results showed that the efficacies of methanol, chloroform, and ethyl acetate extracts from R. Bupleuri chinensis were found to be, in this order, more effective than others with the 48 h-EC(50) and EC(90) values of 3.5 and 6.9, 6.0 and 8.4, 7.4 and 11.2 mg/L, respectively, followed by ethyl acetate extract of R. cimicifugae and chloroform extract of R. peucedani with EC(50) 189.2 and 240.4 mg/L. The promising methanol, chloroform, and ethyl acetate extracts from R. Bupleuri chinensis were subjected to acute toxicity tests for the evaluation of their safety to the host. After 48-h exposure, the mortalities of goldfish were recorded, and the established LC(50) values were 10.1-, 4.2-, and 8.4-fold higher than the corresponding EC(50). These results indicated that the three extracts from R. Bupleuri chinensis exhibit potential to be used as preferred natural antiparasitics for the control of the D. intermedius, especially for the methanolic one.

A bioassay-guided fractionation was performed to evaluate the anthelmintic activity of the crude extract fractions and osthole from Radix angelicae pubescentis against Dactylogyrus intermedius in goldfish (Carassius auratus) in vivo. Among four extracts (petroleum ether, ethyl acetate, acetone, and ethanol), only ethanol extract exhibited the best anthelmintic efficacy with 100% mortality of Dactylogyrus and no death of fish at the optimal anthelminthic concentration of 120 mg/L. Therefore, ethanol extract was subjected to column chromatography to obtain sixteen fractions. The activity was found in fraction F with 100% mortality of Dactylogyrus and no toxicity to fish at dose of 2.0 mg/L. A white crystal was isolated from fraction F and identified as osthole which exhibited the optimal activity with 100% mortality of Dactylogyrus at 1.6 mg/L had and no toxicity to fish at dose up to 6.2 mg/L. This is the first report on the isolation and identification of anthelmintic active compound from R. angelicae pubescentis against D. intermedius in goldfish (C. auratus) in vivo.

Dactylogyrus intermedius is one of the most pathogenic monogenean parasites on the gills of captive fish and can cause serious problem in aquaculture. To attempt controlling this parasite and explore novel potential antiparasitic agents, the present study was designed to investigate the anthelmintic activity of Dioscorea zingiberensis C. H. Wright against D. intermedius in goldfish under in vivo conditions. Bioactivity-guided fractionation and isolation of the compounds responsible for anthelmintic activity was carried out with the ethanolic extract yielding two bioactive compounds. Using MS, (1)H NMR, (13)C NMR spectroscopic analyses, the two compounds were identified as trillin and gracillin. The results of in vivo anthelmintic efficacy assay showed that the 48-h median effective concentrations (EC(50)) are 26.48 mg L(-1) for trillin and 0.18 mg L(-1) for gracillin. The 48-h acute toxicity tests (LD(50)) of trillin and gracillin were found to be 73.11 and 1.40 mg L(-1) for goldfish, respectively. The resulting therapeutic indices for the two active compounds are 2.76 and 7.78, respectively. These data confirmed that both trillin and gracillin are effective against D. intermedius, and the gracillin exhibits more interesting perspectives for the development of a candidate antiparasitic agent.

In search of a natural antiparasitic, in vivo anthelmintic activity of petroleum ether, chloroform, ethyl acetate, methanol, and aqueous extracts of Angelica pubescens roots (Radix angelicae pubescentis), Brucea javanica fruits (Fructus bruceae), Spatholobus suberectus stems (Caulis spatholobi), Aesculus chinensis Bge. seeds (Semen aesculi), and Pharbitis purpurea (L.) Voigt seeds (Semen pharbitidis) were tested against Dactylogyrus intermedius (Monogenea) in goldfish (Carassius auratus). Among the extracts tested, the methanolic and aqueous extracts of S. aesculi were observed to be more efficient than the other plant extracts with EC(50) and EC(90) values of 5.23 and 7.33 mg/L and 6.48 and 12.29 mg/L after 48 h, respectively, followed by methanolic extracts of Fructus bruceae, Radix angelicae pubescentis, Caulis spatholobi, and Semen pharbitidis with EC(50) 49.96, 57.45, 64.92, and 309.47 mg/L. The methanolic and aqueous extracts of S. aesculi exhibited potential results and can be exploited as a preferred natural antiparasitic for the control of D. intermedius.

Dactylogyrus intermedius is a significant monogenean parasite on the gills of cyprinid fishes and can cause serious problem in fish aquaculture. In the present study, bioassay-guided fractionation was employed to identify the active compounds from Fructus Arctii against D. intermedius. Five solvents (petroleum ether, chloroform, ethyl acetate, ethanol, and water) were applied for the extraction of Fructus Arctii. Among them, only the chloroform extract exhibited promising anthelmintic efficacy and therefore, subjected to the further isolation and purification using various chromatographic techniques. Two compounds showing potent activity were obtained and identified by spectral data (infrared, nuclear magnetic resonance, and mass spectrometry) as: arctigenin (1) and arctiin (2). They were found to be significantly effective against D. intermedius with median effective concentration (EC(50)) values of 0.62 and 3.55 mg L(-1), respectively. Arctigenin exhibited higher activity as compared with the positive control mebendazole with an EC(50) value of 1.25 mg L(-1). The 48-h acute toxicity tests (LC(50)) of arctigenin and arctiin were found to be 8.47 and 14.14 mg L(-1) for goldfish, respectively. These results provided evidence that the studied plant extract, as well as the isolated compounds, might be potential sources of new antiparasitic drug for the control of Dactylogyrus.