Dietary supplementation with Weissella cibaria C-10 and Bacillus amyloliquefaciens T-5 enhance immunity against Aeromonas veronii infection in crucian carp (Carassiu auratus).

With the aim to discover novel lactic acid bacteria and Bacillus strains from fish as potential probiotics to replace antibiotics in aquaculture, the present study was conducted to isolate lactic acid bacteria and Bacillus from intestinal tract of healthy crucian carp (Carassiu auratus) and largemouth bass (Micropterus salmoides) and evaluate their resistance against Aeromonas veronii. Based on the evaluation of antibacterial activity and tolerance test, one strain of lactic acid bacteria (Weissella cibaria C-10) and one strain of Bacillus (Bacillus amyloliquefaciens T-5) with strong environmental stability were screened out. The safety evaluation showed that these two strains were non-toxic to crucian carp and were sensitive to most antibiotics. In vivo study, the crucian carps were fed a basal diet supplemented with W. cibaria C-10 (C-10), B. amyloliquefaciens T-5 (T-5) and W. cibaria C-10 + B. amyloliquefaciens T-5 (C-10+T-5), respectively, for 5 weeks. Then, various immune parameters were measured at 35 days of post-feeding. Results showed both probiotics could improve the activities of related immune enzymes, immune factors and non-specific immune antibodies in blood and organs (gill, gut, kidney, liver, and spleen) of crucian carp in varying degrees. Moreover, after 7 days of challenge experiment, the survival rates after challenged with A. veronii of W. cibaria C-10 (C-10), B. amyloliquefaciens T-5 (T-5) and W. cibaria C-10 + B. amyloliquefaciens T-5 (C-10+T-5) supplemented groups to the crucian carps were 20%, 33% and 22%, respectively. Overall, W. cibaria C-10 and B. amyloliquefaciens T-5 could be considered to be developed into microecological preparations for the alternatives of antibiotics in aquaculture.

Isolation of active compounds from methanol extracts of Toddalia asiatica against Ichthyophthirius multifiliis in goldfish (Carassius auratus).

The parasitic ciliate Ichthyophthirius multifiliis infests all species of freshwater fish and can cause severe economic losses in fish breeding. The present study aims to evaluate the antiparasitic activity of the active components from Toddalia asiatica against I. multifiliis. Bioassay-guided fractionation and isolation of compounds with antiparasitic activity were performed on the methanol extract of T. asiatica yielding two bioactive compounds: chelerythrine and chloroxylonine identified by comparing spectral data (NMR and ESI-MS) with literature values. Results from in vitro antiparasitic assays revealed that chelerythrine and chloroxylonine could be 100% effective against I. multifiliis at the concentration of 1.2 mg L(-1) and 3.5 mg L(-1), with the median effective concentration (EC50) values of 0.55 mg L(-1) and 1.90 mg L(-1) respectively. In vivo experiments demonstrated that fish treated with chelerythrine and chloroxylonine at the concentrations of 1.8 and 8.0 mg L(-1) carried significantly fewer parasites than the control (P<0.05). The acute toxicity (LC50) of chelerythrine for goldfish was 3.3 mg L(-1).