This study was aimed to assess the effect of oral application of Lactobacillus plantarum (2 × 10 CFU g feed) as a probiotic on growth performance and immune status of vaccinated rainbow trout (29.5 ± 2 g) to yersiniosis at 16 ± 2 °C for 72 days. Fish were randomly allocated into 12 fiber glass tanks (4100 L) at a density of 80 fish per tank (240 fish per treatment). The results revealed that the activity of lysozyme and alkaline phosphatase was significantly higher in immunized fish fed with diet supplemented with probiotic (vaccine +probiotic) than that in the immunized group fed with basal diet (vaccine group) while no significant differences in levels of hematological parameters, complements, total IgM, proteins, and the intestine lactic acid bacteria (LAB) were detected. Also, significantly a better growth performance in terms of feed conversion ratio, weight gain, and thermal growth coefficient was seen in the vaccine + probiotic group than that in the vaccine group. These results indicate that feeding probiotic after vaccination can enhance the efficacy of immersion vaccination to Yersinia ruckeri.

The antibacterial activities of essential oils and herbal extracts have been demonstrated against a range of bacterial species. In this study, the antibacterial effects of a new combination of essential oils from the herbs Thymus vulgaris, Salvia officinalis, Eucalyptus globulus and Mentha piperita were assayed against common bacterial isolates (Staphylococcus aureus, Escherichia coli and Pseudomonas aeroginosa) and fifteen novel marine bacteria isolates. The sensitivity of different isolates to antibacterial activity of the essential oils was determined using well diffusion assays. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were quantified by micro dilution assays. The data demonstrate that the combination of essential oils had potent antibacterial effects and marine bacteria were more sensitive to growth inhibition (P \ 0.05). MIC rates were 0.77-6.18 mg/ml, and MBC rates were 1.67-12.30 mg/ml. This indicates that the combined essential oils (CEO) can be a new source of antibacterial agents for use in marine aquaculture.

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Indoxacarb is a relatively new pesticide from oxadiazin class, which is used near carp ponds for agricultural purposes. Thus, the aim of this study was to determine indoxacarb effects on common carp (Cyprinus carpio). The fish were exposed to 0 (control), 0.75, 1.5 and 3 ppm of indoxacarb over 21 days and plasma biochemical characteristics and liver histopathology were examined. Exposure to indoxacarb induced fall in total protein after 21 days. Globulin increased after 7 days and then decreased after 14‐ and 21‐day exposure. Plasma alanine transaminase and aspartate transaminase activities increased in 1.5 and 3 ppm treatments after 7‐day exposure. Indoxacarb exposure significantly decreased plasma alkaline phosphatase after 7 days with no change at the second and third samplings. After 7 days, plasma T3 levels had no significant change; however, it decreased after 14 days in the 1.5 and 3 ppm treatments and also reduced after 21‐day exposure to the 3 ppm treatment compared to the control group. Plasma T4 level only decreased significantly in the 3 ppm treatment compared to the control group after 21 days. Different histopathological symptoms such as necrosis, hyperaemia, sinusoidal space extension, pyknotic nuclei, leucocyte infiltration and melanomacrophage aggregates were observed after 21‐day exposure to indoxacarb. The symptoms intensity was dependent on indoxacarb concentration. In conclusion, the present results show that indoxacarb exposure adversely affects common carp health and welfare, which consequently may induce serious problems in this species aquaculture.