Garlic, Allium sativum, which was fed at 0, 0.05, 0.1, 0.5 and 1.0 g per 100 g of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), led to control of experimental infection with Aeromonas hydrophila. At doses of 0.5 and 1.0 g garlic per 100 g of feed, there was a reduction in mortalities to 4% compared with the controls (88%). Moreover, there was a significant increase in growth, feed conversion and protein efficiency. There was stimulation of the number of erythrocytes and leucocytes, a significantly higher haematocrit, enhancement of phagocytic activity, respiratory burst, lysozyme, anti-protease and bactericidal activities following feeding with garlic.

Ginger, Zingiber officinale, which was fed at 0, 0.05, 0.1, 0.5 and 1.0 g per 100 g of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), led to control of experimental infection with Aeromonas hydrophila. At 0.5 g ginger per 100 g of feed, there was a reduction in mortalities to 0% compared with the controls (64%). Moreover, there was a significant increase in growth, feed conversion and protein efficiency. There was proliferation in the number of neutrophils, macrophages and lymphocytes, and enhanced phagocytic, respiratory burst, lysozyme, bactericidal and anti-protease activities compared with the controls.

The development and duration of immune protection against Aeromonas hydrophila infections with garlic as immunostimulant in rainbow trout Oncorhynchus mykiss was studied. Rainbow trout fingerlings of 14 g average weight were fed with 0 g (= Control), 0.5 g and 1.0 g of garlic 100 g-1 of feed for 14 days. Physiological factors, biochemical, immunological, hematological parameters and electrolyte indices were evaluated after a further 14, 21 and 28 days before challenge with Aeromonas hydrophila. Fourteen days after the cessation of feeding with garlic, mortality rates of 12 % (relative percent survival [RPS] = 86 %) and 16 % (RPS = 80 %) were recorded in groups which received 0.5 g and 1.0 g of garlic 100 g-1 of feed, respectively, compared to 84 % mortalities in the controls. The corresponding RPS 21 days after ending the feeding regime was 75 % and 68, respectively. One week later, the RPS had dropped to 55% and 46% in the groups fed with 0.5 g and 1.0 g garlic 100 g-1 of feed, respectively

Aims:  To determine the effect of lipopolysaccharide (LPS) for the prevention of infection by Aeromonas hydrophila in rainbow trout (Oncorhynchus mykiss Walbaum) fingerlings. Methods and Results:  Rainbow trout fingerlings were fed with 0 mg (= controls), 1·875 mg, 3·75 mg, 7·5 mg and 15 mg of LPS per 100 g of commercial feed for 14 days before experimental challenge with A. hydrophila. The results revealed a reduction in mortalities to 5% in the two lowest doses and 15% in the group, which received 15 mg LPS per 100 g of feed, compared with 45% mortalities in the control. LPS exerted a powerful oxidative burst effect and was a potent mediator of phagocytic, lysozyme, bactericidal and antiprotease activities and total protein. However, whereas there were increases in specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) in LPS‐treated fish, the data were not significantly (P > 0·05) different. Conclusions:  LPS was effective at preventing disease caused by A. hydrophila and in stimulating the innate immune response of rainbow trout. Significance and Impact of the Study:  The results of this study highlight the role of LPS in fish disease control.

Allicin was fed at 0 (= control), 0.5 and 1.0 mL of Allimed liquid 100 g(-1) of feed for 14 days to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings before infection with Aeromonas hydrophila with a resultant reduction in mortalities from 80% in the controls to 8% [relative percentage survival (RPS) = 90%] and 0% (RPS = 100%) among the treated fish. Allicin was strongly antibacterial compared to the control, with a minimum inhibitory concentration (MIC) of >400 microL mL(-1) of Allimed liquid. Use of allicin led to a lower number of white blood cells (132.0 +/- 0.4 x 10(3)) compared to 175.0 +/- 0.1 x 10(3) in the controls, but elicited increased phagocytic activity, i.e. a phagocytic value of 39.2% compared to 13.6% in the controls, and serum lysozyme activity, which showed significant (P > 0.05) differences compared to the control at 15 and 30 min after the first reading at 0 min of incubation.