Protection against Flavobacterium psychrophilum Infection (Cold Water Disease) in Ayu Fish (Plecoglossus altivelis) by Oral Administration of Humus Extract

Abstract

ABSTRACT. Humic substances are formed during the decomposition of organic matter in humus, and are found in many natural environments in which organic materials and microorganisms have been present. In the present study, oral administration of humus extract to ayu fish (Plecoglossus altivelis) induced effective protection against experimental Flavobacterium psychrophilum infection (cold water disease). Mortality of fish and development of skin lesions, such as erosion and hemorrhages on the skin, gill cover or mouth, were significantly suppressed in fish treated with 10%, 5% or 1% humus extract adsorbed on dry pellets. Although F. psychrophilum was not re-isolated from gills and erosion lesions of the skin of dead fish, bacterial gyrB DNA could be amplified in these specimens from dead fish and surviving control fish using the polymerase chain reaction. The protective effect of the extract was not the results of direct killing of bacteria or antibiotic activity of the extract since no obvious reduction in the bacterial number was observed at 5 times to 5,000 times dilution of the humus extract having pH 5.45 to 7.40. These results clearly show that treating fish with humus extract is effective in preventing cold water disease.

Effects of dietary humic acid on growth performance, haemato-immunological and physiological responses and resistance of Rainbow trout,Oncorhynchus mykisstoYersinia ruckeri

“…On the other hand, the survival rate of C. carpio , fed with increasing levels of humic acid extracts for 30 days, increased particularly in the 5% and 10% groups after being infected with A. salmonicida while there was no significant difference in increasing or decreasing doses (Kodama & Nakagawa, ). Similarly, a significant increase in survival rate of Ayu ( Plecoglossus altivelis ) fed increasing levels of humus extract for 30 days, against Flavobacterium psychrophilum , was reported by Nakagawa, Iwasaki and Kodama ().…”

Genetic variation amongFlavobacterium psychrophilumisolates from wild and farmed salmonids in Norway and Chile

“…The analysis of gyrB sequencing has been previously reported in literature as an identification method for Fl. psychrophilum (Izumi et al 2005;Nakagawa et al 2009). Recently, Shah et al (2012), in a phylogenetic study of Fl.…”

Dietary fulvic acid effects on survival and expression of immune-related genes inLitopenaeus vannameichallenged withVibrio parahaemolyticus

“…However, it is important to mention that the survival in bioassay 1 was higher than in bioassay 2 because the infection was less severe (see the positive control). In the same way, Nakagawa, Iwasaki, and Kodama () reported that oral administration of humus extract (containing humic and fulvic acids) to ayu fish ( Plecoglossus altivelis ) induced effective protection against experimental Flavobacterium psychrophilum infection. Moreover, Abdel‐Wahab, El‐Refaee, and Ammar () found higher survival (87%) in the common carp ( Cyprinus carpio ) fed 1% humic acid and challenged with Aeromonas hydrophila (0.5 x × 10 8 CFU/ml) as compared to the control group (54%) fed a diet without humic acid, representing 33% of net survival.…”