Induction of innate immunity in fish by humus extract and its protective effect

腐殖物质是在腐殖土中的有机物质分解过程中形成的，并且在许多存在有机物质和微生物的自然环境中发现。腐殖酸浸提液对9种15株鱼类病原菌具有抑菌活性。鲤鱼口服腐殖酸提取物可有效预防实验性非典型杀鲑鱼气单胞菌感染。用10%、5%和1%的腐殖酸浸提液吸附在干颗粒上处理鲤鱼，可显著抑制鱼的死亡率和皮肤病变如溃疡和溃烂的发展。中位存活天数也大于在未经处理的鱼与10%或5%的腐殖质提取物处理的鱼。非典型A.从部分死鱼的溃疡性病变中分离出杀鲑菌，但也从这些鱼中分离出嗜水气单胞菌和黄杆菌属，证实了皮肤病变进展过程中细菌种群的变化。口服腐殖质提取物香鱼诱导有效的保护，对实验性非典型嗜冷黄杆菌感染。鱼的死亡率（65%）和发展的皮肤病变，如溃疡和皱纹显着抑制香鱼与腐殖酸提取物处理。F.从部分死鱼的溃疡病变中分离到嗜冷菌，用PCR方法在对照死鱼中扩增出细菌DNA。用腐殖酸浸提液处理香鱼，成活率达96%，且未观察到肉眼可见的皮肤损伤。在存活的鱼中没有分离到细菌，也没有细菌DNA扩增。这些结果清楚地表明，用腐殖酸提取物处理鱼对预防A。杀鲑病和冷水病。

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. Humus extract exhibited anti-bacterial activity against 9 species 15 strains of fish pathogens. Oral administration of humus extract to carp induced effective protection against experimental atypical Aeromonas salmonicida infection. Mortality of fish and development of skin lesions such as hemorrhages and ulcers were significantly suppressed in carp treated with 10 %, 5 % or 1 % humus extract adsorbed on dry pellets. The median surviving days was also greater in fish treated with 10% or 5% humus extract than in untreated fish. Atypical A. salmonicida was isolated from ulcerative lesions of part of dead fish, but Aeromonas hydrophila and Flavobacterium sp. were also isolated from these fish, verifying bacterial population changes during the progression of skin lesions. Oral administration of humus extract to ayu induced effective protection against experimental atypical Flavobacterium psychrophilum infection. Mortality of fish (65%) and development of skin lesions such as ulcers and hemorrhages were significantly suppressed in ayu treated with humus extract. F. psychrophilum was isolated from ulcerative lesions of part of dead fish, and bacterial DNA could be amplified using PCR in dead control fish. Surviving rate of ayu treated with humus extract was 96%, and no gross skin lesion was observed. No bacteria was isolated and no bacterial DNA was amplified in survived fish. These results clearly show that treatment of fish with humus extract is effective in preventing A. salmonicida disease and cold water disease.