Isolation,Identification and Feeding Effects of a Dominant Strain of Yeast from the Digestive Tract of Shrimp Litopenaeus vannamei

Key words: 
• Litopenaeus vannamei /
• yeast /
• isolation and identification /
• digestive tract /
• feeding.

Abstract: Six yeast strains were isolated from Litopenaeus vannamei digestive tracts,of which the strains HNC-1,HNC-2 and HNC-6 were observed dominant with the frequencies of the colony forming units being 21. 65%,31. 34% and 22. 89%,respectively. The dominant strain HNC-2 was preliminarily identified as Candida nivariensis according to its morphological,physiological and biochemical characteristics and 26 S r DNA gene sequences. The feeding experiment was conducted to evaluate the effects of the strain HNC-2 on the daily weight gain,digestive tract and survival rate of L. vannamei,and on the population density of total bacteria,yeasts and vibrio in shrimp digestive tracts and shrimp culture water by adding different concentrations of the strain yeast HNC-2 into the feed. The experiment result shows that the strain HNC-2 could improve the survival rate and daily gain of L.vannamei significantly（ P ＜0. 05）,and that the groups treated with the strain at the concentrations from 2. 0×10⁵ to 5. 0×10⁵ cfu·g^-1 were obviously different in daily weight gain as compared with the control group（ P ＜0. 05）.Moreover,the 2×10⁵ cfu·g^-1 group had the highest survival rate（ 99. 5± 0. 3%）,significantly higher than the control and other groups（ P ＜0. 05）. The quantity of yeast in the digestive tract of shrimp and culture water tended to increase,and was highly significantly different（ P ＜0. 01） between each treatment group and the control group. The quantity of total bacteria and vibrio in digestive tract of shrimp and culture water increased,highly significantly different between the experimental groups and the control group（ P ＞ 0. 05）. The yeast strain HNC-2could promote the growth and improve the survival rate of L. vannamei.