Application Of Feed Probiotics From Marine Animal For Juvenile Abalone Aquaculture

The rapid development of marine aquaculture in China has brought great social and economic benefits.At the same time,a series of problems,such as frequent diseases?slow growth of mariculture animals and the substantial deterioration in coastal environment have become the limiting factors of the aquaculture development.Feed probiotics from marine animal have become the new focus of aquaculture application because of the promotion of host growth and immune function and the eco-friendly characteristics.The two strains Bacillus stratosphericus A3440 and Phaeobacter daeponensis AP1220 were isolated from healthy H.diversicolor intestines.Due to their properties of bioactivities of digestive enzymes and antibacterial abilities against Vibrio species,they were assessed to demonstrate their probiotic potential applied in abalone aquaculture.In this study,the safety of two strains was evaluated,and the medium composition and culture conditions were optimized.Consequently,two strains were applied in juvenile H.diversicolor aquaculture to decide the effect of growth and disease-resistant of abalone,and to analyse the influence on the microbial structure of intestinal flora.This study will provide the theoretical data for further application and development of probiotics in farming abalone.Firstly,we assessed the safety and compatibility of two potential probiotics.The results showed that A3440 was sensitive to 15 of 28 antibiotics.AP1220 was sensitive to 14 antibiotics and could strongly inhibit 16 of 20 pathogens tested.Both two strains can not cause hemolysis phenomenon,not produce amino acid decarboxylase and nitrate reductase.Two strains could not inhibit each other at the concentration of 105 cfu/mL.Secondly,we optimized the medium composition and fermentation conditions of two potential probiotics.The results showed that the spore yield of AP 3440 increased from 86.7%to 94.3%and the protease activity rose from 166.66 to 294.44 U/mL at the optimized condition.The results showed that the OD630 of strain AP1220 which represented the cell growth rate increased from from 0.83 to 1.10 and the antibacterial activities also was strengthed against pathogenic Vibrio species..Thirdly,the beneficial impacts of two potential probiotics to H.diversicolor was decided on the growth rate,survival rate,the activities of digestive enzymes and immune related enzymes in situ.The increased growth performance of abalones that giving probiotic bacteria,including growth rate of shell length and weight,was significantly higher than those abalones fed basal diet(P<0.05).Similarly,all treatments showed increased trend on survival rates than the control group without probiotics additive.The trypsin activities of group AP3440 and probiotics mixture were significantly increased(P<0.05).Bacillus sp.A3440 supplementation on abalone significantly affected nearly all enzyme activities related to immune response(GSH-PX,CAT,AKP and ACP)compared to group C(P<0.05).Contrary to the performance of highest survival rate of abalone fed with P.daeponensis AP1220(group P),the putative probiotic only obviously increased CAT and ACP activities of abalone.And fed with A3440 and AP1220 significantly increased the amylase activities and three enzyme activities related to immune response(CAT,ACT and SOD)(P<0.05).Finally,abalone gut microbiome on microbial Phylum level showed no obvious differences with or without probiotics addiminantion,but the bacterial diversity and richness from the non-treated group were higher than other treatment groups.After the challenge assays,bacterial richness and diversity of probiotics treatment groups rose at different extent and the A1220 group reached the highest value.Conversely,the non-treated group sharply decreased and kept at the lowest level.The gut microbial composition in probiotic treated animals maintained the relative consistence after and before the challenge test,while the non-treated animals exhibited marked variability.Besides,the richness of beneficial bacterial flora increased and the opportunity bacteria declined of abalone fed probiotics diet.In gerneal,the dietary administration with B.stratosphericu and P.daeponensis in this study have tremendous potential as probiotics for commercially H.diversicolor.