The Impact Assessment Of Fermented Organic Fertilizer On Pond Water Environment And The Intestinal Flora In Grass Carp

With the increase of the cultured density of grass carp in intensive ponds,the environmental deterioration of aquaculture water is becoming more and more serious,which has became the main reason for the frequent diseases and the decline of fish qualities.How to control and improve the quality of aquaculture water is the key to the success of aquaculture.This topic was studied in Gong'an County,Jing Zhou City from July 2015 to June 2016.Water samples,plankton samples and intestinal contents of grass carps were collected each month.We have studied the effects of the fermented organic fertilizer on water quality control,plankton community structure,and bacteria in pond water and the intestinesof grass carp by usingthe ordinary microscope,ultraviolet spectrophotometry,fluorescence enumeration,and high-throughput sequencing technique.The research results are significative to guide the rational fertilization in grass carp pond,improve water quality control technology in intensive pond,andpromote the healthy culture of grass carp.The main results are as follows:(1)During the experiment,the restrained effect of fermented organic fertilizer on the contents of NH4+-N and NO2--N was significant.In rapid accumulation season of NH4+-N and NO2--N,the contents of NH4+-N and NO2--N in the experiment ponds was significantly decreased comparing with the control ponds.At the same time,the DO in the experiment ponds was higher than that of the control ponds,which were significantly differences in July,June,September,and October.However,there were no remarkable effects on p H value and the contents of TN,TP,NO3--N,and PO43--P.The results showed that the fermented organic fertilizer had a stabilizing effects on the high concentration of NH4+-N and NO2--N,and could significantly increase the dissolved oxygen.(2)During the experiment,96 species of phytoplankton was detected,belonging to 6 phyla,46 genera.In the experimental and the control ponds,86 and 73 species of phytoplankton were detected,respectively.The dominant species were Chlamydomonas globoza,Euglenaviridis,Euglena pisciformis,Synedra acus,Cryptomonas erosa,and Cryptomonas ovata.The density of phytoplankton in control ponds and experimental ponds was 1.07×107-3.63×107 ind/L and 2.31×107-7.93×107 ind/L.The phytoplankton biomass of experimental ponds(68.21±25.13 mg/L)was 2.78 times of the control ponds(24.51±12.10 mg/L),which was significantly different(P<0.05).The results showed that the fermented organic fertilizer could significantlyimproved phytoplankton biomass and algae diversity.(3)During the experiment,20 species of zooplankton belonging to 17 genera were found.The dominant species of zooplanktonincluded:(1)protozoan: Didinium balbianii,Askenasia faurei,Askenasia volvox,Colpoda reniformis,Tetrahymena pyriformis,Strombidium viride Stein,Strobilidium gyrans.(2)rotifer: Polyarthra trigla,Asplanchna priodonta,Brachionus calyciflorus,Brachionus angularisand Trichocerca pusilla.The biomass of zooplankton in the experimental ponds and control ponds fluctuated from 2.28 to 21.91 mg/L and from 0.66 to 6.28 mg/L,and the average biomass of the experimental pond(9.83±5.74 mg/L)was 4.35 times than that of the control pond(2.26±1.49 mg/L).The results showed that the fermented organic fertilizer could significantly increase the biomass of zooplankton,especially the biomass of rotifers.(4)During the experiment,a total of 13 phyla and 101 genus of bacteria were detected in the water samples.The main phyla included Proteobacteria,Cyanobacteria,Actinobacteria,and Bacteroidetes.The main genus included Lactococcus,Bacillus,Cetobacterium,Cyanobacteria,Aeromonas,Bacteroides,Arthrobacter,Pseudomonas,12 up,Synechococcus,and Nitrosomonas.In later stage of fertilization,the relative abundance of Lactococcus,Bacillus,Cetobacterium,Arthrobacter and Nitrosomonas were(0.61±0.17)%,(0.89±0.29)%,(0.20±0.031)%,(0.04±0.0082)%,and(0.34±0.037)%,which were respectively 3 times,3 times,2 times,4 times,and 1.42 times higher than that of the control pond.The results indicated that a relative proportion of bacteria increased in pond water with fermented organic fertilizer.However,the conditional pathogenic bacteria(Aeromonas)did not increased.(5)During the experiment,103 genera were detected in 12 intestinal bacterial samples.Among them,Cetobacterium,Lactococcus,Cyanobacteria,Aeromonas,Bacteroides,Bacill,Arthrobacter and Pseudomonas accounted for higher proportions.Lactococcus and Bacillus were 37.04% and 13.44% in the experiment pond,which were 2.33% and 0.88% in the control pond.The proportion of Bacteroides in grass carp gut of the experimental pond was 6.28%,which was 176 times than that of the control pond.The content of Aeromonas in the experimental pond was 2.43% lower than that of the control pond.The results show that fermented organic fertilizer can cause the changes of intestinal microflora in grass carp,the increase of bacteria content,and the suppression of conditional pathogenic bacteria.