Study On The Community Structure And Function Of Zooplankton In The Industrialized Culture System Of Litopenaeus Vannamei

Zooplankton refers to the aquatic animals that live in the floating life.It can be used as a high-quality natural bait for many economic fish and shrimp,and at the same time can regulate the phytoplankton and microbial community structure as consumers.The species composition,quantity distribution and variation of zooplankton are closely related to the water quality of the pond and the logistics and energy flow in the system.It directly or indirectly affects the growth of shrimp and the production performance of the system.However,in different culture models,the zooplankton community structure is different;in the same culture mode,the community structure of zooplankton under the same management conditions also has large differences.In this paper,the characteristics of zooplankton community structure,community succession and its relationship with water quality,Vibrio and phytoplankton were studied in the industrialized culture of Litopenaeus vannamei.The main results are as follows:1.Changes of zooplankton community structure in the industrialized culture system of Litopenaeus vannamei.To explore the variations in zooplankton community in the shrimp factory aquaculture process,effectively manage water quality,and improve aquaculture efficiency,the characteristics and succession of zooplankton community structure,as well as the relationship between the community and Vibrio,phytoplankton,and the environment were analyzed.A total of21 species,belonging to 4 categories were identified from August to November 2018.Protozoan zooplankton species were the most diverse,accounting for 61.9%of the total species,followed by Rotifera(14.3%),Copepoda(14.3%),and Cladocera(5%).The average density and biomass of zooplankton in the experimental pond was about 0.71×10~3 ind./L and11.72 mg/L,respectively.The Shannon-Wiener diversity index(H')of the zooplankton fluctuated between 0.52 and 1.64.Correlation analysis showed that the zooplankton density was significantly negatively correlated with the phytoplankton density(P<0.05).Canonical correspondence analysis showed that temperature,pH,nutrients,etc.are important factors influencing the succession of dominant species of zooplankton.2.Effect of Brachionus plicatilis on water quality under different temperature and salinity conditions.Taking Brachionus plicatilis as the research object,the orthogonal experiment between 4 salinity levels and 4 water temperature levels is designed in this paper.The interaction effect of water temperature and salinity on oxygen consumption rates,ammonia-nitrogen excretion rates and phosphate excretion rates for Brachionus plicatilis were studied.In the interaction effect of above-m entioned factors,the rate of oxygen consum ption varied from 1.010 to 2.158?g/(mg·h),the average value is 1.696?g/(mg·h).And the rate of ammonia-nitrogen excretion varied from 0.069to 0.251?g/(mg·h),the average value is 0.166?g/(mg·h).Meanwhile the rate of phosphorous excretion varied f rom 0.002 to 0.118?g/(mg·h),the average value is 0.055?g/(mg·h).The statistical analysis showed,Under the same salinity condition,the oxygen consumption rate,ammonia nitrogen excretion rate and phosphorus excretion rate increased with the increase of temperature;under the same temperature condition,the oxygen consumption rate and phosphorus excretion rate increased with the increase of salinity;The ammonia nitrogen excretion rate decreases with the increase of salinity under the same temperature condition.the effect of temperature and salinity on oxygen consumption rates,ammonia-nitrogen or phosphate excretion rates for Brachionus plicatilis are significant(P<0.01),and the interaction between ammonia-nitrogen and phosphorus excretion rate was not significant(P>0.05).3.Effects of Brachionus plicatilis on growth performance and quality of Litopenaeus vannameiTaking Litopenaeus vannamei as the experimental object,the initial body weight was(0.5±0.03)g.Six density gradients of Brachionus plicatilis(0 ind./mL,5 ind./mL,10 ind./mL,20 ind./mL,40 ind./mL,80ind./mL)were added to the shrimp aquaculture water.By comparing the water quality index,number of vibrio in water,growth performance,digestive enzymes and non-specific immune enzymes of shrimp between experimental group and control group,the effect of adding Brachionus plicatilis to shrimp culture water was analyzed.Compared with the control group,the addition of the rotifers caused a significant increase in the concentration of ammonia nitrogen,nitrous oxide and active phosphorus in the aquaculture water,and increased with the increase of the rotifer density.The highest concentrations were found in the 80 ind./mL group,which reached 5.84 mg/L,10.62 mg/L,and 2.61 mg/L on the 13th,23rd,and 10th day,respectively.On day 3,the highest value of vibrio appeared in the40ind./mL group,reaching 1.2×10~4 cfu/mL.The results showed that the addition of Brachionus plicatilis in the aquaculture water of Litopenaeus vannamei could increase the water quality indexes.The survival rate of 10ind./mL,20 ind./mL and 40 ind./mL in aquaculture water was higher but not significant.The weight gain rate of 40 ind./mL group was the highest,significantly higher than that of 0 ind./mL,5 ind./mL,10 ind./mL group,and the weight gain rate of 20 ind./mL,40 ind mL,80 ind./mL group was significantly higher than that of control group.The results showed that the addition of Brachionus plicatilis to the aquaculture water of Litopenaeus vannamei could increase the weight gain rate and the survival rate of Litopenaeus vannamei.The digestive enzyme and nonspecific immune enzyme 5 ind./mL of Brachionus plicatilis in aquaculture water had no significant difference from the control group,but the other groups were significantly higher than the control group.The results showed that the activities of digestive enzymes and non-specific immune enzymes of Litopenaeus vannamei increased when Brachionus plicatilis were added to the aquaculture water.There was no significant difference in unsaturated fatty acids between the experimental group and the control group when Brachionus plicatilis were added to the aquaculture water.The results showed that the addition of Brachionus plicatilis in the aquaculture water of Litopenaeus vannamei did not cause the increase of unsaturated fatty acids in the aquaculture water of Litopenaeus vannamei.Based on the above experimental results,it is recommended that the suitable density of the Brachionus plicatilis of the larvae of the prawn is 10~20 ind./mL.