| In recent years,with the increase of human production activities,the pressure of offshore ocean is gradually increasing and the phenomenon of seawater eutrophication is becoming more and more serious.Every year,shellfish farmers in northern China face the problem of large algae infestor,which affects the growth of shellfish.The elimination of drugs and artificial fishing cost manpower and material resources,and the plant protein in natural bait can not be fully utilized,which restricts the healthy development of shellfish breeding industry.In this situation,we need to combine the traditional breeding mode with science to open up a new,green and low-carbon ecological breeding mode.The multi-nutrient level comprehensive cultivation mode can make full use of the matter and energy of the aquaculture waters,the ecological mutual benefit between organisms and the capacity of the aquaculture waters for the aquaculture organisms.Therefore,this topic uses the feeding characteristics of Siganus guttatus and Meretrix meretrix to mix them,realizing the efficient utilization of materials and improving the economic output of the system.Siganus guttatus is a marine omnivorous fish,which mainly feeds on large algae.It is considered to be an excellent variety of aquaculture.It has the reputation of"scavenger" in the sea,which meets the needs of the development of current healthy ecological aquaculture model.Aquaculture density can significantly affect the quality of aquatic products,which is of great significance to aquatic product quality.By conducting some Siganus guttatus and M.meretrix collection experiment,the energy flow within the farming system tracking measurement,and analysis of fish growth,muscle quality and lead to different quality molecular regulation pathway.It is concluded that appropriate collection density,It makes energy and nutrients fully using or recycling,reducing the breeding of nutrition and economic loss,improving biological breeding system capacity,inhibiting algal blooms in the breeding,reducing the risk of these diseases,and guaranting the quality and safety of aquatic products,creating the biggest ecological benefit in per unit area.The stable ecological culture system of Siganus guttatus-Entermorpha prolifera-M.meretrix was preliminarily constructed.1.Preliminary study on the indoor mixed culture mode of Siganus guttatus and M.meretrixIn order to explore the effects of fish density on the growth and muscle,this experiment conducted a preliminary study on the mixed of Siganus guttatus and M.meretrix.The density of Siganus guttatus at the set point was 10 ind·m-3(T1),30 ind·m-3(T2),50 ind·m-3(T3),70 ind·m-3(T4)mixed with M.meretrix.The experiment lasted 56 days.The growth results are as follows:(1)Siganus guttatus:the final body weight and weight gain rate of Siganus guttatus in T1 are significantly higher than T4 group(P<0.05).The specific growth rate and feed rate of T1 were the highest,and the feed conversion ratio was significantly lower than that of the other three groups(P<0.05).There was no significant difference between T1 and T2 groups of viseraosomatic index(P>0.05).(2)M.meretrix:there were no significant differences in survival,final body weight and weight gain rate among all groups.The results of Muscle nutrition are as follows:(1)Siganus guttatus:the total amino acid mass fraction of Siganus guttatus in T3 and T4 was significantly higher than that in T1 and T2(P<0.05).Lysine was higher than other essential amino acids in each group and EAAI was the highest in T3 group,which group significantly increased the content of essential amino acids in muscle,especially Asp,Glu,Arg and Lys.(2)M.meretrix:the total amino acid mass fraction in T2 was significantly higher than that in T1,T3 and T4(P<0.05).With the increase of culture density of Siganus guttatus,the contents of all essential amino acids increased firstly and then decreased.The mass fraction of Leu in each group was higher than that of other essential amino acids.The lowest amino acid score was Val in all groups.The contents of Asp,Glu,Ala,Arg and Lys in T2 group were the highest.The results showed that stocking density of 50 ind·m-3 significantly increased the content of essential amino acids in muscle of Siganus guttatus,and the muscle amino acid composition of this group had better balance.For the M.meretrix,at 30 ind·m-3,the essential amino acid composition of muscle was better than that of other groups,and the balance of amino acid composition and protein quality were the best.2.Study on material utilization in mixed culture of Siganus guttatus and M.meretrixIn order to understand the material utilization of Enteromorpha prolifera in the mixed culture system of Siganus guttatus and M.meretrix,the nutrients in the mixed culture system of Siganus guttatus and M.meretrix were tracked and determined by marker method,and the apparent digestibility of various nutrients in the mixed culture system of Siganus guttatus and M.meretrix was measured.The results showed that the apparent digestibility of crude protein was 66.64%,and crude fat was 60.48%.The apparent digestibility of serine was the lowest,which was 60.19%,and the apparent digestibility of other amino acids was above 60%.The analysis of marker content showed that after ingestion of Enteromorpha prolifera,more than 60%nutrients were absorbed and utilized for their own growth and metabolism,and 12.5%of the excreta of the M.meretrix were used for their own biosynthesis.The results showed that the two species were at different nutritional levels,and the mixed culture of the two species could make full use of energy and nutrients,transforming the excess nutrients in the system into the aquaculture organisms,making full use of bait,improving the aquaculture capacity,and realizing the recycling of substances in the aquaculture system.3.Transcriptome analysis of Siganus guttatus and M meretrix under different density of Siganus guttatusIn order to explore the response of Siganus guttatus and M.meretrix muscle at the molecular level under different culture conditions and obtain the important signal pathways,there are four different densities of Siganus guttatus in this study:F1(10 ind·m-3),F2(30 ind·m-3)and F3(50 ind·m-3).After 56 days of mixed culture with M.meretrix,the different genes of Siganus guttatus and M.meretrix muscle transcriptome were compared and analyzed.(1)Siganus guttatus:the results of GO function enrichment show that the muscles of the three groups of Siganus gultatus are partially coincide in the three functional categories.AMPK signaling pathway and ubiquitin-mediated protein degradation signaling pathway play an important role in muscle quality regulation of Siganus guttatus.When culture density increased,protein degradation related genes were up-regulated and ubiquitin-mediated protein degradation process was activated.(2)M.meretrix:Nitrogen metabolism and various amino acids metabolism play an important role in muscle quality.The expression levels of GDH and CA in 30 ind·m-3 group were significantly lower than those in 10 ind·m-3 group,while the expression levels of GS and NR were significantly higher than those in 50 ind·m-3 group,but there was no significant difference between 30 ind·m-3 and 50 ind·m-3 group.High density mixed culture of Siganus guttatus enhanced the ability of the M.meretrix to obtain nitrate from the outside.The increase of GS expression increased glutamic acid content and enhanced the taste of M.meretrix.The results showed that the mixed culture density had a great influence on the molecular regulation mechanism of muscle quality.The AMPK signaling pathway and ubiquitin-mediated protein degradation pathway play a key role in the Siganus guttatus,and the nitrogen metabolism pathway plays an important role in the M.meretrix,regulating the amino acid composition of muscle,and then affecting muscle quality. |
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