| The disadvantages of using organic fertilizer in the traditional freshwater pearl mussel culture in China are becoming more and more obvious.For achieving sustainable green culture,a new type of culture model is needed to replace the traditional culture.China's aquaculture industrialization model is becoming more and more mature,becoming a possibility of modern culture of freshwater pearl mussels.Freshwater pearl mussel factory culture can effectively reduce the discharge of tail water from pearl mussel culture industry.Another important point is that it can improve the quality of breeds and cultivate high-quality pearls.Hyriopsis cumingii is the main culture target of freshwater pearl mussel in China.This article drew on the existing factory culture model and constructed a set of factory-circulated aquaculture system for H.cumingii and then studied the physiological metabolism and feeding rhythm of H.cumingii,which also studied the effect of supplementary feeding of?-carotene on the growth and inner shell color of H.cumingii,and optimized the feeding technology of bait.The main research contents were as follows:1.Construction of H.cumingii factory culture systemBased on the biological characteristics of H.cumingii,a set of industrial circulating aquaculture systems for H.cumingii was constructed.The system includes5 modules,which are squirrel aquaculture,aquaculture water allocation and supply,algae cultivation and supply,water quality monitoring,and aquaculture tail water treatment.At the same time,it also designed a freshwater pearl aseptic plant.The culture facilities mainly included culture ponds and culture workshops.The culture pond was equipped with a multi-layered delta mussel culture rack and an aeration system.The air temperature was adjusted by the air pump in the culture workshop,and the light was adjusted by opening and closing the top curtain.The temperature control module used solar energy as the heat source,and was equipped with a pool to regulate and control the water temperature.The algae cultivation module included three modes,which were three-level expansion of specialized algae cultivation,algae cultivation in the outer pond and algae production in the cultivation pond.The water quality monitoring module adopted the Internet of Things technology to realize remote dynamic monitoring of indicators such as dissolved oxygen,p H,temperature and water turbidity.The culture tail water treatment module included solid-liquid separation physical filtration and nitrate bacteria chemical treatment system.In summary,China's first freshwater pearl mussel industrial culture system was built.The system started the first cultivation in April 2018,and the density per unit volume was 50 times that of the traditional model,reaching 90 mussels per cubic meter.The removal rate of COD and BOD in the culture tail water reached 80%,the removal of ammonia nitrogen reached90%,and the recycling rate of the culture tail water was more than 80%.The system extended the pearl cultivation period of mussels for 3 to 4 months every year.After two years of cultivation,the ratio of producing high-quality pearls reached 40%.2.Diurnal variation in oxygen consumption and ammonia excretion and feeding rhythm of freshwater mussel H.cumingii under different alga concentrationsHold 1-year-old freshwater mussel H.cumingii with body weight of 18.43±4.21g in 20L plastic buckets at water temperature of 27?for one week of relaying.Then diurnal variation in oxygen consumption rate and ammonia excretion rate of freshwater mussel were measured by indoor still water breathing method.The four initial feeding concentrations of chlorella sp were set to 1.9×109,3.25×109,4.11×109 and 5.05×109(cells·L-1),and then the daily feeding rhythm and food intake of freshwater mussel were measured.The results showed that the oxygen consumption rate and ammonia excretion rate of freshwater mussel presented two metabolic cycles per day.The first trough of metabolism appeared at 12:00 at noon,and then it gradually raised to 20:00 pm,which time was the first metabolic peak appeared.After that it gradually declined until the second metabolic trough appeared,which was between 0:00 and 2:00at night,and the second metabolic peak appeared at 4:00 am.It was found that there was significant diurnal variation in the oxygen consumption rate and ammonia excretion rate in freshwater mussel,significantly higher at night than those in daytime.In addition,it was observed that the daily food intake of freshwater mussel was affected by the concentration of bait feed,and the maximal daily total food intake was observed in freshwater mussel fed the alga at a concentration of 4.11×109(cell·L-1).The findings help to guide the culture management of feeding pattern of the freshwater mussel under industrial culture conditions.Based on the above studies,it was preliminarily determined that the feeding time for H.cumingii cultivation should be at8 pm and between 0 am to 2 am,and the optimal feeding concentration was between 4×109(cell·L-1)and 5×109(cell·L-1).3.Effects of?-carotene supplement in bait on inner shell color,tissue total carotenoids content and growth of different color strains in H.cumingiiPearl and nacre share a similar mechanism of formation.It has been found that there is a significant correlation between the color of pearl and that of nacre.In the study,three stains of H.cumingii,in purple,golden and white respectively,were examined.Experimental group and control group with supplementation of?-carotene were set up.After 90 days of cultivation,the color of nacre of the three stains of H.cumingii,total carotenoid content?TCC?of their organs,and their changes in growth were compared and analyzed.The results were as follows.When the purple H.cumingii was compared with the control group,its d E*value increases by 21.48%?P<0.05?,L*value decreases by 15.72%?P<0.05?,a*value increases from 0.48 to 2.67?P<0.05?and there was no significant change in b*value?P>0.05?.When the golden H.cumingii was compared with the control group,there was a*value increases from 0.07to 1.52?P<0.05?and b*value from 1.37 to 4.43?P<0.05?,and there was no significant change in d E*value and L*value?P>0.05?.For the white H.cumingii,there was no significant change in any of the parameters when compared with the control group?P>0.05?.The hepatopancreas TCCs of the experimental groups of the three color stains were greater than those of the control groups?P<0.05?.Compared to the control group,the TCCs of edge mantle in the purple and gold experimental groups were increased by 55.29%and 39.69%?P<0.05?respectively.For the white H.cumingii,there was no significant change in the TCCs of edge mantle when compared with the control group?P>0.05?.All the growth traits of the three color strains were larger than those of the control groups?P<0.05?.The results confirmed that supplementing?-carotene can enhance the color of nacre and growth of H.cumingii,providing a theoretical basis for optimizing pearl culture technology. |
PDF Full Text Request