Construction And Optimization Of The Rearing Ecosystem Of Symphysodon Haraldi

The Symphysodon haraldi are increasingly sought after by aquarium enthusiasts due to their colorful body,intricate patterns,disc-shaped body,and unique parent care behavior.They are commonly known as the"king of aquarium fish"and are a type of ornamental fish with high ornamental and economic value.During the breeding process,the fish is typically fed with a soft feed made from a variety of ingredients such as beef heart,shrimp meat,and clam meat,mixed with vitamins and minerals premix,commonly named as"beef heart burgers".To reduce raw material costs,some producers have also used duck hearts to substitute beef hearts to prepare"duck heart burgers".However,a common feature of these feeds is high protein content,which can easily dissolve and be decomposed into water,thus affecting the quality of the water environment.Therefore,frequent water changes are required to maintain a stable breeding water environment during the breeding process.However,frequent water changes can result in the waste of water resources,and if the discharged aquaculture wastewater is not treated,it can cause serious pollution and damage to the surrounding environment.Based on this,the study aims to find the appropriate water change frequency for breeding discus fish as the starting point and explore the growth of discus fish and the changes in water nutrient substances during the breeding process.This can help to develop suitable water change strategies and improve the utilization efficiency of water resources.Additionally,three water-cultivated plants are analyzed for their ability to purify aquaculture wastewater,to select suitable plants for purifying the wastewater from breeding discus fish.Finally,a fish-vegetable symbiotic system is constructed using the selected plants and discus fish as the breeding objects.The study investigates the impact of different flow rates on water quality,fish growth,and plant growth,providing a scientific basis and theoretical reference for the construction and optimization of the discus fish breeding system.1.The effect of water exchange frequency on water quality and growth of discus fishThree water exchange frequencies（WEF1,WEF2,and WEF3,which means changing the water once a day,once every two days,and once every three days,respectively）were set up in this experiment,and continuously monitored the changes in water quality parameters（NO₃^--N、NO₂^--N、TAN、TN、SRP and TP）during the cultivation of discus fish.The growth of the fish was analyzed before and after the experiment.The results of the experiment are as follows:（1）Different water exchange frequencies did not have a significant effect on water temperature and dissolved oxygen（DO）levels in the aquaculture water.However,they did have a significant impact on the p H and electrical conductivity（EC）of the water.When the water exchange volume was consistent,the p H of the aquaculture water increased with increasing water exchange frequency,while the EC of the aquaculture water decreased with increasing water exchange frequency.（2）The concentration of NO₃^--N and TN in the WEF1 group was significantly lower than that in the other groups with different water exchange frequencies,while there was no significant difference in the concentration of other nitrogen and phosphorus compounds between the groups.（3）The weight gain rate and specific growth rate of discus fish increased with the increase of water exchange frequency.The body length growth rate and feed coefficient of discus fish decreased with the increase of water exchange frequency,but the differences between different water exchange frequency groups were not significant.In summary,increasing the water exchange frequency appropriately can effectively remove nitrate and total nitrogen from the aquaculture water,stabilize the p H value of the aquaculture water and reduce the EC of the water.This is beneficial for maintaining a suitable water environment for the cultivation of discus fish.However,the water exchange frequency has no significant effect on the growth of discus fish.Based on the comprehensive analysis of water quality changes,fish growth,and water resource utilization,the frequency of exchanging water every 2days is recommended for the cultivation of discus fish under experimental conditions.2.The treatment effect of different plants on wastewater from the cultivation of discus fish.In this experiment,three hydroponic plants,lettuce,gynura bicolor,and water spinach,were used to purify the tailwater of discus fish farming based on a predetermined water exchange frequency.The removal efficiency of nitrogen and phosphorus nutrients（NO₃^--N、NO₂^--N、TAN、TN、SRP and TP）of the tailwater by the three plants was regularly monitored in the short and long term.The changes in the fresh weight and plant height of the three hydroponic plants before and after the experiment were analyzed and compared to select suitable plant species for treating the tailwater of discus fish farming.The experimental results are as follows:（1）In the static short-term experiment,except for no significant difference in water temperature among the groups,there were significant differences in p H,DO,and EC among the different plant groups.Among them,the p H value and DO level of the lettuce group were the highest,and the EC of the gynura bicolor group had the smallest value.（2）In the static short-term experiment,the three plants showed certain removal effects on N and P contents in the tailwater of the discus fish,with lettuce showing the best removal effect on NO₃^--N,NO₂^--N,TN,and SRP.gynura bicolor showed the best removal effect on TAN and TP.Water spinach showed a poor removal effect on various nitrogen and phosphorus compounds in the tailwater of the discus fish.Except for NO₃^--N,NO₂^--N,SRP,and TP,the removal effect of lettuce,gynura bicolor,and water spinach on TAN and TN after 48 hours was significantly better than that after72 hours.（3）In cyclic water exchange conditions,the removal rates of various nitrogen and phosphorus compounds in the discus fish culture tailwater by lettuce,gynura bicolor,and water spinach ranged from 12.17%to 16.29%for NO₃^--N,43.55%to 69.93%for NO₂^--N,42.24%to 58.22%for TAN,6.47%to 8.66%for TN,9.88%to 10.83%for SRP,and 5.64%to 10.95%for TP.Among the three tested plants,the lettuce had the best removal effect on TAN,SRP,and TP,gynura bicolor had the best removal effect on NO₂^--N and water spinach showed strong removal effects on NO₃^--N and TN.（4）In the experiment,the lettuce showed a bolting phenomenon,with significant growth of stems and yellowing and wilting of old leaves.The growth of gynura bicolor seedlings was slow.Water spinach had the best adaptability and the best growth.At the end of the experiment,the three hydroponic plants,lettuce,gynura bicolor,and water spinach,had a relative increase in fresh weight of 73%,9.06%,and 230%,respectively,with water spinach producing the highest yield.In conclusion,lettuce,gynura bicolor,and water spinach all have a certain effect on removing nutrients from the tailwater of the discus fish aquaculture.Among them,water spinach can effectively purify the water while providing the largest plant harvest,resulting in the highest additional economic benefits.Therefore,among the three tested plants,water spinach is more suitable for use in the treatment of discus fish aquaculture tailwater.3.The impact of flow rate on water quality,fish,and plant growth in aquaponic systems.A fish-plant symbiotic system was constructed with the selected plants and discus fish as the species for cultivation in experiment 2.Different flow rates（0.8,1.6,and 2.4 L/min）were set,and the NO₃^--N、NO₂^--N、TAN、TN、SRP,and TP contents of the aquaculture water were measured regularly.The growth changes of discus fish and plants before and after the experiment were analyzed and compared to reveal the effects of flow rate on water quality,fish,and plant growth in the fish-plant symbiotic system.The results of the experiment are as follows:（1）During the experiment,the water temperature of the aquaculture system ranged from 26.2 to 27.9℃,p H values ranged from 6.58 to 8.30,DO levels ranged from 5.50 to 8.50 mg/L,and EC ranged from 535 to 615μS/cm.These conditions were able to meet the growth and development requirements of both the discus fish and water spinach.（2）The flow rate has a significant impact on the DO level in the aquaponic system.The average DO level in the medium and high flow rate groups was significantly higher than that in the low flow rate group.（3）Different flow rates have a certain effect on the removal of nutrients in the water for raising the discus fish.The removal rates of various nitrogen and phosphorus compounds in the system are NO₃^--N（33.76～37.50%）,NO₂^--N（52.94～70.83%）,TAN（84.85～89.74%）,TN（8.12～23.39%）,SRP（20.42～34.12%）,and TP（17.65～29.27%）.The removal effect of NO₃^--N is the best at 1.6 mg/L,and the removal rate of NO₂^--N is negatively correlated with the flow rate.In the later stage of the experiment,the concentrations of NO₃^--N,NO₂^--N,and TAN in the water for each group can be stable at a low level.（4）The specific growth rate of the discus fish and the growth rate of water spinach increased with the increase of flow rate.The feed coefficient of the discus fish decreased with the increase of flow rate,but the differences between groups were not significant.In summary,different flow rates have a certain effect on the removal of nutrients in the water of the culture system for the discus fish.After the experiment,the concentrations of harmful substances such as NO₂^--N and TAN in the water can be controlled at a low level.Different flow rates have no significant effect on the growth rates of fish and vegetables.Considering that high flow rates can significantly improve the DO level in the culture water and promote the healthy growth of fish,it is more positive to set a higher flow rate.However,considering the cost of production,a flow rate of 1.6 L/min is more suitable for the fish-vegetable symbiotic system using water spinach and discus fish as the cultured species.