Preliminary Study On Pond Juanyang Technology Of Monopterus Albus

Cage culture has always been the main method for raising ricefield eel（Monopterus albus）,but it has led to many problems such as the inability to remove waste,deterioration of water quality inside the cage,and frequent occurrence of diseases,which have hindered the healthy development of ricefield eel farming.Therefore,it is necessary to explore new models for healthy ricefield eel farming.The Juanyang mode,as a new type of intensive and circular water farming model,has innovatively improved the sewage discharge rate and the solid waste discharge rate can reach 90%to 95%.The comprehensive benefits of ecology,economy,and society have been greatly improved.This study explored the effects of suitable density and hiding structures on ricefield eel pond culture,with the aim of providing basic data for establishing a new ricefield eel pond culture model.Wild ricefield eels with consistent specifications were selected as the research objects,with an average initial body weight of 23.52±2.96 g and an average initial body length of30.30±1.90 cm.Three density gradients were set up:the low-density group（LSD）with 850tails/circle（1.59 kg/m²）,the medium-density group（MSD）with 1700 tails/circle（3.18kg/m²）,and the high-density group（HSD）with 2550 tails/circle（4.77 kg/m²）.Each gradient had three replicates,with the hollow lotus grass（Alternanthera philoxeroides）as the hiding structure.In addition,two different hiding structure groups were set up:the artificial ricefield eel nest group（FND）and the hollow lotus grass group（WPD）,each with three replicates,with a stocking density of 1.59 kg/m².The experimental period was 90days,during which the growth index,blood biochemistry,antioxidant and non-specific immune index of the ricefield eels,as well as the physical and chemical indicators of the water were measured continuously.The results of the study are as follows:1.The effect of cage density on the growth performance,physiological function,and pond water quality of ricefield eels（1）Under different stocking densities,the average final body weights for LSD,MSD,and HSD groups were 69.39±4.49 g,60.48±4.32 g,and 52.45±2.81 g,respectively.Throughout the rearing period,the final body weight,weight gain rate（WG）,and specific growth rate（SGR）of ricefield eels decreased significantly with the increase of cage density（P<0.05）.The survival rate showed no significant difference among the different densities（P>0.05）.After 45 days,the feed intake rate（FR）and feed conversion ratio（FCR）of the HSD group were significantly higher than those of the LSD group（P<0.05）.At 90 days,the condition factor（CF）of the LSD group was significantly higher than that of the HSD group（P<0.05）,but there was no significant difference in the visceral index（VSI）and hepatic index（HSI）among the different densities（P>0.05）.（2）Cage density had no significant effect on the serum Glucose（Glu）and total protein（TP）levels of ricefield eels（P>0.05）.In the later stage of rearing,the total cholesterol（T-CHO）and alkaline phosphatase（ALP）levels in the serum of ricefield eels increased with the increase of cage density（P<0.05）,while the triglyceride（TG）,albumin（Alb）,and aspartate aminotransferase（AST）levels in the serum were significantly higher in the HSD group than in the low-density group（P<0.05）.For the antioxidant and non-specific immune performance of ricefield eels,the malondialdehyde（MDA）content in the serum of the HSD group was significantly higher than that of the LSD group（P<0.05）,while the activities of catalase（CAT）,superoxide dismutase（SOD）,and lysozyme（LZM）were significantly lower than those of the LSD group（P<0.05）.（3）Under stocking conditions,the temperature of the outer pond water changed faster than that inside the circle,and the p H and dissolved oxygen（DO）levels were much higher than those inside the circle.There were no significant differences in temperature（T）and dissolved oxygen（DO）among the density groups（P>0.05）,but the p H decreased with increasing stocking density,and there were significant differences at multiple time points.The physicochemical indicators of water quality,such as ammonia nitrogen（NH₄⁺-N）,nitrite nitrogen（NO₂^--N）,and nitrate nitrogen（NO₃^--N）,increased with increasing stocking density,and there we re significant differences between the HSD and LSD groups（P<0.05）.2.The effect of hiding structures on the growth performance,physiological function,and pond water quality of ricefield eels（1）During the stocking phase（0～15 days）,the survival rate of the FND group was significantly lower than that of the WPD group（P<0.05）,but during the rearing phase（15～90 days）,the survival rate of the WPD group was lower than that of the FND group.At different hiding structures,the final density of the FND and WPD groups was 2.90±0.6kg/m² and 2.93±0.7 kg/m²,respectively.Throughout the rearing period,there was no significant difference in the final body weight and length,as well as WG and SGR between the FND and WPD groups（P>0.05）.During the 15～60 days period,the FR of the FND group was higher than that of the WPD group,but there was no significant difference in FCR（P>0.05）.There was no significant difference in VSI and HSI between the two groups（P>0.05）.（2）In the cage culture system,at 45 days,the GLU content in the serum of the FND group was significantly higher than that of the WPD group（P<0.05）,but there was no significant difference at 90 days（P>0.05）.There was no significant difference in the serum levels of TP,T-CHO,ALP,TG,Alb,and AST between the two groups with different hiding structures（P>0.05）,and there was no significant effect on the antioxidant and non-specific immune performance of ricefield eels（P>0.05）.（3）At different hiding structures,there was little difference in water temperature between the two groups.The p H and DO in the water of the FND group were higher than those of the WPD group,and the difference was significant at multiple time points（P<0.05）.The NH₄⁺-N and NO₂^--N levels in the water of the WPD group were significantly lower than those of the FND group（P<0.05）,but the NO₃^--N level was significantly higher.In summary,the HSD group of ricefield eels showed physiological dysfunction and inhibited growth performance,with a significant increase in toxic substances such as NH₄⁺-N and NO₂^--N in the water,but the economic benefits were significantly higher than those of the LSD group.Using hollow lotus plants and artificial ricefield eel nests as hiding structures resulted in similar aquaculture performance,but hollow lotus plants can absorb harmful substances such as NH₄⁺-N and NO₂^--N in the water and are inexpensive and readily available,which is beneficial for water purification.Considering the growth performance,economic benefits,and ecological benefits of ricefield eel farming,it is recommended to control the stocking density between the LSD and MSD groups,with a density of 1100～1300 tails/cage.Preferentially choose hollow lotus plants as the hiding structures.