Trapping Effect Of Artificial Reef On Fish And Its Application Effect In Nansi Lake

An artificial reef usually refers to an artificial structure that is put into a predetermined target water area to gather fish and other aquatic organisms.The principle of its function is based on the tendency of aquatic organisms such as fish and the effects of flow field,bait and enemy avoidance after the artificial reef is placed,and finally a habitat suitable for fish survival is formed.At present,the research on artificial reefs is mostly concentrated in the marine field or aimed at marine organisms,and there is a lack of research on artificial reefs for freshwater fish and artificial reefs for freshwater lakes.In this study,Culter alburnus,Carassius auratus,Megalobrama amblycephala and Aristichthys nobilis were taken as indoor reef models.Through experiments,the differences in the trapping effect of five different artificial reef models on different fish were compared,and it was found that the artificial reef models had good trapping effect.In the analysis of the application effect of artificial fish reef in Nansi Lake,the water quality and fish community structure of artificial fish reef in Nansi Lake were investigated in October and December of 2021 and July,August and September of 2022,and the water environment quality was evaluated.At the same time,from the aspects of fish species,diversity,dominant species and unit effort catch（CPUE）,the differences of fish resources between artificial reefs with different materials and control areas were compared and analyzed,so as to evaluate the conservation effect of fishery resources after artificial reefs were put into use,and provide reference for the construction and research of artificial reefs in the fresh water field in the future.The main results are as follows:1.In the indoor artificial reef simulation test,the average distribution rate of Culter alburnus,Carassius auratus,Megalobrama amblycephala and Aristichthys nobilis in the control group without artificial reef model and the average distribution rate after five artificial reef models were placed were different in different degrees.After the artificial reef was placed,the average distribution rate of four kinds of fish in the artificial reef model was:Carassius auratus>Megalobrama amblycephala>Culter alburnus>Aristichthys nobilis,which attracted all the Culter alburnus,Carassius auratus and Megalobrama amblycephala,but had no obvious trapping effect on Aristichthys nobilis.2.All the five artificial reef models have certain trapping effects,but the trapping effects are different under the conditions of different artificial reef models.T1 and T2artificial reef models with channel design have advantages in passability and covering effect,so they have better trapping effect on experimental fish than other artificial reef models.3.The water quality test results show that the p H of the plastic artificial reef area in Nansi Lake is maintained at around 8.4,and the average dissolved oxygen in the alkaline water body is 9.57 mg/L,and the transparency varies from 0.24 m to 0.56 m;The p H in the cement reef area is also maintained at about 8.4,and the average dissolved oxygen in the alkaline water body is 9.51 mg/L,and the transparency varies from 0.26 m to 0.80 m..There is little difference in p H,dissolved oxygen and transparency index between the two reefs.In October,2021,the concentration of Chl.a among the three areas was significantly different（P<0.05）,and in September,2022,the concentration of Chl.a in the control area was significantly higher than that in the two reef areas（P<0.05）.In December 2021,the TN concentration in the cement reef area was significantly lower than that in the control area（P<0.05）,and in July and August 2022,the TN concentration in the plastic reef area was significantly lower than that in the control area（P<0.05）.There was no significant difference in the concentration of COD_Mn among control area,plastic reef area and cement reef area（P>0.05）.The water quality evaluation shows that the water environment quality of the two artificial reefs has reached the Class III water standard and both are in a slightly eutrophic state,indicating that the artificial reefs have improved the water quality to some extent.4.The investigation results of fish resources show that the number of fish species in the cement reef area is 1.5 times that of the control area,and the catch weight and mantissa are 2.5 times and 1.9 times that of the control area respectively;The number of fish species in the plastic reef area is 1.7 times that in the control area,and the catch weight and mantissa are 2.1 times and 1.4 times that in the control area respectively.Compared with the two reefs,the catch weight and mantissa in the cement reef area are 1.2 times and 1.4 times that in the plastic reef area,respectively.The fish in the two artificial reefs include all the fish in the control area,and most of the newly added fish in the two artificial reefs belong to freshwater sedentary fish.There are differences in fish diversity index and richness index in different investigation months.In December 2021 and September 2022,the diversity index and richness index of two artificial reefs reached a high level.According to the data of dominant species and unit effort catch（CPUE）,the results showed that the dominant species in the two artificial reefs were more than those in the control area,and the artificial reefs included all the dominant species in the control area.The average CPUE of fish in cement reef area is 2.5 times that of the control area,and that in plastic reef area is 2.1 times that of the control area,which shows that artificial reef area in Nansi Lake has the effect of attracting fish.Based on the above results,the following conclusions are drawn:The main results are as follows:（1）In the indoor simulation experiment,the effect of artificial reef model is:Carassius auratus>Megalobrama amblycephala>Culter alburnus>Aristichthys nobilis,which is related to the differences of feeding habits,living habits and self-behavior habits of four kinds of fish.（2）Different artificial reef models have different trapping effects on fish,and T1 and T2 artificial reef models with channel design have better trapping effects.（3）After artificial reefs were put into Nansi Lake,the water environment quality and comprehensive nutritional status of plastic reefs and cement reefs were improved to some extent.（4）Compared with the control area,the fish species in the plastic reef area and the cement reef area increased,and the fish community diversity was further enriched,and the effect of attracting fish in the cement reef area was better than that in the plastic reef area.Both artificial reefs made of different materials had the effect of conserving fishery resources,which was helpful for the construction and research of artificial reefs in more fresh water fields in the future.