Study On The Physiological Characteristics Of Two Kinds Of Loach And Their Hybrid At Different Salinities

Loach is highly sought after by consumers because of its good taste,good flavor,fast growth speed,strong adaptability to the environment,and both edible and medicinal values.As one of the important aquatic products in foreign trade export,China sells more than 4000 tons of loach to Japan,South Korea and other countries every year.In order to meet the expanding market demand,the scale of loach breeding continues to expand,and many subsequent problems continue to appear,such as the limited area of freshwater breeding,the aggravation of water pollution caused by industrial and agricultural production,the change of environmental factors of breeding water body under the mode of high-density breeding,and the frequent occurrence of fish diseases.Taking Taiwan loach（Paramisgurnus dabryanus）,local loach（Misgurnus anguillicaudatus）and their hybrid progeny populations as the experimental objects,this paper preliminarily identifies Taiwan loach,local loach and their hybrid progeny populations through the classification of external morphological characteristics,and analyzes their differences.96 h single factor indoor static experiment was used to study the acute toxicity of different salinity to loach,and the changes of respiratory metabolism,antioxidant enzymes and other related physiological indexes of Taiwan loach under different salinity were measured by setting different salinity gradients.This study is expected to provide theoretical support for the artificial cultivation of loach in saline and alkaline waters,and provide basic physiological data for the further study of the tolerance of loach to salinity.The main experimental contents and results are as follows:（1）By using the method of principal component analysis,the external morphological characteristics of Taiwan loach,local loach and their hybrid offspring were preliminarily identified,and their differences were analyzed.The results showed that the average body weight of hybrid loach,hybrid loach and Taiwan loach was 17.415±6.809 g<17.961±5.473 g<33.369±6.987 g;The average body length of hybrid loach（123.970±26.372 mm）<Taiwan loach（126.203±11.966 mm）<local loach（155.565±12.048 mm）.In the principal component analysis,the contribution rate of the first principal component is 73.46%;The contribution rate of the second principal component fish head factor was 21.844%.Mainly in the degree of body symmetry and head size,indicating that the three kinds of loach have good differentiation in morphological characteristics.（2）The tolerance limits of local loach,hybrid loach and Taiwan loach to salinity were investigated for the first time.It was found that the LC₅₀values of salinity to Taiwan loach experimental fish at 24 h,48 h,72 h and 96 h were 17.141,17.027,16.561 and 16.299respectively;The LC₅₀values of hybrid loach experimental fish were 17.610,17.159,16.688 and16.461 respectively;The LC₅₀values of experimental fish of local loach were 16.673,16.447,10.609 and 10.438 respectively;The corresponding safe concentration values（SC）are 4.887,5.040 and 4.801.Among them,the 24h LC₅₀value of hybrid loach is higher than that of Taiwan loach,hybrid loach and local loach in all time periods,that is,hybrid loach has higher tolerance to salinity,and hybrid loach has stronger adaptability to higher salinity environment.（3）The effects of salinity mutations（0,4,8 and 12）on ammonia excretion rate of local loach,hybrid offspring and Taiwan loach were studied.The ammonia excretion rate of experimental fish in salinity 4 group was higher than that in control group,salinity 8 group and salinity 12 group;The ammonia excretion rate of hybrid loach experimental fish in salinity 4group was higher than that in other groups;The ammonia excretion rate of experimental fish of Paramisgurnus anguillicaudatus in salinity 8 group was higher than that in other groups.The ammonia excretion rate of the three loaches was lower than that of the control group,salinity 4experimental fish and salinity 8 experimental fish,indicating that the higher salinity had an inhibitory effect on the ammonia excretion rate of the experimental fish.（4）The changes of related enzyme indexes in muscle tissue of adult Misgurnus anguillicaudatus under 12 stress modes of salinity stress were measured,and the effect of water salinity on its tolerance was obtained.On this basis,its adaptation mechanism to salinity was further analyzed.The adaptability of three loaches was compared.Samples were taken at different time points to determine the activity and content of superoxide dismutase（SOD）,hydrogen peroxide（H₂O₂）,catalase（CAT）and malondialdehyde（MDA）in muscle tissue.The results showed that in the salinity acclimation experiment,salinity had a significant effect on the activities of related antioxidant enzymes in the muscle tissue of Misgurnus anguillicaudatus（P<0.05）.In conclusion,within the salinity range of 12 in this experiment,the three loaches are more sensitive to the change of water salinity,show strong salt tolerance and adaptability,and can quickly adapt to the salinity of surrounding water within 6 days.However,too high salinity will inhibit the body,and appropriately increasing the salinity of aquaculture water body is conducive to improve its survival rate and aquaculture yield.At the same time,it can promote the respiratory and metabolic rate of the body and activate the non-specific immune system and antioxidant system.Among them,hybrid loach showed stronger adaptability to salinity than local loach and Taiwan loach under salinity 12 stress.There are 9 figures,5 tables and 124 references in this thesis.