Effects Of Hypoxia And Hyperoxia On The Morphological Changes Of Gill And Enzyme Activity Of Tissues In The New Strain F₅ Of Megalobrama Amblycephala

Blunt snout bream?Megalobrama amblycephala?,also known as wuchang fish,is an excellent freshwater economic fish in aquaculture in China because of the wide range of food,low breeding cost,delicious meat quality and other good quality by the promotion.However,the dissolved oxygen in the water fluctuates greatly under the influence of sediment,algae,plankton and stocking density.When the concentration of dissolved oxygen is low,the fish's food intake decreases,the growth rate slows down,and the disease resistance decreases.When the dissolved oxygen is too saturated,it can also cause fish oxygen poisoning and even death.The change of dissolved oxygen will directly change the oxygen transport in the blood,break the oxidative balance in the body,lead to changes in the morphology of fish tissues,and make fish make stress adaptation strategies.Nowadays,the researches on the effect of dissolved oxygen change on Megalobrama amblycephala mainly focuse on the hypoxic response mechanism.However,there are few studies on hyperoxia,and the physiological activity and response mechanism of Megalobrama megalobrama under hyperoxia are still unknown.In this study,the new strain F₅of Megalobrama amblycephala was used as the research object.After being treated with low oxygen?DO:1.7±0.2 mg/L?and high oxygen?DO:19.3±0.5 mg/L?for 0,4,7 days and normal oxygen?DO:7.8±0.3 mg/L?for 7 days,respectively.Firstly,paraffin sections and microscopic observations were made on the gill tissues of the new strain F₅ of Megalobrama amblycephala.Blood smears were also made and the number of red blood cells in the blood was recorded.To study the effects of different concentrations of dissolved oxygen on the enzyme activities of tissues of the new strain F₅ of Megalobrama amblycephala.Antioxidant related enzymes:Malondialdehyde?MDA?content,Catalase?CAT?activity and respiratory related enzymes:Succinate dehydrogenase?SDH?and Lactate dehydrogenase?LDH?activity in four tissues of gill,hepatopancreas,intestine and muscle were determined by the kit.The results showed that the red blood cell number increased by 26.92%at 4 days with hypoxia and by 45.51%at 7 days with hypoxia compared with that at normoxia.After 4 and 7 days of hyperoxia,the red blood cell number decreased by 15.92%and22.93%compared with that at normoxia,respectively,After the recovery of normoxia,the red blood cell numbers recovered,but there was still a significant difference from before treatment?P<0.05?.Gills are the expiratory organs of fish.Gill lamellae have significant effects on respiration,ammonia-nitrogen balance and acid-base balance.Under low oxygen stress,the exposed area of gill lamellae of Megalobrama amblycephala increased,and they extended outward to absorb more oxygen.When the dissolved oxygen returned to normal,the gill filaments of Megalobrama amblycephala began to reshape,and the morphology gradually recovered.The results of paraffin section showed that with the increase of hypoxic treatment time,the interlamellar cell mass of the new strain F₅ gill filament decreased.The average intervals of gill lamella widened and increased by 127.96%and 156.27%at 4 and 7 days of hypoxia compared with that at normoxia.Similarly,the length of gill lamella was more outward-extending,and increased by 13.97%and 22.26%,respectively,after hypoxia 4 and 7 days compared with that of normoxia.In addition,the breadth of gill lamella decreased by38.30%after 4 days of hypoxia compared with that of normoxia and 27.99%after 7days of hypoxia compared with 4 days of hypoxia.After a week of normal oxygen recovery,the gill tissue of the new strain F₅ of Megalobrama amblycephala was basically restored to its normal shape,and all data recovered,but there was also a significant difference?P<0.05?.Under high oxygen stress,the interlamellar cell mass of the new strain F₅ increased.The average intervals of gill lamella decreased by 13.65%and 40.42%at 4 and 7 days of hypoxia compared with that at normoxia,respectively.The breadth of gill lamella also increased gradually under the condition of high oxygen,and increased by 25.32%and 40.57%after 4 and 7 days respectively compared with that under normal oxygen.After 4 days of hyperoxia treatment,the length of gill slices decreased by 22.76%compared with that of normoxia and 23.52%after 7 days of hyperoxia compared with 4 days of hyperoxia.After feeding normal dissolved oxygen for a week for recovery,the gill tissue morphology recovered and all data recovered,but there was also a significant difference?P<0.05?.There was no significant difference between the length of gill slices and that before treatment?P>0.05?.The results of enzyme activity test showed that:Under the condition of low oxygen,CAT activity decreased first and then increased in gill tissue and hepatopancreas.It went down in the intestines and then went up;and it rose sharply in the muscles and then fell.MDA content in gill tissue decreased continuously.It continued to rise in the hepatopancreas;In the intestines,it first decreased and then increased.It rose and then fell in the muscle.The data of the two groups varied irregularly and there were significant differences between the data of the two groups?P<0.05?.The activity of LDH increased significantly in all tissues.The activity of SDH continued to decrease with time.The values of LDH and SDH at 7 days of hypoxia were significantly different from those in the normal group?P<0.05?,after a week of normal-oxygen recovery,it recovered in all tissues,but there was still a significant difference from the pre-treatment level?P<0.05?.With the increase of hyperoxia stress time,CAT activity continued to decrease in both gill and intestines tissues.It continued to rise in the hepatopancreas;In the muscle it rose and then fell.MDA content first decreased and then increased in gill tissue.It continued to rise in the hepatopancreas;It went down in the intestines;It went down first and then up in the muscles.CAT activity and MDA content varied irregularly and there were significant differences between each group?P<0.05?.LDH activity continued to decrease with the treatment time.SDH activity in all tissues continued to increase.The values of LDH and SDH at 7 days of treatment were significantly different from normal values?P<0.05?,and after a week of recovery from normal oxygen,different enzyme activities recovered in all tissues,but there was still a significant difference from the pre-treatment level?P<0.05?.In summary,the growth activity of the new strain F₅ of Megalobrama amblycephala was promoted by proper hyperoxia.The concentration of dissolved oxygen in water significantly affected the growth,survival,immunity and metabolism of the new strain F₅ of Megalobrama amblycephala.This study provided basic data for the effects of dissolved oxygen on the gill tissues and enzyme activities of various tissues of Megalobrama amblycephala.It also laid a foundation for breeding and breeding of new strain F₅ of Megalobrama amblycephala.