Effects Of Salinity On Gill Osmoregulation Of Juvenile Scatophagus Argus

This paper is divided into three parts:one is to study the effect of salinity change on the morphology and structure of gill mitochondria rich cells and its osmotic regulation mechanism;the other is to study the effect of different salinity on the morphology and structure of gill mitochondria rich cells and its osmotic regulation mechanism;the third is to study the effect of salinity on the Na⁺-K⁺-ATPase activity and Na⁺-K⁺-ATPaseβgene was analyzed.Objective to explore the osmoregulation of juvenile Scatophagus argus under acute and chronic salinity stress.1.Effects of abrupt salinity change on morphology and structure of mitochldria-rich cells in Scatophagus argusWith the sudden change of salinity,young fish can not adapt in a short time and produce acute stress response.Gill filaments and gill mitochondria are abundant and cells participate in osmotic regulation.In this paper,the morphological changes of mitochldria rich cells（MRCs）in gills of juvenile Scatophagus Argus were studied by means of microscope.The morphological changes of MRCs in gills of juvenile Scatophagus Argus were studied by means of microscope.The results showed that the long diameter and short diameter of MRCs were（9.517±1.390）μm and（7.150±1.448）μm significantly higher than those of the control（7.317±0.986）μm and（7.317±0.986）μm（P<0.05）,and the number of MRCs increased significantly at 6h.Two types of MRCs were differentiated:type Ⅰ MRCs,oval in shape with irregular nuclei,well-developed inner ridges and closed or open apical openings;type Ⅱ MRCs,round,with regular round nuclei and multiple apical openings.With different shapes of mitochondria,type a mitochondria were slightly stained,showing short and thick shape;type b mitochondria were more deeply stained and small granular.These results indicate that the juvenile of MRCs argenteus will produce a response mechanism through the changes of MRCs volume,quantity,shape and structure,and the shape and structure of mitochondria to maintain the stability of the internal environment.2.Effects of different salinities on the mechanism of gill osmoregulation in juvenile Scatophagus argusUnder different salinities,fish have two regulation modes:in freshwater environment,fish generally adopt the hypertonic regulation mode of"drainage and salt preservation";In the seawater environment,fish regulate by the way of"draining salt and keeping water".The structure of gill filaments and gill lamellae as well as mitochondria rich cells will change accordingly.The morphological changes of mitochondria rich cells（MRCs）in gills of juvenile goldfish（Scatophagus argus）were studied under different salinity（salinity gradient:0,5,10,30,35）and natural seawater（salinity 20）.Results:the diameter of secondary gill in salinity 5 group was（11.750±1.388）μm,and that in salinity10 experimental group was（92.050±9.408）μm,which were significantly larger than those in control group（P<0.05）In the low salinity environment,the gill lamellae was wide and long,which was conducive to the full contact between gills and the external water environment;the diameter of secondary gill pieces in high salinity group was（80.250±4.682）μm,which is significantly smaller than the control group（P<0.05）,which mainly increased the contact area volume with the external water environment through gill filament lengthening.There may be a transition type of type I with small opening,which can reduce water loss and has an important role in absorbing calcium ion(Ca²⁺).It is an ion absorbing type of mitochondria rich cells.The transition type of type I in salinity35 experimental group replaces type III MRCs under hypertonic condition.The number of MRCs in seawater increased from salinity 5 to salinity 30,and the number of type Ⅲ MRCs was the most in salinity 30 group.Therefore,type Ⅲ apical membrane opening was the main morphological type of seawater type MRCs.The results showed that:in low salt environment,the contact area between gill filaments and external environment was increased by changing the opening size of MRCs,widening of primary gills and growth of secondary gills;under high salt environment,the number of MRCs increased,the depression degree of apical membrane was significantly deepened,and the gill filaments widened to increase the contact area,so as to adapt to the external water environment Environmental change.3.The effect of salinity on Na⁺-K⁺-ATPase activity and Na⁺-K⁺-ATPaseβgene expression in Scatophagus argus gillsMarine fish have certain adaptability and tolerance to salinity changes,which can cause a variety of physiological and biochemical stress reactions.The changes of Na⁺-K⁺-ATPase activity and relative expression PCR（real-time quantitative）in gills of juvenile Scatophagus argus gills under different salinities were studied to explore its physiological,biochemical and molecular mechanisms of osmotic regulation.Observation results:the enzyme activity of salinity 5 and 35 groups increased within 12h at the beginning of operation,and reached the maximum at 24 h.The relative expression of Na⁺-K⁺-ATPase in salinity 5 and 35 groups showed the same trend with time,and reached the highest value at 48 h.The relative expression of Na⁺-K⁺-ATPase in different salinities was as follows:salinity 20>salinity 5>salinity 10>salinity 30>salinity 0>salinity 35.Except for the experimental group and freshwater,the relative expression of Na⁺-K⁺-ATPase decreased with the increase of salinity.The relative expression of Na⁺-K⁺-ATPase in salinity 20 was the highest,and that in high salinity group was significantly lower than that in fresh water group The relative expression in low salinity group（P<0.05）.The results showed that the changes under low salt stress were greater than that under high salt stress,that is,the ability of regulation and adaptation was stronger than that under high salt stress;Under different salinities,the expression in low salinity environment was better than that in high salinity environment,and salinities of 5-10 were more suitable for the desalination culture of juvenile goldfish.