不同盐度水平对金钱鱼幼鱼鳃线粒体丰富细胞结构的影响

Effects of different salinities on the structure of gill mitochondria-rich cells of juvenile Scatophagus argus

为研究盐度对金钱鱼(Scatophagus argus)幼鱼渗透调节的影响,将(6.31±0.25)g金钱鱼置于不同盐度(0、5、10、20、30、35)下养殖30 d,观察分析不同盐度下金钱鱼幼鱼鳃线粒体丰富细胞(mitochondria-rich cells,MRCs)形态结构的变化。结果显示:盐度5组次级鳃小片直径(11.750±1.388)μm,盐度10组初级鳃小片直径(92.050±9.408)μm,盐度35组初级鳃小片直径(80.250±4.682)μm,与对照组相比差异显著(P<0.05)。MRCs顶膜开口分为:突起型(Ⅰ型)、凹陷型(Ⅱ型)、深洞型(Ⅲ型),以及一种Ⅰ型的过渡类型。研究表明,金钱鱼幼鱼在不同盐度条件下MRCs均发生适应性的结构改变,有利于金钱鱼在不同盐度水体中生存,这种适应性结构变化与金钱鱼具有较强的盐度适应性密切相关。

Scatophagus Argus,also known as golden drum fish,belongs to Perciformes and is widely distributed in the Indo-Pacific waters.It is a widely salty subtropical bony fish and has strong adaptability in osmotic regulation.The change of water environment salinity will destroy the homeostasis of fish’s internal environment.Under the seawater environment with different salinities,gill mitochondria rich cells mainly play the role of ion absorption and ion secretion,secreting chloride ions(Cl^(-))to the outside under the condition of low permeability,and secreting and absorbing sodium ions(Na^(+))and potassium ions(K^(+))under the condition of high permeability.Its quantity and shape will change accordingly due to the change of external salinity,so as to adapt to the change of external water environment salinity and play an important role in fish osmotic pressure regulation.The experiment set the salinity gradient as 0,5,10,20,30 and 35.Taking the local natural seawater(salinity 20)as the control group,salinity 5,10,30 and 35 were prepared by adding different proportions of sea crystal to fresh water.Three juveniles were randomly selected from each water tank,dissected on the ice plate,and the gill filaments of the second gill arch on the left were collected.After calibrating the photos taken by the optical microscope with Imager proplus 6.0 software,the diameter of primary gill flakes and secondary gill flakes on the gill filaments of different groups of goldfish was measured,six groups of data at the same part were randomly measured,and then the average value was taken.The experimental data(SD±SEM)were recorded in SPSS 24.One way analysis of variance(ANOVA)was performed on the software,and Duncan multiple comparison method was used to test the difference between groups(P=0.05).The results were tabulated in Excel 2016 for analysis.Results showed that the mitochondria of juvenile Scatophagus argus were abundant in freshwater environment,and the diameter of primary gill flakes was(57.350±9.114)μm,significantly lower than that in the control group(75.367±8.429)μm(P<0.05),and the diameter of secondary gill lamella in salinity 5 group was(11.750±1.388)μm,significantly higher than that in the control group(7.817±1.298)μm(P<0.05),and the diameter of primary gill lamella in salinity 10 group was(92.050±9.408)μm,significantly higher than that in the control group(75.367±8.429)μm(P<0.05),indicating that in the low salinity environment,the gill filaments of Scatophagus Argus were wide,and the gill pieces were wide and long,which was conducive to the full contact between the gills and the external water environment.By absorbing inorganic ions in the water,the internal environment was stable and the contact area with the external water environment was greatly increased,so it was a freshwater adaptive structure.The diameter of secondary gill lamella in salinity 30 group was(6.830±1.405)μm,significantly lower than that in the control group(7.817±1.298)μm(P<0.05),but the gill filaments became slender.With the increase of salinity,the width of gill flakes gradually decreased,indicating that in the high salinity environment,Scatophagus Argus eliminated salt and absorbed water by shortening the spacing of secondary gill flakes and the change of gill filament structure,and the number of mitochondria rich cells also increased significantly.Under high salinity environment,the secondary gill flakes become slender,which was conducive to increasing the contact area with the outside world.The mitochondria were rich,the number of cells significantly increased,and the color was deeper,indicating that there were more mitochondria in the cells,so it is a seawater adaptive structure.With the increase of salinity,the degree of depression of apical membrane opening increased,and there were protrusion type(typeⅠ),depression type(typeⅡ)and deep hole type(typeⅢ).Different from other studies,there was no obvious apical membrane opening in fresh water group and salinity 35 group,there was a transition type of typeⅠ.It was speculated that the transition type mitochondria rich cells of salinity 35 groupⅠreplaced the typeⅢmitochondria rich cells under hyperosmotic conditions,so as to adapt to the hyperosmotic environment.The mitochondrion rich cells in salinity 30 group were dissolved,with the phenomenon of rupture and abscission.The nucleus was round,and the apical membrane opening was deep hole type(typeⅢ).The number of typeⅢmitochondrion rich cells increased from salinity 5 group to salinity 30 group.Therefore,it can be inferred that typeⅢapical membrane opening is the main morphological type of seawater type mitochondrion rich cells.In this study,the apical membrane opening is typeⅡand typeⅢmitochondria rich cells.By increasing the contact surface with the outside world,they swallow seawater and discharge Na^(+),K^(+) plasma.They are ion discharge mitochondria rich cells.The apical membrane opening is typeⅠmitochondria rich cells with small openings,so as to reduce water loss and play an important role in absorbing calcium ions(Ca^(2+)).They are ion absorbing mitochondria rich cells.