大鱼不显示出来，请大神帮忙支招

var momObj = function() //大鱼
{	
this.x;	
this.y;
this.bigEye = new Image();	
this.bigBody = new Image();	
this.bigTail = new Image();
}
momObj.prototype.init = function()
{	
this.x = canWidth * 0.5;	
this.y = canHeight * 0.5;	
this.bigEye.src = "img/bigEye0.png";	
this.bigBody.src = "img/bigSwim0.png";	
this.bigTail.src = "img/bigTail0.png";
}
momObj.prototype.draw = function()
{	
ctx1.save();	
ctx1.translate(this.x,this.y);	
ctx1.drawImage(this.bigEye, -this.bigEye.width*0.5, -this.bigEye.height*0.5);
ctx1.drawImage(this.bigBody, -this.bigBody.width*0.5, -this.bigBody.height*0.5);	
ctx1.drawImage(this.bigTail, -this.bigTail.width*0.5 + 30, -this.bigTail.height*0.5); 
ctx1.restore();
}