window.addEvent('domready', function() {


$$('img.img_Cat').each(function(el) {

var cloneimg = el.clone().injectAfter(el);
var cloneimgsrc = cloneimg.getProperty('src').replace(/^(\S+)\.(gif|jpg|jpeg|png)/, "$1_hover.$2");


cloneimg.setProperty('src', cloneimgsrc);
cloneimg.setStyle('opacity','1');
var fx = new Fx.Style(cloneimg,'opacity', {
 duration:800,
 wait:false});
var fx2 = new Fx.Style(cloneimg,'opacity', {
 duration:800,
 wait:false});
 cloneimg.addEvent('mouseenter', function(){
 fx.start(
 '0'
 );
 fx2.stop();
 });

 cloneimg.addEvent('mouseleave', function(){
 fx2.start(
 '1'
 );
 fx.stop();
 }); 
 });
});