I'm assuming that you have clips in your library with linkage class names set to tiny1_mc, tiny2_mc, and so on up to 18. The way you attach a clip from the library is:
var libClip : Sprite = new MyLibraryClipsLinkageClassName();
Since you have these things numbered and want to dynamically add them you gotta do something a bit tricky:
PHP Code:
import flash.utils.getDefinitionByName;
...
for (var i:int=1; i<18; i++){
var libClass : Class = getDefinitionByName( "tiny"+i+"_mc" ) as Class;
var tFish : Sprite = ( new libClass() ) as Sprite;
tinyHolder.addChild(tFish);
}