nice rainbow Leonard, definatly a fine fish but I have to be a buzz kill and say its hard to belive it to be 13lbs. Check out this chart http://www.flyanglersonline.com/begin/fishweight.html
it would have to put on 10 inches of length to be that weight. But then again the picture is dark and hard to tell but it is a fat fish for sure. I will show you a picture of a silver salmon that is 8 lbs not sure of the lenght or width but i would say atleast 25 inches long and 17 around