Kaos - Without actual length measurements and from my estimated lengths of each bass (start 115mm, end 228mm in 48 days) and calculations the bass would have had to grow 2.3mm per day. I've recorded fast growing predators can grow up to 2mm per day. We have to keep in mind that a few of the stocker bass could have been slightly larger than the one you photographed. If the pond was full of the right size foods, this amount of growth for F1 bass is possible as ewest says. One way to be more confident that the July 03 bass came from the ones stocked is if you can catch several others which indicates they are from the ones stocked back on May 14.
Try fishing soon for more of them AND get some actual length measurements of them so a better estimate and record can be obtained. Then I can put this growth info in the bass management archives section. When you are catching and measuring more, there should be a normal size variation of slower growing vs fastest growing bass as shown in this example where some 3" stocked bass were 8.75" and a few were 11" after 4.5months.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=377877#Post377877
