A couple months ago I bought 3 senegals that were ~3" at the time of purchase. Now, two of them are a good 6-7"+ and pretty fat, while the third doesn't look like it has grown at all. At most it hits 4". Should I be worried that it may have something wrong, or is it just a slow grower? The small one doesn't seem like it is bothered by any other tankmates, and will fight over food with the bigger ones like it's not afraid at all.
