I bought 4 yellow labs on the 7th of this month and he said that the dark one (almost orange) was for sure a male. Since I got them there is another lab that now has black on its bottom fin. Out of the 4 labs I think only 1 maybe 2 are females. The next day, I went out and got 2 cobalt blue zebras and one red blotch zebra. They all have dots on their bottom tail so I assume they are all males. I want to know what else can go in with them and not be to big. my tank is a 55 gallon tank and I have a aqua clear 70 and a fluval c4, plud one to the left which is a filter but I just use it for current.