There is no way to know for sure that you have a male or female other than maybe the female may have a swollen belly. The only sure fire way is to fillet them and then it is to late. I am wondering is it a certain size that will be the best breeder size, like 9"-11" or larger sizes like 12"- 17" as not being able to tell the true sex of crappie any other way. The only other way would be just not fish for crappie during the spawn,but I don't want to even go there because this is when I catch most of my fish during the Spring of the year. Also when a fish is caught even if you throw it back the chance of it living or being able to spawn afterward is no known. Some lakes have a slot limit and I am wondering if this is the reason the wildlife wardens or game biologist do this. I would like to know what everyone thinks about this myself. But please be careful on this one it can really be a sensitive subject on this. I would not want to cause any conflicts. I love to fish but I also want the younger kid's coming along to have a good fishery. Remember if it is legal please place a little fish habitat this will help put back what we take out. Thanks for sharing your thoughts.