Only way to 100 percent accurately sex a fish is by use of a capillary tube around spawning time -- Or the expellsion of sex products by gentle squeezing.

The capillary tube in probed into the urogenital oriface and tilted back and to the side. However, if not done correctly you can injure the fish. The presence of eggs in the tube is a dead ringer. All other methods are not 100 percent.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.