Choosing Your Breeders
by Norm Ruebsamen
When starting with a new species of killifish, it is always a good idea to start with more than one pair. Initially you will want to breed your fish by mixing and matching those you have purchased until you have a nice sized group of fry coming along. As you move your fry to larger containers, cull out any deformed fry or fry that are not swimming properly or those that look questionable. As they begin to sex out in the aquarium, you will note several of the male fish dominating the center of the tank. These will most likely be the largest, strongest fish. Separate these as they are your best candidates from which to choose your breeders.
It is equally important to choose good females. Its not as easy as choosing the males since most killie females have little color. That said, there are many subtle differences in females: darker versus lighter body color, size, shape, finnage, healthiness and breeding potential. Plus, most females have their own desirable markings and spots.
Rivulus xiphidius is a good example of a fish that you can make or break with the proper female. If you prefer a male with dark blue bands and good orange color in the fins, choose a dark female whose lateral line carries into the tail fin; a female that is robust in size and has the proper body shape. Elongated, skinny females, rarely make good breeders. If you look very close, you will note some tint of color in the fins of the female Xiphidius, the more colorful, the better.
Even when starting with a nice diverse group of 3 pair of fish, you will eventually need to add new blood if you want to continue to have healthy, robust fish. Keep you eyes open at shows and club auctions for a good male or female that would enhance and compliment the fish you already own. Also, keep in mind that to lock in certain traits, colors and finnage, it is a very good idea to back line. Back lining is taking your best young female and spawning her back to her father. And if you have a longer-lived type of killie, you can back line again, father/granddaughter. It is my opinion that if you like the traits your fish are showing, back lining will keep these traits much long into future generations.