Several things will contribute to recruitment of koi/carp. I may not deal with all of them.
1. Amount of good spawning habitat. The better the type and more quantity of shallow shoreline or shallow structure for egg attachment the more eggs will hatch. Shallow grassy, weedy areas prime spawning habitat. Just about any firm underwater surface will hold carp eggs.
2. Amount of cover for fry fingerlings. This is pretty self explanatory.
3. Food for carp fry is normally not a limiting factor in a pond like yours. Food source should be ample for good carp fry survival. Fry are planktivorus.
4. Your pond has very few predators present of hatched carp fry until they are bigger than 1+". Survival to 1"+ should be very good.
5. HSB and IMO trout tend to be more open water predators. I welcome other opinions on preferred habitat of RBT or HSB. Small carp (1"-5") will be bottom oriented due to feeding habits. YOur predators and prey do not have behavior habits that cause a high amount of interaction thus IMO this will lead to high survival rates of fingerling carp.
6. Adult mature koi are sexually dimorphic (adult males and females with external recognizable features). A single sex koi population is possible and suggested.
