Not all species of fish have or occupy separate niches. Depending on the species, Many times the niches overlap, behaviors and competition occur esp in small habitats (ponds vs lakes). Sometimes fish will adjust their feeding habits and use another fishes' niche and competition occurs. The more fish species you add to the pond the more chances this will happen. The fittest, the most adaptable and the most prolific will be most successful. Some species will not be able to compete or spawn and relatively soon, be eliminated from the system.
You are dealing with adaptable live critters here that do not read the books so sometimes their behavior is not by the book and not what you expected. Pros and cons to this. It's your pond; experiment as you will, but as Shan says "you may need to start over if your "plan" does not work. The fish don't care what you think ought to happen.
I've seen big bass 20"-23" develop on just bgill and bass for forage but not a lot of them per acre. I don't think numerous really big bass can be produced per acre. But to get really big ones, the bass population has to be carefully manipulated to reduce competition at the proper times and bgill forage needs to be at the correct abundance and size as the bass grows.
My local fish hatchery guy (ex state hatchery assistant mgr. w/some college coarses) is convinced the best way to grow big bass in the north is to use goldfish as forage. However I'm not sure I completely believe this. Check out the biology and relative growth rates and sizes of goldfish. I can ask if he also recommends bgill with the goldfish. I can give you his name and website if you want to contact him.
www.ridgeviewfinfarm.com Goldfish will compete w/ bgill for a lot of the same food items. Thus you may have fewer quality sized bgill when goldfish are present. Plus I don't think goldfish are very good table food and not much sportfish value except for bass food.
It will be pretty hard to find several fish that will not have overlapping niches in a small pond and not be a competitor with your main stocked or primary preferred species. Primarily because the pond is small and habitats are limited. HOwever if you want diversity for fishing variety then adding extra species is accecptable for your pond goals. You just need to keep the consequences of these additions in perspective and be able to deal with any negative results.
Fewer food sources are available in small ponds compared to larger lakes. Some lakes have higher fish diversity and a corrresponding higher carrying capacity which is due to the different species of fishes utilizing different or multiple niches and more different kinds of food sources. Carrying capacity of a pond is increased by fertilization, feeding, or stocking different species.
