What critters can I add to a pond that won't eat goldfish eggs and fry?

[Hop-frog]

I want to add some other critters to my pond that can live peacefully along with goldfish and koi. Currently I have a variety of 50 or so fancy goldfish and comets that are mostly under a year old, but will get big fast.

• I don't want anything that will eat the goldfish or koi eggs and fry.
• It should be a friend of the fish, not snack.
• If it has some benefit, like cleaning detritus, cleaning parasites off the fish scales, or eating mosquitoes, that is a plus.
• I don't want something that will become so happy living in my pond that I end up fighting a massive population, e.g. I think some snails can end up having an out-of-control population.
• They have to survive the winter (the pond won't freeze over due to the fast current of the pump, but does get very cold still).

I'm thinking turtles, crabs, triops, horseshoe crabs, freshwater clams, freshwater octopus, crawfish, shrimp, frogs, newts, periwinkles, snails, water birds, platypus or other aquatic mammal, etc.

What is a good option?

 

[Mmathis]

Where do you live and what is your year-round weather like?

I think most of us here have come to the conclusion that adding “other” critters to a man made pond just doesn’t work, for one reason or another. But if your pond really is going to be 20,000 gallons, you might have better luck. Do a Google search that meets your criteria, including your climate zone. I don’t know about fresh water shrimp, but crawfish are predatory. Turtles can be predatory, but there is also the chance that they won’t stay around.

I’ve never heard of freshwater octopus....wait a minute! Platypus??? OK, at first I thought this was a legit question, but, really? And you live in the USA? Not only are platypus a protected animal and native to coastal areas of Australia, but they are carnivores — and are venomous!

 

[Hop-frog]

Yes, it is a serious question. Yes, the pond is more than 20,000 gallons, in fact the present design is 17,0000 gallons, but I've hired a backhoe and they're deepening it, so it might more than 35,000+ gallons.

By listing platypus, I'm simply meaning I'm inviting creative ideas. The pond seems to be big enough for ducks, but my city laws won't allow the keeping of these creatures.

I live in the US southwest, region 6a. Average low temperature in the winter is 10 degrees F for the whole winter. The summer is mild, no more than 90 degrees F, 100 F was a rare record high.

 

[Stephen Noble]

You mention the city won't let you keep ducks but then list water birds as a choice? I too will assume you aren't joshing us and suggest your pond will attract untold wildlife without adding anything.