I have put several variety of plants in last fall and they seemed to be flourishing and this spring when I expanded my pond I transferred all the plants to the larger pond containing fish. Now I only have a few twigs left, some did get sucked in to the down spout but what happened to the rest about 1/3 of the pond (2450 gal) had vegetation this spring and now nothing. I don’t want to invest any more money into plants if they are going to be eaten, any suggestion as to what plants I should get that the fish do not eat?

Are these submerged plants, floating plants, and/or marginals? Do you see the fish eat them? What does the damage look like? Goldfish and koi will eat most submerged plants so I don't worry too much about those. I add a batch in the spring but they eat most of it. The fish can't get to marginals once they are growing up but can bite off the growing tips of them when they first start out. Plus, my spawning goldfish and raccoons have spilt some of my marginals. Once done repeatedly, this effectively kills off the plant. You can make a blockade to keep the fish out of the shallows if you have marginals in the shallows. Which species of plants have you tried and how were they situated in the pond? The fish will nibble on most plants except the ones they can't reach!

I had Hornwort, Four-leaf clovers, Parrot's Feather, Iris, Umbrella Palm, Creeping Jenny, Anacharis, Purple Cabomba, Narrow-leaf Ludwigia , and Pennywort. By this spring my 300 gal upper pond was totally full of these plants and string algae, I cleared out the string algae and put all the vegetation into the large pond where all the fish are. I have 5 med size koi 1 large 14” koi, 3 fancy goldfish, 4 comets, a bunch of rosy reds, and tons of mosquito fish and tadpoles.

Koi and goldfish love to eat the submerged plants you listed: hornwort, anacharis, cabomba, and ludwegia. They will also eat four-leaf clover, creeping jenny, and pennywort if they can get to it. The parrot feather, iris, and umbrella palm I would have thought would have avoided being eaten. Did those plants die too? If so, perhaps the big koi rooted them out (depotted them)?

Did those plants die too? If so, perhaps the big koi rooted them out (depotted them)?

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I think they are the stems and twigs that got caught in the down spout. The lily is the only thing that survived since I did not place it into the lower pond. But it looks like the mosquitoe fish and the two comets I have up there are munching away cause I see little bite marks all along the peirmeter of the leaves. Is there any plants these guys won't eat? I feed them twice a day and am going thru alot of food. I go thru about 3 lb of the tetra floating sticks every three weeks. They say to feed them until they finish within 5 mins., but they must be still hungry to eat my plants also. I think they are now starting to eat the tadpoles, because their population is diminishing. They were everywhere all along the outer perimeter of the pond and now they seem to be gone.
I did not realize ponding was such hard work.

What do you mean by the plants got caught in the downspout? Fish and tadpoles may nibble on vegetation but don't rule out insect pests or land animals coming to feed. Turn over the leaves to look for insect larvae and snails who could be eating vegetation too. Being well fed doesn't stop fish from rooting and eating plants; it just reduces their desire to do so.

What species of tadpoles do you have? The fish may eat the tiny ones. Could some of them have already turned into frogs and left?