Black Japanese Trapdoor Snails - I would never add these exotic nuisance snails into a sport fish pond. A few fish farmers I know hate these big snails. They are a pest. As I know it the only thing that around ponds eats the big ones is otter. One of the farms sells the snails to the zoo as food items. If you introduce the snails and they reproduce to a be a pest how will you get rid of them? Big problem. A fish renovation chemical rotenone may not even kill them. I would only stock them if the seller says he will remove them if you find them to be a pest. You want to minimize snails in the pond because they are a vector for fish parasites and swimmers itch. RES will keep snail populations to a minimum and maybe eliminated. I do not and never encourage snails. IMO the only beneficial snail the the common pond snail Physella. They have thin shells that many fish can easily eat including YP and sunfishes. A newish rocky lined pond I am working with had an infestation of Physella. Owner was concerned about fish parasites of black spot, and white, yellow grubs and swimmers itch. Last year and this spring we added RES. August of this year I was there testing water quality and I could not find any snails on the rocks.

This is copied information from a seller of trapdoor snails.
"The Black Japanese Trapdoor Snails (Viviparis malleatus) are the preferred snail species for pond owners and water gardeners. Japanese Trapdoor Snails are one of the few varieties that will survive in northern climates. Pond snails are helpful in keeping algae under control in your pond as they groom your plant containers, rocks, liner sides and plants. Trapdoor snails will consume excess fish food, fish waste and decaying leaves from the bottom of the pond. Japanese Trapdoor Snails are live-bearing and only breed twice a year. They will not over reproduce and become a nuisance like egg laying snails. To have a positive effect on algae growth, a minimum of 10 snails per 50 square feet is necessary. Large natural ponds would require at least 200 snails per acre to be effective."

This information above is just a sales pitch to sell these snails. They MIGHT be okay for a lily garden pond but IMO never put them into a sport fish recreation pond. Eventually the pond will be over populated with these big problematic snails as some fish farmers discovered and see the problems the trapdoors are contributing. Nothing you want around will eat the adult trapdoors. The sales pitch promotes them as "helpful for algae control" All snails eat algae but never enough to control or impact algae enough of the abundant fast growing algae that can grow in a sport fishpond.

If you want BENEFICIAL algae control and all things trapdoor are promoted to do --- stock a few tilapia each year and then in fall ----- catch and eat the tilapia. How good is that??? Now that is effective wise pond management algae control. What other chemical algae control can you later eat?? Yes you can eat the snails but you can't have fun catching them on a fish pole! Plus the tilapia will never promote fish parasites and each year you can adjust their density in the pond for optimizing algae control by buying more or fewer individuals. Tilapia also eat and digest fish waste and the tilapia small offspring groom the "plant containers" and rocks. Tilapia will not just eat algae but they also as algae becomes limited eat the more delicate submerged weeds such as Chara, small pond weed, Naiads, etc. Tilapia in Ohio will absolutely NEVER overpopulate your pond from one year to the next year - Guaranteed - or I will come fix the problem for free.