I would try and remove the goldfish. IMO it is good the herons are eating the goldfish. As noted by esshup they (GF) when reproducing can cause water clarity problems. The cold water temps may prevent them (GF) from thriving in the pond. For your small cold water pond with good regular water flow through exchange, I think your best and most usable option is to use trout.
As aptly noted by Theo you don't really want fish in there reproducing that will need added management concerns.
With trout Start with a low number of trout such as 5 - 10 - 20. There are several species of trout that could be used depending on what local fish farms provide. If you plan to harvest some you could stock 25-30 to harvest about 5-10 each year. Fewer trout means you would be adding less fish food to keep them growing. You will be able to control their growth rate by how much you feed them. No feeding them at all means they stay small (9-10") , more or less stunted. Feeding 10 trout a day a cup of food a day means the 10 are growing pretty fast - maybe to 3 to 5 pounds each. Invite friends over for a grilled or smoked trout party. Harvest and restock according to your harvested number. They won't live forever so if you decide when and if you want another type of fishery it will be relatively easy to do. Just add the new stockers.
Please, please return periodically and tell us about the progress of your very interesting small cold water fishery. We are interested and some are even jealous.
Being the water exchange is relatively rapid, I assume the algae problem is an attached specialized cold water form of filamentous algae because planktonic algae blooms would be constantly leaving the pond system. Plus most planktonic algae species do not really thrive in cold water to produce fast enough to cause green water. It does happen, but it is not common. As noted by esshup,,,, algae control would be manual removal such as raking or dipping floating mats and/or using the safe hydrogen peroxide based algaecides such as Green Clean Pro or Phycomycin. These algaecides have no copper in the formulation to harm copper sensitive species.
Last edited by Bill Cody; 03/28/26 12:55 PM.
