I had a mini-pond
built a couple years back and all has been well. We have really enjoyed the serene beauty of having a pond in our backyard with blooming lilies and lotus, the chorus serenade of who-knows-how-many types of frogs at night, and time spend with all the wildlife it supports (deer, birds, etc). There was a post here about it, but I initially stocked it with FHM/RR, CNBG, a few RES, four TP, and the handful of little goldfish that were in the galvanized stock tank on our property. The first month or so, I saw one or two fish didn't survive the introduction to the pond, but I have not (knock on wood) had any issues since. In fact, I don't believe I've seen a fish die since the first month or so of populating.
I intentionally didn't add any predator species to the pond, so unless the birds have brought in some eggs in the last two years, the species distribution should be as mentioned above. The exception, well until today, was Moby Dick. One May 31, 2018, I put one albino channel catfish (about 4 inches long) in the pond as a novelty. Sometimes neighborhood kids come and feed the fish (Purina Aquamax for the win!) and I thought it might be a fun experience to have a big white catfish playing hungry hippo before their delighted eyes. Well, that was the plan anyway.
I hadn't seen Moby in almost a year, so I didn't really know if he was still alive in the pond. This morning, he was floating. I scooped him out and was unable to see any puncture wounds, so I don't believe he fell prey to the Great Blue Heron I've been seeing recently... besides, I assume he would have been food had that been his demise. However, the catfish's skin seemed to be sloughing off... almost as if it was being shed. Is this typically due to a fungal or bacterial infection?
Some water logistics: I've had Vertex membrane bottom diffusers running 24/7 since there was water in the pond. I live in zone 8b and the pond is at most 1/10th of an acre and 7.5 feet deep in the center/deepest point. The water temperature this morning was 80 degrees Farenheit about 18 inches below the surface with a pH of 7.19Here is a photo of the channel catfish's condition after scooping him out this morning.
I probably will not replace the fish since it was intended to be something fun for the kids and it never surface fed at any point in time. The furious splashes of the Bluegill will have to entertain them in lieu of Moby Dick.
Thanks for any advice or help you might be able to offer me in solving the mystery. Obviously, my concern is danger to the remaining population of fish. I have not observed anything else unusual or of note and I'm at the pond every day. If there is something else I should look for, please let me know.