fish dying for unknown reason

[g. mcclean]

We have lost 5 fish in the past 10 days. They are last years babies. Our water is crystal clear. We have a set up that includes an upper pond that acts as a biological filter (lava rockthat was seeded last year) and a mechanical filter by virtue of plants that have extended an extensive root system. Our water also circulates through a UV light and a skimmer. We have underwater plants to add oxygen and extensive floating and marginal plants. I see no sign of disease. I wondered if a critter might be "playing" with them ie. getting them but then letting them go. We also have 3 fairly large bullfrogs that came as hitch hikers on some plants a year or so ago. Could they be harassing them to the point of death? Any suggestions?

[brianfl]

Bullfrogs are fairly slow and if they catch them, they would probably eat them depending on the size. Other critters you have seen? Any marks?

[g. mcclean]

:confused: Our fish are still dying. Water was tested and all was perfect. The only symptoms we see are that the fish lays on the bottom with what appears to be distended gills. He will eventually swim away, but more than likely be dead in the next day or so. We are still losing about one fish a day. Our pond shop said maybe fill fluke. Opinions? How to treat?