Second dead goldfish, wondering why

[Jkm]

My pond is new and doing well, but two days ago I lost a goldfish, and this morning I lost another. They were both about five inches long. The first survived my Pond of Death massacre last summer and spent the winter in the barn in a horse water trough, and joined the new set of 4”-5” goldfish when the temperature was right - a couple of months ago. Two days ago I found him floating in the water hyacinths and very chewed up, which I attributed to the six crawfish in the pond, but I couldn’t tell what killed him. I found the second one dead in the skimmer this morning, not chewed up, so I looked him over. He looked well except that he had stringy white goop in his gills, which I know is wrong. I suspect they both died of the same cause. What does the stringy white goop in the gills sound like? (I failed to take a picture, which would have helped a lot, I know).

Pond is about 10,000 gallons. Ultimate II biolfilter, Savio skimmer, waterfall pipe and subsurface water returns. Strong aerator in the drain running 24/7 except when we turn it off to look at the fish. No chemicals or additives added to the pond.
Ammonia zero, nitrites zero, nitrates zero, pH 7.6+ (well water).
17 goldfish (now), six crawfish, six bullfrog tadpoles, and three hi-fin banded sharks.
I don’t want to feed, but I’m not sure the pond is mature enough to feed them all yet, so I feed the goldfish about a teaspoon of goldfish pellets twice a day.

A week ago I decided my pond plants needed more nitrates than the pond is producing yet, so when I changed the water in my two long-term healthy nitrate-heavy aquariums, I poured the old water into the pond, all along the marginal and bog plants.

The only behavioral issue I notice is that when the aerator is off some of them will grab for food at he surface - sometimes it’s bugs I can see and sometimes I can’t see what they are grabbing at. They don’t seem to be gasping for air, or stressed at all, but maybe that’s a clue?

So, anyone have any ideas about what killed them? Or at least the second one? And ideas about what I can do to prevent more losses?

Thanks very much,
Julia

 

[Ray G]

your pond looks very nice. The white goop on the gills could either be white spot disease (Ich) on the gills (it sometimes only attacks gills) or a fungal infection of the gills or a reaction to gill flukes attacking the gills. without photos it if hard to tell but all three I have listed are possible. However they fish would have been agitated well before they died and struggling to breath for quite a while. NOTE usually if a fish is sick it will hide and I am wondering if these 2 did that and therefore you didn't see them suffering before they died?
Ray

 

[Jkm]

That’s one of the odd things - we count them several times a day, and I don’t remember either of those fish hiding or being “off” before I found them dead. I think now we’ll just keep watching the rest and see if it happens again. I don’t see any of the remaining fish looking distressed, but it’s quite impossible to catch any of them for a closer inspection. I’ll look up all three of the possibilities you mentioned, and if it happens again I’ll take pictures. Thanks for your reply