Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Minor fish kill?

Over the past two weeks, I've had a few dead fish floating each day. I measured water temperatures (3-4 feet down) last week around 87 degrees, and I know there were a few days 2 weeks ago when it was noticeably warmer than that when swimming.

Initially I was just seeing larger perch (7-9 inch), but then I saw some smaller perch (4-6 inch) and, more recently a few bluegills (5-6 inch) and a couple baby LMB (2-3 inch...didn't know they spawned).

I assumed that it was just getting too hot for the perch, but it's concerned me a little more that I've been seeing BG lately.

My pond is 1.5 acres. 1 acre has a max depth of 12-15 feet, and the other half acre is flat at 5-6 feet. I have aerators going 24/7 with 3 diffusers. *** We did have a power outage for the last 2.5 days, and I ran a generator on the air pump for around 10 hours during that time. There were heavy rains and some wind that stirred things up a little bit...and actually I've noticed fewer dead fish during that time.

Vegetation is reasonable. I have a moderate ring of american pondweed around much of the shoreline, but I have cleared some manually and also sprayed some of it recently. I did treat the algea about 3-4 weeks ago with copper sulfate (maybe 1/2 the shore line with 10 pounds). The water was noticeably MUCH clearer about a week later (less so now). Prior to that, I had never had much visibility. For a little while there it was up to about 4+ feet and may have helped warm the water during a hot spell.

I don't have anything to test for diffused oxygen, and I haven't gotten into a panic yet, but I figured I should ask around anyway. I haven't kept track, but if I had to guess, I'd estimate over a 2 week period, I've lost (personally seen floating): 6-7 large perch, 6-7 smaller perch, 5-6 bluegill, 2 baby LMB, 1 large golden shiner.

Any thoughts? Should I be worried? It does seem to have slowed the last couple days, but I don't want to get slammed all of a sudden either.

Sounds like a few things could be happening at once. First colder water is more dissolved oxygen it has. So transversly hot water <80 F has less oxygen. Generally speaking still enough oxygen for fish to live but things happen sometimes.

One key component you mentioned was fact that you have had recent rains. When cold rains mix with hot water that new water becomes denser that and sinks to bottom of a pond. This can cause a turnover which can lead to a fish kill. Have you noticed any reaction of fish themselves. Fish coming up to surface acting listless and swimming on side. Gulping for air at surface, all these can be visual cues that dissolved oxygen levels are low.

As far as not seeing bluegill until a few days later this can be common. One response of bluegill is that they die sink to bottom of a pond and then a few days later gases start to accumulate in fish body cavity which then forces them to surface.

SO big question should you be worried. Yes. Anytime you start seeing dead fish in your pond pay attention to what is going on. Keep an eye on an behavioral changes in your population and aerate your water to help minimize likelihood of additional fish kills.

I've been watching closely during this period. I walk the outside of the pond a couple times a day (with my net to scoop out dead fish).

I have not noticed any odd behavior. I've watched for air-gulping or hanging out near the surface and have not noticed this.

As for the rains, those came in recent days, after most of the damage seems to have been done. I've seen far fewer dead fish in the last few days than I was seeing before.

The reason I was concerned about the bluegills is that I figured that perhaps a small bit of fish-kill was to be expected if I had perch in water that reached 85-90 degrees. I just heard that water temperatures in Michigan (in general) are the highest they've been in several decades. My worry with the bluegills is that I'd expect them to handle the warm water much better than the perch, and if they are kicking the bucket also, then perhaps there is something more serious going on.

Though I lost power for a couple days, it is back on now, and the pond is being aerated 24/7 like usual. Interestingly, I seemed to notice fewer dead fish during the recent days w/o power (and w/o aeration) than I did before when it was going full time.

Thanks for the response.

All that seems plausible. Generally speaking if you have a fish kill that kills multiple species you are dealing with either an oxygen depletion or a organic toxin that went through your system.

Yes hot water temps can definitely effect your perch but shouldn't effect your bluegill.

If you aren't seeing any odd behavior start looking for an introduction of some foreign body that killed fish.

My money is still on oxygen depletion.

Assuming I am looking at low oxygen, what can I do about it (now, or in the future)?

The pond is only 4 years old with no inlet or outlet, so there isn't that much muck or debris breaking down. I did have two families of Canadian geese nesting (and pooping) near my pond, but as soon as they were old enough to fly, I was able to get rid of them (couple weeks ago).

Again, with no inlet or outlet, I don't no how I would get any significant toxins introduced.

I have a good vertex aerator with 3 diffusers going 24/7.

Vegetation levels, in my opinion, seems appropriate.

Not sure what to do, other than scoop out a couple more fish each day.