Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Bass Dying all of a sudden

My 1 3/4 ac pond seemed to be doing well but over the last several weeks I've found 4 mature dead bass floating - found a couple large ones maybe three weeks ago floating -- both in ther 4lb range and today I found a couple more in the 2lb range.

I had a good bloom going from late may to the end of July 18" to 2.5' visibility. The water cleared up around beginning of August and it was shortly after that I started seeing floaters.

I'm leaning toward killing off all the remaining watershield in the pond as I think that is what killed the bloom. I'm thinking maybe the bass were having trouble feeding in the clear water (noticed the last bass I caught looked skinny) and/or the O2 levels dropped.

We did have some big rain storms but I don't think the pond turned over as I didn't see any dead BG - normally when I get some turn over I see a few dead BG - never had an issue seeing dead bass before.

Sorry to hear.

Do you aerate?

Sorry to hear this news also. Please keep updated with progress.

So far you have witnessed mortality of around 20 lbs of LMB. So not sure how you should estimate how many were actually lost but chances are that 1 to a few were not observed. As a remedial, if this happened to me, I might consider stocking one (1 lb LMB) for each LMB lost. Growth should be good after this event as the LMB biomass is currently under represented.

No

Sorry to hear about your fish kill.

I am NOT an expert on this topic, so I am just repeating what I have learned on Pond Boss.

If your fish kill is due to a low oxygen situation, then it is typically the largest fish that suffer the highest mortality rates. (I think it is a surface area of gills to body mass ratio issue, which gets worse as a fish gets larger.)

Lots of Water Shield usually means lots of shallow water. It also means very poor wind mixing due to the surface layer of your plants. At the start of August, you probably had very warm water in your shallow areas plus unoxygenated, unmixed water in your deepest spots. That is perfect conditions for a cool summer rain to cause your pond to turn over and put your fish into that unoxygenated water. Further, your pond water probably gets most of its oxygen from the Water Shield, rather than normal wind mixing. Several cloudy days in a row, either before or after the rain, would have shut off your oxygen generating plants. Finally, when your algal bloom died off, the decomposition process actually CONSUMES dissolved oxygen in your pond.

I think you got hit by all of the possible "bad" things at the exact same time.

Can you go out to your pond right at dawn? That will be the lowest oxygen point of the 24-hour cycle. Can you observe your bass and BG piping at the surface for oxygenated water? If so, you are still in the middle of your low oxygen event.

I do not believe that your Water Shield killed the algal bloom, I believe it was more likely just part of the bloom boom-and-bust cycle. However, I am pretty certain you do NOT want to kill your Water Shield right now. That will only make things worse with additional decomposition of plants in your pond!

Lots of speculation above on my part. Hopefully we can get some more expert advice into your thread to give you some better guidance.

I stocked some tiger bass fry earlier in the year.

I suspect the fish kill was a combination of not enough forage and lower O2 so more inclined to build up the forage bass rather than stock bass.

I'm leaning more towards the bass being stressed by lack of forage and that the extensive water shield is providing too much cover for smaller fish. I do think the bloom was keeping the water very oxygenated and a lower o2 level may also have a impact.

I absolutely believe the watershield was competing with the bloom for nutrients - the pattern seems that the bloom kicks off every summer around late may and visibility drops from 3'-4' to maybe 12" to 2' and then clears up in late summer as the watershield is at peak.

I suspect the bass were able to catch forage better in the lower visibility conditions of the bloom using their lateral line.

i noticed that the BG were much more aggressive feeders when the bloom was on. They seem much more leery of feeding in the clearer water (3' to 4' visibility).

I've been battling water shield over last 5 years - it all tends to die off by November and creates something off a bloom then. I plan to kill it off in sections.

As far as shallow water - I think my pond may not have enough shallow water as I'm not sure my BG are breeding fast enough to support the bass. Most of the pond drops to 4-5' deep within a few feet of the shore. The water shield seems to grow in water up to about 6' deep. I wonder if it is getting too thick for the BG to spawn effectively.

Just a thought, and ez to check out. This spring I found a newly deceased walleye , 23" long , still very flexible and decent coloring.
Opened up stomach , back half of a plastic creature bait in stomach and stuck into exit to intestines. it was very skinny. I've had back 1/4 to 1/2 of plastics bit off my self on occasion, clients tell me of this happening to them , and no doubt that fishermen , not thinking of consequences , throwing badly damaged plastics in water , rather than taking home to garbage. Once in the currents of the BOW, they appear as food. Just a thought , if these fish are skinny , might double check stomachs , especially if a lot a plastics used in your BOW.

FishinRod Has posted a very good & very likely senario.

About 25+ years ago our 3 acre retention pond was full of weeds & we had a week of hot 90s, overcast, with very little wind type weather. We lost about 20 LMB & 20 grass carp all in the 2-3 lb & above range. The smaller fish seemed to tolerate the low O2. Called the local fish farm for advice & he said other ponds in the area had the same problem. I really do not think it is a lack of food problem. Lack of food would be a weeks or months problem to kill the fish. I now have a long term, 20 yrs, over population of LMB. Rws of 75 & below, they are not exactly health but they have adapted & survive.

Doing RWs of your LMB is the key to telling you if your LMB are getting enough to eat. If the Rws are low then there is probably to many LMB in the pond for the amount of forage fish.

That watershed is part of your ponds natural ecology. The fact that it consumes some of the nutrients is a balancing & stabilizing factor. With no littoral zone plants & all the nutrients available for the algae you may have tremendous boom-and-bust cycles & frequent times of extreme low O2 with large fish dying. One of the fish farms has a very good article as part of their web site about how the cycles develop.

https://americansportfish.com/fertile-ponds-and-plankton-blooms/

The littoral zone is where the forage fish survive, hide, & grow. Where they get a chance to become 2-4" fish. Your 2-4lb LMB are thankful. The lack of a well developed littoral zone is one of my problems. The fry & fingerlings get eaten well before they get a chance to become good forage fish.

The pond is a balancing system: A change here will always produce a change somewhere else.

I don't think it is them consuming plastics. I have had a few bass break off with crappie jigs but I didn't see any jigs in the dead basses jaw. I let a kid fish the pond a bit but that is nothing new.

The water has been on the cooler side this august - july was super hot - Id say the water temp has been in the mid 70s as the nights have been cool.

I am leaning toward lack of forage simply because none of the bass have been real chunky and the last bass I hooked this week was definitely emaciated.

I have other grass and cattails on ponds edges. I also have several brush piles for small fish to hide.

One site I read said you shouldn't have excessive brush piles as it would hurt the ability for bass to eat . That was one of reasons I'm leaning toward removing some of the shallows of water shield.

I have a lot more BG than bass and it seem like they should be able to breed faster. I'm thinking the water shield may be so thick in the shallows and cutting off all light to the extant that it interferes with spawning. Hence I think I'm gonna remove it from one of the shallow ends and see if that improves anything.

I also added 10 lbs of baitfish last friday and hope to have 70 lbs of shiners delivered next friday.

Found another rotting dead lunker bass today (for a total of 6 known dead bass) but I also caught a nice 4lb bass on my ultralight so I didn't lose all my good bass.

I have noticed that the dead bass have been in the water shield in areas that were sprayed with herbicide so I suspect low O2 combined with the polaris herbicide killed them. Some of the areas that I sprayed with the herbicide didn't seem to have had much affect on the water shield but still had dead bass so I'm wondering if the herbicide itself is somewhat toxic to a bass in marginal O2.


Hadn't had an issue using Polaris in past so a bit mystified.

My bet is that the herbicide spray combined with no aeration and high water temps created an O2 crash, and without aeration it is taking the pond a long time to recover. I saw it in a friends pond that I have been after him to get aeration in for the past 6-7 years. It finally bit him in the butt. 3' TGC, 20+" HSB, 4#-5# LMB and 8"-10" BG dead 3-10+ days after spraying about 1/4 of the pond for coontail/algae. He has been guessing at water temp too, and finally broke out the thermometer to actually check water temps.

I checked the O2, and in the afternoon when the O2 typically is highest, he had 5-6 mg/l, but go down 3 feet and it was in the 4mg/l range and below 4 feet it dropped to the 3mg/l range. 6 foot was below 1 mg/l. Surface water temp was in the low 80's. He first noticed the fish stop feeding, then a few days later started seeing dead fish. The O2 would vary according to water temp, and a suppressed feeding response was a good indicator of dangerously low O2 levels.

We threw in a bottom diffusion aeration system with 2 single disc diffusers with a 1/4 hp compressor in the pond, but that still isn't enough for a 2 ac pond with a max depth of 12'. A larger compressor can't be used, the power supply can't support it. We tried with a 1/4 hp and 3/4 hp rotary vane compressor and the air output was less than with the 1/4 hp rocking piston compressor. That will be changed for next year, and a 3/4 hp rotary vane compressor will be used with 2 more airstations.

It took 3-4 weeks for the O2 in the pond to come back up to where the fish are feeding now, and in part I think that is due to cooler water temps (by 5-6 degrees).

Multiple fish don't die at the same time from starvation or low food availability - it was an O2 crash. The herbicide used had no effect on the fish kill other than killing the plants that then decomposed and the bacteria that was decomposing the plants sucked up the O2 which in turn caused the fish kill.

Don't want to intrude, but how are you checking the O2?

Esshup or others. I'm curious if there are times of the year that killing pond weeds should be avoided or minimized. O2 levels are lower or at least the water has the ability to hold less of it as the water is the warmest in the summer. With no aeration I would guess that this is the least favorable time to treat with chems. Are spring and fall the best times to treat or is it more that you have to treat with the plants are actively growing and if that's summer....go with smaller treatment areas?

esshup delivers fish to customers. He has a very nice (expensive) DO meter.

I think you can find a discussion of various meters if you search the old threads.

"O2 levels are lower or at least the water has the ability to hold less of it as the water is the warmest in the summer."

You got it! The warmer the water the less O2 for the fish, even without a vegetation kill.

Much safer in the cool months. Chemicals most effective when plants are putting energy down in the roots to over winter & next springs growth (Fall).

You can play it safe by doing your pond in stages, so that everything is not all decomposing & using up O2 at the same time. Perhaps doing just some areas & leaving others natural & see if you have the desired effect your are looking for? 20% is often mentioned as a minimum goal for the surface area of a pond to be covered with weeds. An area for biodiversity of the pond.

Not an expert, but agree with JEC on timing.

I also seem to recall some threads about submerged plants developing "seeds" that are subsequently spread around the pond. I suspect the best time to treat those types of plants is right before full seed out. The plant has exerted lots of its energy reserves and you can kill it BEFORE the seeds spread.

I think the O2 was low because we received a lot of rain and the cool water did a bit of a turnover (not too bad as I didn't observe BG at the surface) and it also completely killed the Bloom that was helping keep the O2 levels high.

I can see why the bass hiding under dying water shield would die but they also died in areas were I sprayed herbicide but the water shield wasn't very affected. Maybe it was affected enough to stop producing O2 during the day?

One of the reasons I want to cut back on the water shield was that by middle of summer it gets so thick the bass are almost impossible to catch under it. I also suspect it is making it hard for BG to breed in shallows as all the shallows get very congested.

On plus side I plan to stock a bunch of shiners this week and they might have a chance to catch on. Pond was probably near peak bass load before the die off. Pond has a bit of a bloom going now.