By Bob Lusk

Check that—he’s grown some great fish

This massive fish kill was caused by an environmental issue, golden algae. When you see many sizes of many species die like this, it’s not a disease.

Got a call from Ron Morgan in January. Ron and his bride, Robin, have a gorgeous place west of Fort Worth, Texas.

To say that Ron is a fishing fan is an understatement. The word fanatic doesn’t touch it. I think he crossed that line many years ago, maybe when he crossed the border on one of his multitude of fishing trips.

Today, Ron is retired and has built Robin’s dream home and his very own unique fishery. Er, maybe that’s an understatement, too. The Morgan’s bought a tract of land nestled along a winding, mostly dry creek. The far side of the creek is a steep bank, some of it sixty feet higher than the near side. In order to stay above the natural flood plain of the creek, engineers told them to build a house pad and raise the site by as much as ten vertical feet. In order to do that, they needed fill. Presto-chango, they dug a couple of holes.

Guess what happens to holes?

Yep, you got it. Ponds. Well, they live in porous soils, so the ponds were lined with plastic liners and shaped with stacked rocks. There’s a couple of lovely waterfall features, and Ron with his designers, figured out how to keep the water moving and healthy. But, he couldn’t leave the creek alone, either. With permits in place, he built a series of rock weirs to retain water during times of flow.

Fast forward to January. In its third year, Morgan’s ponds and weirs have begun producing some really good fish. Check that—he’s grown some great fish. But, we’ll save the other stories for later. You’ll want to know how he built what he has, how he stocked it, and how he manages the water and the fishery.

For today’s tale, it started with a phone call just days after record-breaking cold temperatures and a heavy rain.

“Bob, I’m losing some of my larger bluegills. Can you help me figure out what’s going on?”

Folks, if you haven’t lost some fish, you probably haven’t been around a long time pushing your waters to do what they can do.

But, how do you diagnose what’s going on when you start to see issues with your fish? Here’s a basic dichotomous approach to assessing your problem, so you can figure out how to solve it. First off, we have to deal with clues so as to figure out what steps to take for an accurate diagnosis.

When fish are dying, it’s often too late to solve the problem, whatever it may be. But, there’s a process to figuring this stuff out.

Fish get sick because of a handful of reasons. First, they’re stressed. That’s a symptom of the actual problem. Your job is to figure the cause of the stress. Maybe the water quality has deteriorated. Maybe natural toxins have reached a lethal concentration. Maybe too many plants led to an oxygen depletion. Maybe the temperature rose or dropped so fast as to cause distress to your fish. Maybe a bacterial infection or parasite outbreak has occurred. Maybe the fish have eaten something bad.

Here are some hints to begin tracking down what the problem actually is, so you can choose a course of action.


Here’s a clue; When large fish die, it can be a disease, but maybe not. It could be environmental.

If different sizes of different species of fish are dying, you have water quality issues, not a disease problem. If one species of fish is showing signs of distress, you may have water quality problems, or a disease issue. If one size of one species of fish is dying, you likely have a disease issue or something explicitly environmental. See how simple this is? Here are some caveats…the time of year also has an influence with your diagnosis. If summer, the event may be triggered by heat. If winter, the event could be triggered by cold. If spring or fall, the event may be triggered by a rapid rise and fall, or vice versa, of the temperature.


Here’s where it becomes dichotomous. If summer, and you see fish behaving strangely, look closely. If your fish aren’t feeding, and you can see some catfish lying near shore, or their heads close to the surface, you’ve got water quality issues. If you see bluegill or bass nearby, and they’re acting lethargic, you can bet your water is deteriorating fast. Your action plan will be to aerate, exchange water, whatever you can do to relieve the water of its causative natural toxins, most likely fish waste from overfeeding or oxygen depletion from a variety of sources.

If summer and you can see a few fish of the same size, same species, acting strangely, capture some and take a close look. Some parasites seem to peak during summer months.

In the fall or spring, if mature fish are bunched together in big schools, this is a symptom of a disease. It could be viral or it could be bacterial. Oftentimes, bacteria manifest itself with sores, wounds or reddish bumps on the skin, or open lesions somewhere on the fish, often around the fins. This time of year is also the time some parasites peak, especially ich, a common parasite found in overly-crowded fish populations and slightly soft waters.

In winter months, some species of fish have lower cold tolerance than others. Southern fish don’t do quite as well in cold environments as north fish of the same species, and vice versa. If you’ve stocked your Ohio pond with fish raised in Arkansas, you are more likely to see the effects of cold.

Diagnosing is difficult. If you see very many of your precious fish perishing, seek help from your nearest pro. While he or she may not have immediate answers, they have resources you don’t, especially fish pathology labs.

If you are confident of your diagnosis, take appropriate action. If you catch fish with obvious red lesions and sores, you can medicate your feed, if these fish are feed-trained. If you think your water quality is deteriorating, exchange fresh water from another source, a well, a nearby pond, or whatever you have in your master plan. If no fresh water is available, aerate. Be sure to speak with a pro who knows how to aerate. It’s not enough to just fire up an aerator, especially during the summer months. You can create bigger problems by aerating stratified water.

Here are some real world situations I’ve come across. Years ago, I met a fellow who wanted to raise channel catfish to help feed his family. He bought a few hundred fingerling catfish, headed to the feed store, bought a few sacks of floating fish food, and went at it. He called about two years later in a panic. Seems some of his fish weren’t acting right and a few looked dead. I headed over there on that August day and he had at least a dozen big catfish, pushing four or five pounds, beached like little whales. His pond covered less than half an acre and he’d stocked 600 catfish in it. He fed them faithfully. I also saw a few little sunfish trying to beach themselves.

What was the problem?


A quick cut up the gut showed no obvious signs of parasites. There were no visual signs of external bacteria.

His water quality was deteriorating. It happened over a long period of time. His faithful feeding slowly began killing his fish. He was killing them with kindness. Let’s assume half the catfish survived the original stocking (it was probably more than that, actually). That means 300 catfish pushing four or five pounds. That’s 1,200-1,500 pounds of catfish in that half acre pond. That much biomass digesting and processing feed every day yields quite a bit of fish waste. The pond, in all its glory, couldn’t process the waste fast enough with that much fish in it. He’d followed through with his plan—except he wasn’t harvesting fish for his family to eat. We rounded up a pump and began picking up the deepest water and showering it over the pond to relieve as much gaseous waste as we could. With that in place, he and his family ate some fish—a lot of fish.


Another time, I got a call from a neighbor. Seems he was losing some 3-4 inch long bluegills. Nothing else. I drove over there, walked out into the field and started trying to figure out what was going on. He’d fed his fish sporadically. We’d just had a big rain. It was spring time. Sure enough, there was fifty or sixty otherwise healthy little bluegill lying around the edge of the pond, some of them stranded where the water had receded that morning, after the rain. Picking up a few, I noticed their little bellies were bloated. Pulling out my pocket knife, I made a cut right up the gut of one of the fish. Its belly was packed with fire ants. So was the next one and the next one. The rain had flooded quite a few fresh fire ant mounds. When the ants came out, they floated in rafts. The greedy little bluegills gorged themselves and fell victim to the poison of their windfall.

Once a call came in from a guy who had raised largemouth bass on feed. His pond was fairly small, maybe an acre and his bass were pushing past four pounds at three years of age. One day, toward the end of winter, he rang my number. He noticed several bass hanging out under his dock, lethargic. A trip over there showed hook marks in the bass’ mouth and a fungus growing on their sides. He’d gone down there on a bluebird day, caught a few fish to see how they were doing. When he caught those bass, he didn’t think about wetting his hands before handling them. You could see on the two fish we were able to capture that they had slightly red hook marks and each one had a reddish imprint of fingers on at least one side. When his dry hands diffused the slime on the fish, bacteria attacked. Since the water was cool, the fish didn’t heal quickly, and the spots he touched became inflamed and infected, which allowed a fungus to attack and weaken the fish.

Okay, what’s dichotomous about this?

It’s either water quality or something else.

If it’s water, work on the water. If it’s something else, figure it out. Either it’s a disease or it’s not. If it’s a disease, it’s either a bacteria or a virus.  If it’s not, then it could be a parasite or not. If not, then it’s likely something else environmental.

While I wish I could give some solid answers to fish problems, there’s not a good way to do that, except to understand that the majority of fish issues begin with something to do with your water. Pay attention to your water. Eliminate that as the source of your problem, first.

What was going on with Ron Morgan’s bluegills? While some of the samples showed definite signs of a bacterial infection, not all the fish had manifested sores. Then, it hit me. He’s meticulous about tracking water temperatures. I asked him what his temperatures were over the last ten days. He had a four inch, flushing rain followed by drastic temperature drops. There were several days close to the single digit mark and several of those never saw the freezing mark. He has water circulators and bottom diffused aeration. With water being moved in every direction it could be moved, including pumping from the lowest weir in the creek to the liner ponds in front of the house, he never saw any ice form. That means he had water temperatures push into the lower 30’s, much colder than even the coldest pond in Minnesota on those days. Minnesota’s ponds were insulated with a thick layer of ice and the bottom water there was a balmy 40-41, compared to Morgan’s 34-35. Knowing he’d stocked some adult coppernose bluegills and they were pushing two pounds and five years of age, the answer seemed to come. The water was cold, these bluegill can’t stand water so cold. They laid on their sides and some didn’t recover. The answer for Ron Morgan? Temporarily turn off your aeration and water circulation systems and let the water do what it can to not be cooled so fast.

What might you need to do?