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Tilapia...Nature's Insurance Policy?

Raising fish isn't rocket science. Well, maybe it is. Pond Boss subscriber and frequent contributor to the website discussion forum, Larry Harley is a rocket scientist. He’s a NASA engineer. He also enjoys his ponds, immensely.

Nestled in deep southeast Texas, Hartley not only enjoys his ponds and their bounty, his background in engineering has ingrained a deep desire to know "why." So, naturally, and by training, he is paying close attention to what goes on under the waters of his 3 1/2 acre, 2/3 acre and 1/4 acre ponds. So far, he has one season of tilapia experience under his belt.

He experimented and, according to Hartley, "We had great results." At the same time, he wants the world to know, "I have no personal interest in tilapia…just a private pond owner looking to improve his fishing." Refreshing.

Although Hartley’s experiment isn’t pure empirical science, it brings solid conclusions for thoughtful pond owners trying to make a decision whether or not to use tilapia.

Traditional thinking is tilapia are a niche fish, since they are semi-tropical. They die at moderately cool temperatures. Some species give it up at 52 degrees F. Others make it to 42. Tilapia are nature’s rabbits, reproducing prolifically thus the attraction. Some biologists and pond owners see tilapia as a preferred creature to temporarily diversify the food chain, especially with over crowded bass.

Here’s a different twist…Hartley says, "Even in death, tilapia add value. Before dying, tilapia become sluggish and game fish gorge themselves. I’m totally convinced my largemouth bass and hybrid stripers had a huge feast on dying tilapia. It’s the only explanation for the lack of visible dead fish in the ponds which have hybrid stripers and largemouth bass."

Not to mention better than average predator fish growth. There’s a bigger story to tell. His experiment was originally designed simply to determine if tilapia would provide needed supplemental forage for his game fish.

The biggest pond, a 3 1/2 acre gem, is three years old. Hartley originally stocked Florida strain largemouth bass, hybrid stripers, triploid grass carp, threadfin shad, fathead minnows and coppernose bluegill. The pond has considerable structure, varies in depth to 25 feet, has clear water, and was supported with artificial feeding from three feeders during the growing season. Also, aeration was added to the pond in spring 2004. Two somewhat expensive ($500 to $700) attempts at establishing a viable threadfin shad population for supplemental forage provided limited results in the past. Predators wiped out threadfins each time they were stocked. Fertilizing created extensive filamentous algae growth, which required treatment with algaecide chemicals to control. The pond had a growing pondweed explosion, which grass carp were originally intended to control. Twenty pounds of Tilapia Mozambique were stocked on April 1, when water temperatures were reliably at and above 60 degrees in the East Texas area.

Hartley studies the pond. "The coppernose bluegill population, which had been severly impacted by water turkey predation the previous winter, actually expanded significantly in number and size over previous winter, actually expanded significantly in number and size over previous years presumably due to additional forage offered by tilapia. Hybrid stripers grew from a stocking size of 3-4 inches in the spring to 9-10 inches by fall. Largemouth grew significantly larger, but unfortunately sampling proved difficult due to ample forage (provided in part by Tilapia) and "learning." Largemouth could only be caught using small live coppernose bluegill as bait. Algae problems were completely eliminated. Pondweed was well under control by seasons end. The bottom of the pond, which in three short years had already begun to show the effects of bottom sludge and muck building up was "cleaned" of all sludge and now is clean to the sand and clay except for limited vegetation." Quite impressive results.

Hartley picks up the story, again. "The second pond measures 3/4 acre and is estimated to be about 50 years old. It's stocked with native largemouth bass, native bluegill, and native small minnows, which resemble fatheads (probably gambusia). This pond was choked with algae and pondweed. It was not fishable. Migratory water turkey predation and poaching reduced the population of largemouth bass to virtually none. Even the native bluegill were few and far between and very small. In short, what had once been a thriving small bass pond (with bass up to seven pounds) had been reduced to holding water for livestock as its only value. Seven pounds of tilapia were stocked April 1.

Results were nothing short of spectacular. By fall, the bluegill population had exploded with many native fish (no artificial feed) 6 to 9 inches in length were before they were almost nonexistent. The largemouth population also increased significantly with one to two pound bass plentiful (no re-stocking). Most remarkably, algae and pondweed were completely eliminated. The pond was transformed from an unfishable mess to a delightful fly rod and popper-fishing hotel. I did not observe or fish this pond over the growing season and when first fishing it again in the fall, it was simply stunning to see the change. I would not have believed it, if I had not seen it myself."

While tilapia obviously made a difference, it might be a bit of a stretch to give them all the credit. For this experiment, tilapia apparently were able to get control of rambunctious plants before underwater salad enveloped the pond in the spring. The consequences of this environmental change were a shift of nutrient load from plants to animals. At the same time tilapia took pressure off a naturally stretched food chain and small numbers of predator fish were able to feed and thrive. So, minimized vegetation, coupled with available forage fish, with added forage fish, changed the dynamics of this older pond. Last, but certainly not least, is the 1/4 acre pond.

Hartley tells the story, "This small pond is used exclusively for livestock watering and is estimated to be 70 plus years old. Cattle extensively fertilized this small water and as a result it was completely locked up with thick mats of algae every year. Droughts has eliminated fish populations that were once present. Three pounds of Tilapia were stocked (just for the heck of it) on April 1. Again, results were remarkable. Algae was completely eliminated and the pond had a freshly cleaned look. Tilapia did not grow to sizes seen in other ponds but exploded in population with numerous 4 to 6 inch fish. The pond looks so great that now I’m considering making it a catfish pond for food, fun and grandkids."

As fall wore on, Hartley knew things would change. They had to. We can’t forget, even with such a great result, tilapia won’t make cool temperature. Tilapia Mozambique are the species which give up the ghost at 52 degrees. As predicted, they gave it up.

Let’s let Larry tell the tale. "This much anticipated and somewhat feared event, in fact, turned out to be less of a happening than predicted or feared. Some experts predicted massive fish kills requiring huge clean-up efforts. To add to my apprehension, about a month before the die-off, I observed a large school of suspended tilapia, in excess of a hundred fish, in the larger pond’s deeper water. What would happen to all these fish when they died? Here’s what happened as best I can surmise: Tilapia began dying as the water temperatures hit 55 degrees. Deaths accelerated with dropping temperatures around Christmas time. A very remarkable difference in the three ponds was observed, however. First, for purposes of this discussion small Tilapia fish are defined as 4 to 6 inches, medium fish 7 to 10 inches, and large fish over 11 inches.

In the two ponds that had resident populations of predators (LMB and HSB), there were no small dead Tilapia observed, none…only a very few (about half a dozen) scattered medium sized fish were observed. In the 1/4 acre pond, which did not have any LMB or HSB present, there was an extensive fish kill. Several hundred small dead Tilapia were observed floating along the outside edge of the pond. For a photo of this see the picture above. This was expected, but what happened in the other two ponds? Why were no small dead fish observed; why only a few medium sized dead fish; what happened to the rest of them? I wish I knew the answers.

One likely answer is largemouth bass and hybrid stripers consumed lethargic smaller tilapia as temperatures reached lower critical. As they approach the end, tilapia spin into a spiraling death dance and are easy prey for largemouth bass and hybrid stripers to pick off. I actually observed this happening…but what happened to the large tilapia? Perhaps they just sank to the bottom and are never to be seen again. If many tilapia were consumed by largemouth bass and hybrid stripers, as I believe to be the case, it further supports the forage value of this fish for pond owners."

Here are Hartley’s conclusions: "Based on this somewhat limited, unscientific experience, I offer the following conclusions:

  • Tilapia are absolutely terrific for cleaning up existing ponds. Their stocking costs ($10 per pound in my case) are far surpassed in savings provided by eliminating need for undesirable chemicals for algae and weed control.
  • Tilapia offer a solid alternative forage fish for LMB and HSB. They showed no evidence of competing with BG or FH minnows and in fact helped the bluegill population expand in both size and numbers.
  • Tilapia do not require any supplemental feeding; when available, they will eat fish foot but on a limited basis.
  • Tilapia are difficult to catch, but are great fighters when caught and a terrific eating fish, albeit difficult to fillet.
  • Large initial stocking rates are unnecessary…five (5) pounds per acre is plenty unless you just want to grow the stockers out to be big Tilapia for catching/eating. A few of my initial stockers hit 3 pounds at the end of the season; most of the initial stockers were about 2 pounds.
  • Tilapia begin dying at about 55 degrees and appear to be gone by about 50 degrees water temperature. A gradual temperature decline to those levels is a good thing; they don’t all die at once that way. Also, largemouth bass and hybrid stripers have a chance to consume dying tilapia so they are not wasted. Even approaching death, tilapia are providing forage benefit.
  • If you want vegetation in your pond, do not stock Tilapia. They eat just about everything that is green.

Bottom line, as I said in a previous Pond Boss post on the forum at, they clean like a janitor, reproduce like rabbits, fight like a banshee, and taste better than chicken. What more could you ask of a fish?"

Pond Boss Magazine Dedicated to Managing Private Waters Vol XIII, No.5 March-April 2005 by Bob Lusk with Larry Hartley

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