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#383571 07/29/14 03:53 PM
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Hello fellow fish fighters
I have a 1/4 acre pond that is surrounded by Eucalyptus trees. An asian friend of mine says the leaves are toxic to fish?
Any truth in that?

Are there certain leaves that are toxic to fish?

Lots of tress means lots of dead leaves in bottom of pond, so after a couple decades, I have a good amount of decomposing sludge of leaves in the pond bottom. Ive been trying to figure out how to get a backhoe close enough to the water edge to dredge a little, but still would not be able to reach very far, even with an extended arm reach of the backhoe of some 20 feet.
Does anyone know how to resolve this?
thanks

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Justin,

I think I'd contact your local Extension Service Aquaculture coordinator. You should be able to find that person by searching for Extension Service and your county's name.

Australian native trees are very different from Northern Hemisphere varieties, even though they have lived in the country for a few centuries. I don't know a lot about Australian trees, and I certainly don't know much about California eucalyptus plantings, other than I've seen miles and miles of them when traveling along the coastal highways.

I know that that Koala bears have developed immunity to the toxic effects of Eucalyptus leaves. I have also read where Australian Aborigines used eucalyptus leaves to stun fish so they could easily be caught, much like Native Americans have used the hulls of black walnuts to stun fish so they can easily be caught. The toxins do not affect humans.

Maybe one of our West Coast friends will pop in with advice. But, in the meantime, I'd rely on the advice of your local aquaculture extension service agent. Most are PhDs, at major universities, with extensive aquatic plant and fisheries experience.

Ken


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TN prof says some species of eucalyptus has been reported to be toxic to fish, but species that aren't commercially available.
http://plantsciences.utk.edu/pdf/PlantsthatPoisonFish.pdf

Certain native Australian eucalyptus have been reported hazardous to fish.
http://www.ecofilms.com.au/toxic-plants-around-your-aquaponics-system/

Gehrke et al. (1993) showed that accumulated litter under river red gums, Eucalyptus camaldulensis, in the Murray Darling Basin produces polyphenols associated with 'blackwater' when inundated, and these compounds are highly toxic to fish if the water is not well flushed.

Gehrke P., Revell M.B. and Philby A.W. (1993). Effects of River Red Gum, Eucalyptus camaldulensis, litter on golden perch, Macquaria ambigua. Journal of Fish Biology 43, 265-279.

Eucalyptus spp. contain high levels of phenolics and terpenoids which can be toxic. Animals such as the koala which eat Eucalyptus have developed methods for detoxifying the compounds in the liver. In addition, they have bacteria that degrade tannin-protein complexes. Most animals do not have this ability.
http://www.ansci.cornell.edu/plants/medicinal/eucalyp.html

Dissolved organic carbon (DOC) can induce lethal and sub-lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds.
MORRONGIELLO, J. R., BOND, N. R., CROOK, D. A. and WONG, B. B. M. (2011), Eucalyptus leachate inhibits reproduction in a freshwater fish. Freshwater Biology, 56: 1736–1745. doi: 10.1111/j.1365-2427.2011.02605.x

So I think the answer is some eucalytus may be harmful to fish under the right conditions. From quick read of some of the above, getting the leaves out or decomposed would not hurt. Flushing and keeping high DO levels also sounds beneficial.

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Like DNickolaus said, before you talk to your extension agent, I'd identify the species of Eukes that you have dropping leaves into the pond.

IIRC they were brought to So. Cal. because their wood was valuable for railroad ties. They do well there because of the fog coming in off the ocean. It collects and drips off the leaves, effectively watering the trees.

I was told not to use the leaves or ground up branches in my compost pile, or for mulch.


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Originally Posted By: esshup
Like DNickolaus said, before you talk to your extension agent, I'd identify the species of Eukes that you have dropping leaves into the pond.


This is not to go against anything my very good friend ESSHUP/Scott posted.

I have many friends in the Extension Service. They are certainly under attack by stringent budget cuts. But, even under extreme job distress, they remain very faithful to their passions. All that I have ever worked with have been very willing to come out and identify problems. My guess is, they would be more than willing to come to the site and identify the species of eucalyptus to determine if it is a problem. If it is, they would make a pretty good on-site determination.

If their budget constraints keep them from traveling, bring some leaves to them. They will quickly identify them and give good advice.

Regards,
Ken


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Justin, 3 quick thoughts come to my mind when first reading your post/question.

First, Do you have fish in your pond?

Second, if so your leaves must not be toxic.

Third, if no fish, get some cheap fathead minnows or Rosey Reds at any pet store and see if they live and reproduce.

My first impressions of the blackwater quotes above instantly seem misleading since the water is "hypoxic" and blackwater comes from low flush, high tannin exposure. Those are not exactly great water quality conditions for fish to begin with. Merely having a "toxic" eucalyptus around wouldn't concern me, as it is likely the chemical reactions in a hypoxic condition that actually releases the leaf toxins mentioned, and not the leaf litter creating the hypoxic condition. Like I said, it is merely my first impression so I am in no way saying my reasoning is right on this.



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Many thanks to Catmandoo, Dnick, Rainman, and Esshup !!!

Yall are true experts, and very much appreciate all of the advice and direction

yes, I actually do have lots of fish, but all are mosquito fish, thousands of them, plus a couple of koi I just noticed. Funny didnt see them for 6 months until I shined a flashflight at night on the water, and 2 koi popped up. All fish are very much alive and perky. Which implies maybe the leaves are not that toxic.

My goal is to raise fish for the dinner table, maybe bluegill and a predator, like LMB.

But I think there is enough reason to cut the trees down, if for nothing else than preventing the continuing of the 1 to 2 feet of muck and decayed leaves at the bottom of the pond.

I have so much muck that its probably near impossible to get out and probably not a good idea to allow it to increase by continuing falling leaves. being a novice pond owner like myself, I cant think of a way to get a 4 wheel backhoe close enough to the water edge without getting stuck to dredge all of that muck out. Even if I could get it close, I can only reach so far with the bucket.

I dont think I could fit a track hoe down to the edge, since I would need a large one to have a longer reach than the 4 wheel backhoe I can rent. plus a large track hoe is very expensive.

I can rent a 4 wheel hoe with a 15 ft reach (might even be 25 ft reach extendahoe cant remember now).

I have ~40% of the pond about 3 to 4 feet deep with 2 of it being muck. It would be nice to remove the muck and maybe get another foot or two so deeper.

But how????

The rest of the pond is 6 to 9 ft deep or so.

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If all I had was gambusia in a pond, I'd be tempted to drain it and clean it out properly.
Then you think about long-term preventing a recurrence of the muck build-up. Might be achieve with aeration and regular leaf clean-outs. Hate to toast good trees.

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I'd drain and re-do too. A track hoe will create less ruts in the ground. If there's any possibility of soft soil, there is a good chance that the 4-wheel excavator might get stuck....

Just remember that all the muck that you take out will have to be put somewhere. That somewhere has to be far enough from the pond so that any rain won't wash any of it back into the pond.


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Call in a vacuum truck to vac the bottom good luck


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