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Issues with water wisteria toxicity

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Hey everyone,

Just wanted to see if anyone else has delt with any issues with water wisteria (hygrophila difformis) killing off certain species of fish.

For context this has happened to me twice now in different aquaria. In each case the issues occurred almost immediately after introducing the wisteria (multiple bunches containing both emersed and aquatic growth). The first aquarium contained medium discus and 1.5-3" clown loaches. Only the clown loaches were affect and this resulted in a rapid die-off of the whole school (roughly 15 fish). In the second case the aquarium contained hillstream loaches (Sewellia lineolata), turqoise rainbows, young geophagus winmerlii, bolivian rams, and juvenile gold red spot severums. In this instance all six of the severums died within five minutes of adding the wisteria - no heavy breathing or death throws, they simply fell out of the water. In both cases all other occupants of the tanks were completely unbothered

I've done a quick search and found a few instances of people discussing this but have not seen any examples of this sort of event actually happening. I'm curious if anyone else has experienced this problem and whether it fits the same mold of only killing certain species and happening after transferring the wisteria (containing both forms of growth) between aquaria. And if so what other fish has it affected for you.

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274 Posts
There's some information available such as this 2012 study, and a 2015 USDA report.
The research shows that Hygrophila difformis does have a self-defence mechanism in the form of compounds produced by its leaves which are harmful to pest organisms. There's a note in the USDA report which suggests aquarium toxicity may be short-lived. So therefore it's possible that adding the plant during the tank set-up phase (cycling without livestock) would avoid any toxicity, but adding it to an existing tank may be harmful to the livestock there.
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