Not sure about Mesquite. I don't have any of them. I learned the hard way about oaks. The tannins killed everything in a pond for me. I use cedars and, according to Lusk, they last about 4 years.

You can ask Lusk. He has a Facebook program on Wednesday nights.
Or test it yourself. Get a bucket of pond water, add 5 or 6 minnows and a piece of fresh mesquite. See what happens.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP