I believe there have been several statements on this forum that wild cherry pits contain a poison (cyanide). There could be other reasons your fish died after the storm. Those include a sudden change in PH, toxins such as pesticides or herbicides carried by the rain, a lightning strike on the pond, pathogens carried by the storm after passing over other ponds or parasites carried on debris in the storm. My money would be on the lightning strike but I would double check water quality with a good test kit and I would treat the water for parasites and maybe even feed medicated food for 10 days. Sandy

from:http://www.addl.purdue.edu/newsletters/1997/fall/planttox.shtml

Wild Cherry (Prunussp.) - Wild cherry toxicosis can affect all animals, but ruminants are at the greatest risk. All parts of the plant are potentially toxic, however, damaged leaves of the plant are the most toxic. Clinical signs include anxiety, breathing difficulties, staggering, con­vulsions, collapse, and death. Signs usually develop rapidly. Wild Cherry contains cyanogenic precursors that release cyanide when leaves are damaged (maceration, frost, drought, wilting). As little as 2 ounces of ingested, damaged leaves can kill an animal. Blood from animals with cyanide toxicosis is often cherry-red because hemoglobin cannot release oxygen to tissue. Cell death occurs because cyanide binds to the ferric (+3) form of cytochromeoxidase, thus halting cellular respiration. Diagnosis is made by evidence of ingestion of the plant with appropriate clinical signs. Diagnosis is supported by analytical evidence of cyanide in forage and samples from affected animals. Samples for cyanide analysis should be frozen immediately and held frozen until analyzed. Death is frequently so rapid that treatment is not possible. However, if it is possible, treatment consists of sodium nitrite at 10-20 mg/kg with 500 mg/kg sodium thiosulfate as needed. The treatment is directed at breaking the cytochrome-cyanide bond with the nitrite forming cyanomethemoglobin. The thio­sulfate then reacts with the cyanide via the enzyme rhodanase forming thiocyanate which is readily excreted in the urine. Other plants that can under the right conditions contain toxic concentrations of cyanide include sorghum/sudan grass and Johnson-grass.

Koi may have eaten the leaves!!

fred