Pond Deaths

by Sue
(OXON, UK)

Sadly, I have found 4 dead fish in my pond. None show similarities in terms of appearance. Can I upload an image to see if anyone can help me find the problem and then how to fix it?
Thanks

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Grant's Reply


Hi Sue

Looking at the image it doesn't appear that the fish were in poor condition before death, especially the fish at the bottom.

This indicates a swift death.

With spring well underway in Oxon, water temperatures will be rising. With this comes an increase in bacterial, fungal and parasitical numbers.

Your fish are most vulnerable to attack by these pathogens because they are coming out of hibernation or semi-hibernation and are also preparing for the breeding season.

A common pathogen at this time of year is the protozoan parasite Costia, which kills rapidly.

Go to the Costia disease page to view different treatment options.

If it isn't Costia it will be poor water conditions that during winter didn't affect the fish, but when water temperatures have risen, so has the number of pathogens.

A cheap water test kit such as the API Freshwater Master Test Kit will tell you if you have an ammonia or nitrite spike in your pond, both chemicals are deadly to fish at even low levels.

I would do a full water change to check the state of any remaining fish, and if they look ill, salt the whole pond at 0.3% or 1 tablespoon per gallon.

The cheapest source of a large amount of pure salt (without any additives such as iodine) is swimming pool filter salt.