Fish and Chinese water chestnuts

Years ago it used to be common to read on permaculture sites how people would grow Chinese water chestnuts (Eleocharis dulcis) in those plastic clam shell pools.  People would usually also speak of having guppies in the water over the growing period.  Back then I was researching how to grow water chestnuts, and thought it was a great idea, but there were no tiny fish in the local rivers so I grew water chestnuts in buckets without any fish, and it worked well.  

Late 2023 I tried to read up on this again to see if people had noticed any difference in yield, and for some reason I couldn't find much mention of people growing Chinese water chestnuts with tiny fish.  Perhaps people no longer do this because it makes no noticeable difference to yield, or perhaps it was useful but has been mysteriously forgotten about?  

There are plenty of tiny fish in the local rivers where I now live, so thought I would give this a try and see what I can learn.  I have two identical buckets, put a pot of soil in each, and planted one water chestnut corm in each.  The buckets are next to each other.  I left them to grow for some time, then put some fish in one bucket, and no fish in the other bucket.  

From here I will see if there is any noticeable difference in the yield from each. 

Fish in bucket on the left, photo taken 02/02/2024 

After a month or so of growth there were not a lot of noticeable differences.  The plants looked much the same in terms of size and vigor.  Perhaps the one with fish had slightly thicker leaves, I am not really sure.  

It was obvious early on that there was significantly less azolla and duck weed on the bucket with the fish.  Perhaps the fish were eating some of it, or maybe the fish were eating something that helps the duckweed and azolla grow.  I'm not really sure.  

By the end of February the difference in duckweed and azolla coverage is pretty dramatic.  The bucket on the left with fish has less than 10% coverage, the bucket on the right with no fish has over 90% coverage.  Often it is fully covered by azolla and duckweed, this gets disturbed when I fill up the bucket with water.  

Still early, both plants look similar 

Fish in this bucket - hardly any azolla and duckweed

No fish in this bucket - plenty of azolla and duckweed

I probably should have done this with no azolla or duckweed, but it is too late for that this year.  

I tend to grow a mix of azolla and duckweed on top of the water as it prevents mosquitoes from emerging.  Duckweed seems to eliminate any algae growth.  The azolla also sequesters nitrogen from the atmosphere and releases this when it dies and breaks down.  

Perhaps the fish are eating the azolla and duck weed, maybe they would starve without it.  So perhaps it is for the best that I did include it.  All I know is the bucket with fish has considerably less azolla and duck weed.  

Perhaps fish are eating the azolla and duck weed 

Now that autumn is upon us the leaves have yellowed and mostly died back.  It won't be long before I can lift these pots, let them dry slightly, then harvest the corms.  

Both buckets were growing in my greenhouse, I think the amount of shade will reduce the number (and average size) of corms produced in both buckets.  They both have significantly less leaves than the ones grown in full sun.  

The bucket with fish still has limited duckweed and azolla, the bucket with no fish is covered in azolla and duckweed.  I am keen to compare the yield of these buckets, both in terms of number of corms as well as the size/weight of corms, and see if there is any noticeable difference between the two buckets.  I probably won't get around to digging them up until some time in winter.  

Most winters I sell water chestnut corms, and duck potatoes, through the for sale page on this blog.  Being dormant over winter means they handle postage really well.  If you are interested, they are normally ready mid to late winter.  At this stage I only sell within Australia.