In the last seven years I've had three significant fish kills and four other times that I've lost a few fish from what I believed to be temporary periods of poor oxygen. I have six ponds total, and although all die offs are disappointing, I don't consider this statistic to be shocking or even surprising given the fact that I've sometimes exceeded recommended amounts of fish biomass in my ponds.
I've carefully documented all of the water and air conditions before and after all of these events, and I've found some commonalities that may be useful to others, but I'm especially interested to see if other pondmeisters have seen or heard of similar situations.
1. All seven times the water had recently become discolored.
2. Each time I had documented excellent clarity in the preceding weeks and significant macrophyte growth, in my case sago pondweed.
3. Sudden decrease in Secchi readings occurred right after massive loss of macrophyte viability. I.E. Rooted plants died, then water visibility decreased.
4. Right before loss of the macrophytes (Sago pondweed) once I had two days of significantly cloudy conditions, twice I had extremely windy and hot conditions. Three times I had just experienced 48 hours of nearly completely calm and very hot weather. The other time was in mid-October with typical cool, breezy conditions.
5. Each time I was given a forewarning, some of which I recognized and some of which I blissfully ignored.
A. Smallmouth bass swimming lazily near the shoreline with poor coloration.
B. No feeding for ten days.
C. No feeding for five days.
D. Dead grass carp.
E. Fish languishing near the shoreline.
F. No feeding for six days.
G. Dead grass carp again.
H. Grass carp parked like cars about two inches from the shoreline gulping.
6. The water is always brown during and for awhile after the fish kill.
Anyway, this is how I've pieced together the supposed events into something that makes sense.
A pond with generally clear water and no silt/runoff problems gets stocked with fish, then fed artificial feed. The nutrients are easily assimilated into rooted vegetation. The sago pondweed thrives, utilizing the phosphorous and nitrogen. Then some event precipitates death of the macrophytes, either change in weather, light levels, or water temperature leaving a lot of nutrients available for single-celled algae. The algae thrives but in it's massive numbers the water clarity is decreased and outcompetes itself. Suddenly you've got rotting vegetation in the form of macrophytes and microphytes inundating the entire water column, O2 levels crash and fish with higher oxygen needs like grass carp start to choke, leading to a cascade event of death and sadness.
Maybe this post could serve the purpose of throwing a red flag for another pondmeister about a potential dieoff, or maybe it could elicit a little discussion about my logic. I could be wrong about any or all of my assumptions.
