Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Tilapia Dying Off

I found two large tilapia dead this afternoon.(NE Texas)

I’m surprised I haven’t seen more.

I never see very many dead Tilapia. I did find fishless Tilapia fins on top of a fence post a couple of weeks ago - something may have perched up there and ate one.

Pretty fish. Love the golden hues. What county are you in Tbar?.

The paper below recorded Cold Degree Days and associated mortality for Moz TP and Blue TP. This is similar to degree days we often see in agriculture but instead of temps above freezing they measure the degrees below 16C (~62F). The experiments were in Israel and the original MozTP were from South Africa. MozTP from southern part of their range happen to be only modestly less temperature tolerant than blues. Anyways, and this is confirmed by other experiments, there tends to be mortality over a couple of weeks. Starts off gradually and picks up pace over 3-4 days and then decreases until all are dead. In the second experiment, they reduced temperature by .45 DegF each day (.9 DegF/day in the first). Using Mozambiques began dying at around 30 Cold Degree Days ... Mortality ramped up at around 72 Cold Degree days ... and finally all were dead by 96 Cold Degree Days. Blues followed a similar pattern but there were more Cold Degree Days at onset, ramp up, and total mortality. No fish in their study over numerous experiments survived more than 142 Cold Degree Days. Using a DFW climate ... in an average year ... I get the onset of mortality November 25th, the ramp up on December 4th, and total mortality by December 9th. It may be the ramp up where most are noticed because there will be more of them and so greater chances to observe them.

https://www.researchgate.net/publication/227190021_Cold_tolerance_of_tilapia_species_and_hybrids

Tbar,

Did you weigh and measure the length of those fish? Also, what size were they when you put them in?

I have see some die off in the brood ponds, but nothing in the big lake yet. I Expect that is coming soon but may be a little delayed due to the warmer temps expected and the spring water entering the big pond.

No, I didnt weigh and measure them. I should have.

There are 3 Caracara in the yard eating them this morning.

So how would that equate for USDA Hardiness zone 5b?

Scott,

I haven't worked up climates by hardiness zone. I use a nearby city or county and historical average temps. If you are asking about Indiana ... I did work up a climate for Boone County where RAH resides. Using it ... and the Moz TP Cold Degree Days ... I get October 19th for onset of mortality, October 27th-October 29 for the ramp up of mortality, and all Moz TP dead by October 31st. For blues I get the onset on October 22nd, Ramp up 10-29-Nov 1, and all blues dead by November 6th.

Temps vary from averages ... of course. Hope that was helpful.

In Texas, if one is close enough to the Gulf ... Moz TP will overwinter in most years. There are some places further north where they shouldn't based on climate but do for other reasons. I think most commonly sufficient spring flows to give temps above 55F in parts of the pond.

Congrats to the Hoosiers for winning the Big 10.

jpsdad, Starke County, Knox Indiana. Boone County is 6a.

Purdue has a 64% chance of winning it all.

On average, the Cold Degree Days are achieved earlier in Stark County by 3 days.

I am not so sure how important it is when TP die. It's more important to know the climate favorable for growth. That goes from 68F to 68F. The hotter the better for them. A body should probably start harvesting when temps fall below 72F in late summer/early fall when they are feeding more and brooding (and brooding success) is falling off. For Stark County this is the first half of September.

I totally agree with harvesting by angling at or before the 72F water temperature. This is when TP are still in the spawning phase and most or many of them are in or near the shallow spawning areas. These areas are very likely the same spawning areas that are used by the bluegill. Another good area for anglers to catch some TP is near the area where the fish are fed pellets. This is where I catch most of my havested TP. Any TP that one can remove is removing accumulated nutrients from the pond. Accumulated nutrients is what actually grows the filamentous algae and weeds. Not removing fish from the pond in reality says that more TP will be need to be added next year because more nutrients are growing more algae.

I have never been able to catch them. My voracious bluegill always get the bait.

I think you need to move up to a larger bait. Even large BG have pretty tiny mouths. The tilapia should be able to slurp down anything you can entice them to hit.

I found a few dead Tilapia in the second brood pond over the last few days. It seems like the end for them however, the big pond is warmer and deeper, so I expect them to die off later in the year.