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Hey team!

I usually like to figure stuff out myself but I guess this forum is here to help!

The last few days a few of my blue tilapia fingerlings have been dying mysteriously....here is the break down

800 L tank...the same of grow bed
All water quality tests normal, ammonia 0, nitrite 0, nitrate 5-10, ph 6.5
58 fish 2-3 inches feeding 42% protein trout food, all been eating except the 3 that died who turned pale grey and sank over last few days. Gills and major organs seem fine and no sign of lesions or disease. Plenty of aeration from bell syphons and recently added air stone...although a few times I have seen them gulping at surface after a bigger feed but pretty confident it's not a DO problem

These guys were troopers during cycling and only now when everything is doing so well I start losing fish??

Any ideas would be appreciated! Do I just put this down to weaker fish dying off? I have an aluminum screen over drain would this be an issue? Grasping at straws peeps!

Thanks in advance!

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I call these mystery die offs

I think it always goes back to a weak, dying, beat up or dead  fish poisoning the water.  That poison does not and will not show up with your test kit. The common thread seems to be overcrowding with fry at system launch and when they hit puberty someone gets beat up and loses out. Then you have a dead fish and the cycle of chaos begins.

Thanks Jim, ...from research it seems a general stocking density has 1pd fish to 5 to 7 gallons so I'm pretty close to that mark I think

You can do everything right after finding that dead fish and the numbers always look good, but the fish keep dying.  The water needs to be changed out PDQ before the others get sick.  If you don't, the nasties get into everything, media, etc and it's almost impossible to fix without a complete tear down.

Once an AP grower here in Phoenix with mystery die off found out his bug guy was being extra helpful and sprayed his grow bed for him...  so think outside the box too

@ Nathan:  

I know the rule of thumb - 1 pound of fish in 5-7 gallons as 1 fish per 5-10 gallons - IF you have everything perfect ie: a commercial system with big filters and huge tanks and everything is perfect and regularly monitored (regularly means HOURLY) by skilled technicians you can probably get away with that heavy population ratio but it is unnecessary.  I have never met one of these skilled technicians because they are paid six figures to use their knowledge at work, not given away free on the web...

That said, I have 2 - 700 gallon systems.  They both have 40 fish, my original system has adults; the other system fish are 4"- 6" now.   By your calculations I should have 140 fish! (700/5)  I have more nutrients than my system can use. Check out this picture of my original system:  it has a 700 gallon in-ground pond with a 4x8 grow bed.  The 4 foot high shade enclosure is literally filled with plants. The cherry tomato spills out 2 feet on 3 sides and hangs to the ground.  I get handfuls of tomatoes everyday for the last 2 months and it is still blooming.  The pond is completely covered in lily pads, water iris and water hyacinth, which have completely choked out the duckweed. 

It wouldn't grow like this if there was shortage of nutrients.  

a - grow bed - check out the tomato hanging out the sides

b - swirl filter

c - 700 gallon in-ground pond - there is a waterfall on the left 10 feet out of the frame next to the red brick patio with a babbling" brook flowing back into the pond.  The" big rock is for the 10-12" turtle to sun himself.

Do yourself a favor, try my fish density of 40 fish per 700g   (700/40 = 17.5)

so if you have 58 fish in a 1/3 full 900 liter tank it is much worse than I thought...

you have 58 fish in 300 liters (80 gallons)

Thanks Jim, ...my fish tank is only 1/3 full

try filling your tank to 900l / 230 gallons

calculations for proper fish density:

230g/17.5 is 13 fish  -  so figure out something to do with the extra 45 fish you have for a while (barrel) and see if your problems don't go away. 

Be sure to follow ALL the guidelines above (in order) for resurrecting your system. 

Thanks Jim, will certainly try some of that...

come on and do it all; not just "some of that"  -- I want to win one of these "mystery die-offs" so I can help other people with the same problem!

(I'll bet you have a trickle for water flow too, crank that thing up! What it gonna hurt? Turn over the 230 gallons every hour.  That means if you have the pump turned off for 45 minutes of an hour it needs to flow 230 gallons in 15 minutes!)   

good luck

Thanks again Jim,

Am really trying to get to the bottom of the issue though and 'mystery die off' from 'nasties' is a hard one to swallow...I think we are both talking about a bacterial problem so agreed with all the water changes asap!

I have not found a single 'completely' dead fish in my tank yet...I check it constantly through the day and when I see one that looks lethargic/loss of colour/not eating I move it to a smaller quarantine tank...its then after a few hours/sometimes a day that I lose them 

No 900L is 1/3 of my tanks total volume...is a large 2500 fibre glass ex hatchery tub...so have volume on my side 

I have a 2500L/hour pump going 24/7 so no issue with water flow

Good to hear about the water tank size and pump volume.

Fill up that tank, they will like the space.

Are you growing DWC?

keep the faith

Hi Nathan,

I'm suspecting oxygen problems due to too many fish... Water has a maximum saturation point for DO, after it is 'full' you can't really get any more in there. So if you have too many fish, then there won't be enough O2 to share around (I learned this the hard way and lost 39 trout when I should have had no more than 30!! A lot of filleting that afternoon!). This saturation point becomes lower at higher temperatures, so I think raising your temperature could even compound your problem here.

For 800L, (approx 210 gallons) even at extremes I wouldn't be putting in more than 40 fish maximum (one fish per 5 - 10 gallons). But personally I would even go 20 - 30 just for the safety buffer and to give them room to grow. If you don't plan on eating them as they get bigger definitely go on the twenty side of that.

The fact they have been gulping for air after feeding is another thing that indicates there's not enough oxygen to go around - due to too many fish. None of them are getting enough and you will be in danger of losing the lot.

I would reduce your stock to 20 - 25 (if it hasn't self-reduced by now), and make sure you have your aerator running.

Ahh just saw the second page. Excellent, like Jim said, fill up the tank. You have a pump that can handle it and the extra water volume will be able to hold more oxygen for the fish. Go to 2000L and I I bet things will improve. Your fish may have been too stressed by lack of oxygen already (if they were trout they'd be dead!), but hopefully they recover. Tilapia are hardy. You do have an aerator, or some sort of splashing at the surface?

No more fish!

Remember to let chlorine gas of before adding water to the system if you are adding from city water.

Best of luck! I think you are close.

Cheers Tim, appreciated...I set up another 700g/h pump as soon as the fist fish got sick and had that full throttle on the surface for more DO but is likely that a low level caused it...the first fish that died came after a power outage that left main pump off for 10min before I could get the generated going...that might of triggered the onset...just seems strange that Lanna has had the same issue at the same time!

Anyway going to increase water, reduce stock and keep everyone posted...thanks again!
I too have the same issue, and I think I got my fish roughly the same time as you two. Would love to know your source but I am losing roughly a fish a day. I have a 260 gallon tank with. 175 gallon sump tank, 2 40x48 inch 12 ince deep media grow beds. My readings for nitrites, nitrates, and amonnia are similar to yours, very low. I fish less cycleed in April and May got my fish May 23. Everything was fine u til June 30 when first fish died. Then two days lat another. Took readings 0 for nitrite and nitrate, o.25 for amonnia. I have had 6 fish die this week so far.

Lanna said:

To add to Nathan's Discussion:
I got my fish the same time and place as Nathan. Mine started dying about 3 weeks ago, 1 or 2 a day, then maybe nothing, then more dead the next day. Most of the dead guys have looked fine, however during the last week a couple have now had lesions on their sides..... dissected a couple and they haven't had any food in their bellies. We salted the whole system and have put the fish in a salt bath but hasn't done any good. We have lost about 30 now.....The closest guess we have at the moment is dropsy but we have no idea what's happening.

Water quality/temp is fine. They have grown really well and always ate fine, (feeding trout food).

Thanks for any ideas!

Hi Mike-
Sorry to hear, it is a painful, frustrating process! We got them outside of Port Albirni

Mike Madigan said:

I too have the same issue, and I think I got my fish roughly the same time as you two. Would love to know your source but I am losing roughly a fish a day. I have a 260 gallon tank with. 175 gallon sump tank, 2 40x48 inch 12 ince deep media grow beds. My readings for nitrites, nitrates, and amonnia are similar to yours, very low. I fish less cycleed in April and May got my fish May 23. Everything was fine u til June 30 when first fish died. Then two days lat another. Took readings 0 for nitrite and nitrate, o.25 for amonnia. I have had 6 fish die this week so far.

Lanna said:

To add to Nathan's Discussion:
I got my fish the same time and place as Nathan. Mine started dying about 3 weeks ago, 1 or 2 a day, then maybe nothing, then more dead the next day. Most of the dead guys have looked fine, however during the last week a couple have now had lesions on their sides..... dissected a couple and they haven't had any food in their bellies. We salted the whole system and have put the fish in a salt bath but hasn't done any good. We have lost about 30 now.....The closest guess we have at the moment is dropsy but we have no idea what's happening.

Water quality/temp is fine. They have grown really well and always ate fine, (feeding trout food).

Thanks for any ideas!

Yeah sorry Mike...it really does suck...I hate losing even 1 fish!!

I think the problem stems back to the supplier though...in our case we couldn't find any supplies on Vancouver Island for months and when we found someone local we jumped at the chance....however the risk of buying off a 'backyard' breeder is the risk of inbreeding and therefore fish that are less immune to disease...I thinks thats what happened to Lanna and I. Mike did you get yours from a legitimate breeder?

I have tried everything above but am still losing 1 or 2 a day...some things that I have noticed make the issue somewhat worse is feeding and higher temps...so try and avoid those and provide lots of DO...I have been looking into medication but really want to avoid at all costs...so for now still plenty of water changes...keep me posted Mike!

Thanks Nathan. I just added a huge air stone in my sump tank, if it is DO then it should stem the problem. I had two more die today, could have been building up. My fish swim close to the surface now they use to swim deep. I got my fish from a breeder in Florida.

Some people have told me to salt the fish, still thinking about that, trying the airstone for a while see if that stems the death. I will keep you informed.


Nathan Harben said:

Yeah sorry Mike...it really does suck...I hate losing even 1 fish!!

I think the problem stems back to the supplier though...in our case we couldn't find any supplies on Vancouver Island for months and when we found someone local we jumped at the chance....however the risk of buying off a 'backyard' breeder is the risk of inbreeding and therefore fish that are less immune to disease...I thinks thats what happened to Lanna and I. Mike did you get yours from a legitimate breeder?

I have tried everything above but am still losing 1 or 2 a day...some things that I have noticed make the issue somewhat worse is feeding and higher temps...so try and avoid those and provide lots of DO...I have been looking into medication but really want to avoid at all costs...so for now still plenty of water changes...keep me posted Mike!

Both Lanna and I tried using salt without much effect on the die off...I tried both non iodized and Epsom salt but only at around 1-2 ppt...I think Lanna tried higher...at low concerntrations it can't hurt

If you can see your fish in the tank, check to see how they are floating in the water column.  If you have tilapia hanging at about a 45 degree angle instead of flat; I'm afraid they may be doomed already or at least very compromised.

Let us know they are hanging funny please, thanks

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