Consistently High Mortality Rate

[Jake Livesay]

I received 100 tilapia fingerlings on July 1st and have been losing one per day, every day, with a few ups and downs (I'm down to probably 30 to 40 fish now).  The fish were all less than one inch long when I received them (although now some are as long as 3 inches while some are still else than an inch).  For the most part, the fish all looked perfectly healthy to me at the time of their death.  Some were bloated, some had slightly cloudy eyes, and some had been partially cannibalized.

 

I have all the following parameters within recommended ranges:

Ph (7.5 - 7.8)

DO (2 - 5 mg/L)

Tank Size (250 gallon)

Temperature (83)

Feeding (crushed small pellets from tilapia company)

Ammonia (as close to zero as I can read from the test kit)

 

I recognize that there could be some bullying, but I don't see the signs I would expect to see, such as mangled skin, fins and tails.  

 

Parasites?  Streptococcus?  Any advice will be most welcome.

[TCLynx]

What sort of filtration do you have? 

How much pumping and aeration? 

DO of 5 ml/L may be within the acceptable range for tilapia but down to 2 mg/L is too low for comfort.

 

Do you have any nitrite or nitrate readings?

 

I would probably start by salting the system to between 1-3 ppt of salt.  That would be 1-3 kg per 1000 liters.  I usually use the cheapest solar pool salt or solar water softener salt.  I would dissolved the salt in a bucket of system water before dumping it into the system.  This will work as a general tonic for the fish and can help against nitrite toxicity if you have a nitrite spike going on and at 3 ppt can even treat parasites like Ick.

 

If your system isn't pumping 24/7 and if you have any algae going on, fish could be running out of dissolved oxygen overnight.

[Jake Livesay]

Many thanks for the reply ...

 

I'm using a pond 'mini beast' with an extra air line below the bio-balls, and another air line connected to an air stone at the bottom of the tank - according to the pump speed, the water should be filtered more than twice per hour.  I'm a little dubious about the DO since the 'color test' technique is pretty subjective ...  Do you think adding another couple air stones would get me comfortably above 5 mg/L ?

 

Nitrite and Nitrate are both reading zero (as far as I can tell with my naked eyes).

 

I haven't tried the salt trick yet, but will happily do so this week.

 

The system is running 24/7 and I have not seen any evidence of algae...

 

 

 

.

[TCLynx]

Hum, in that case it doesn't sound like a filtration or aeration problem.

 

Unless there is a problem with your test kit, you can always take a water sample to the pet store as many of them will run water tests for you which can help make sure there isn't a faulty re-agent in your kit.

 

One other possible issue could be the feed.  How old is it?  Has it been kept cool and dry?  Really high protein feed for fry doesn't keep very long.  I had to get rid of half a bin of feed not too long ago when I was having trouble with unexplained fish deaths.  I think I've only lost one since I got rid of that feed.  I now only buy fry and grower high protein feed in 5 lb bags.  I only buy 50lb bags when it's the lower protein grow out feed for all the fish.

 

The salt trick may help then.  If you have any strawberries in the system or other salt sensitive plants though the salt will probably not be good for them.

[Jake Livesay]

i got a water test at a local pond-and-aquarium store ... my levels were consistent with what they found, but they didn't do a DO test ... i guess because oxygen will come out of solution on the way to the store ...

 

i really appreciate your advice ... would you tell me where you buy tilapia food ... ?

[TCLynx]

Well I don't actually grow tilapia anymore but I've been feeding the same feeds to my catfish and bluegill as I fed to tilapia.

 

I have an advantage of Having Aquatic EcoSystems local to me so I can go in and pick up a 5 lb bag of feed from them without dealing with the shipping.

 

For my 36% (? maybe it's only 32%) protein feed I use Aquamax Dense Culture feed or Aquamax 4000.  It is a purina mills product.  Lets see I'm sure I have written a blog post about buying fish feed. Here it is it's the last paragraph that tells about getting feed locally.

[Sylvia Bernstein]

You are getting great advice from TC here, Jake.  I just wanted to jump in with a link for an excellent source of tilapia food if you don't have access to local Aquamax - http://www.theaquaponicstore.com/Tilapia-Feed-s/71.htm.  This is a family owned (he is a member of this community site) small batch, high quality producer.  I hope the salting works!

[TCLynx]

Ah there you go, good feeds in reasonable quantities.  (Just curious, who is our feed producer?)

 

[John Jay]

It has not been stated, just to remind you  on pump speeds,, many pumps lie about the gph  and head hight and back pressure reduce flow.  My fish are provided a 8 inch PVC tube to duck the current  or they have to swim .

[Jake Livesay]

never thought about that one ... they can get exhausted from fighting the current .... thanks.

John Jay said:

It has not been stated, just to remind you  on pump speeds,, many pumps lie about the gph  and head hight and back pressure reduce flow.  My fish are provided a 8 inch PVC tube to duck the current  or they have to swim .

[Jake Livesay]

i got feed from the same folks i got the fish from: r&d aquafarms ...  it's meant to be the same stuff they feed the fish while they have them ...

TCLynx said:

Ah there you go, good feeds in reasonable quantities.  (Just curious, who is our feed producer?)

 

[TCLynx]

Oh, actually that question was for Sylvia

[Jake Livesay]

Update: 

 

I added 3 lbs of salt and two more air stones to my system...