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Background:
I've got a small aquaponics setup with a 150 gallon fish tank and about 500 gallons of floating raft space.  I got my tilapia a little over three months ago from a friend's brackish pond down in Kapoho on the Big Island of Hawaii.  The system was previously cycled w swordtails before adding the tilapia.  The current population is about 50 wild-caught Mozambique Tilapia ranging in size from 1" to 10" with the majority around 3 inches and only three in the 10" range.  Also I have about 35 koi fingerlings in the same tank.   Water quality is testing at excellent levels, pH 7.2, temp 75 degrees F, no nitrites, no ammonia, almost no nitrate readings - maybe 3 ppm, and dissolved oxygen at 6 ppm all day and night.  I'm feeding small amounts (only what they can get on their initial pass - maybe 30 seconds) three time a day never leaving any excess.

Problem:
Some fish look bloated w eyes bulging out, and cloudy.  Not eating, staying near the bottom, and flashing color to darker shades.  In a couple of fish I've noticed one of the pectoral fins sticking to the body and it swimming only with the other.  After catching or agitation it would start using the "stuck" fin again.
So far I've lost 5 or 6 fish.  I cut one open to find an empty gut and eggs, but probably not enough for the bloated appearance.  And I've transferred a dozen of them to a 50 gallon holding tank where I added 6 ppt of Salt, stopped feeding, cut out most of the light, and aerated heavily.  They have been doing fine in there for the last few weeks.  No deaths, but they also don't seem to be getting much better.  I originally lost two when I first caught the fish three months ago - I remember they were also flashing colors but I don't remember the eyes bulging.

Best Guess Diagnosis:
Streptococcosis

Does all of this sound correct?  Is it worth continuing to treat the fish in a holding tank, or should I cull all of them and start over with some non-wild-caught fish?  Or is it possibly still the adjustment from the brackish to fresh water?  Can this disease spread to my koi?

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Hi Christian,
Sorry to see your fish like this. I don't have any experience with fish diseases but if the fish have not improved over this time, it may be past the point of recovery. But let's wait to hear from the people in the know. Found this link.

http://www.thefishsite.com/articles/190/streptococcus-in-tilapia
Hi Christian, I have a really slow connection so I can't really load the photos. I'll look at them tomorrow when I'm in town. A few questions:
How do the fins look? are they ragged or do they show blood vessels clearly?
Do the fish have any lesions showing on their bodies? (either white, pink or bloody?)
How do their gills look? Are they bright red or are they pink or are they white to pinkish white in places?
I would cut one open too and look at the guts- but then again I have stains and a microscope. . .

I would tell you that getting rid of them is the thing to do in any case and start from scratch with some disease free stock you've gotten from a reputable fingerling producer. It's always easier to start disease free than to get disease going and then try to get rid of it. If your fish are bloated in any way, remove them immediately and get rid of them. Salting primarily helps with skin and gill diseases.

The fins look great.

No lesions.

I caught two from the hospital tank and checked their gills and they were a nice blood red color, no spotting.

 

Sorry, I know this discussion is old.  However, I have been having the same problem with my male O. Hornorum (specifically the eye issue) and was wondering if you ever determined your problem was strep or not?

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