6 replies to this topic

[az9]

I produce and sell several species of native fish in ponds and small scale recirculating systems. Recently received 300 blue tilapia fingerlings for a seperate project and have had issues from the get go. Now keep in mind, tilapia are typically bullet proof compared to other species, with the inside joke among aquaculturists that you can almost raise them in gasoline.

I've been losing up to 5 per day with ammonia and nitrites reading zip. Plenty of oxygen in the 150 gallon circular tank they are in, serviced by 3 cubic feet of plastic media tumbling in a 55 gallon drum, and another drum preceding that which acts as a clarifier. Suspended solids are fairly low and settleable solids are removed on a regular basis.

Here's the thing: In my cool basement I heat the make up water from a well to about 81 F. From 51.6 F. in a 24 hour period. I have two drums in a tandem circuit and siphon with one packed with fiter material that removes the precipitated iron. In the past I didn't heat it that much and used a larger pump to circulate the water between the drums.

Aditionally I rerouted the pump flow from the top of the clarifier tank to the top of the moving bed biofilter vs. the bottom due to some mulm building up in the longer waterline to the bottom of the biofilter media drum.

Could the additional heating in the make up water tank, smaller circulating pump reducing the exposure of the water to air to off gas the heated water, and rerouting of water to the top of the biofilter have set my fish up to gas bubble trauma?

I've been beating my brains out trying to figure out what is stressing these fish and can't come up with anything else.

My source is a very reputable source and I had no problems the last time I got fish from them.

Thoughts?

Edited by az9, 26 August 2015 - 09:04 PM.

[az9]

Have ruled out gas bubble trauma. Fish probably have either parasite and/are some type of bacterial issues that were brought in with the fish.

Put the biofilter off line and treated the fish tank with 2 mg/l potassium permanganate. After 2 hours the pink seemed to turn to brown so added one more mg/l of PP. After four hours added hydrogen peroxide to neutralize and remove the manganese precipitate.

I have lost a few more fish but it's hoped those fish were probably already on the way out and the PP treatment was the coup de grace.

Most of the fish are feeding well and the water is gin clear.

Advised to do up to two more PP treatments spaced apart to kill any residual parasites if that indeed is the culprit.

If that does not do the job will euthanize all fish and sterilize the entire system including the biofilter and start over.

Previous antibiotic treatment in the feed was not effective. (Fish are not destined for the table but for control of filamentous algae in ponds)

Edited by az9, 31 August 2015 - 05:22 AM.

[sbtgrfan]

Have you done a necropsy on them to try to identify parasite/bacteria? How did you rule out gas bubble trauma?

[az9]

No necropsy as I don't have the skills or equipment for that yet. Did see some skin damage on a couple of fish close to death that looked either parasitic or bacterial. A few of the fish appear to be bloated before death and exhibit exophthalmos. After the PP treatment the number of morts has decreased by at least 50 percent.

My problem is this is the first time I've ever had an episode of this many deaths. Normally the fish I hatch myself (yellow perch and bluegills) are very healthy and do exceptionall well in the RAS'. Nearby fish health experts are nonexistent and my experience with Purdue's fish health testing has been less than steller.


As far as the GBT I filled a test tube with water and sealed, and did not observe any airbubbles on the inside of the tube next day. Have been vigorously aeratng the make up water ever since and not allowng the exit water line to one of the drums of the iron filter/ make up water to stay submerged.

Not an expert by any means when it comes to fish pathology but hope to eventually have a small lab set up with all the right equipment.

Will also set up a quarantine tank and treat incoming fish with PP or a Salt dip! Used to dip the fish from the ponds in a 3 percent salt dip. Will start doing so again!

[az9]

So far morts and morbidity are all but nonexistent. Getting ready for third and final treatment of PP and started a second antibiotic treatment. (PP treatment after 5 day antibiotic treatment). The first antibiotic treatment I had doubts fish were feeding well enough to get the amount of antibiotic treatment required from the treated feed. However after the PP treatments the fish are feeding voraciously.

The particular broad spectrum antibiotic I'm using says a second treatment is O.K. as long as the treatment is spread out enough.

As said earlier these fish are NOT destined for the table. Might as well be ornamental fish as are my other species sold whole frozen at trophy size to fellow taxidermist and replica makers. Going to be used for filamentous algae control next spring in enclosed ponds with NO outlet.

My thinking is due to an unknown stressor, fish were susceptible to bacteria and or parasites. The PP treatments spaced apart are nailing various stages of parasites, and the antibiotics are addressing opportunistic external and systemic bacterial pathogens.

I'm not a big fan of antibiotics but have a sizeable investment here.

You can be sure my bluegills that will be coming in from my hatchery pond soon, will get a 3 percent salt dip before going into a tank! Will set up a quarantine tank in the near future and all fish destined for the tanks will get a salt or PP dip!

Edited by az9, 06 September 2015 - 08:11 AM.

[Matt DeLaVega]

Glad you solved the problem. However it sure would be nice to know what the problem was.

[az9]

Glad you solved the problem. However it sure would be nice to know what the problem was.

Yes it would be!

Bringing in several hundred bluegills in a different system soon. Hopefully no issues with them.