[Rare Angels]

Hello Lee,

I have a question concerning fish developing bacterial infections in an established system. The fish were all moved from individual tanks to a central breeding system. After 2 months several of them have developed a bacterial infection.

I have treated new fish for bacterial infection while in QT but I have never had a bacterial infection arise in established fish and system. The new breeding system had been running for several months with roughly the same bio-load.

Do I just treat the sick fish or do I treat the entire sytem? This is something I haven't run across before.

Thanks for the help

Dave

[leebca]

Hi Dave,

For some reason the fish were stressed. Bacteria is pretty much around the fish all the time and the infectious kinds are opportunistic. So something stressed the fish or the fish are in a continuous stress, which allowed their natural defenses to be compromised. You should work at trying to find the stressors -- Even if the infection is cured, if the stressor(s) are still present, the cure won't last long.

One stressor is that the infection is a prelude to some other illness or condition or parasite attack.

Another stressor is that the bacterial bloom is so large or of such a kind in the breeding tank that the fish couldn't stand them off. That is, numbers or types of bacteria new to the fish.

You may find other possible stressors from this: Stress (and the Single Marine Fish)

Being a breeder I'm sure you're conscientious about nutrition. Still the scenario you painted implies a possible nutritional stressor. At this point in time, you should be feeding the fish beta glucan to help them recover.

A possible stressor may be an acclimation problem. Maybe the acclimation wasn't done properly or given enough time; maybe the two waters were different in pH or some other component.

Ideally, you'd like to know what kind of bacteria they are so you can choose the right antibiotic. Assuming your system isn't a reef, I would treat the entire system with a gram negative antibiotic first. If that doesn't work, switch to a gram positive or a potent positive/negative antibiotic. A system treatment with a gram negative antibiotic (like Maracyn Two for Saltwater fishes) should leave the biological filter running and in tact. If it comes down to switching antibiotics to a gram positive killer, you'll probably kill the biological filter you have on that system. So if a switch is needed, and before the switch, you'll have to decide where to treat them.

Monitor for ammonia and nitrites every few hours before, during, and after treatment.

The most likely stressor is one you say is not possible: the bio-load was almost the same. This stressor leads to biological filtration interruption which causes a water quality decline that leads to a 'poison' stressor to the fish. A sudden/large shift in quantity AND/OR type of bio-load in a system has a direct affect on the biological filter and an indirect effect on the fish from poor water quality. In such a case as this, the aquarist may (or may not) detect a short-lived spike in ammonia and/or nitrites which poisons the fish enough to let infectious bacteria get a foothold. This is quite often a prime stressor leading to QT fish bacterial infections, which are seen quite often.

Watch for secondary problems or the fact that this may be a secondary problem.