in the past, i have had brackish and saltwater native fish that i have kept that have been struck with the fish killer, Pfiesteria piscicida. i was actually able to catch the nasty little dinoflagellate red handed when i took a skin scraping of the sores that were affecting them. i ended up completely destroying the tanks, because it simply wouldn't go away. well, i think i have encountered it again, this time in my freshwater tanks.
back info: I recently acquired some beautiful native fish from a recent NANFA outing and began slowly acclimating them to my tank. i left them in about five gallons of water and slowly changed their water out with water from my 65 gallon display tank until they were in essentially the same water as what was in my tank. i replaced the tank water in the tank with prepared dechlorinated tap water, as i have always done. the first night, sunday night, all seemed well.
the fish seemed healthy, calm, and content. they even ate a little for me. the next morning i woke up and found that a couple fish had small white spots on them. i tested the water params, 0 ppm ammonia, nitrites were less than .5(enough to read a presence, not enough to quantify on the test i have) and my nitrates were up around 15 ppm. i added CO2 at that time as that always help s my plants pull the nitrates out. the temperature was about 76 degrees and pH was about 7.2. later that day i saw some fish starting to twitch and dart quickly around the tank until they slammed into a wall and knock themselves out. one fish swam up the output of a power-head and managed to make it to an impeller. it didn't fare well at all. at least it was quick... i did a 50% water change and added some dechlorinator just in case i may have had residual chlorine. a couple chlorine tests later revealed no chlorine(liquid drop test, not strips). i added aquarium salt and melafix as treatment and raised the temp to about 79 degrees. by Monday evening the fish looked for the most part OK, except for a few tiny spots that i wasn't even sure was caused by a pathogen(i did just recently handle all of them after all) and strange behavior exhibited by a few of my fish(twitching, darting). the next morning a couple fish were dead and the small white spots non the remaining fish had turned into nasty looking bleeding ulcers. the tank already had a several fish in it, one dollar sunfish(who remains unaffected) one blue spotted sunfish, and a small population(about 6) of gambusia halbrooki. the gambusia were affected, as well as the blue-spotted sunfish. several of my new fish(most of the crescent shiners) had ulcers on them. i added a little more salt and another dose of melafix and did a water change. my tap water has about(at least) .25 ppt ammonia in it, so i try to avoid water changes if i can. i then got dressed and went to work this morning.
tonight, when i got home, i had about twelve fish dead in my tank. i removed all the dead fish( did a thorough search) the deaths include all of my crescent shiners that were less than 1.5 inches long(6 or so), all three Roanoke shiners, and a few rosy-face shiners as well as my blue-spotted sunfish. the blue-spotted sunfish went from having a fuzzy white patch on its dorsal fin to the entire upper half of its body being an ulcer. it was alive when i got home but died withing a couple hours after that. since i have been home, nearly every fish has developed ulcers, except for my dollar sunfish.
for treatment i decided to nuke the tank. i know that my new natives prefer a lower pH, but i have NEVER seen a pH change do this to fish. i did little autopsy of my blue-spotted sunfish and was able to determine that its entire digestive tract was riddled with hemorrhagic ulcers and its liver was very swollen and had a lot of hemorrhagic regions as well. a skin swab revealed small round spores under the microscope. i don't have any agar handy so i cant do a culture on it. since the fish was already dead, i decided that it probably wasn't the best specimen to swab, so i took one of my live affected fish and swabbed its affected area. what i saw under the microscope shocked me. there was an amoeba like creature that i have seen before. as i watched, the water on the slide began to evaporate. as it did, the organism shifted forms into a perfectly spherical cyst. i added a little more water to the slide, after it had completely dried, and the cyst came back to life within a few minutes and assumed a different form, complete with flagella. i have seen this before, but never in freshwater.
what i believe i have is pfiesteria piscicida. looking through literature, there have been instances of it killing fish in practically fresh water, and im sure i haven't been helping the situation by adding salt to the tank. i thought i was doing the fish a favor. looks like i was just giving the pathogen a leg up.
i have already nuked my tank. i turned the filter off, added a large bubble wand and left the power head running(it produces riffle0like currents.) i may have gone a little overkill on the fish treatments this time,(erythromycin, ampicillin, and tetracycline as this stuff leaves them wide open for bacterial infections, if it doesnt kill them) but if i am right, the fish are dead anyway, its just a matter of time. the amoeba thing i saw is one of the toxic stages of piscicida, and it WILL kill all of my fish eventually. When it penetrates the slime coat on my dollar sunfish, it will kill it too. i am removing him into tank by himself, since he doesn't appear to be affected yet.
anyway, since i have been typing this, i have had three more fish die and the sores i see have actually gotten larger. and that is even in the ones i have isolated in hospital tanks. this is some nasty stuff.
i may end up destroying all of the fish plants and fish involved and sterilizing everything in the tank with bleach.
if this truly is caused by a rogue form of piscicida, im not taking any chances and im not playing games. i am fascinated by the little dino, but since i understand what it is capable of, it scares me.
Edited by Auban, 30 May 2012 - 12:00 AM.