Hi all.. so let me just say I've been at this hobby for awhile, and had thought I'd seen most cases of strange fish deaths attributable to disease, stress or some sort of catastrophic water quality issue. Well, that concept has gone quite out the window. I'm pretty much pleading for any thoughts/suggestions people may have on how I lost four tanks of fish in the last 72 hours.
So this is the background. I'm maintaining a small breeding facility for zebrafish, Danio rerio. Equipment is four ten gallon tanks, each with five fish, with visitherm 50W heaters holding steady temperature at 78F and an aquaclear 201 PH at the lowest setting with a quickfilter attachment for biological/mechanical filtration. Water quality pH 6.8, very very soft water (almost entirely RO/DI with a little reconstitution), stable kH/gH, but I dont recall values at the moment. No substrate, only plastic floating plants to allieve stress. No ammonia or nitrite readable, nitrates holding at 5. Water changing is twice weekly at 40%. Feeding BBS 2x daily and basic flake 1x.
So here's the story: I go on vacation for six days, leave measured amounts of refrigerated hatched BBS for my stand-in to feed (less than I usually feed to avoid overfeeding problem). She faithfully attends to the fish but makes no water changes. All is well, temperature holds, filtration holds. I arrive home (Day one) to four tanks full of happy fish. No changes in water quality values, but nitrate comes up to 5-10 range. I change water at usual 40%.
On day two I find two males have dropped dead in just twelve hours. A rough layer of mucus, whitish in color, develops. I'm perplexed, change water on their tank, bring temperature up slightly to 80F and watch the remaining males eat heartily their BBS and flake. All the other fish in separate tanks look great and eat well.
Day three, just sixteen hours later, I have lost all the remaining fish (15 of them). All the bodies look like the first two males with a thick rough mucus coating that shakes off the body in small flakes, if you will. The tanks, which were crystal clear when I left them, are extremely cloudy.
Does anyone have any idea how these fish died? Is there any good explanation for their very sudden deaths and the mucus buildup I am finding on their bodies? I did a very crude necropsy on one of the males earlier today and discovered that the gills were very inflamed (almost as is seen with ozone overload in a tank) and some of the internal organs had bled into the body cavity (hemorrhaging?). A search online suggests a protozoan infection of the skin such as Chilodonella.. but would that kill, what appeared to be healthy animals, overnight?
Also, there have been absolutely no additions/changes to their environments or schedules except my vacation. Did the lack of water changes kill these fish? And, if a parasite is more likely, what could be a source? (BBS eggs?? Flake food?? Its a sterile water source by UV so I just dont understand how they would have got it.)
If you've got some answers, pointers or really anything at all I'd be greatly greatly appreciative. These were important fish and I need answers. Thanks for reading this far!
So this is the background. I'm maintaining a small breeding facility for zebrafish, Danio rerio. Equipment is four ten gallon tanks, each with five fish, with visitherm 50W heaters holding steady temperature at 78F and an aquaclear 201 PH at the lowest setting with a quickfilter attachment for biological/mechanical filtration. Water quality pH 6.8, very very soft water (almost entirely RO/DI with a little reconstitution), stable kH/gH, but I dont recall values at the moment. No substrate, only plastic floating plants to allieve stress. No ammonia or nitrite readable, nitrates holding at 5. Water changing is twice weekly at 40%. Feeding BBS 2x daily and basic flake 1x.
So here's the story: I go on vacation for six days, leave measured amounts of refrigerated hatched BBS for my stand-in to feed (less than I usually feed to avoid overfeeding problem). She faithfully attends to the fish but makes no water changes. All is well, temperature holds, filtration holds. I arrive home (Day one) to four tanks full of happy fish. No changes in water quality values, but nitrate comes up to 5-10 range. I change water at usual 40%.
On day two I find two males have dropped dead in just twelve hours. A rough layer of mucus, whitish in color, develops. I'm perplexed, change water on their tank, bring temperature up slightly to 80F and watch the remaining males eat heartily their BBS and flake. All the other fish in separate tanks look great and eat well.
Day three, just sixteen hours later, I have lost all the remaining fish (15 of them). All the bodies look like the first two males with a thick rough mucus coating that shakes off the body in small flakes, if you will. The tanks, which were crystal clear when I left them, are extremely cloudy.
Does anyone have any idea how these fish died? Is there any good explanation for their very sudden deaths and the mucus buildup I am finding on their bodies? I did a very crude necropsy on one of the males earlier today and discovered that the gills were very inflamed (almost as is seen with ozone overload in a tank) and some of the internal organs had bled into the body cavity (hemorrhaging?). A search online suggests a protozoan infection of the skin such as Chilodonella.. but would that kill, what appeared to be healthy animals, overnight?
Also, there have been absolutely no additions/changes to their environments or schedules except my vacation. Did the lack of water changes kill these fish? And, if a parasite is more likely, what could be a source? (BBS eggs?? Flake food?? Its a sterile water source by UV so I just dont understand how they would have got it.)
If you've got some answers, pointers or really anything at all I'd be greatly greatly appreciative. These were important fish and I need answers. Thanks for reading this far!
