Diagnosing Flukes

[bouttreepriddy]

The past couple of days I've seen some odd behavior from my fish that I suspect could be flukes. I am planning to try a freshwater dip on my emperor angelfish to check. Any other recommendations for diagnosis or things I should be on the lookout for?

Timeline of aquarium additions:
- June 2025 - eye fluke outbreak wiped out most of my tank. After five rounds of prazi the issue appeared to be under control
- 3/15/26 - Added two tangs from my LFS after completing 14 days of chloroquine phosphate and 4 doses of prazi 8 days apart.
- 4/15/26 - Added two tangs and an angel from a quarantine vendor. One of the tangs died while in an acclimation box inside the tank. I attributed this to stress from shipping.

Symptoms:
- Most of the tangs and emperor will occasionally swim into a powerhead for a few minutes
- Starting to see HLLE on blue tang
- Emperor angelfish is breathing heavily and lethargic today
- Blue green chromis died after 3 years in the tank
- I don't see any obvious eye cloudiness
- No obvious symptoms from either of my dwarf angels

See video attachments below. Any ideas?

 

[bouttreepriddy]

The past couple of days I've seen some odd behavior from my fish that I suspect could be flukes. I am planning to try a freshwater dip on my emperor angelfish to check. Any other recommendations for diagnosis or things I should be on the lookout for?

Timeline of aquarium additions:
- June 2025 - eye fluke outbreak wiped out most of my tank. After five rounds of prazi the issue appeared to be under control
- 3/15/26 - Added two tangs from my LFS after completing 14 days of chloroquine phosphate and 4 doses of prazi 8 days apart.
- 4/15/26 - Added two tangs and an angel from a quarantine vendor. One of the tangs died while in an acclimation box inside the tank. I attributed this to stress from shipping.

Symptoms:
- Most of the tangs and emperor will occasionally swim into a powerhead for a few minutes
- Starting to see HLLE on blue tang
- Emperor angelfish is breathing heavily and lethargic today
- Blue green chromis died after 3 years in the tank
- I don't see any obvious eye cloudiness
- No obvious symptoms from either of my dwarf angels

See video attachments below. Any ideas?

 

[bouttreepriddy]

Adding one more video showing heavy breathing, tattered fins, and some kind of mucus from the eye of the emperor. Other fish are eating as normal.

 

[Jay Hemdal]

Adding one more video showing heavy breathing, tattered fins, and some kind of mucus from the eye of the emperor. Other fish are eating as normal.

The emperor angels are very prone to Neobenedenia flukes. Neo is tough to kill with prazi, I use hyposalinity in a fish-only tank. It does look like Neo on your angel, but I can’t explain why at least some f your other fish aren’t showing similar symptoms.

The HLLE is unrelated to flukes.

 

[W31Olds]

Your Emperor is in distress and should be moved to a Hospital Tank. You could try a FW Dip as Angels usually tolerate them well however yours is very sick so there is risk. You need to begin Prazi once again. I doubt your Tang died from Stress in the acclimation box. BTW, how did you acclimate your last batch of fish? A Salinity mismatch can lead to problems. I have a problem trusting QT'd Fish and would at least observe them in a separate Tank. It's pretty easy for something to slip through,

 

[vetteguy53081]

I would not do a series of dips which are capable of stressing this fish out and mismatch of salinity unlikely a trigger. Some signs associated with flukes are red or swollen with rapid breathing, fish acting lethargic or swimming near the water surface, hiding in the corner of tank or behind rocks, loss of appetite, shaking its head, flashing/darting, develop clamped fins, , or scratching against objects. They may also exhibit what looks like yawning from gill irritation develop, cloudy eyes and loss of color which the fish appears to have.

 

[W31Olds]

I would not do a series of dips which are capable of stressing this fish out and mismatch of salinity unlikely a trigger. Some signs associated with flukes are red or swollen with rapid breathing, fish acting lethargic or swimming near the water surface, hiding in the corner of tank or behind rocks, loss of appetite, shaking its head, flashing/darting, develop clamped fins, , or scratching against objects. They may also exhibit what looks like yawning from gill irritation develop, cloudy eyes and loss of color which the fish appears to have.

I understand the symptoms associated with Flukes and agree with Jay's diagnosis. I viewed the Video and the OP's fish are clearly Scratching and Flashing (Hippo and Sailfin). I would run Hypo also, but OP's Emperor is in bad shape, and it takes time to get to Therapeutic levels.
The OP lost a Tang in March while in an acclimation box per his quote which is why I commented on how they were acclimated.

"- 4/15/26 - Added two tangs and an angel from a quarantine vendor. One of the tangs died while in an acclimation box inside the tank. I attributed this to stress from shipping."

 

[bouttreepriddy]

The vendor ships at the same salinity as my tank and recommends only temp acclimating so I followed their guide. It was a small naso that looked pretty stressed out in the bag but no obvious illness and the other fish looked fine.

I wasn't sure that I was observing flashing and scratching as much as it looked like tang aggression but it was likely wishful thinking along with ignoring the swimming into the powerhead. I figured the blue's hlle was also related to stress from no longer being the only tang in the tank. The emperor was eating vigorously yesterday before lights off and was consistently the first fish to greet me at the glass so I wasn't particularly worried until it stopped eating and became discolored which happened overnight. All other fish are still eating fine.

I moved the emperor to my frag tank (same system but fishless) and dosed prazipro on the whole system. I used general cure for previous treatments in qt so I switched in case it was something wrong that batch. Hypo will likely be difficult for me to manage given the size of my tank and the amount of coral in it. I will change my qt method moving forward to include hypo since this is the second time I've run into this and will stop using others for quarantine.

 

[W31Olds]

Emperors will often show discolored patches with a milky appearance when something is bothering them. I lost one last year that looked similar to yours that probably had Gill Flukes but did not respond to treatment quick enough. My current one will show some small, discolored dots usually when stressed. The problem with Prazi is it loses its effectiveness after repeated doses due to bacteria breaking it down. A Qt Tank is a better option for treatment because it's easily reset. You may want to check General Cure as I believe it has a lower Dose of Praziquantel and we don't recommend it for Flukes.

 

[Jay Hemdal]

The vendor ships at the same salinity as my tank and recommends only temp acclimating so I followed their guide. It was a small naso that looked pretty stressed out in the bag but no obvious illness and the other fish looked fine.

I wasn't sure that I was observing flashing and scratching as much as it looked like tang aggression but it was likely wishful thinking along with ignoring the swimming into the powerhead. I figured the blue's hlle was also related to stress from no longer being the only tang in the tank. The emperor was eating vigorously yesterday before lights off and was consistently the first fish to greet me at the glass so I wasn't particularly worried until it stopped eating and became discolored which happened overnight. All other fish are still eating fine.

I moved the emperor to my frag tank (same system but fishless) and dosed prazipro on the whole system. I used general cure for previous treatments in qt so I switched in case it was something wrong that batch. Hypo will likely be difficult for me to manage given the size of my tank and the amount of coral in it. I will change my qt method moving forward to include hypo since this is the second time I've run into this and will stop using others for quarantine.

One problem I didn’t mention is that multiple prazi treatments on the same tank grows a population of long-lived bacteria that actually consumes it. After 4 to 5 treatments, prazi is rendered ineffective against flukes. This gives rise to the “prazi resistant flukes” that you read about - but the flukes aren’t resistant, the tank is!

 

[bouttreepriddy]

For now, I've started dosing prazi. I moved the emperor to my fishless frag tank connected to the same system but unfortunately lost it shortly after dosing prazi. The rest of the fish started showing obvious scratching symptoms after prazi (with the exception of my two dwarf angels and firefish) but fortunately no additional losses have happened yet.

Where were these flukes most likely to come from? Could they have remained in my tank from my outbreak a year ago and due to the low stock of the tank weren't able to reproduce enough until recent additions? Or is more likely a failure of my qt protocol for the additions?

For long-lived prazi consuming bacteria do we expect that they are still present at an elevated level in my tank from prazi dosing a year ago or is long-lived likely closer to a few months?

 

[Jay Hemdal]

For now, I've started dosing prazi. I moved the emperor to my fishless frag tank connected to the same system but unfortunately lost it shortly after dosing prazi. The rest of the fish started showing obvious scratching symptoms after prazi (with the exception of my two dwarf angels and firefish) but fortunately no additional losses have happened yet.

Where were these flukes most likely to come from? Could they have remained in my tank from my outbreak a year ago and due to the low stock of the tank weren't able to reproduce enough until recent additions? Or is more likely a failure of my qt protocol for the additions?

For long-lived prazi consuming bacteria do we expect that they are still present at an elevated level in my tank from prazi dosing a year ago or is long-lived likely closer to a few months?

Prazi doesn’t kill fluke eggs and it has been demonstrated that one egg can start an infection.
The prazi bacteria is active for at least 6 to 8 months in my experience. I’m not sure how long it persists.

 

[bouttreepriddy]

Preparing for my third dose of prazi on Wednesday and so far there have not been any additional losses and symptoms have subsided.

The hlle on my blue tang has also now gone away. Dosing prazi coincided with stopping carbon and UV so either that or reduced stress seem like the likely causes.