Peacock mantis shrimp issues

[WingerBlast]

Hi everyone,


I’m having a strange issue with my peacock mantis shrimp (Kaiju), and I’d appreciate any experienced eyes on this because I’ve had a previous mantis (Ace) pass away with similar symptoms.


Background

• My previous mantis (Ace) lived 7 months, molted successfully, then suddenly developed violent “burst” spasms and died 3 days later.
• I performed a water change, waited a few days, and added a new mantis (Kaiju).
• Kaiju acted completely normal for ~3 weeks (hunting snails, eating well, exploring).
  The only unusual behavior was swimming up the glass, which I assumed was a pre-molt sign.

Current Issue With Kaiju

• Kaiju molted successfully last Saturday at 6pm (complete shed visible).
• Day 2 after the molt, he began having the same spasms Ace had (violent bursts around the tank, then recovery).
• Spasms are not daily, but have happened about once every 1–3 days.
• After each burst he recovers within minutes to an hour, returns to his PVC burrow, and moves normally.
• No discoloration, no cloudy eyes, no rot. He arrived missing one raptorial appendage and had some shell damage, but most improved after molt.
• He has not hunted since the molt. He ignores emerald crabs completely and only responds to frozen foods.
• I fed him clam yesterday; he ate about 1/3 of it.
• He sometimes swims upward, hits the glass, or falls on his back but then rights himself quickly.
• He occasionally sits in the same corner under the heater for 20–60 minutes.
• No uncontrolled constant seizures like Ace had in her final days.

Water Parameters

(Checked multiple times over the past week)

• Temp: 78°F
• Salinity: 1.026
• pH: 7.8–8.0
• Ammonia: 0
• Nitrite: 0.25 (has been elevated since the molt)
• Nitrate: 10–20 ppm
• Tank is grounded, GFCI outlet, titanium probe
• Filtration: Seachem Tidal 35 (Matrix, sponge, filter floss) + PolyFilter + CupraSorb (did not change color) + activated carbon
• Domino damsel and two emerald crabs are acting perfectly normal.

What I’m Trying to Figure Out

• Could this be a post-molt neurological issue?
• Could a nitrite spike cause intermittent spasms like this?
• Could this be bacterial, fungal, or parasitic since only mantis shrimp are affected (not fish/crabs)?
• Is it possible there is some contaminant that only affects stomatopods but not fish or crabs?
• Is there something else I should be testing for?

Other Notes

L

• Kaiju is active between episodes, explores, walks around the tank, flinches normally, and reacts to light.
• Last burst was Friday 7am.
• Had burst today

Any ideas or similar experiences would be extremely helpful. I’m trying to figure out if this is recoverable or something systemic in the tank


Thank you.

 

[Fish Fan]

Welcome to Reef2Reef!

#WelcometoR2R

@Stomatopods17 is a good resource for Mantis related concerns.

Good luck!

 

[Stomatopods17]

As said in DMs; I'd have to see what these spasms look like but typically larger specimens will do these suddenly twitching motions over the course of a few days / weeks while their shell grows back in isolation.

In other words if the molt went well with a sealed burrow and all you probably shouldn't even be able to observe these spasms visually. It is a very stressful time and that could contribute to neurological problems but just unsure if thats the case here without actually seeing it, they need to be dark and sealed during this time.

Example of how they'll fidget for while;