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Discussion Starter · #1 ·
I have a breeding population of 6 R. imitator (nominal) in my tank that have established a colony in a single large brom. 2 of the 6 started growing about a month ago and have not stopped. The largest is almost the size of a quarter now, which is now the largest imitator I've ever seen, and is so fat that it looks like it swallowed a marble. Its also starting to lose its yellow all over its head and half way down its body and beginning to turn burnt orange. I'm curious if anyone else has seen this?

My main hobby and profession is saltwater fish so I'm thinking that maybe its the same sort of hierarchical system we see with clownfish. One is female, one is male, and the rest remain sexless. I'm certain that there are no sexless individuals in this population, but the point is that two become dominant and significantly larger and the others remain small. Can anyone verify my theory? I might be able to provide a picture of the largest individual if I can catch it.
 

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Sounds to me like you have a female that reached sexual maturity - they can get wide!
Coloration can change with maturity, but diet can greatly affect it, as well.
IME, a breeding group of 6 imitators slowly dwindles down to a pair, unless it is a large vivarium, with plenty of hiding places and visual barriers.
 

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Discussion Starter · #3 ·
Ok, that makes sense. Yeah the tank is roughly 200gal with a ton of broms. I'll have to snap a picture of her, she's huge.
 

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I would think that you would have less of an issue in a tank of that size, but it is still very possible. I'm having trouble finding it, but I read a fairly recent paper by Dr. Kyle Summers (yeah, R. summersi) and a few others (Brown and Morales IIRC, might help you find the article if you're interested) that estimated imitator home range at ~10 square meters (high variance based on density of available breeding sites) per pair from the three locations they observed. They did see some territory overlap IIRC, but even with all of that space in nature, territory defense & intrasex aggression have been recorded pretty frequently.

You're right, clownfish do tend to have similar issues, and the solution is pretty similar.. I've read a few accounts of people solving their issues with multiple pairs by adding RBTA's (bunches of broms) at opposite sides of the tank and live rock (tall plants or driftwood) between as a visual barrier. Same concept, and just like with clownfish, adding broms/visual barriers isn't guaranteed to solve the problem... but it will help your chances a lot.

It's possible that the two largest are both females, and the others are male... imi females are usually way bigger (sometimes by up to .5") and fatter than the males. Either way, keep a close eye and have an extra tank ready just in case. I hope that helps.

Also, I really like parentheses.
 

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Discussion Starter · #5 ·
I was able to catch and snap a picture of the largest individual. I should have measured her while I had her in my hand but I didn't think of it. She's about 3/4-1" from anterior to posterior end and when she flattens her belly on a surface her abdomen is about the size of a dime. I haven't noticed any dominance as of yet, but that's not to say that it hasn't happened. They have 15 broms to hang out in with multiple pieces of drift wood, but they all tend to keep to the same large brom towards the bottom of the tank. Oddly enough I usually find eggs in other locations but they spend all their time in the big one.

I'll upload the pic when I get home so I can get it off my phone.
 

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There are those who have success keeping imitators in groups. I personally wouldn't do it (although in a 200 gallon tank you're far more likely for success than those who keep their group of six in a 40 breeder).

I"ve heard a number of horror stories about keeping imitators in groups. Wouldn't surprise me if dominance is starting to show if they're entering into sexual maturity. Imitators tend to display monogamous tendencies (monogamy in imitators is discussed at length in the article “A Key Ecological Trait Drove the Evolution of Biparental Care and Monogamy in an Amphbian” by Jason Lee Brown, Victor Morales, and Kyle Summers) and so the group setting don't seem to go very well for these guys....
 
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