Mandarin male turned Aggressive!

[Alexraptor]

Was hoping someone could help me figure out a sudden change in behavior.

I had a beautiful Mandarin pair in my 25 Gallon tank that got along just fine. They would sleep and forage together, everything seemed fine... until today.

Today I woke to finding my female hiding in a corner amongst a macroalgae patch, with her fins torn to shreds. As soon as she saw the male she would cower in fear, and the male would start chasing her.
The male has now been exiled to my reef tank where he can cause no more harm, and my female now seems a bit more at ease and is out foraging again.

So.... what the heck just happened??? 4 months, and everything has been fine, better than fine, and then the male just suddenly snapped?

 

[ginpang]

Hypothesis no1) Could your " female" have been a juvenile male?
Hypothesis no2 ) 25 gallons no matter how old even packed with live rock will not sustain a Mandarin let alone two... Probable aggression is dwindling food source.

 

[ThRoewer]

How big are they?

Hypothesis no1) Could your " female" have been a juvenile male?
Hypothesis no2 ) 25 gallons no matter how old even packed with live rock will not sustain a Mandarin let alone two... Probable aggression is dwindling food source.

Food is rarely a direct factor in mandarin fish aggression, especially male on female aggression.

I have 2 mandarins in a 25 gallon and they are doing OK in there for a year now. It isn't ideal, but doable with enough attention on supplementing their food. The statement that they are out hunting for food all day in the wild isn't universally true. They are mostly active in the morning and evening hours and seek cover in holes and crevices during the day.

Maybe we can't tell a juvenile male from a female, but the mandarins themselves can do that very well without looking for the elongated fin.

Most likely the male wants to mate and the female has no eggs.

The other reason could be that the male is too small for the female and that she doesn't accept him as a mate. The male needs to be at least 1/4 more in length than the female, 1/3 would be better. I had that with my two who were of equal size when I got them. There were some fights until the male grow big enough.

 

[Alexraptor]

Hypothesis no2 ) 25 gallons no matter how old even packed with live rock will not sustain a Mandarin let alone two... Probable aggression is dwindling food source.

A myth that just won't die. I've actually successfully sustained my female mandarin for an entire year in a 10g tank primarily on what she can forage in the tank.
Its not just about size, but creating the conditions where food organisms thrive, which IME requires a high nutrient system.
I only upgraded to a 25 because I wanted space to get my female a partner.
Both animals are well nourished.

Most likely the male wants to mate and the female has no eggs.

Sounds like the most logical explanation so far. She is definitely a female as I periodically see her abdomen swell up with eggs.
The male is also much larger than she is, so its not that.(though once at the LFS I did see a female viciously attack a juvenile male and trash him around by one of his pectoral fins, wasn't pretty.)

 

[laga77]

What have you been supplementing their diet with? Worms, BS, Mysis?

 

[Alexraptor]

Lobster Eggs from Ocean Nutrition.
Everything I have loves the stuff, even my Hammer Coral that's become something of a minor celebrity.

 

[ginpang]

Mandarin male turned Aggressive!

Hypothesis 3 intolerant pig male ... Never occurred to me since my male has patiently waited 14 or 15 months for the female to be ready with no aggression whatsoever, he basically ignored her until they started to lock fins and danced.
Hypothesis 4 .... Unfit male because of size ... Wouldn't that make for female aggression mostly not the other way around?

N.b. Hypothesis 2 was of course meant for natural multiplication of Copepods in live rock without anyone bending backwards for growing or buying supplemental pods or other likewise appropriate live food.[emoji57]

 

[davocean]

I won't side w/ an undersize tank being a myth, for the most part it is very true, though I will say you can overcome this issue if you take other means to provide what they will need, though for many of us this may not be practical.
Also for every mandarin I have had they definitely eat pods all day long, not just morning and night, 2-3 pods per minute.
I do think your issue could be the male seeing a pod competitor more than a mate.

 

[Alexraptor]

After 4 months without the slightest "hint" of aggression or irritation?

There is definitely more than enough pods to go around.

 

[Giants13]

they won't get along in that small of a tank, u have to think of it as a marriage, eventually they need a little time apart but in a 25gal, that won't happen, I JUST GOT MY PAIR TO EAT RODS FOOD!

 

[davocean]

Being that they can take a year to starve out quite often 4mo means nothing IMO, but I can't see your tank or what you see, maybe you are looking at pods crawling all over your tank, I try to stay open minded, but I will always see keeping mandarins in a small tank to be a challenge to say the least, and generally speaking would not advocate it, not unless you are actually cultivating pods and dumping them in on a regular basis.

 

[Alexraptor]

Honestly, keeping Mandarin's in 10-25g tanks has been one of the easiest experiences in my life.
They are absolutely not starving as they both have "gained" weight, since being acquired.
I've had my female for soon two years, and she is at the point where she is egg producing, still is.

Its not as much "challenging" IME as it is having to truly dedicate and plan every aspect of the tank around a single species.

 

[ThRoewer]

they won't get along in that small of a tank, u have to think of it as a marriage, eventually they need a little time apart but in a 25gal, that won't happen, I JUST GOT MY PAIR TO EAT RODS FOOD!

I have a pair in a 25 gallon tank and they get along just fine now. At some point the female would be beating up the male because he was too pushy and too small for her. After he picked up eating Mysis and grew substantially everything is fine.

Mandarins do not need large tanks to survive. All they need is sufficient food supply. If you can keep that up in a 10 gallon tank you can keep them there without much issues.
For a pair I would still advise a much larger tank as they need space and especially height for their "spawning dance".
My pair will soon move to my new 100 gallon tank that is right now cycling.