Aggressive Pencilfish? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 04-08-2011, 02:30 PM Thread Starter
Algae Grower
Join Date: Apr 2011
Location: Freedom, Indiana
Posts: 24
Aggressive Pencilfish?

Hey all!
New here, but have been reading info on this forum for quite awhile!

Here's the setup:
Coralife T5 slim lights
CaribSea substrate on ends with aragonite sand in the middle
New plants, and adding more...(many different kinds)
3 pieces of large driftwood
pressurized CO2 setup, low tech with two 80g spongefilters

9 Beckford's (golden) Pencilfish
6 Red Belly Pristellas
2 Sparkling Gouramis
1 Albino Lyretail Bushynose Pleco (tiny baby )
1 Ghostshrimp (planning on more shrimp...)

My pencilfish lived for several weeks in my 10 gallon tank where they colored up nicely and were very peaceful. I transferred them to the 75 one week ago. The largest male went full color in two days, totally stunning with red from nose to tail (the most colorful out of the bunch). Now he's become aggressive and seems to be herding everybody and anybody, to the point where some of the other pencils have lost color and are hiding. He actively seeks them out and tries to put them into the group. He occasionally chases the pristellas and gouramis too...

Is this normal behaviour? It seems kind of odd... I'm to the point where I'm ready to snag him out of there and put him back in the 10g, just to ease the stress off of everyone else.

Any thoughts on the matter would be appreciated!

BTW, LOVE this forum LOL!
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post #2 of 6 (permalink) Old 04-08-2011, 02:38 PM
Are these real?
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Join Date: Jun 2003
Location: Monterey, CA
Posts: 15,468
Welcome to the Planted Tank!

This does sound odd. A single Beckfordi harassing others in a 75gal? You could definitely move it back into the 10 for a little while to give the others a chance to "catch up" and then move the big guy back. On the other hand, since you have 9 of them, plus other fish, the "aggression" should be very distributed, and nobody should get hurt.

I can't really imagine a single Pencil being successful in suppressing so many other fish in a 75gal tank. Wouldn't he exhaust himself in no time?
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post #3 of 6 (permalink) Old 04-08-2011, 02:39 PM
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Join Date: Jun 2010
Location: Vernon, CT
Posts: 611
I'm interested to hear what anyone says....I've always thought about getting Pencilfish. I have a group of dwarf pfish who are very well behaved.
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post #4 of 6 (permalink) Old 04-08-2011, 02:56 PM
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Location: Tampa, Florida
Posts: 24,403
Welcome to TPT!

I'd try what Wasserpest is suggesting. It's not really all that uncommon for this type of behavior to happen with ANY fish- even normally peaceful schoolers like tetras- especially after a big change- if one fish finds it is larger and/or can get away with it.

Isolating the rogue guy for a few weeks may do the trip, as the social dyamic would change to him being "the new kid on the block" once added back to the tank.

Occasionally there is no "cure" and you just have a rogue fish to re-home, however.

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post #5 of 6 (permalink) Old 04-08-2011, 02:59 PM Thread Starter
Algae Grower
Join Date: Apr 2011
Location: Freedom, Indiana
Posts: 24
Thank you for the welcome!

I absolutely love these little guys, the way they are always somehow in motion (like little hummingbirds). I've seen my smaller males 'battle'? It's rather funny to watch, but no one ever gets hurt and nipping is not part of it. The big guy however is like a shark, constantly on the move, hunting down anyone he can'd think he'd quit since he's obviously established his dominance but he just keeps on going. He didn't act this bad in the 10, though he was still the boss (not bossy, but the others would watch him before they made a move to come out in the morning, etc)

I have to make my decision on him soon, as two or three of our LFS are going to be getting Galaxy Rasboras soon (my goal for the showpiece school) and they're so tiny and frail when they come in that I don't want him stressing them to death...

He is the only one in the group that's acting like this though...even the smaller males that are semi-aggressive to each other aren't this bad...I thought at first maybe he was rounding up the girls and establishing territory, but this just doesn't seem right.

I think I'm going to toss him back in the 10 for awhile, but unfortunately he can't stay there long either as my son wants pea puffers and the 10 is just about ready for them (it would have been ready when the pencils were removed but my son (who's 6 ) decided he wanted a different color substrate, different decorations, etc....sheesh LOL
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post #6 of 6 (permalink) Old 01-01-2013, 02:01 PM
Algae Grower
Join Date: Jun 2012
Location: Worcester, Ma
Posts: 108
I have 4 Pencil fish in my 6.6 and one is also extremely aggressive, the others spent most of their time in the corner of the tank, I don't really get it either, why do schooling fish sometimes go rogue.

I caught him, tossed him in a 2g tank with a betta for a while, let him try to pick on Bruce....

I really like them, they've surprised me with how much they color up, But I really don't want aggression in something that's supposed to bring calm.
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