Pencilfish - Bad Male/female Ratio?

[myrtle]

Hi, I have a 2' tank with One-Lined Pencilfish (plus a few assorted shrimp)and over the past few months I have had a few deaths. Water parameters are fine and it is a heavily planted, low light tank. My problem is that it has been mainly females that have died leaving me with a count of 7 males and 3 females. Understandably, the males are becoming more 'aggressive' with each other (as far as pencilfish get) and I was wondering whether it would reduce their stress to remove some of the males to my 4' tank where there would be more space for them. However, the 4' is home to a rather large Angel fish amongst other smaller fish so would they be more stressed by the angelfish or by being in a largely male shoal? I am loathe to just go and buy more females to even it out unless this is the best soloution. Is this actually a problem or am I getting it out of proportion?
Thanks.

 

[nmonks]

Pencilfish generally aren't aggressive, but yes, adding at least four more females would go a long way towards making the school work better. It's hard to imagine a tank big enough for angels would be small enough to become overstocked by adding four more pencilfish!

With that said, I wouldn't put it past the angelfish to be the main reason for the deaths. Nannostomus are small enough to be prey animals for large angelfish, and even if they aren't eaten, an angelfish might be big enough to stress the pencilfish simply by being there.

Cheers, Neale

 

[myrtle]

They are in 2 different tanks at the moment, the pencils are in their own 2 foot tank and the 4 foot community tank has the large angel plus red-eye tetra, clown loach and corys. My options are:
1. Add more females to the 2 foot tank to balance the school,
2. Take some of the males to the 4 foot tank which contains the angel or
3. leave it as it is.

I was wondering which would cause the least stress options 2 or 3? I have had the pencils in the 2 foot tank for 3 years so I believe that old age was the most likely culprit for the deaths (4 in 6 months). I am loathe to buy more females as since I bought them I have learnt (perhaps incorrectly) that the majority of pencilfish are wild caught and I would prefer to but captive bred fish.
I hope that clarifies things.
Thanks

 

[nmonks]

It is true that pencilfish tend to be wild-caught. Buying wild-caught fish certainly isn't unethical, and in fact has some benefits. Wild-caught fish place commercial value on pristine habitat, making it easier for local people to make a living. Small fish like pencilfish suffer massive mortality in the wild -- most live less than a year -- so removing a small percentage as aquarium fish will have little to no impact on wild populations. There's no evidence freshwater fish collecting has ever caused the extinction of a tropical fish species, though some tropical fish we often keep, like red-tail black sharks, have gone extinct in the wild for other reasons.

Fish farms are not better simply because they farm the fish! Monstrosities like balloon mollies were created on fish farms, and the prevalence of diseases such as neon tetra disease, dwarf gourami disease, mycobacterial infections, and velvet infections is very well known. But with that said, farmed fish do tend to be easier to keep because they're already used to aquarium conditions -- provided you buy species that have done well on fish farms as opposed to those, like ram cichlids and dwarf gouramis, that suck big time.

If you have more males than females, then really adding more females is the only way to balance things out. If you don't want to buy more, then giving them away to someone who has these pencilfish would be an ethical solution.

Cheers, Neale

I am loathe to buy more females as since I bought them I have learnt (perhaps incorrectly) that the majority of pencilfish are wild caught and I would prefer to but captive bred fish.
I hope that clarifies things.
Thanks

 

[myrtle]

Thanks for the detailed reply - I have to do more reading on ethical fish-keeping by the sounds of it, so far I've been doing what I hate others doing by making an uninformed decision (albeit one I am prepared to rethink!). I don't want to give them away, and I'm doubtful about putting any in with the angel so as you say, buying a few more females may well be the answer.
Thanks again, I'm off to search for previous discussions re ethical fishkeeping (although technically I suppose keeping wild animals in tanks could be seen as unethical by some in itself).

 

[frothhelmet]

What did you end up doing in the end?
 
I have a group of 9 one-lined pencilfish (nannostomus unifasciatus) in a 20 liter tank with an even mix of male/females and they are crazy aggressive until the lights off. At which point they peacefully school. During the day they maintain little territories that are the same for each fish. The females are easily every bit as aggressive as the males. There was also one fish that was weaker and constantly hounded so I had to put it in its own tank. It's tail-fin was chewed up rather nastily by the other pencils but healed in a few days. I tried adding 6 more pencils to the 20 liter but the aggression didnt dissipate. The 6 just kept getting chased constantly by the established 9 fish, so I put them in their own tank for the time being. Basically I think the only solution is to put them in a much bigger tank so they can all have their own territories, or to add a big fish to scare them into schooling. gert blank kept angels with uni's and had no problems - see youtube. The pencils school quite nicely in this situation and are big enough not to be seen as food.

 

[N0body Of The Goat]

I have a group of 9 one-lined pencilfish (nannostomus unifasciatus) in a 20 liter tank with an even mix of male/females and they are crazy aggressive until the lights off. 

 Pencilfish are small, but they are territorial with their own kind, a typical 20l is far from suitable.
 
I started with 6 Nannostomus beckfordi ~18 months ago, the alpha male was a bully with the other male and the four females, when in my 620T ~130l tank (~62x39x55cm). When I moved them to a 4-footer, the males had more space and everything was fine.
 
I lost half the group while on holiday last September, while they were in a ~120x45x55cm, in hindsight the African killis I had bought ~6 months previous had grown up and become fiesty in that tank of generally small/peaceful fish (they have since been rehomed). I then bought some more tank bred replacements and as a group of 10+, they have been good as gold in the above 4-footer and my slimline 120x30x37cm.
 
I suspect your group (and mine) would be fine in a 75x30x30cm tank where there are ~2:1 females to males, where besides having one long side open to swim against a moderate current, the other sides have a reasonable number of floor to ceiling plants/ornaments to give line-of-sight barriers... But one size tank I do not have in my collection of seven, is a 3-footer!

 

[frothhelmet]

thanks I am aware of the problem. shopping around for a 200l tank to house them in atm- but from the sounds of things this might not even be enough given your problems with only 6 beckfordi with 1:2 male/female ratio in 130l! I will add a large 'scare them' fish (that can't really do them harm) and see if this doesn't get them to be buddy-buddy.

 

[frothhelmet]

or you could go the insanely overcrowded route...
 
https/www.youtube.com/watch?v=Df1LwvR7o-c