Will My Harlequin Be Lonely?

[wpascarelli]

I am in the process of establishing a 55gal community tank. I am completing the cycle and plan to bring in a school of cardinal tetra and some dwarf rainbowfish and cories. My friend who is getting out of the hobby is giving me one female irian rainbow fish and one harlequin rasbora, both older fish. I know Harlequins need a school. I do not want to get a large school of rasbora at the cost of not having room for any of the other schooling fish that I planned. I know it will probably be suggested that I find someone else or a pet store to take this one rasbora. I would like to keep him if I can. 
The rasbora has lived for years without any other rasboras and at least appears to be happy and healthy and colorful and does not appear to be depressed or scared or visibly stressed. I would like to know what everyone here thinks. 
Also, I am curious if this sounds like a better situation: Get a few less cardinal tetra, and get 2 more harlequins instead. That will still give me the school of tetra, plus maybe it will give the harlequin some friends of his own kind, though not a school. Does this sound better than leaving just the 1 harlequin in the tank? Or is it really still very highly suggested that I find someone else to take the rasbora?

 

[Byron]

This is one of those situations where it may be best to leave the fish alone in familiar surroundings (though I understand this is a new home for the fish).  Similar situations occur when one has a group of a species and due to old age (or whatever) there is eventually only one or two fish.  One can add more juveniles of course, but sometimes if I am ready to move on to other species I just let the last fish live its days peacefully in the tank it is used to, or in a tank with fish that will not pose threats.  I've no idea how old this fish may be; if it is relatively young (1-2 years) then finding someone with this species who could take it would be a good option.  But an old fish moving to such an environment might not do so well as leaving it alone.
 
If you did acquire more, you would want a lot more than just two or three.  Shoaling fish are better in larger groups, depending upon tank size, and with this particular species (Trigonostigma heteromorpha, presumably, the common Harlequin) a group of 7+ is best when starting out, or adding replacements.
 
I'll explain something about shoaling fish...they need a group for several reasons, depending upon the species in some cases.  Clearly the fish feel less vulnerable, and will be less prone to stress (which is the cause of 95% of all fish disease) and thus healthier, with as large a group as reasonable.  But some species also develop hierarchies and with insufficient numbers this can cause even worse stress.  So my suggestion would be either get a group of say 7, or leave this Harlequin alone.  If he is in with shoaling fish that are peaceful and not likely to threaten it, this seems to work, in my experience.
 
You don't mention how many cardinals, but here again the more the merrier.  Rainbowfish and cories also needs groups.  With corys, definitely the more the better.
 
Byron.

 

[wpascarelli]

Thanks for your reply. I believe this rasbora to be older than 2 years old, and probably not older than 4. I planned on getting quite a good sized group of Cardinals, and then a small but acceptable sized school for the dwarf rainbows and about 6 Cories. I do not think I have enough space after all that for a large school of the Harlequins, and I dont want to totally eliminate any of the schools that I already planned. Like I said I understand that ideally the Harlequin would have 7+ but I thought having 3 might be better than having 1. But if you think just leaving him as the lone rasbora in this peaceful tank where he "appears" to be happy without other rasbora is fine, then it seems that I can just do it that way. Thanks.

 

[Byron]

Thanks for your reply. I believe this rasbora to be older than 2 years old, and probably not older than 4. I planned on getting quite a good sized group of Cardinals, and then a small but acceptable sized school for the dwarf rainbows and about 6 Cories. I do not think I have enough space after all that for a large school of the Harlequins, and I dont want to totally eliminate any of the schools that I already planned. Like I said I understand that ideally the Harlequin would have 7+ but I thought having 3 might be better than having 1. But if you think just leaving him as the lone rasbora in this peaceful tank where he "appears" to be happy without other rasbora is fine, then it seems that I can just do it that way. Thanks.

 
I would aim for 10-12 corys.  Same species, or you can mix, but if mixing have several of each species if at all possible.
 
Dwarf rainbowfish (Melanotaenia praecox) are best with a ratio of 2 females per male, as you may know.  A group of 8-10 perhaps?
 
You could still have the Harlequin group, 7-9, that's up to you.  Lifespan is generally suggested as 5-6 years.

 

[wpascarelli]

Wow thats alot more fish than i was really interested in keeping. 12 corys, 10 dwarf rainbowfish, 7-9 harlequin, 15-20 cardinal tetra, thats like 50 fish. You think all of those fish would be fine and not being anywhere near being overstocked in a 55 gallon? Was thinking 6-7 corys, 6 dwarf rainbows, and the 1 harlequin.

 

[Byron]

Wow thats alot more fish than i was really interested in keeping. 12 corys, 10 dwarf rainbowfish, 7-9 harlequin, 15-20 cardinal tetra, thats like 50 fish. You think all of those fish would be fine and not being anywhere near being overstocked in a 55 gallon? Was thinking 6-7 corys, 6 dwarf rainbows, and the 1 harlequin.

 
Stocking an aquarium involves much more than just considering the fish mass to water volume ratio.
 
Fish under stress impact the biological system more than the same fish not stressed.  When it comes to shoaling fish, as I said previously, the more the better, meaning less chance of stress, so in a way having a few more will be less of an impact on the system than having too few.  Shoaling fish always settle in quicker, and remain healthier, all else being equal, with more of them.
 
If this were me, my aim would be for 9 dwarf rainbows (3-4 males, 5-6 females), 9-12 corys, 12-20 cardinal tetras.  If you want Harlequins, as well as the fore-going, a group of 8-9.  With a decent filter (suited to a 55g, not "over" as that achieves nothing), live plants including floating, and weekly partial water changes of 50% of the tank volume, this would work well.
 
These numbers will mean more "normal" behaviours from the various species, and are certainly not close to causing trouble.  You need to provide what they need though...sand for the corys, plants, chunks of wood.
 
Byron.

 

[BeckyCats]

Might it be possible that the harlequin would be happy enough with the cardinals and/or rainbow fish that he may not need others of his own kind? I ask this because I see in a tank at work that there is one male platy that hangs out with black skirt tetras like he is one of them. He follows them around wherever they go. He had no interest in the white skirts for some reason, but he really likes the black skirts. Before the black skirt tetras were introduced, the platy engaged in almost constant glass-surfing. He appeared to be very discontent. Once the black skirts came in, he no longer glass-surfs. He appears to be so much more content now.
 
Could this possibly happen with the harlequin here in question? If so, maybe the harlequin could be kept with only the one or two others that Wpascarelli was thinking to put with him, with no problems?

 

[Byron]

Might it be possible that the harlequin would be happy enough with the cardinals and/or rainbow fish that he may not need others of his own kind? I ask this because I see in a tank at work that there is one male platy that hangs out with black skirt tetras like he is one of them. He follows them around wherever they go. He had no interest in the white skirts for some reason, but he really likes the black skirts. Before the black skirt tetras were introduced, the platy engaged in almost constant glass-surfing. He appeared to be very discontent. Once the black skirts came in, he no longer glass-surfs. He appears to be so much more content now.
 
Could this possibly happen with the harlequin here in question? If so, maybe the harlequin could be kept with only the one or two others that Wpascarelli was thinking to put with him, with no problems?

 
I don't think I can offer much more than I already have on this question.  I would however point out that the "need" of a shoaling species (tetras, rasbora, danios, barbs, etc) for a group of its own is much more crucial to the fish's well-being than with fish like platies that are not true shoaling fish but might live in large numbers.
 
Given the age of the rasbora in question, and its assumed previous history, leaving it on its own should not be as detrimental as it would for younger fish acquired from a tank of their species.  The main thing if this is done is to ensure the tankmates are not in the least "threatening," as this could cause serious stress for a fish that is not in the environment for which it has evolved.  Dr. Loiselle's comment in green in my signature is apropos.
 
Byron.