Who's The Culprit?!?

[guppy2002]

my white male betta is getting nipped in the community tank. and i'm not sure who is doing it. heres the stocking:
3 guppies
3 harlequin rasboras
1 oto (though he is so peacefulvi couldnt imagine him doing it)

 

[Paradise3]

I'd say most likely the guppies or the Rasboras.
 
The guppies because they can be nippy towards each other guppies and betta's don't get on.
The rasboras because there is only 3 of them.

 

[Blondielovesfish]

I would say it is most likely the harlequin rasboras. They can be nippy, and I imagine yours especially are with being in an inappropriate school number.
 
Getting nipped would be stressing your betta out, it would be best for you to get him his own tank.

 

[SimpleDog]

It could actually be either way. More than likely bored rasboras, but male guppies will nip too, especially if they want to be dominant in the tank.

 

[betta fish]

Could you post of pic of your betta and nipped tail?

 

[fuzzynicki]

Guppies are never recommended as companions for bettas, as they are very nippy with bettas.  From what others have said above the same seems to apply for rasboras.  Although I have heard of rasboras living happily with bettas before. ???   It often depends on the nature of the individual fish.  I'd definitely suggest giving your betta a home of it's own

 

[Paradise3]

Guppies are never recommended as companions for bettas, as they are very nippy with bettas.  From what others have said above the same seems to apply for rasboras.  Although I have heard of rasboras living happily with bettas before. ???   It often depends on the nature of the individual fish.  I'd definitely suggest giving your betta a home of it's own

 
Rasboras can live quite happily with Betta's when in the correct group size. These ones may be nippy because there are only 3 of them rather then the recommended 6 They become more nippy the lower their numbers.

 

[Wildbetta]

Unfortunately your stocking is not ideal which means that any of them (besides the otos) could be the culprit.  Including the betta himself nipping his fins from stress. Guppys are notorious for being nippy to any fish with longer fins which puts them as not being great tankmates for bettas.  Rasboras depending on the species can be ok tankmates for bettas but they have to be kept in correct numbers to keep them from being nippy.

 

[l_l_l]

It can actually be both of them, as everyone else mentioned.
Rasboras need to be at least 6, Guppies like to be the prettiest. 

 

[Jasperwolf]

It could be the guppies or rasboras, unless the oto is hungry, in which case I have seen cases where they suck on the fish.
Otherwise it could be that fake plants or decorations have been tearing his fins? How big is your tank, if it's smallish then he may be stressed out with the guppies being pretty?