warm and fuzzy cannibals

[GaryofMontreal]

I got Brachyrhaphis roseni a while ago, and had a devil of a time keeping them from eating all their young. The fish is pretty, but I was questioning my sanity for getting them. Once I had half a dozen two cm fry, I moved them and my three adults to a 40 gallon long. They began to breed like guppies, and every drop left a few survivors among the fry. In the larger tank, they weren't as single-minded in their pursuit of their edible children.
I sold and traded a bunch, and moved the remaining group, now composed of young adults from my tanks, to a 20 gallon. They have begun to breed now.
Fry swim right under their noses without being attacked.
Have there been any studies of social groupings in such fish? I have read of aquarium cannibalistic rainbows not eating eggs or young when raised together in a stable group, in a tank where the decor does not change. The roseni dealt with tank change, but there does seem to be a different dynamic with the larger group all raised together. It could be coincidence, but.
Could fry eating be partially boredom?
Could it be displaced or poorly channelled aggression when fish that are used to big rowdy social groups are kept in pairs or trios?

I have killies that will eat younger siblings that hatch in the tank until the older fish reach 1.5 cm total size. I always thought that was a hormonal/growth mechanism, but now I realize that I usually buy one or two pairs of killies, but that by the time their young get to 1.5 cm, they have become a little group of a dozen or more fish. So maybe...

Anyone care to either speculate or point to fish behavior articles on this obscure question?

[catinthehat]

I think there could be lots of different reasons, for example Stan Shubel the famous guppy breeder said in his talk at the 2010 ALA that he puts his female guppies that are ready to drop in a small container ( I believe he said 1 to 3 gallon ) and if the female eats even 1 fry she is culled.So I guess he breeds for that trait......

[OldMan]

I have been experiencing the extreme cannibalism among my Brachyrhaphis that you alluded to Gary. In my case, my 5 fish are in a 10 gallon that has heavy cover, with killie mops among other things, in their tank. I have yet to see a fry in the tank although the fish have been in there for a full year now. The adult Brachys look much better than they died when I first got them and the females have shown obvious signs of carrying fry. Putting all of that aside, the fry never seem to survive long enough for me to see them.

[GaryofMontreal]

I really got nowhere til I put them in a larger tank. My secret weapon was cheap dollar store wreath or decorating "plants" - fine leafed strands about two feet long, with five or six strands per one dollar piece. They form a really good tangle.
Even at the most ravenous, the roseni here only ate young in the first week. It took half a dozen drops before one lasted a week though. That corresponds to when I put in the plastic tangle.
It's so strange to see them not even bother their fry now. Weird.

I have a pair of pretty old Brachyrhaphis terrabensis that was recently given to me, and they are eating their way out of hope. I'm trying to get a few fry as there aren't many drops left in them, but they seem even meaner than roseni.

[Melody]

I think a lot of what you describe is a simple dulling of the instinct. It's an old trick for breeders to add smaller and smaller fry to tanks to get the colony accustomed to having them around, then they ignore them unless they're hungry, or they'll just gobble up the weaklings. As soon as I have enough fry in the tank, the adults leave them alone for the most part.

Otherwise, they're food - the chase instinct kicks in and they go after them if they're hungry or not. If they're used to them flitting around, they don't trigger that instinct.

You can see the fish perk up, go on alert and gobble the fry if you watch them. If they were German Shepherds, their ears would go up :laugh: . It's the same kind of reaction. If there's rabbits everywhere and the Shepherd gets used to them, he doesn't have that strong drive to chase them. My cat is that way with squirrels too - she used to get as excited as she did with a mouse, now she doesn't even get up.

But as with any animal, there will always be exceptions.