Growing multi community

[TaffyFish]

My multis now have 10 young, the oldest of which are seemingly ready to set out on their own away from the parental group of 4 shells....which is pretty much centrally positioned in a 2 x 1 x 1.5 ft tank.

A couple of weeks ago I placed 2 new groups of shells, one at each end of the 20g. The parents seem to be escorting one of their young to the new shell group on the right, as if expanding their own territory. They allow this youngster back to the parental group whenever it feels the need.

However, they have chased away another young to the shells on the left, and the female in particular is keen that it does not return. The male spent some time yesterday piling substrate on its shells!

I figure the favoured youngster is a male and the parents are helping it to establish his own ground. Could it be that the unwanted youngster is a female and that the mother doesn't want competition?

....or maybe it's the other way around? Any views?

 

[yslexdia]

Shelldwellers are far from my expertise...but let me give it a shot.
The male (the slightly larger individual...may also have a red fringe on the dorsal fins) with fervently defend his shell & territory from any invading male. If one fish is being chased away and one is being welcomed in, I'd guess you've got a male and a female respectively. Chasing away an unwanted male seems logical, and allowing another female in would also seem logical.

 

[TaffyFish]

Makes sense yslexdia.....the young being treated as if they were "new" to the group once they reach some point of maturity, additional pressure being space because they have 10 young and only 4 shells.

Let me suggest why the "outcast" might be female. When I bought the 2 adults they were not a pair, so I introduced a second female from another source a week or so later, just to add some new blood to the breeding. The original pair at first rejected the newcomer, but she persisted and the male gradually accepted her but the female always refused to allow her to share the pair's group of shells.

Both females then darkened and seemed to be spending more time in their respective shells, the male seemed to share his time between them. The original female then spawned and the second female was then kept UNDER her shell, she was not even permitted to come into view though she seemed to be feeding OK. About 2 days later I found her dead, not sure what the cause was except I would exclude starvation. So much for harem spawning!!

Right now it's the female parent and not the male that is actively excluding the youngster from the group. The male occasionally checks in but doesn't actively chase it away. If the outcast were male, wouldn't the father be more active in the casting out? After all, the competition would be his and not the mother's.

Here's another query that might settle this.....which sex would first show their stripes? These two were spawned together but only one has stripes evident.