Do most schooling / shoaling fish end up as harems in an aquarium???

[Magnum Man]

I've noticed this with my Denison barbs, that the male is really intolerant of other males around his females, and often the tanks just aren't big enough for the offending male to get away, and dies of stress, and quite quickly ( when this last happened, the offending male was not physically beaten up, but forced into a corner, and after the 1st time, didn't want to leave the corner, and quickly died... now I still have a group, but suspect, I have one male , and 4 females... I would suspect the reverse could happen, with an alpha female... watching this, with the barbs makes me question how many of these fish groups are truely a community, with the small boxes we put them in??? even my tetras start out as a bigger group, and there are mysterious deaths, then the group size stabilizes... I'm wondering if that is actually related to sexuality, and the size of the box, being the deciding factor on group sizes??? I also suspect ( tank size related ) if there are multiple males, if they decided they can live with each other, either one is clearly dominant, maybe they recognize each other as brothers or friends, and the others stress out and die???

 

[GaryE]

I would argue harems don't exist in the fish world. I think it was looking at fish through a male fantasy world in the 1930s onward. Male fish don't have females.

There are male hierarchies, and in too small a tank they'll kill each other down to one survivor. The same an happen with territorial females. But the females don't end up connected to the guys. They go about their business and spawn with whomever they like. They're more like a seventies Disco than Genghis Khan's harem. If there's only one surviving male, then he'll do. But it's much more common for a female to collect several males. For breeding tetras I like to have several more males than females, and that's a standard ratio for the cory group.

Losses when you get a group of tetras are tank size, crowding or shipping injury.

Denison's barbs are big torpedo shaped fish. They're muscular, and with their shape I doubt they're a slow water fish. They have energy and strength. Most likely, they'd be just great in a 16 foot tank, and you'd have no losses. Males would sort rank, females would sort rank, and everything would go swimmingly. To me, denisons are in that tier of fish I admire, but will never have room for. My largest tank is a six footer. But with the fish that do fit, some species are communities and some are ever shifting social structures we limit by tank size and inappropriate choices.

They are so beautiful - but I think they aren't great for 95% of the aquariums they end up in. And for other, smaller species, small tanks skew our view.

 

[emeraldking]

If you take a group of fish (no matter if they're schooling fish or not), it can depend on multiple factors whether dominance will occur or not. So, we can't state as a rule that we can't have multiple males in a group to avoid this. Yes, tank size is one of the factors. The amount of fish can be a factor. The number of females can be a factor. And gain, the same goes for the number of males. And how many dominant males or females will develop in a group? How crowded is the tank itself (so, not just the number of fish as I've already mentioned but also the plants and deco in there that may tighten the open space. Even the amount of food given can be a factor. The more dominant males will be the first that get to eat. That way more submissive males don't get the chance to reach the dominant level as well.
But yes, if the males keep dying, the mre females are left for the remaining males (which are mostly the dominant males). And then it will become a harem. But because the level of dominance in a group of fish will differ per individual group of fish. And there will be groups of fish that doesn't know any dominance. So, dominance is not always present in a group of fish.

 

[GaryE]

When I had wild type, or wild caught mollies, a problem was how little the males tolerated each other. I think that was independent of their relationship to the females though. They would kill each other in aquariums, but when I watched large male latipinna in Florida, they'd approach females who approached them. They tended to be in long straggling chains of fish over shoreline plants, sometimes 30 or 40 of them with males every foot or more. The females had no connection to any one male. No harem.

In Belize, Poecilia orri (I think) males were spectacular with scarlet fins, but they circled each other squabbling around some large Cichlids at a dock. There was a lot of circling going on. Females would appear, alone, and check them out. That was like a real nice fishtank with no walls. Crocodiles though.

Shoalers are one thing, Cichlids another and ditto for livebearers. They're all different. Since we started with shoalers, I think we probably have a twisted view in tanks unless we put something like emeralds in a six foot/two metre tank.

 

[anewbie]

Some males are territorial and others are not. The ones that are territorial are more likely to create a situation you consider a harem. My new pink-lips are territorial (the first pencil fish i've owned that is territoral); my epesi, margaritus and marilyn show no indication of territorial behavior.

As to are they harem - probably only in a very limited glass box.

I hope in 24 to 30 months i can set up a 12x5 (feet) blackwater aquarium and then maybe it will be big enough to see better behavior though i suspect in that will be too small.

As for barbs - not my thing - i think it will take me several hundred years just to explore the tetra and dwarf cichild in south america - how can i consider moving on to another area.

 

[GaryE]

As for barbs - not my thing - i think it will take me several hundred years just to explore the tetra and dwarf cichild in south america - how can i consider moving on to another area.

It's easy - just get a stupid number of tanks, like me!

 

[anewbie]

It's easy - just get a stupid number of tanks, like me!

Well once i design my water saver system i can use more water - right now .... I think i have to stop at 20.