long time no see
i just got bitten by the Mada-bug myself.
rooted through the book by De Rham & Norissat and through a buckload of articles.
can't help you with all the questions, but for some I found answers;
Typical breeding size?
they should be about ready with you. 6"-8" is mature. they can get bigger, but I've read breeding reports that stated at 6" or so they can begin to breed or at least pairbond
Is there a reliable way to sex them (other than venting)?
not that I'm aware of. I know a tank with fully grown P maculatus wich are 9-10" or so (huge!) and they all look the same.....
P menarambo is really closely related, so it's still a bit of assumption, but I'm afraid venting is the only way.
If a pair breeds/forms, will moving them to a separate take break the pair bond?
the best success (with nourissat for example) is keeping them in a group in a large tank or pond. pairs will form and after rearing fry the fish will group up again.
maybe try it out? I've got bad experiences with transferring mated pairs...it's not just the Tanganyikan Julidochromis wich break bond at the drop of a hat. many, many cichlids flip out.
maybe remove the non-paired ones?
Are there spawning triggers?
I'm quite curious about this myself! Paretroplus seems to be a snaileater (I'm right out of snails atm) and mine (I have maculatus) keep 'playing' with the empty ramshorn shells left over by the granulosus.....
other fish that feed on snails are triggered into breeding when confronted with their favourite food.....I've had great success with Labrochromis ishmaeli for example.
not a Madafish, but they didn't breed until I've fed Ramshorns. they even went after baby Trumpetsnails.
same for Neolamprologus tretocephalus. when fed snails they get really impressive.
start a snail breedery?
or relieve someone from a Trumpetsnail infestation; this way it cuts both ways
What is optimal tank size for a breeding pair? how about for the entire colony of 7?
according to Nourissat 1 pair would need at least 400L/100US gallon.
but I think from what I see here that keeping them in a group (you have 7 now) is a much better plan and you'd best go for the largest tank you got.
I have my Paretroplus in a 315G (I have 11) and the group behaviour is incredible. like a peaceful Tropheus, sort of. there's a lot of interesting group action, pairs separate and reintegrate in the group, liplocking, groupgrazing, solo sandblowing behaviour, you name it.
once they swim in the upper parts of the tank the synchronity is amazing.
go for the 265!
How do they normally do with other fish of similar size and temperament?
as far as I can see they do just fine. but if you want to breed....from what I read they're quite bad at parenting. any other fish could snatch the eggs, perhaps?
I got mine with Ptychochromis, halfgrown frontosa's and some catfishes, they do fine. I'vve even seen adults with a 2 feet Arowana and some Oscars without any harassment either way.
Finally, are there any conservation efforts currently going on to re-introduce this fish to the wild?
not that I know of; and their natural habitat is now totally overrun with Channa and Tilapia/Oreochromis.
unless someone manages to eradicate those, I don't see it happening.....the environment has been changed too much, same for the pressure of fishing; too much
I think, like the many Victorians; these are gone for good and we can keep them in captivity like the Prezwalsky Horse or the Red Tailed Shark or the Sumatran Rhino.
their natural habitat is destroyed for ever, overrun by humans, exotics and pollution. it'll be one of those sad reminders that it's all too easy to destroy and almost impossible to create.
"And he piled upon the whale's white hump the sum of all the rage and hate felt by his whole race. If his chest had been a cannon, he would have shot his heart upon it"