06-17-2011, 03:40 AM
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I have found that Mollies can be a naturally aggressive fish, particularly in more confined tanks, a 10 gallon doesn't really give them much space to stay out of each others way (if need be), a 20 gall. would be the minimum I would keep Mollies in. I noticed too, when I kept them, as well as other livebearers, that the females aggression would increase when pregnant and be more intolerant of her tankmates, they usually have an increase in appetite too, so it may be a survival instinct as well, in trying to lessen the competition for food etc. by keeping them away from her territory.
Now that the male has gone she is probably showing more dominance than before. I would put his death down to going through the cycling process more than anything else, but the added stress from harassment definitely wouldn't have helped matters. This is just a guess, but if it is only the other orange Molly she is focusing on, it could be a colour thing and another fish of the same colour is perceived as a threat perhaps.
I'm not sure what you can do in a small tank to avoid aggression other than isolating her, but keeping them in a breeders net for too long can stress them out a lot, a QT would be a better. Adding more Mollies to even out any aggression isn't an option for your size tank. You could try a divider in the tank to keep her isolated, but I think the tank is a bit small for that. Sometimes rearranging the decor helps or add taller plants (fake ones are fine) to help keep them out of each others line of sight. Maybe feed more to lessen hunger, but you want to avoid overfeeding them though. Providing more space would be the best way to help the situation.
Last edited by Beaches; 06-17-2011 at 03:44 AM..