Sudden Platy Aggression

[mtv8dmarine]

Hello all! I'm new here and to tropicals so I hope to learn along the way with the information on this forum and through asking hopefully appropriate questions.

I have a 55 gal. tank thats moderately planted, 1 long driftwood and 1 tree stump (both imitation). I currently have in the tank, 2 peppered cory cats (used to be 3 until recently eaten), 10 platies of various types, marigolds, red wags, sunburst, etc., 2 angelfish, and 1 Hammers blue cobalt crayfish.

I noticed an aggression issue last night after doing my weekly 25% water change/gravel siphon. On of the Marigolds, now appearing to be the largest Platy of the group is super aggressive towards the others around. He will ram any fish around him which often brings the others from around the tank to investigate and thus picked on too. When a lot of them submit and head towards the plants or other cover, he'll focus on one and continue. This morning I still had all 10 in the tank (not sure if lights out at night helped diffuse the situation or not really) but he began doing it again when I turned the lights on before feeding. The other fish did assert himself back but was on the losing end of the stick by then and swirled a net inside to diffuse it before I had to leave for work.

Should I segregate the marigold? Is this typical fish dominance and it will work itself out when roles are established? Both times I had fed them only minutes prior. Could I be underfeeding or the marigold establishing a higher feeding priority among nearby Platies?

Thanks in advance! =)

EDIT: Noticed the topic was moved. Sorry! I'll get the hang of things shortly. I should note too that these Platies have been in the tank for a month...so they aren't brand new.

 

[OldMan47]

It is a bit unusual to find a platy that is so aggressive toward other platies. It may well be that much of his ancestry was swordtails. Many of the modern fish we call platies are derived from crosses among the Xiphophorus family and some species of swordtails are known for dominance type aggression of their males. If your platy has a lot of swordtail to him, he will continue to dominate the other male platies in the tank.

 

[mtv8dmarine]

It is a bit unusual to find a platy that is so aggressive toward other platies. It may well be that much of his ancestry was swordtails. Many of the modern fish we call platies are derived from crosses among the Xiphophorus family and some species of swordtails are known for dominance type aggression of their males. If your platy has a lot of swordtail to him, he will continue to dominate the other male platies in the tank.

Thanks for the info. I thought swordtails derived from crossbreeding platies and another species though? Do I understand it backwards? I came home today and he seemed well behaved. I did introduce 4 new Corys since I was down to two after my crayfish I think might have gotten hold of the other during the night. It was interesting to see a Cory chase off a platy clear across the tank.

I had a theory today that a slightly larger community fish would help neutralize things in the tank. The angelfish certainly aren't a species (at least as young as mine are) to really put up a fuss if ever picked on. I did do a 3:1 ratio with the swordtails of female to male since limited male population with higher female population keeps the aggressiveness of the males down.

That ratio though has me thinking maybe I should take a count on the sex of my platies. Perhaps it's a higher male population that ideal...certainly something to just keep in mind.

 

[mtv8dmarine]

Update...

The one platy continues to harass but I've been able to sit and observe a bit more. The aggressive platy doesn't harass any other fish. They may slow up and meet & greet if passing but he's not aggressive with any others.

The two orange and black platies spend a lot of time I guess courting and mating. They swim and chase each other all around and then after awhile will settle down and one will rub up next to the other for 10 seconds or so.

Is the aggression perhaps because they appear to be mating? They have always acted this way (the mating pair) since I got them a month ago.

 

[OldMan47]

Both swordtails and platies have been derived from crossing various Xiphophorus species. If you happen to have a male from a primarily swordtail population, that may be a partial explanation of what you are seeing. If you have lots of interaction without any aggressiveness, that is nothing at all to worry about. I thought, from my interpretation of your first post, that you had severe aggression issues in the tank.