# Sudden fish aggression



## Spades (Aug 10, 2012)

I have a 20 gallon long freshwater aquarium that I have been keeping for about a month now. It is fully cycled, I transferred water from the old smaller tank and still use the same filter. I'm keeping 4 platies- 2 males and 2 females, 4 danios- 2 males, 1 female and one I'm not sure about. I also have a common pleco, several ghost shrimp and a male betta fish. Two problems have suddenly come up involving fish aggression. 

One of my male platies has started chasing the other one around within the past two days. They've been together a little less than a month and all four of them were doing fine before. The one being bullied doesn't have any ripped fins or injuries, but the aggressive one chases him until he is in a corner or hidden by plants. The one being bullied seems afraid to leave the corner and doesn't swim around like he used to.

The other case of aggression is more serious with my danios, who have been together several months. The one whose gender I wasn't sure of has its tail fin shredded and in bad condition. I check on my fish several times every day so it had to have happened within the last 24 hours. I read that as long as the base of the fin wasn't injured, the fin can repair itself. The danio is now in a 5 gallon by itself hopefully recovering. It seems to have trouble staying under the surface of the water and slowly and gradually floats up. It has some sort of fuzzy clear material covering its belly that I just noticed as well that none of the other fish have. It keeps swimming in a downwards diagonal but is much slower than a danio should swim. One of the other male danios also has its fin torn but it is not near the base, and I thought I should leave him in the tank until I see it get worse. I think the culprit is the second male danio since he has been chasing all the danios around the tank, and his fin isn't torn.

I know my female/male ratio is not ideal but I did my best to find lots of females at the store. The male platy that is being bullied looked like the perfect example of a female at the store with the fanned rear fin, but it has slowly turned into a gonopodium. Is he being bullied because he is an adult male now?

I guess my questions are should I just exchange the danio I think is aggressive? Would buying more females of both fish solve the problems? What do you think caused the sudden aggression when there's been no changes in the tank I'm aware of? And is the fuzzy stuff on the injured danio some kind of disease? Is it a goner?

Thanks for staying with me this far! I know this is long, but I wanted to make sure everyone was informed!


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## NeonShark666 (Dec 13, 2010)

Male livebearers sometimes become very agressive (mating drive?). This is usually the Swordtails and Platys. Mollies and Guppies don't do this This is part of who they are and really can't be changed. To have peace in your tank, take your male platys out and put them into another tank.


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## navigator black (Jan 3, 2012)

If you mistook the male platy for a female, then he was a late bloomer. Xiphophorus, the Genus platys are from, have two waves of males - early and late. Early become alphas and live short lives, late live longer lives and are less aggressive. Alphas hate late bloomers, and what you have is puberty hitting. If you had a group with four or five males and ten or so females, it would spread out, but with teo or three males, someone always loses.

The zebras are different, yet similar. The thin bodied fish (look down at them) are the males. Sometimes you get an individual zebra that is bad news. It can be either sex. Do you have between six and twelve of them? 

The body fungus is a bad sign - like birds, fish will often do in a sick member of the flock, and your fish is very sick. What you are describing is an injury in a tank that isn't really clean (sorry). It could be the cycle, but are you doing weekly 25% plus water changes? That will usually keep such things under control.


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## Spades (Aug 10, 2012)

Thanks so much! I had no idea about the late developers. I'm due for a trip to the store, so I will either exchange one of the males for a female or buy 2 new females to help with the aggression. I know there's supposed to be 2-3 females per male platy.

The one I'm not sure about is probably a male, but it's shaped a little differently than my 2 other males. It's kind of strange that the fungus happened when I still did the 25% water changes every week. I had changed the water 2 or 3 days before he was attacked, and as soon as he was I did another 25% change just in case. Do you know if he can heal if left alone and in clean water? 

I bought the danios when I was setting up a new tank, so I started with 2 so the tank wouldn't be overwhelmed. One of course picked on the other, so I bought another a few weeks after and the aggression lessened. I bought the fourth one and the fighting stopped completely so I thought I had found the minimum. I might get another danio when I go deal with the platy issue


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## navigator black (Jan 3, 2012)

Danios are pack animals - everything is rank. They sort it out by biting and chasing, but once everyone knows his/her place, it calms. Usually, six or more let them spread their running battles around and everyone is happy. 
They are very closely related to barbs, who do the same thing. 

Usually, slow developing male platies have higher backs than early developers. It's even more pronounced with swordtails, but the aquarium forms of both are hybridized with each other and with a third species, variatus, so it gets mixed up.


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## Spades (Aug 10, 2012)

Hopefully I can get to petco before they close, the fungus is spreading on his body. I was thinking of getting API Pimafix. Does anyone know if Pimafix is toxic to invertebrates because of the shrimp in my tank? I would like to treat the main tank just in case... Also I read somewhere that when the fish is injured, it is more likely to get a fungal infection. I think that is what happened here, because I have looked and looked and see no more outbreaks in the main tank, and it should have been clean anyways.

The male definitely has a higher back. I was thinking of getting more platies anyways, does anyone know if the male will stop trying to defend the females if there are more of them? Or should I just exchange it because the early and late are bound to hate each other? I'm kind of attached to my fish..


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## Spades (Aug 10, 2012)

I got the API Pimafix for the danio. I don't know if it is too late for him, but I guess we will find out in the next few days. He seems to be swimming around faster than he was a day ago. I also bought another female platy and a danio. The danios started acting normal when I took the injured one out of the main tank, even with the three of them alone. But with the four of them (and hopefully five if the sick one recovers) everything should be more stabilized. I guess I'll keep posting as we go...


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