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I think all this started with my all-male tilapia having babies this week, but I'm not sure.  I have 4 fish in a 60 gallon tank - 2 medium tilapia (8 - 10"), 1 small tilapia (about 4") and an Oscar.  I"m testing pump timing and aeration in this tank so I started with a low stocking density and am adding more fish as I'm comfortable with their situation.  A couple days ago I noticed a school of about 30 fry swimming around in the tank (totally hilarious, a blog post coming on this later today) that I have just removed and put into a nursery tank.  I've also noticed in the past day or so that one of the bigger tilapia has become very territorial and aggressively guards his/her corner of the tank.  I heard somewhere that when you have a schooling fish like a tilapia and you put them into a more isolated situation that this can happen.  These 4 fish went from a 300 gallon tank with about 50 fish to where they are now.  I just added in 6 more tilapia, and will keep an eye on them to see if he/she continues to guard her corner but I'm wondering if anyone else has seen this.  Do you think it is because this schooling fish is no longer in much of a school?  Or is it because of the babies?

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A male tilapia will guard his area usually 2 to 3 times its length. In a breeding situation a flower pot is used to make his arena this would be his area, he is not able to view the rest of the area of the aquarium when he is in his cave. They will usually mellow out once you put the flower pot in. if it’s a female it could be because of the babies. I had a 4-5 inch female keep 6 other fish twice her size trapped in a corner guarding her babies. By the way my females are about 4-5 inches long have about 150-300 at a time. If you only got about 30 where the rest, they could be hiding at the bottom of the tank somewhere and mama is guarding them; also tilapia are less aggressive in a crowded situation
Outstanding information, Earl! Thanks. I'll put a flower pot in there tomorrow. On it's side, I presume? I have that back part of the tank covered so it's hard to see back there but now you have me curious about finding the rest of the babies! Too dark to see now but you can bet I'll be out there looking at daybreak. I'll let you know what I find.
Funny how that happens eh? "All Male" means "mostly male" depending on how they were produced, and sex reversal can reverse over time, leading to lots of babies and (I would imagine) some very confused fish. : )
Can you imagine what would happen if this were humans? I'm envisioning the storyline for a very bizarre science fiction movie.

I'm not seeing 100 babies in there - only about 20 or so more - so I'm afraid the rest were someone's lunch. C'est la vie. When I went to put the pot in there were 2 tilapia hovering anxiously in that corner, and the other 8 had been herded to the other side. Seems the bully has a friend now, or husband...
This is certainly interesting! The tilapia in the tanks at work are hard to observe, given that the tanks are dug into the ground. However, Jesse and I have both noticed that there are quite a few very small fish mixed in with the much bigger ones. We had assumed that they just had been bullied out of getting any food by the big ones, but perhaps there is something else going on!
Tilapia can be quite aggressive when it comes to mating behavior. I've had several tilapia deaths due to "domestic tilapia violence" As noted the males can get really aggressive when trying to win mates and some will be biting the females and chasing them around enough to stress them to the point of disease and even death or simply jumping out of the tank or the males them selves jump out in all their exuberance. I've also had females holding a mouth full of eggs get very aggressive as the babies are hatching. I've had one of those aggressive females kill other fish in the tank as they were trying to create a safe place to release the fry.

Of course mating behavior also distracts from eating/growing which is why most people growing out tialpia commercially will use all male stock since they grow faster in the first place and if you have a dense population of all males it tends to dissipate or at least spread the aggression out enough that it isn't as problematic. But of course that requires plenty of additional aeration and filtration to run those kind of densities.

For those trying to breed their own tilapia, I've heard of people performing surgery to remove the upper lip of the breeding male tilapia so he was less likely to cause damage to the females in the breeding colony, this operation is not always effective though since some of the females are simply stressed to death or battered and not necessarily being bitten.

I found that the females became more receptive to the mating endeavors of the males as the water temperature got up around 86 F. When I had them in a 73 F aquarium the females were just not in the mood and being horribly battered by the male.

Most of my observations are not very scientific and are only from about 18 months of keeping blue tilapia. I've given them up after this past hard winter and concentrating more on catfish since we like the big easy fillets with less bones to worry about and no stress about keeping them warm over winter.
Yeah, imagine how simpler life would be without that pesky reproduction thing! Thanks everyone for your thoughts and ideas. I think the pot-int-the-tank suggestion from Earl did the trick as they aren't all cowering in the corner anymore.
I just emptyed the fish from a 168 gal rubbermaid tank. I placed them into 2 180 gal rubbermaid tanks. I raised 116 fish in the 168 gal tank with absolutly no problem except keeping the pump pumping. The fish were always happy. About a week ago I looked into the tank and saw these little eyes looking back at me. I quickly got a small net and a bucket of water. I fished out about 200 tiny tilapia. I took them in the house as I am working on having a tank for babies. In the house I have a 20 al aquariam with about 100 or more fry. They are about 3 weeks old. Even with all those fish in the tank they were able to breed and I could rescue 200 or more. They seem to appear when the water gets very warm in mid afternoon. I have some large flower pots and some drain pipes in the bottom of the tanks but I can never tell what is going on. Everyday at about 3 pm I check the corners of the tanks for the babbies swimming with the guppies. I don't believe that I will have to buy any more young tiliapa.
This is off the subject but I had a bad thing happen. I lost 4 large Tilapia this week. They were 2 oz short of a lb. This happened because of 2 things. I got to sure things never change. I have been testing NH3 every week except the last 2 weeks. I got busy. I also had a freind feed the fish a few days in the evening. I think he gave them way to much food. The NH3 went through the roof in 4 tanks. I am luck to only loose 4 fish. I do know my fish are ready to eat though and in a week or so we are going to have a fish fry to celebrate. It took 7.5 months to raise some of them to 1 lb. I am pleased. I now am not going to feed them in the eveningon the day I don't come home. I have water hyacynths on top all the tanks for shade and hiding places. They just chomp on those or the little bit of algae on the side of the tank. I learned my lesson on testing. It is important.








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I have a question about tilapia and aggression. I understand a high density tank population tends to have less aggression problems, but what is the situation in a low density tank? As in a starter situation where the tank is stocked with the number of fish it will support when the fish are mature, but now they are small? Do they now have room enough not to feel aggressive? Is there going to be a point where that same number of fish will become aggressive as they become larger? Or, because it is a gradual transition, do they not ever become aggressive?
Great questions, Rebecca, and I sure don't know the answers...but I'm hoping someone jumps in here who might because I'd like to know as well.
I've had issues when I had only like 3 fish in a tank. Like one male and two female. The boy really wanted to get it on but the water was too cool for the girls to be in the mood and they would get all beat up till I put a divider in. I don't think I ever really had much trouble with about a dozen fish in a really big tank (well at least none of them were stressed enough to die over other fish picking on them in that situation) and I don't recall having much aggression issues with really small fish either. Only times I've had fish get sick, die, or jump out from the aggression situation was when it was only a few fish in a 100 gallon or less tank.

But keep in mind that I only kept tilapia for about a year and a half.

With my breeders consisting of 1 male and 5 female, I put in a clay flower pot. This flower pot does two things it makes a territory for the male. When he is in his territory he cannot see the females on the other side of the pot. I also put PVC pipes on the opposite side of the pot for places for the females to hide. This usually slows the aggression down. The territory is usually about 2.5 the size of his body where he can see, so the pot is put in facing the wall of the tank. Aggression also happens with the females when one is holding eggs sometimes the un-bred female will hit her in the side trying to get her to drop the eggs . I always take the females out when they are tumbling eggs and put her in a separate tank. Hope this helps, by the way I rasied 1500 fingerlings from this colony.
Rebecca Branham said:
I have a question about tilapia and aggression. I understand a high density tank population tends to have less aggression problems, but what is the situation in a low density tank? As in a starter situation where the tank is stocked with the number of fish it will support when the fish are mature, but now they are small? Do they now have room enough not to feel aggressive? Is there going to be a point where that same number of fish will become aggressive as they become larger? Or, because it is a gradual transition, do they not ever become aggressive?

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