Inter-relationship of Pygocentrus species and S. brandtii

by Pete Spaeth

This article is based on the aquarist view of his home aquarium housing piranhas and pirambeba.

All photos on this page are the property of Pete Spaeth


KEY WORDS: Pygo and red  (Pygocentrus; cariba, nattereri, piraya), rhoms and serras (S. rhombeus), ternetzi (P. nattereri Argentina/Paraguay)




My name is Pete Spaeth and I have been keeping piranhas for just over 18 yrs now. I've focused the majority of my time on caring for Pygocentrus species. The common red belly (Pygocentrus nattereri) is about all a person can get at pet store in my area except for the rare exception of a small Serrasalmus species. I got one of my friends hooked on piranhas a few years after I fell in love them. About 8 years ago he called me up and told me that he had bought these three black piranhas ( S. rhombeus) from a pet store and they weren't getting along so he asked me if I wanted a couple. I jumped at the opportunity because exotic species were so rare. Neither of us had a clue as to what kind of a fish a Serrasalmus was. All we had ever known at the time were reds. At the time I had 3 reds in a 40 gallon tank with the biggest fish measuring about 11" or 11 1/2" and the other 2 closer to 6". My 20 gallon tank was open so put the two little 3" or 4" rhoms together. That didn't last long and one was dead. There was a time when I needed the tank space and had to combine the three Pygocentrus and the smaller S. rhombeus together. 


At this time the S. rhombeus was closer to 6" and the largest red was closing in on 12". The other two reds were probably closer to 9". That lasted a month or two until I got my 75 gallon tank. I put my reds in the 75 gallon and kept my rhom in the 40 gallon for a while. I tried mixing them one more time in the 75 gallon but once again failed. I never had any fatalities but the fin nips were enough to convince me that it wasn't a good idea. I held on to the rhom for a few years until I decide to let him go because I really wasn't into the solitary species.

Since then I have learned a lot about the behavioral patterns of the different species. A few years back I shared an apartment with a friend of mine ( the same guy who gave me the little rhom) and he had a couple of serra. species so I had some time to observe their behavior. Piranha behavior fascinates me and that's why I think I prefer the pygo's over the serras. I love to watch them interact. Don't get me wrong the physical appearance and the tenacity of the serras has always impressed me but what it lacks for me is the interaction among fish. I tried the mixing species years ago so I could have the best of both worlds and it didn't work. I figured even a 75 gallon would be too small but I just had to try it. Now I have a 750 gallon tank and I figured it was time to try it again.

I was actually toying around with the idea myself about picking up this brandtii myself. It was a guy I knew that was selling the brandtii and he told me he was a nasty little fish and recommended not mixing him in with my pygos, so I backed off the deal. Little did I know, my friend was talking to him behind my back telling him to convinced me that I don't want this brandtii. My friend was buying this brandtii for me for my birthday. On Feb, 2, 2005,my friend released an 8" brandtii into my 750 gallon tank with 20 ( now 21) other pygos ranging in size from 6 1/2" to over 13". Here is a list of the fish I currently have in the 750 gallon tank.

4 ternetzi 1- 10", and 3 between 11 1/2" and 13"
5 caribas 1- 7 1/2" and 4 between 11 1/2 and 13"
3 piraya 3 around 11 1/2"
9 reds. 3 around 11 1/2" and 6 between 6 1/2"- 10"

When the S. brandtii was first introduced he was fine for about a week with minimal fin nips among the fish. Then he started to concentrate most of his attention on the larger fish. One fish he liked to pick on the most was my 11 1/2" one-eyed red. He made an easy target for the brandtii and I also believe he set a good example for the other pygos as to what this new piranha was all about. This continued for about a week. During that week I witnessed a few occasions where the brandtii would try and take a nip from the pygos dorsal fin, and the much larger pygo would make a solid attempt for a pygo, but a feeble attempt if you want to catch a brandtii, to chase him down.

The brandtii took a break for a week or so and let the majority of the fins to heal up until he decided it was time for another round. For the next week he began to focus his attention on the smaller pygos. For the first few weeks the smaller pygos went unscathed but now it was their turn. He probably spent about a week picking on the smaller fish and then settled down again. During this time all but one of the larger pygo's never got a nip. The only one to still take a hit every once in a while was my big one- eyed red. Once again he settled down for a short period of time and then decided to focus all of his attention on one fish.....the one-eyed red. The brandtii had the reds fins pretty chewed up almost to the point where I thought the pygo's were going to finish him off. My smallest cariba had this red pinned to the ground as the red was laying on his side. I thought that was it. For no reason the fish backed off. The next morning the one-eyed red (I call him c.j.) was sitting on the brandtii perch on top of the block with all of the self-confidence in the world. He really hasn't been touched since and that has been about two weeks now. The last couple of weeks have been pretty mellow in the tank but that never lasts long.

As of right now I'm keeping my options open as far as whether the brandtii stays in the mix or goes on his own. I have the tank space available in case of emergency so we'll see how it goes. At this point I'm not too worried about fatalities because the brandtii seems to focus his attention on the dorsal fins of the pygos and the brandtii is too fast for the pygos to catch. This could all change by tomorrow morning and I'm prepared to deal with the consequences.






PIRANHASince starting this experiment back on the second of Feb. I've had a lot of time to observe my fish. On the average I would say I spend 3-4 hours a day observing my fish interact. That has pretty much become my ritual way of unwinding at the end of the day right before I go to bed. I usually get about 2 or 3 hours a night to observe them and then about another hour or two during the afternoon. One thing that I have noticed is that they appear to be more active at night. My tank is in the basement so as far as light goes the daylight doesn't make much difference. All of the attacks that I have witnessed from the brandtii have occurred at night. That is not saying that they don't happen during the day. I spend far more time observing at night than during the day time so that definitely could be a factor. Just from my overall observations I would have to say that the aggression level in my tank seems to be higher at night.


This tank has only been set up since Jan. 5-05 so Nothing is settled yet. In every one of my pygo tanks in the past a hierarchy has always been established. I just moved into my new house on Jan 5-05 so that's why this tank is so new. I planned on getting this tank when I purchased this property almost 2 yrs ago. When I got the property I bought 3 dime size ternetzi and two 2" piraya as seed fish for this tank to go along with my other six 10+" pygos that I had in my 165 gallon tank. I was planning on raising these 5 fish in my 75 gallon until the new house and tank were ready. By the time I moved, one of the terns was 13" with the other 2 not far behind and the 2 piraya were both about 11 1/2". In my 165 gallon I had a 13" cariba that ruled the tank. In my 55 gallon I had 4 other good size pygo's with the largest one being 11 1/2" cariba with a bad attitude. I was expecting a battle to happen when I combined these 3 different established communities together. That battle has still not happened. There is really no recognizable pecking order among the pygos yet which I find extremely strange. The only fish to really establish any kind of territory in the tank has been the brandtii. He sets up shop right on top of a cinder block that I have in the tank. When he is in his attacking phases he will slam the pygos from above on the dorsal fin and retreat back to the top of his block before they knew what hit them.


He likes to stay in close proximity to the pygos yet have some place to retreat to where he feels safe. Just in my opinion this fish is on a different intellectual plane than my pygos. Where my pygos attack and then sit there and wait for a retaliation, the brandtii attacks and retreats before the other fish knew what hit them. The brandtii never really seems like he intends to kill when he nips, his nips seem to be geared more towards defending his territory and the occasional snack. When he picks on my weak one-eyed red however, I feel he is displaying his dominance and trying to set an example with a much larger, inferior fish.


PIRANHAJust when you think you have them figured out they surprise you. For the first time in my 18 yrs I actually thought I was going to witness a cannibalistic act. My smallest cariba had the one-eyed red pinned to the ground and the red was twitching then the rest of the pygos came swarming to that end of the tank and then they all just backed off for no reason. I didn't want to see it happen but I want to let nature happen in a case like that. The red is an inferior fish due to the loss of his eye and would probably be taken out in the wild because he is a weak link. My 6" one eyed red was taken out before the brandtii ever entered the scene. If I ever see one of my strong fish in jeopardy I will take action. In a case such as this I saw it as "survival of the fittest". Apparently the other fish decided he was worthy of living and decided to leave him alone. The morning after the attack I woke up to find the one-eyed red on top of the cider block (the brandtii post). Since then he has been left alone by both the brandtii and the pygos. It hasn't been nearly long enough to make any predictions as to whether or not this will work because these fish are so unpredictable. For the last couple of weeks things have been quiet so I will try to keep using this time of peace to keep catching you up on what has happened in the last couple of months until new developments happen.




PIRANHAThe last couple of days have been promising. When I first introduced the brandtii to the tank he almost instantly grew an attachment to one of the two cinder blocks in the tank. He would chase off any of the pygos if the came in the area. The big problem with that was that the way I had the tank set up at the time was that if you owned the block you owned about 1/3 of the tank. With 21 large pygos sharing the tank with him that wasn't very realistic. The pygos were constantly roaming into his area and this could have had a lot to do with the number of fin nips in the beginning. After observing him in what I thought to be his comfort zone, I attempted to create him a new comfort zone, only this time controlling a lot less territory. I attempted to move his cinder block into the corner and created a nice little cubby for him out of driftwood and his favorite block. The pygos never really even used that corner before he entered the tank. I thought maybe I could keep him out of trouble. He hung around for a couple of days but never really looked satisfied with his new home so he took over some new real-estate on the other side of the tank. On top of the other cinder block. It was right in the middle of the mix of pygos. Of course the nipping increased at this point until he was well established. This is where he has spent the majority of the last couple of months.


PIRANHAOn Tuesday night ( 3-29), I decide to increase my filtration by adding a wet dry. When I did this it really stirred the fish up. Whether it was the increased current or change in water quality, or just a general noticeable difference in the tank, it changed things. Last night the brandtii starting hanging out in the territory that I created for him almost a couple of months ago. He wasn't defending it yet but he was definitely checking it out. He's spent a little time there before but he never defended it yet so I wasn't going to get my hopes up. Tonight I actually saw him start to defend my spot. I'm hoping that if he claims this area he will be able to stay out of trouble. The pygos don't need it because they usually group up tight on the other side of the tank. That was half the reason behind setting it up in that corner. I set it up so driftwood defines the boundaries and the lot covers at least 150 gallons. I'm hoping that's enough water for him to claim to keep him out of trouble. The limits are clearly defined so the smart pygo should know enough to keep out. He still hasn't really settled in enough for me to feel comfortable that he's staying. Tomorrow he may be right back up on his old perch nipping fins. Who knows? Even if he does settle in in the area that I made for him it definitely doesn't mean that he's staying out of trouble. I just pictured this spot as the path of least resistance for him. We'll see what happens. Hopefully he settles in and stays chilled out.


The brandtii is still set up in the area that I had created for him. In the last couple of days there has been a significant amount of fresh fin nips. I have witnessed him defending his new home quite a bit in the last couple of days. The increase in fin nips was kind of expected at this point due to the change in territory and the need for the brandtii to let the rest of the fish know that this is his new home.


The one-eyed red is once again beat up along with a few nips on some of the other larger pygos that used to swim through that corner on their laps around the tank. I'm hoping that when the newness of things settle down, peace will be at an all time low since the mix. If the brandtii still causes trouble in this secluded area my hopes for this experiment will start to deflate.


I would like to see this work because from my experience with the serra species, they only eat what they need to survive. They definitely kill more than they can eat but when it come to actually eating they're weak in comparison to pygos. The serras, don't usually have competition for food because they are on their own so they only have to eat what they need at the time. Whatever they don't feel like eating now will still be there later. No one's going to take it away. In this tank the brandtii has almost adopted the pygos feeding habits. It seems like he feels the urgency to eat as much as you can now or starve later. With this many fish in one tank the urgency to get your piece while you can is incredible. The brandtii feels it and he stuffs himself on many occasions. There has been a bunch of times when the brandtii grabbed a bigger chunk of food than he could handle and got chased around the tank by the pygos as he's trying to force it down. The competition definitely makes them eat more.


What also might play a factor in curving my brandtii appetite is the fact that I feed my piranhas whole fish. They get the heads, guts, fins, and all. When the brandtii isn't hungry enough to pull chunks off the feedings, he will still chase the pygos around as they are picking apart their feast while picking off scales and fins that are left behind. He's still getting his fill of what he's used to without having o harm my pygo's. That doesn't mean he's not going to harm them, it's all in the nature of the beast.


I've always fed my pygos whole fish and this just kind of played right into the brandtii diet. You should seem him chase those scales down like flake food. I'm trying a lot of different things that play into the brandtii feeding and behavioral patterns. If this doesn't work with this much water, I'm throwing in the towel. He is showing promise by moving into the territory that I set up for him. That is definitely the path of least resistance. If problems still continue I may have to terminate this experiment. It's definitely a roller coaster ride. Things are fine for a week or two and then the brandtii decides to make a change and start nipping again. Hopefully things will settle down in the next couple of days and it will stay peaceful for a while.



It has been six days since the brandtii decided to relocate and he is still there. He was defending his new territory pretty hard for the first couple of days. For the last few days the fin nips have stopped and he really seems settled in. The pygos have learned to stay away from that corner and the brandtii has been leaving them alone unless they venture too far into his territory. Even then he just swims slowly at the intruder and the pygo will swim off. The last few days have shown a lttle more promise. There is still a long way to go but any hope is encouraging.



The brandtii spent the day once again in his new home. He spent the entire evening in his new spot until about 9 p.m when I decided to feed my fish some venison. All of the fish gorged themselves including the brandtii. After dinner he decided to go back to his old perch and spend some time over there while he digested his food. It almost looked as if he was thinking about moving back. After a couple of hours for some unknown reason he decide to move back to my comfort zone and settle back in there. I keep on changing the variables with the filtration and the food source so it's hard to tell what, if anything, is triggering the changes. It may just be his mood changes or maybe I am doing something unconsciously to trigger a reaction. When the water finally stabilizes to the point where it will remain I can finally start playing with the variables one by one to see if I can't figure something out to calm the beast.


It's possible that a red meat diet may trigger something internally in a piranha. Maybe for the brandtii, eating red meat instinctively means some kind of change to come in his eating habits so his behavior must change back to what he was comfortable with. He hasn't really gone back there since the move after feasting on the bluegills. Maybe red meat just sits a lot heavier in their stomachs than fish do and he wanted to digest where he felt most comfortable. There is no scientific fact in anything that I just stated, in fact there wasn't even to much thought put into the theories so take it for what it's worth. I was just brainstorming out loud. The brandtii definitely acted different tonight after eating the red meat but it just as well might have been his mood for the night with no connection to the food at all. 


I thought by feeding my fish whole bluegills it would play right into the brandtii feeding habits. He has the scales and the fins to eat plus a nice big chunk of flesh or even guts. This is the first time that the brandtii has participated in a red meat feeding since he's been in the tank. He was acting noticeably different than he did when he ate fish.


Red meat has always seemed to hold my piranhas over longer than fish. It really seems to fill them up more. When I add red meat to their diet I can usually skip the next feeding on the schedule because they're usually not that hungry. My pygos have also appeared to be more docile the day after eating red meat as opposed to eating fish. It almost looks like the after Thanksgiving dinner effect. It's like all the fish just want to relax and digest their food. Maybe a little more red meat in the diet may relax the brandtii. It's definitely worth an experiment when the tank is stabilized. 


This is going to be a roller coaster ride to get through this but hopefully something is proven when it's all said and done. I really want to give this a chance but I also like to have perfect looking specimens so my hope are not high.There really hasn't been a stretch of much over two weeks where there was not a flurry of fin nips. This tank is still in the experimental stages of "perfection" so I really haven't given it a chance to settle down. I've been changing a lot of things and it seems like whenever I do the brandtii acts up. When I have this tank set up the way I want it and I let everything settle down it will be the true test. I have been messing with the tank too much since he has been in there and that seems to spark him. I have a long way to go till I'm done changing the world around on these fish. I'm hoping by the end of the summer to have everything on the inside of the tank complete. I hope he doesn't push the limits before then. I plan on removing my skeleton and one of the cinder blocks and making my tank more natural by adding a bunch of driftwood and maybe some live plants. If the brandtii can't learn to back off on the fin nips at this point he may have to go out on his own. I have a 75 gallon and a 165 gallon tank that he could move into any time. I'm hoping for the best but expecting the worse. I'm constantly reminded that things are on a day-by- day basis. With little or no warning signs things could change. It's been two months now and I still have yet to find my comfort zone with this mix. There is a lot that remains to be proven before I can feel comfortable.



Things have continued to be mellow since the brandtii decided to make the move to the corner as opposed to right in the middle of traffic. The brandtii continues to defend his territory and the pygos respect that and give him his space. The brandtii has yet to get a scratch on him since being moved into the tank in the first week of February.

Construction season is starting up again here in Wisconsin so I was called back to work on 4-11. Since I have been back to work my lights in the tank are only on for about 3 or 4 hours a day. I turn them on when I get home from work and I turn them off before I go to bed. My fish have definitely been acting different since the change in lighting hours. Up until now the lights have been on for about 10-12 hours a day. There might be a connection between the hours of daylight your fish sees and the aggression they show towards each other. Who knows? Either way it works for me and it seems to be working for them so I will continue the low light pattern.



It's almost been five months now since mixing the brandtii in with my pygo's. All is still going surprisingly well. There still hasn't been any serious flesh wounds and the few minor ones that have occurred have been pygo to pygo nips. The fin nips have stayed pretty minimal for quite a while now. Since my last update things have been peaceful.The brandtii actually received his first fin nip. I noticed tonight his anal fin had a tiny little nip in it. I suspect one of the little reds had enough. My smallest red also had a nip in his tail. Some nights he wants to hang out in his little cove by himself and not be bothered and some nights he swims right along side of the pygos. He likes to chase more than the pygos but he rarely bites. He just likes to push the pygos around sometimes and they usually retreat and the chase ends shortly. I really do believe the 10' in length and 4' of width to retreat to make a huge difference. The brandtii isn't a distance runner. He usually only chases them for a foot or two and the pygo swims well out of the area where he is no longer a threat to the brandtii and the brandtii relaxes. It's not like he is relentless. I usually only see him chase maybe a a couple times a night in an hour or two and some nights he doesn't chase at all.


The longer he has been in there the more it seems he conforms to the pygos way of life. In my opinion he is eating more than he would be if he was in a tank by himself. He knows there is competition for food so he keeps going back for more. He is usually the one to get it going if the pygos aren't that hungry. When I first started this experiment back in early Feb. I thought things would get worse and it was very possible the brandtii would be removed by now. I have 7 other pygos growing in my 75g tank and they are ready to come into the big tank. My plan was to add the other pygos when I changed my decor to all driftwood so there would be confusion in the tank and the little guys would stand a chance. In my 75g I have 2 piraya, 1 cariba, and 4 ternetzi, all between 6" and maybe 8". I also thought I was going to have to remove the brandtii when I did this but now I don't know. I still want to give it a little time so I can spend a little more time watching how the brandtii gets along with my reds comparable in size to my new additions. I hope to have the pygos in by the end of the summer if I can find the right pieces of driftwood and the brandtii continues on his best behavior. When I do add the new fish I plan on taking out all but a few of the reds and putting them in my 165g to make room for the others. So far the spacing seems more than enough but that's probably going to change as the fish get bigger. I'll keep you updated on my decision when it comes to that time. Unfortunately summer doesn't allow me much time for the computer or my fish but if it comes time to writing about my fish for the hour or two I have to myself a night or watching them, I'll have to take watching them. I'll keep you posted on any changes. In the winter I'll fill you in on the details.







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