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Discussion Starter · #1 ·
The following is a thread that I started at another site that may contain some useful information regarding the topic of growing Serrasalmus Rhombeus in captivity. Please feel free to post your views and experience on this subject, as this is how we all have the opportunity to learn from one another.

Recently I had the opportunity to talk with Oliver Lucanus about the availability of different rhom variants. I mentioned that I was looking for a particular rhom from the Orinoco river system, and needed it to be at least 13" in length. Oliver stated that he did not understand why so many people are willing to pay huge amounts of money for large rhoms, when they can be easily and quickly grown in the home aquaria. I then expressed to him that the common knowledge about captive rhom growth that I had heard over the years was that growing a rhom to a size much larger than 12" in captivity is almost unheard of. Oliver said that this line of thinking was nonsense, as he has on many occasions seen rhoms in Asia that were raised from 5 + 6" fish, that grew to sizes larger than 16" in captivity. When I asked him if they were doing things differently than the norm, this was his response.

The first thing that Oliver said that was lacking in most of our rhom tanks is a sufficient amount of current. He stated that rhoms are typically found in much faster water than pygos, and the Asians have learned to reproduce this flow in their home aquariums. This made sense to me, since they would expend a lot more calories striving to hold position against the current. They would therefore need to consume a larger quantity of food, which would in turn promote better growth.

The second thing that Oliver mentioned to assist in growing out a rhom was to have an automatic drip system to keep the nitrates down to a minnimum. Apparently these systems are much more common in Asia, and he believes that this too plays a huge role in helping the rhombeus to grow large in captivity. I am very familiar with the automatic drip system, since I have used it to grow pygos in my own tanks, so this too was a method that I was in complete agreement with.

Although it wasn't mentioned in our conversation, a quality and varied diet is also something I believe is crucial in growing a large rhombeus, or any piranha for that matter. It has always been my belief that whole fish (with heads and guts in tact) should make up the bulk of this varied diet, as this is what our adult flesh eating rhoms consume most of the time in their natural habitat. I also like to regularly rotate shrimp into the mix, and periodically will throw in some earthworms or catfish fillets as a change of pace. On very rare (due to the risk of disease) occasions, because I still greatly enjoy watching piranhas in the act of predation, I will feed live fish stuffed recently fed with a high quality flake food or pellet.

I am trying out these methods with a new rhom that I have recently acquired, and will keep everybody posted on the results. He is currently between 11-12" long. Of course, I still have my theory that one of the reasons our captive rhoms do not grow as well as pygos is because they are not forced to compete for food in the home aquarium. In most cases the captive rhom is kept solo, whereas our pygos shoals seem to sometimes eat just to keep their tankmates from getting any food. I am hoping that the added current will counter this pickyness that many of our rhoms often times exhibit, but time will tell. UPDATE: I have now had the above mentioned rhom for around six months now. He has grown to about 12", and I think he was closer to 11" or so when I got him. Although that is not all that significant when it comes to growth even for a rhom, keep in mind that the first few months I was fasting him periodically, to train him to eat the foods that I wanted to feed him to promote good health and growth. Due to the very stubborn nature that many of our captive rhoms seem to possess, he ate very sparsely at first. I expect that he will begin to grow at a much more accelerated rate, since he is now readily and aggressively eating all the foods that I want him to.
 

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I certainly agree with Oliver and I think your on the right track John. Still, I wonder why captive rhombeus in large public aquarios (1,000 g plus) stay small in stature? Perhaps the drip system is one of the answers.

I hope you physically took the fish out and measured it. Eyeball measuring (as you probably know) will skewer any results. Good luck.
 

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Discussion Starter · #4 ·
hastatus said:
I certainly agree with Oliver and I think your on the right track John. Still, I wonder why captive rhombeus in large public aquarios (1,000 g plus) stay small in stature? Perhaps the drip system is one of the answers.

I hope you physically took the fish out and measured it. Eyeball measuring (as you probably know) will skewer any results. Good luck.
Frank, I do think the automatic drip system is one of the main ways one can promote growth on a captive rhom that normally would be stunted in the home or public aquarium. The reason has to do with something you posted on the "How big do Xingu Rhoms get?" thread. The automatic drip system is constantly adding fresh water to the aquarium, and flushing and/or diluting the old water. Therefore, the growth inhibiting hormones that are released by our rhoms are being continually flushed away, thereby allowing the fish to grow freely, unhindered by this particular process.

Another point, which I am sure you already know, but others may not. One reason that I think a very large percentage (but not all) of captive rhoms do not grow very large is due simply to their predetermined genetic footprint that allows them to only reach a certain maximum size. Humans have been known to reach 8' tall, but that doesn't mean that my genetic footprint would have allowed me to grow that tall, even if I ate all the right foods and lived in a perfect growth-promoting environment. I believe that many of these rhoms that stopped at 12-13" in captivity would have never grown any larger if left in the wild. However, some of them probably did have the potential to grow much larger, and that is why we need to share information about how to get them to do so.

As far as my measureing technique, I'm afraid I only take my fish out and measure them when there is the need to relocate them. I know that my method is not the most accurate, but since I am only writing to inform and not by any means offering my measurements as being precise or scientific, I suggest that the readers take them merely as guidelines, not gospel. Keep in mind too that whenever I talk of measurements of my fish, I am referring to total length (TL), with tail and bottom jaw included. I am glad you pointed that out though.
 

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Peace....Through Superior Firepower
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WOW .........
Thank you Knifeman so much for this valuable information .........

This is a Diamond Gem Thread


Read Up Fellas
 

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OPEFE
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Very interesting...keep us updated...
!
 

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Discussion Starter · #8 ·
NavinWithPs said:
how long do you guys wait before you know for sure that your rhom isn't going to grow anymore? a year? more?
Good question, but there is no definitative answer. That is the reason many people (including myself at times) will opt to spend the extra money on a fish that already is large. Unfortunately, there is no way of knowing if your fish has stopped growing completely due to genetics, or is perhaps just in a phase where he has temporarily stopped growing. This may or may not be due to something in his diet, water, etc...that you may or may not be able to control. Therein lies the problem in growing huge fish, regardless of how well you keep them.
 

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I also wanted to add about that very cool thread on predfish some time back about how this dude had a piraya that grew to like 17 inches real fast while another one with the exact same water conditions only managed to get to 12 or something. This would support the argument that every fish has a predetermined footprint on how big it can get.

Now if only we can isolate this gene and great SUPER-rhombeus
 

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Xenon said:
I also wanted to add about that very cool thread on predfish some time back about how this dude had a piraya that grew to like 17 inches real fast while another one with the exact same water conditions only managed to get to 12 or something. This would support the argument that every fish has a predetermined footprint on how big it can get.

Now if only we can isolate this gene and great SUPER-rhombeus
I think you're talking about Als, he started with 3 pirayas at 5-6"; one grew to 16-17" and died, another is currently up to 16" (but took much more time than the first one to reach this size) - so genetics does play a role in all this.

But I don't think genetics play a role as sever to limit a fish's size in half..in your example Knifeman you mentioned an 8ft human, and the average is 6ft - this is easy to swallow than an average of 4ft.

Therefore I don't think a rhom that is capable of reaching 24" is limited on 12" by genetics (which apprently happens with many rhoms) - there are definitely other factors including/excluding genetics.
 

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Discussion Starter · #11 ·
kouma said:
I think you're talking about Als, he started with 3 pirayas at 5-6"; one grew to 16-17" and died, another is currently up to 16" (but took much more time than the first one to reach this size) - so genetics does play a role in all this.

But I don't think genetics play a role as sever to limit a fish's size in half..in your example Knifeman you mentioned an 8ft human, and the average is 6ft - this is easy to swallow than an average of 4ft.

Therefore I don't think a rhom that is capable of reaching 24" is limited on 12" by genetics (which apprently happens with many rhoms) - there are definitely other factors including/excluding genetics.
That is a good point, and may be true to a certain degree, but you can never look at a science like genetics which varies so much from individual to individual (not to mention the VAST difference from species to species) and make a mathematical formulation about it. This is only a rough example, and only meant to point out one of these differences, but I believe rhoms have bred at 6-7" in length, with is roughly 1/4 of their maximum potential size for the species (using your formula, not mine). If your formulation were correct, people would be reproducing at two feet tall, in which case a lot of parents out there (including myself) need to be watching their todlers playing much more closely.


On a serious note, almost all collectors of wild fish in S.A. will tell you that a 12" rhombeus is not typcially thought of as a medium sized fish or "half grown" fish, but instead a larger than average one. I know that the time that a sexually mature fish breeds has to do with age as much as size, just like it does in humans as well. I agree that there are other factors besides genetics that play a part in growth, which my thread points out. But if you study genetics and the laws of Mendel, you will see that an organism cannot exceed it's growth potential beyond it's pre-programmed genetic footprint, no matter what type of environment and nutrition it receives. This applies to fish, people, and other species as well.

Very valid point...keep em coming!
 

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Wow....Great post John. I actually think grim has grown some since he has been in my care. I dont know for sure, but he apears larger then when I first got him....I know his fat reserves are much larger than they were...and he eats an amazing amount of food. I also think getting him out of the 75 he was in, to the 120 he is currently in may have given him a little spurt in the first few month of the change.
Anyways, great info!
 

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Bean Power!
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I still have my theory that one of the reasons our captive rhoms do not grow as well as pygos is because they are not forced to compete for food in the home aquarium. In most cases the captive rhom is kept solo, whereas our pygos shoals seem to sometimes eat just to keep their tankmates from getting any food.
This was always one of my thoughts to. I noticed when keeping pygos singly, their drive to attack food decreased dramatically. Infact, though interested, they seem to let it lie and rip off chunks at their leisure. And, I saw extremely slow growth from one cariba I had solitary until, I tossed him in with buddies, and then he started blooming fast!

Excellent post John. What's your thoughts on tiny water changes everyday opposed to the drip system? (wich most of us are not able to do)
 

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Discussion Starter · #14 ·
Serrapygo said:
I still have my theory that one of the reasons our captive rhoms do not grow as well as pygos is because they are not forced to compete for food in the home aquarium. In most cases the captive rhom is kept solo, whereas our pygos shoals seem to sometimes eat just to keep their tankmates from getting any food.
This was always one of my thoughts to. I noticed when keeping pygos singly, their drive to attack food decreased dramatically. Infact, though interested, they seem to let it lie and rip off chunks at their leisure. And, I saw extremely slow growth from one cariba I had solitary until, I tossed him in with buddies, and then he started blooming fast!

Excellent post John. What's your thoughts on tiny water changes everyday opposed to the drip system? (wich most of us are not able to do)
Nick, I think that if a person can be disciplined enough to do just a 5% water change daily and not be tempted to do more, it can have nearly the same positive effect on growth as what the automatic drip system has. However, as you know most of the work in a water change is involved in getting out the stuff to do the change, and then putting everything back in its proper place. While it is an awesome idea and something that most of us can do, it is not very practical for most people due to time constraints. But if you or anyone else can do it for a period of say six months, I think the dramatic growth results that will be seen will make the effort worthwhile.

It is my belief that small frequent water changes are better for our fish than changing large amounts of water (40% or more) every couple of weeks or so. I also did a post on this after speaking to a very knowledgeable fish keeper at the Newport Aquarium in KY, and the conversation has changed my water changing habits as a result. This gentleman really knew his stuff, and I would be doing him an injustice if I attempted to translate all of the information that he passed on to me (much of it went over my head, I must admit). Maybe I'll see if I can round up that thread and post it a little later?...
 

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However, as you know most of the work in a water change is involved in getting out the stuff to do the change, and then putting everything back in its proper place. While it is an awesome idea and something that most of us can do, it is not very practical for most people due to time constraints.
True. But, in my case, the damn hose is always stretched across my floor and ready to go.
I guess to me, it's not worth the effort to pack it away.

It is my belief that small frequent water changes are better for our fish than changing large amounts of water
I agree. I took my water removal percentage way down awhile ago. To me anyway, living in an apartment, the tiny changes are more realistic. I think I'm going to give the method a test run.


I also did a post on this after speaking to a very knowledgeable fish keeper at the Newport Aquarium in KY, and the conversation has changed my water changing habits as a result. This gentleman really knew his stuff, and I would be doing him an injustice if I attempted to translate all of the information that he passed on to me (much of it went over my head, I must admit). Maybe I'll see if I can round up that thread and post it a little later?...
Sounds good. Looking forward to it.
 

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Discussion Starter · #18 ·
Serrapygo said:
I also did a post on this after speaking to a very knowledgeable fish keeper at the Newport Aquarium in KY, and the conversation has changed my water changing habits as a result. This gentleman really knew his stuff, and I would be doing him an injustice if I attempted to translate all of the information that he passed on to me (much of it went over my head, I must admit). Maybe I'll see if I can round up that thread and post it a little later?...
Sounds good. Looking forward to it.
Sorry man...I can't seem to find that thread anywhere.
 

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Knifeman said:
Serrapygo said:
I also did a post on this after speaking to a very knowledgeable fish keeper at the Newport Aquarium in KY, and the conversation has changed my water changing habits as a result. This gentleman really knew his stuff, and I would be doing him an injustice if I attempted to translate all of the information that he passed on to me (much of it went over my head, I must admit). Maybe I'll see if I can round up that thread and post it a little later?...
Sounds good. Looking forward to it.
Sorry man...I can't seem to find that thread anywhere.
Nice example on mating and genetics.

How about this water changing routine; everyweek 40-50% and 10% in the middle of the week.

So for a single rhom in a 75+ tank, this should assure the Nitrates level to be zero or a little bit over zero; since the rhom won't have enough time and still water to poluted fast enough. Also the 10% in middle of the week doesn't have to including gravel siphoning, it is just a matter of replacing water.
 

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I have a 16 inch rhom in a 150 gal that at first posed water changing problems.
I asked in an earlier post about an automatic water changing system, due to the fact the fish was skittish at first. He did'nt like me in the tank! I was wondering if my system was similar to a drip system. I have an overflow skimmer, draining water outside. I also have a 100 gallon horse/cow rubbermaid resivoir holdig water
at the right temp. There is a pump of about 150 gph with a adjustment valve to
regulate flow. There is also a one-way anti-syphon on the pump output because
of back -flow, due to the fact the pump output is 2/3's of the way down in the tank.
This system is on a digital timer for timed larger changes, or flow can be adjusted
with adjustment valve so it can run continuously daily. I am looking for the right
rhom to try some of these growth experiments, as I read some info a while back
about growing large rhoms fast.
 
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