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Discussion Starter · #1 ·
I'm going to use this thread to post some interesting morphological, or body, characteristics of the Red Bellied Piranha I have observed over the past 20 or so years of keeping these unique fish. Don't hesitate to add your own observations to this thread too.


Buccal Valve:

One of the easier things to see different about these fish and most others, besides the teeth
, is the presence of a buccal valve. As piranha spend most of their time with their mouths open, only rarely closing them, breathing could pose a problem as oxygenated water, obviously, has to pass through the mouth over the gills. An open mouth will prevent this but these cleverly designed little fishes have this buccal valve that can easily be seen just by looking into their mouths.... careful of your nose!


This is a survival adaptation which becomes very apparent when the fish has a large morsel of food which it is carrying about before eating. I have seen my fish swim about with food for a little while before actually consuming it. Only then do the advantage of this valve become apparent. With a widely open mouth piranha can still breath as this valve allows water to enter the mouth and then closes behind it to force it through the gills. Clever fish.
 

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Hinged Jaws:

Don't know if anybody else mounted a skull of one of these fish but if you were to look at the jaws from behind there is a very rigid but flexible hinge in the center of the jaw much the same design as a piano hinge.

When feeding, watch the action of the jaws, if they don't eat too fast that is....
They can spread twice as wide as they look when the fish is relaxed. This is a pretty unique adaptation to these fish which may allow them to maximize their bite size. First impressions can be misleading. The fish appear not to have large mouths but a good yawn gives the large gape away.

The most obvious hint of this can be seen in the cheeks. When a big morsel is taken the cheeks puff out. This is the jaws widening on the hinge.

Anybody else take notice of this?
 

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Nasty-assed Teeth

As you are well aware these fish have teeth. Why else would all us piranha freaks have them!!
There are a number of incredible attributes to these teeth that serve these fish well.

First of all, sharpness can't be underestimated. They are needle tipped with razor sharp edges even after the fish are finished and shed them. Shedding occurs about every two months in stages. They can't afford to go about with a mouth full of no teeth so they have a strategy. They shed a quarter of the mouth at a time.

New teeth are made in the jaw, much like our own and unlike sharks, and when they are ready they just rise, pushing the "old" ones out all at once (per quadrant) and within one to two days the new ones are in place and set strongly. Couple of weeks later another quadrant, usually the ones opposite the new ones, do the same. This will continue for about a month until all teeth are in place again.

This ensures the fish will always have 3/4 of it's teeth remain for defense and feeding.... a necessity when all your neighbours are well armed.


The teeth themselves are set such that there is a little cusp at the back of each upon which the rear teeth sit firmly upon. Not only does this produce a solid cutting surface without any gaps between the teeth but it causes the teeth to become very strong. If one of the rear teeth encounter bone, the force is shared with the teeth in front to prevent breakage or loss. If a tip is broken it stays that way until shedding of the entire set occurs.

The two front teeth of the lower jaw aren't connected to each other but are very close such that when the hinged jaw opens they stay together.

The bottom teeth are about three times larger than the top ones and, when the mouth is closed, sit behind the top much like an overbite. They don't, as many books on the subject say, fit between the gaps in the top teeth. The top teeth only act to hold the prey while the bottom ones slice. This is very effective for quick feeding as a long channel of meat can be cleaved off and swallowed simultaneously. The top teeth grip and the cleavers slice, the top teeth shifted further up and the slicing continued. This allows for very rapid removal of meat from a large animal... let's say a bloody cow!
............. Small round bites aren't what skins a cow but the stripping off of the meat.................. mmmmmmmmmmm
..............Small morsels like feeder fish or mice are just bitten into.

Incidently, if one was to hold an 11 inch Great White Shark in their hands, it wouldn't be a problem reaching in and touching the teeth. No offence to the mighty shark but there's no comparison as a full thumb would be snipped off in a heartbeat if it was tried with our little snappers.
 

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Rigid Skull

Most fish when dissected have many loose bones which make up the skull, even the powerful jawed wolffish which eat clams, snails, lobster, sea urchins.... When the flesh is removed the bones come apart like a puzzle.

Piranhas have a skull that is completely rigid and almost look like a freaked out humanoid with goth teeth :laugh:

Seems the strength of the jaw muscles are powerful enuf to warrant a solid mass of fused bones. There's also a pocket on either side where the large cheek muscles sit. These muscles are huge compared to other fish and are attached to the jaw further to the front to maximize biting power.

The jaw itself is very rigid and solid for it's size. There's nothing to compare the jaw with as no other fish comes close to it's thickness and strength for it's size. The joint where it attaches to the skull is remarkable as well.

These fish are full of unique adaptations


Note: This image has been copied from an avatar on this site. I can't remember who I got it from but if you recognize it please let me know so I can put your name as the source.
 

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omg i can't believe i
actually read the whole thing... interesting stuff man gj
 

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Discussion Starter · #8 ·
Thanx guys


As a fish biologist I have been interested in these marvels of adaption piranha have and where else to discuss this stuff than with a bunch of other like-minded individuals who are equally amazed with these small deadly finned animals.
 

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Discussion Starter · #9 ·
T-Beam Ribs

As is very apparent piranha of all species share a flat body shape much like a discus fish... with some variation. Why not just have an elongated torpedo shape instead? ..
Ahhh.. these fish have a method to their madness....

For starters, watch two fight. They start by doing their threating displays to each other by puffing out the fins, gaping their jaws, and waving their bodies back and forth. The next step is to put up or leave the area. Those that continue the fight will try and take a bite out of each other. This seems to be impossible to do if the fish are attacked on the side and I have witnessed this many times. The teeth can't get a grip. They will also do their best to protect their top and bottom and will always turn their flat side to each other to avoid showing any area vulnerable to a bite. I have seen fish slash repeatedly at each other and as long as it's at the flat side, it does no harm.

When schooling, opportunities for sucker bites from other piranha abound but as long as the other fish don't try and get above, or under the target, they are safe from each other.

Eating any type of fish one occassionally comes across small bones which are thin and roundish in cross-section. Piranha, on the other hand, have strong, solid ribs which, if taken in cross-section, are like T-beams. This lends tremendous strength to them preventing bending during an attempted bite. Bending would allow the teeth to get hold of the side and would be sure to cause a fatal wound.

Fish that do receive a bite from above, below, or of the tail area quickly give up the fight and flee for their lives.... or disappear within seconds like so much other feeder foods
.
 

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Wow, this is very interesting, PB!!!
Thanks for sharing


I'll pin this baby for now: maybe we can gather all information and make it into a new article for our Information Section.
So if you have more, and are willing to share, please do...
 

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Discussion Starter · #13 ·
Glad you are enjoying this stuff.... these fish are just plain FASCINATING!!!!


I always wanted to meet the gang from the Simpsons ..... how y'all doin'
 

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Flared Nostrils

When looking at a piranha head-on two projections looking like little satellite dishes with an opening on the side of it sit on the front of the err... "face". On closer inspection there is another opening at the rear of these "dishes". These are the nostrils, or nares, and that projection acts like a funnel to direct water into the forward opening.

The path of the water through the nares is observable in still water containing tiny particulate matter. Close inspection will reveal a flow is created which enters the front opening and leaves the rear one. Looking into the rear opening small reddish channels are visible looking like a labyrinth. They are heavily lined with blood and sense receptors. Within these are tiny cilia or hairs which beat and create the current so that when the fish is not moving the water still passes over the sense, or olfactory, organ.

Salmon, a fish requiring a strong sense of smell to home into it's river from the sea, doesn't even have this advanced set-up with large dishes directing water into the nares.

This allows the piranha to continually read it's environment. With a sense of smell reaching one part per billion, very little by the way of odor escapes their alertness.

It is known they can smell blood but any fluids leaving injured flesh is picked up. For that matter they can also smell healthy, uninjured fish much like a bloodhound can smell the individual odors of it's quarry. When feeder fish are placed in the tank, they all have their own distinct proteins and chemical signatures which can be picked up by these fish and the piranha know they are in the water even when they can't see them once they get the scent.

When I thaw out food for my fish, I place it on the edge of the tank to melt quickly. Little drips of melting ice enter the 150g tank and within moments of the first drip Kilzses (see avatar
) is there awaiting.... seemingly drooling for his dinner.
His head almost comes out of the water when I raise my hand due to his expectation of food.

I got him to pose here so you can see what I am talking about
...... err... a little blurry
but you can make out the nares and "dish"
 

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Discussion Starter · #17 ·
Good question amoor33... the redness of the eye...


This is the iris of the eye and like people, can be coloured differently in individuals and not all piranha have red eyes. The iris is responsible for the light levels entering the eye and opens and closes in response to varying light intensities like the diaphram in a camera. I haven't read anything in particular about iris coloring but it wouldn't surprise me if there is an advantage to having the iris red. One thing I have noticed is that the red reflects the mood of the fish. The deeper red it is the more comfort these fish feel. Nervous or frightened fish lose the intensity and it is very noticeable.

Looking at one of these fish in an aquarium is different than seeing one in the wild. Light levels and water chemistry are quite different in natural conditions. These fish live in waters which look like steeped tea, called black-water, or in murky, silty waters and the red iris may have some advantage in light or energy absorption. Maybe all red-eyed piranha share common elements found in their respective environments.

When something shows color it is actually absorbing all the other colors of the light spectrum and reflecting the color of the object and the red eye of the piranha is absorbing all the blues, yellows, and greens from the ambient light conditions while reflecting the reds. This is just a guess but it wouldn't surprise me if there is a physiological adaptation to changing light conditions which may be picked up by the coloration and sensed internally by the fish. Similar effects can be observed by many other animals and most plants. Blues are found in daylight but disappear during mornings and evenings while red wavelengths are longer and visible. Perhaps these fish respond to that. Again..... this is just a guess.

Colors are pigments and many pigments can absorb energy from their respective absorbances of light. Photoperiod and photointensity plays a very important role in the breeding and growth conditions of plants and many animals.
All this being said, it may just be an intimidation strategy mature fish display for dominance or breeding as red eyes are rather threatening looking.....


But while on the eyes.. you all would have noticed the amazing alertness these fish have. They seem to be aware of everything in their surroundings.

From the perspective of the fish, their world is all-encompassing. That is, they see virtually everything around them. Humans and other organisms with forward-facing eyes see what is in front of them. Things can sneak up behind without been seen. Piranha have eyes on the side of their heads giving them full coverage of their total surroundings. These fish can see you when you are directly behind them near the tail. In fact, next time one is back on to you look for the eyes. You won't see the whole eye but will see the projection of the lens. That's all that is needed to catch the slightest movements through the peripheral vision.

I have tried to sneak up behind my fish and he's on to me instantly... turning and facing me with both eyes ... then I'm in his sights in 3-D.

Oh... and night vision... yep these fish got that too.
All that is needed is the slightest amount of ambient light which can be provided by moonlight or even possibly starlight. When we stumble around in a dark room these fish can see quite clearly and are still watching us. Blackness to us is only twilight to them.
 

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Discussion Starter · #18 ·
Memory:

As many of you would have noticed, these fish can distinguish between different people coming to the tank. This is pretty unique to these fish.

A typical fish responds the same no matter who approaches the tank. A forever hungry oscar will approach a complete stranger the same as it would it's owner, not seeming to distinguish one person from the other. This is the same for many fish, people all look much the same to them..... and they pretty well all look the same to us too...


This isn't the same for the piranha as they respond differently to different people, being most responsive to the owner, and then less responsive to someone who makes a "regular" appearance, and they just sit and watch complete strangers, even when presented with food.

I have seen this many, many times. Once there were seven people looking into my aquarium and I suggested they watch my fish's behaviour when I stick my head in amongst the group.. then there were eight heads in total. Immediately he came over to me..... I repeated the action, this time going to the end of the tank... same thing. He swam directly to me. He recognized my face amongst all the others.


This explains why they will eat in front of you but not in front of others. Those people are strangers and these fish watch the new person intently. New people sitting and staring, as they are apt to do... and why not, you can sit and stare at most other fish,...... will only creep these fish out. It's better to casually observe them and go about your business until it's comfortable that you aren't "overly interested" in them. Just because they have a nasty set of blades doesn't mean they rule the aquatic world. They have their own predators and enemies too. River dolphins, giant river otters, and electric eels are some of their natural predators so they are forever vigilant. The Amazon jungle is one of the most competitive places in the world and you have to be constantly alert to survive. Danger exists everywhere and these fish show it.

Objects in the tank are remembered well too. One time I moved a stick and my fish noticed it in a new place... he acted pissed off and wasn't his self for a couple of days and looked paler than usual. Nothing I could do could stir him up. He just ignored me for those days. This is why changing the layout of the tank when adding new piranha is important. It changes the scenery and territorality boundaries, reducing the potential for dominance.

During feeding another time I had a bag with three goldfish. One of the fish was a dark brown feeder. Sitting the bag in the water, my fish came out, swam by and took a look, and then went back around his stump. Then, without him knowing I released the feeders. Immediately the dark brown one disappeared into the deep vegetation. The piranha came out, spotted the two gold feeders and got them, then it went into a search pattern looking for the other fish. I videotaped his search. He started scouring the bottom, then went mid tank, and then near the surface. Sure enough, as he got near the corner where the other feeder was hiding he spotted it, darted in and came out with his reward. Then he was satisfied, the search was over, and went to his stump to digest his meal.

So all this leads up to a very interesting question, ......... can they also count????

It has been proven a number of small animals have the ability to remember low numbers up to four. It seems these fish might have that ability also. Hear hear for the clever piranha!
 

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Discussion Starter · #20 ·
Err.... 20 years my good man.
........... hmmmmm... that's a long time to be sittin' in front of a tank ain't it ...
 
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