Morphological Characteristics of Piranha, Clever Adaptations

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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.
 
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.
 
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!
 
Finnage:

Well mr freeze opened the floor to the finnage of these fish. Sure they have the typical finnage as many other fish but to what extent are they the same or different...

For starters, piranha show the basic finnage of an "old" class of fish whereas something like a perch, with it's spiny first dorsal, second soft dorsal, absence of adipose, and position of the pelvic fins is of the "newer" fish in the evolutionary scale.

All fins are used for balance, with the majority of fish using only the tail, or caudal fin for propulsion. Some have come to make use of the pectorals for this purpose, ie: angels, sticklebacks, etc. but still retain the use of the tail but not for much, just fleeing or darting.

Other fish with the same fin design and layout, most notably the salmonids ... now where do these fish come into it??? (mentally squash a trout from head to tail and compare the finnage)......have much smaller, softer finnage and primarily use the tail for propulsion with all other fins only holding the balance of the fish in suspension.

Piranha also do this but to a slightly different extent. They do hold themselves completely still using finnage, mostly the pectorals and the dorsal as can be seen by the slight flicking of the rear of it, but also the anal fin. The two pectorals are used extensively during moments of relaxation but things change very quickly when action ensues.

For starters, the pectorals fold to the body when piranha dart swiftly to their prey and virtually all the momentum then comes from the tail. It is a large, water-displacing fin with powerful muscles motoring it. It is only soft on the trailing edge but the leading edge is composed of very large, partially-fused solid bony rays. The "wrist" of the tail is thick and strong. These fish are fast-moving as can be seen in the excellent videos on feeding that can be seen in Piranha-Fury.

But what about the large dorsal and anal fins... couldn't they just be small and still help hold the fish upright? The flat shape of the body should also assist in that. Wouldn't large fins just make the fish more vulnerable to attack by others??

It is when the fish is into a substantial meal much, much larger than itself and with a tough hide or connective tissue such as tendons or ligaments that the finnage makes more sense. If the fish can't bite through the prey just by the jaw action it then reverts to a very rapid sideways thrashing which then brings tremendous leverage to the fish with the help of the dorsal but even moreso the anal fin which also has a solid leading set of fin-rays. Note the placement of all the large fins, from halfway down the fish to the rear there is considerable finnage. If the pectorals didn't serve the purpose of forward balance and turning, all finnage would be to the second half of the fish.

This is another selective advantage of both the body shape and placement of the large fins. Visualize a flat plate in the water and trying to move it side-to-side... a tremendous amount of water resists it. Do the same with a cylindrical object, the shape of most other fish, and there is no comparison. Piranha take full advantage of this leverage to remove tough pieces of flesh from the bones.

Try and hold a piece of meat from these fish. My 11"er will snatch anything from my hand even if I hold it with locking forceps. I have even been covered with water from the thrusting action of the flat body and large finnage from the fish intent on getting his meal. An 11" trout or perch wouldn't have the leverage or make such a commotion or especially hold the food.

Seeee... even the fins have special advantages with these lil' super fish!!!
 
Piranha Language:

Now I know you must think I'm a little nuts to bring up such a topic. I can hear a collective "Piranha don't talk!!" from all my colleagues here on the forum but lend me your ear and open mind to this observation....

All animals communicate and fish are no exception. Whereas terrestrial and flying animals have vocal expressions fish have been ignored when it comes to relaying information to each other but make no bones about it they do this quite frequently. Sometimes even with sound from the air bladder. Fish with electrical potential use crackles and other recordable, but inaudible, signals.

Most of the communication behavior of fish comes from their physical actions to defend their territory and piranha are no exception. In fact, they have quite the ability to be very interactive with their "owners". Owners is in brackets because, although we believe ourselves to be the owner, the fish are in a different frame of mind and look at us as outsiders in their habitat.

If they are nervous and intimidated by their surroundings and lack of natural settings it will be hard to see this language so the comfort level of the fish is paramount. Nervous fish are “quiet” whereas dominant fish “say” what they want.

One of the most obvious forms is in the body display. Finnage, jaw placement and movement of the body directly registers the intent of the fish. There is a distinct difference between the moods of the fish and the owner can take advantage of this and even have some fun with it.

Fish with wide open pupils, pale color, and a skittish nature will be hard to interact with. They are uncomfortable with their present conditions and aren’t totally relaxed. Mimicking their environment will allow their true behavior to emerge. To get some effect it is best to try with a comfortable fish with good color and eyes with a “world weary” look - totally relaxed and in it’s place.

When they are comfortable one can interact regularly with them but you have to read the signs carefully for the best results. Staring face-on is not the best way to do it. As these fish feel the need to be king of their domain they should be the ones doing the staring. If you stare back you are much, much larger and they will back down. The best way is to turn away if the fish looks at you directly. It is not hard to see when they look at you.... just look at the top of Piranha Fury web page at the pix of the fish. You can see they are looking directly at the camera and most piranha do to watch everything that is going on. This can be seen if you do something near the tank, like a task of some sort, without paying attention to the fish. Their curious nature gets the best of them and they have a look to see what you are doing. If I am “playing” with my fish he comes up to eye level. When I am munching on something, he becomes very curious as to what I have in my mouth and has even tried to bite at it, even after being fed himself. He seems to just want to steal it from me!

When you turn away the fish then looks directly at you. When it begins to turn away itself, you then look at it, turning away when it faces you again. Doing this stimulates what these fish do to each other. Observing them together you will notice they rarely stare at each other’s face and when they do it is only when a fight is brewing. When provoked they usually attack only the body when there’s an opportunity, not the face of the opponent. This is preceded by lateral displays where the fish’s fins are held out, the jaws gape, and the fish rocks back and forth, flicking it’s tail at you, or another fish. What it is actually doing is throwing water in your face. If the glass of the tank wasn’t there you would feel a pulse of water hitting you squarely in the gob. This means “Get out of my space ***hole or you’ll get it!!” Saucy fish they are!

It is not difficult to stir up the fish’s aggressive behavior. When the fish faces you and you turn away you are letting it know you respect its position and are not dominant. By looking at it as it turns away provokes it to come back. Turn again... try and avoid direct eye contact. That speaks volumes to them. If you place the side of your head against the tank the fish may very well come close enough to scrutinize it’s opponent. Moving away will encourage them to continue and convince them that the tank is theirs. If you sit and stare it goes back to it’s holding area and doesn’t respond.

This will work with a single piranha very well, not so much with two or more and totally ineffective with a shoal as they are much more interested in their real tankmates than you. Give it a try and let us know what happens!
 
Emotions:

I have seen in a number of articles over the years with reference to fish having no emotions. I never could understand how this conclusion was made as I have always seen the opposite and I can rest assured there are plenty of members on PFury who have also witnessed emotional swings in their fish. Piranha are excellent specimens to use to observe this phenomenon.

Being very alert aquatic creatures who are totally aware of their environmental conditions and the presence of other organisms, be they food or enemies, these fish’s emotions range from excitement to fear depending on their current situation.

When relaxed, these fish go into a calm state and just “chill out” while displaying their best colors. Most times this color will manifest itself by showing the dark phase of the fish to the point of almost hiding the bright colors such as the reds or yellows. It is in this state the fish isn’t bothered by anything and will most times ignore approaches until they persist. Looking at the eyes shows the fish not to be focusing too intently at the observer.

Quiet but serious reflection can also be noted as the fish is observing a newcomer to the tank. This occurs when strangers appear and the piranha is “reading” the threat level. This is important as these fish never stray from the perpetually expectation of threat from the environment – they are from one of the most dangerous places on earth where death can come in many forms. In this case the eyes rarely stray from the stranger, only to periodically look at the owner of the tank but the newcomer is never lost from the line of sight.

Excitement through the expectation of foodstuffs is readily apparent. In the case of my fish, he swims rapidly back and forth along the glass with a particular look of pure anticipation and all fins erect. The look in his eyes is priceless, rather gleeful if I can put a tag on it. This is when one wants to be extra careful when feeding as in his excitement the top of his head breaks the surface of the water and the floating duckweed can block his vision and one’s finger can be mistaken for a piece of dinner.

Nervousness is also readily seen. When there is something out of place, and which is the prevalent condition found in the vast majority of fish tanks as the natural environment is replaced by a sterile, alien glass tank with exposure to a room with large alien people staring at them, the fish will go pale and be rather skittish, commonly hiding at the back of the tank. Take a look at the eyes. The pupils are wide open, the color is pale, the fish is rigid in its pose tilted often at an angle with relation to the bottom, and its fins are flicking at a rapid pace. The mouth is almost closed which actually takes more energy to do than let it remain partially open. These are the signs of stress.

Fear can be readily seen when the fish just thrashes back and forth at the back of the tank or make mad dashes when startled. If you hear a thumping as the fish bangs into objects or glass walls, the fish really feels threatened. Switching on a bright light in a dark room or approaching a fish in a small tank, particularly with strangers, will many times elicit that response.

Anger is something these fish can be provoked into. If I thump my head against the glass as Kilzses is swimming away, it startles him and he gets very mad, making a rush towards me hitting the glass and making biting motions at me reflecting his pissed-off state. He has even thrown duckweed everywhere.

Another state of emotion is just plain happy. Now I may be chastised by my biology colleagues to be saying a fish can be happy but I have had some fun just “hanging” with my fish and many times I feel “accepted” by him and we are within inches of each other with only the glass separating our faces. He spends lots of time being interested in things in the tank then. Bright things on the floor of the tank such as white stones or even pieces of uneaten food are approached for a second for a sniff (see flared nostrils post) and then the fish comes back to the glass This is when he almost shows a happy face. His eyes are showing it and his mouth is in what I would describe as a partial grin. It is also during this “phase” he blows mud from the small stones in a corner in a manner not unlike a piranha preparing a nesting surface. Then he turns again to face me, usually then laterally displaying and flicking a pulse of water at me with his tail. (hence the moon smilie )

Variations on these emotions can be observed in many other species of fish but I have never seen it as prevalent as it is in piranha. This is undoubtedly due to the high level of alertness in these fish. As anyone owning piranha can attest, they actually observe their owners as much as, or more than, their owners observe them.

I have seen many instances of emotions being shown by all the piranha I have raised over the years and if anyone wants to add or otherwise, ... feel free.
 
A fish tank is far from the home these fish have adapted to. If I can use an analogy of a tiger in a cage, piranha show similarities. If the tiger is put in an empty cage without any of the stimuli found in its natural environment the cat becomes stressed and paces the back of the cage away from prying eyes. It is very uncomfortable. If one changes the cage to an enlarged enclosure containing vegetation, trees, stumps, and real earth and plenty of "comfort zones" the big cat will display more natural behaviours and may even be approachable by the zookeepers. What the cat senses are the sights, sounds, and particularly smells of the natural world.

I have been using that approach with my tank to make the living quarters of my fish emulate the natural environment from which the fish came from. My approach is to have a "pond in a box" using all elements of nature. This tank contains live plants, sticks, large rocks, gravels, dead leaves of many kinds, mud, and a large stump. This is what is found in virtually any freshwater aquatic environment. A vital element I find that works well is infusoria or freshwater plankton. Within the water there lives many species of algae, diatoms, good bacteria, protists, and invertebrates. These microscopic organisms are what constitutes the vast amount of living biomass in any aquatic system and they cycle nutrients in the water. The surface of all plants, stones, and sticks are covered by Nitrosomas bacter, an ammonia "eating" bacteria. All these components give the water its particular natural flavor which the fish can smell and taste and that makes him feel at home.

As far as light, my tank is exposed to lots of it. In fact, whenever I flick on a switch and can see into the side of the tank Kilzses is already at the glass watching me intently. Incidentally they can see very well in the dark

Another suggestion is to not sit and stare at the fish. It makes them feel uncomfortable being the center of attention. Let the fish begin to take an interest in you. Look at it periodically but don't spend too much time showing interest. The fish may begin to observe you. But this usually doesn't happen until it's very happy with its surroundings.

A bit of advice I can give you, or to others who want an interactive fish, is to NEVER raise more than one in that particular tank. Piranha are not unlike parrots in that if you want attention from them they have to be alone. Others in the tank will only distract the fish's attention and create different behaviours. Let the fish concentrate only on you and not others of the same species. Other species of fish in the tank don't affect piranha in the same way. These are intelligent fish capable of being stimulated by the presence of its owner and as long as the tankmates aren't of the same species the fish will observe its competition for dominance and that will be you.

Not sure I would change the position of the tank though. Mine is right in the center of the house where all the action takes place and he watches everything intently. .... and there's nothing more interesting to visitors than a very cool, interactive maneating fish.

With the water change, do it a little at a time. Instead of changing 50% at first, only replace about 20% this time. Next week do the same and continue that until the water is satisfactory. As well, a dark bottom to the tank really reduces stress so replace bright gravels with dark substrate.

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