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Start Skeletonizing!

Keep your pet fish for posterity.


By Ivan Mikolji

For more information on FRESHWATER BONES click HERE.

I have visited many museums and I have always been fascinated by the skeleton structures of extinct dinosaurs and other animals which they have in display. I was once at a museum in Caracas, Venezuela taking some pictures of different skeletons of Inia geoffrensis commonly called the freshwater dolphins, reptiles and amphibians and I was amazed that they had no fish bones.

I asked Prof. Francisco Provenzano which is the curator of the ichthyologic museum of the UCV in Venezuela if he knew the process of skeletonizing a fish. He told me that it was actually quite easy and I wrote down his process on a piece of paper. Once I left the museum and drove back home I wondered which fish would be interesting to see as a skeleton. I tried visualizing the bones; the fish would have to be big and impressive. The first fish that came to my mind was a Hoplias aimara commonly called the monster wolf fish, which is one of the most aggressive freshwater fish in the world. I thought it would look amazing due to its large dog like teeth and size for they grow past 4 feet in length. I couldn’t stop thinking how amazing a 4 foot skeleton of it would look in a glass container as they are displayed in a museum!

As I didn’t have an aimara and the 15 hour drive and 15 hours back trip to fish one was out of the question, I decided to use a fish that was more accessible to me.The thinking process started again and I decided to use a large Pygocentrus cariba commonly called the red bellied piranha, which is one of the most common piranhas in the aquarium trade. I knew of a small little creek 5 hours away, where I have found the largest cariba in the wild. So I quickly put the fishing trip together and went piranha fishing!

We left at 6 am and got to the little creek at 11am. We fished for 4 hours and caught many Serrasalmus irritans, Serrasalmus elongatus and Pygocentrus cariba. We kept the large cariba and threw the smaller ones back in the water. At 3 in the afternoon we left the creek and drove back home with the largest 3 cariba which were almost a foot long each. We got back tired from our trip so we only degutted the cariba that night. We placed them in the freezer and decided to start the Skeletonizing process early the next morning.


ABOVE: Frozen Pygocentrus cariba.

Early the next day I started Provenzano’s procedure. It is important to try and freeze the fish in the position you would like the bones to finish up looking like. In my process I laid it down as flat as possible. We checked our fishes teeth and head structure to be sure they were not damaged before taking the time to skeletonize them. If you are using an aquarium fish which has died, you may not have this problem, but in the wild some fish lose their teeth as they eat or if they bite the metal hook to hard.

First we put some water to boil in the largest pot I had which could fit the cariba. It is important for you to tie down or use wooden stakes if you plan to skeletonize it in a bent position so the fish doesn’t straighten out as you boil it. In our process we left it straight.  Once the water was boiling we threw in the cariba and let it boil for twenty-five minutes. The twenty-five minutes are not a standard time, it may vary depending on the species or size of your fish. We cooked our fish until the meat would come off the bones easily when moved with a fork. It is easier to reboil a fish than it is to reattach the whole bone structure, because it will all fall apart if it is over cooked. Afterwards, we took the fish out of the pot and lay it flat on a tray to cool off. At this moment I actually took a couple of bites of the piranha to see what it tasted like. It tasted so good that I regretted not putting salt or vegetables in the water, which would have made an incredible piranha soup!

eating piranha

ABOVE: Agustin Tabares eating the cariba with lime!

The next step was the actual removal of the meat. Once it cooled off we started by taking all of the meat and skin of the body. As we were not doing this procedure for scientific reasons where you need all the bones, we threw out everything that was not attached to the backbone, including the pectoral, ventral and dorsal fin spine systems. Cariba also have a series of bones that are located in the bottom of the fish which looked like a second ribcage, those we threw out as well for they were not attached to the backbone. The best way we found to get rid of the meat easily was to place it under running water in a sink and gently pull it off. Just make sure you have a large strainer under the fish so you don’t clog your draining system and it will also catch any small bones you happen to accidentally drop.

piranha skull

ABOVE: A good picture of all the gill covers or operculum will be of great help if you don’t have a video camera.

BELOW: This is what the skull looked like after disassembling it

piranha bones

Once we removed all the flesh from the backbone we removed the head carefully from the backbone with a scalpel. We did this by cutting carefully through the cartilage that joins the last vertebra to the head.
When you start working with the head it is advisable to have a video or photographic camera at hand. You will be amazed at how many little bones the scull is made out of. Once you disassemble this organic puzzle you will need a blue print of where everything went so you can put it all back together again. So I preferred to use a video camera and taped the 5 to 10 minute disassembly procedure. If you have a photographic memory you can omit the video or photos.

piranha skelleton

ABOVE: This is what the cariba bones looked like after removing the meat, before the peroxide bath.

The next step is to submerge the bones in a 50% hydrogen peroxide & 50% water solution. The hydrogen peroxide used is the regular one you can get at any pharmacy which is used for cleaning wounds or cuts. To be able to cover the cariba bones I had to buy a couple of containers which added up to a gallon of peroxide to which I added a gallon of water too. I mixed this concoction in a cooler and placed the bones in overnight. The hydrogen peroxide eliminates some of the oils inside of the bones and gets rid of some small amount of meat. It also loosens any of the leftover meat and the “silverish” skin that covers the operculum bones or gill plates. It is important to know that the hydrogen peroxide can loosen the cartilage that is holding the backbone together so for smaller fish a few hours could be sufficient time.

cariba skelleton

ABOVE: This is what the cariba bones looked like after the peroxide bath.

The next morning we used an old toothbrush, (I recommend not to use your daily toothbrush if you plan to use it again.) to gently remove the little bits of leftover flesh. After completing this delicate job, I finished by rinsing them over running water in a sink to remove any hydrogen peroxide from the bones. By then the bones had a light beige color to them. This is the bone color “look” that you see in the museums.

Being a very impatient person led me to discover the whitening phase, which Provenzano didn’t know about. I wanted to start gluing the bone puzzle together right away but the bones were wet. I came up with the idea of placing them in a microwave to dry them. I placed the bones in the microwave on top of a napkin. I used a napkin for some bones have some cartilage or meat which is impossible to remove and it gets really sticky after the hydrogen peroxide bath. I thought it would be better for them to stick to the paper than to the microwave. I placed the first bone in for 30 seconds which made it almost dry up completely. I placed it in again and put it in for one more minute which made it completely white. The microwave evaporated the oils in the bones which give them the beige color and what came out was a dry white bone that resembled porous porcelain or a very dry white seashell. The downside is that they become brittle and break like glass if you drop one. One of my mistakes was to place large bones with smaller ones, as the small bones dry up quicker some of them started burning and turning brownish, so it is very advisable to place bones of the same size and keep an eye on them.

After my entire fish puzzle was cooked “aldente” it was time to start putting it altogether. I started by trying to make sense of all the little pieces. As I was going to use crazy glue to attach them, it would be impossible to detach the bones without breaking them once they were adhered together. 99% of your puzzle should be the skull because by now you should have a nice, one piece, white backbone. I started to sort all the bones into 2 groups which of course would be the left side bones and the right side bones of the skull. Once I managed to make sense out of left and right I looked at my video and without gluing them I tried to put them together using small amounts of regular molding clay. I started using yellow clay and had to throw it away and go out to buy white clay because some of the clay gets into the miniature bone pores and it is impossible to remove; white clay was less noticeable.

piranha skelleton

ABOVE: These are the cariba skull bones we were left with to glue together.

After the puzzle made sense, I started gluing everything together with regular crazy glue which dries in seconds. After the crazy glue had dried in every gill plate section, I applied epoxy glue in the backside to give them a stronger bond. The epoxy glue I used was a clear epoxy consisting of 2 containers that have to me mixed together or “catalyzed” for it to be able to dry.

cariba skull

ABOVE: The cariba skull before gluing it to the backbone.

This picture was published in the “Piranhas” book from Barron’s written by David M. Schleser.

The last advice I can give you is to try to use the clay as much as possible to put everything into place before gluing. The lower jaw will have to be glued to the bottom part of the gill plates for the muscles that held it in place which are obviously not there anymore so if you glue the gill plates too close to each other, the lower jaw won’t fit.

piranha skelleton

The whole process without including the fishing trip took approximately 2 days.
Skeletonizing was actually fun and reminded me of model building when I was a kid, being a fish hobbyist, this was much cooler than a ship, car, or plane model. It also gave me a good view of the osteological aspect of the fish. I was also glad to have started with a 1 foot piranha; practice wise.

piranha bones

This could be a good way of taking advantage of any of our aquarium fish that happen to die, instead of throwing them away. For example, it would be extremely interesting to see the bones of any Symphysodon (Discus Fish) which are probably very high in the dorsal area. A large Koi, Astronotus ocellatus (Oscar), or any large fresh or saltwater Angel Fish, would be good options too.  In my case, I think the next step will be the 4 foot Hoplias aimara.

For more information on FRESHWATER BONES click HERE.







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