I bought 8 columbian sharks in May 2001. Unfortunately only about 3 months after I had purchased them, an outbreak of Ich occured and I lost 4 of my sharks due to this. I have kept columbians for most of my life now, ever since my father brought home a pair when I was about 10. I fell in love with this species of fish and never looked back since. Columbian sharks are a very attractive and active fish. I've found that they tend to change color from a light silver with very light fins to a dark greyish black with jet black fins, depending on their foreground. As a reaction to this, I keep mine with black gravel because I find them very attractive as dark specimens. Feeding these sharks is not a problem at all since they do and will eat anything and everything they can fit into their wide mouths. Presently I am feeding mine shrimp pellets, tubifex worms, cut up beef heart and occasionally throw in some feeder goldfish. In the past I have found it difficult to find the correct water for these fish, but with a lot of experimenting I have found that they do best in fairly warm salty water. Mine are kept in fairly brackish water almost to the volume of pure saltwater, and the fish are doing great and thriving. However I do not use aquarium salt but rather sea salt used for saltwater fish. With alot of care these fish can grow very big and surprisingly fast. I recommend these fish to anyone looking for something different. They are predatory fish and so tankmates should be careful chosen. I personally keep the 4 and only the 4 columbians in a tank to themselves as they do well in groups and are fast eaters which may limit your choice of tankmates. Great fish, try them and maybe they'll be the last species of fish you'll keep!
I would like to add something about the Silver/Black/White Tip/Colombian Shark (whatever you like to call it). They are very cool fish, BUT WILL EAT YOUR OTHER FISH! I got mine about a year ago when the one I had, that was about 7 months old, died during a five day power failure in an ice storm (water got to about 5°C). Well, of course he was just about a 3 cm baby when I got him and now he is almost 18-20 cm long. He got such a reputation that we named him Mack the Knife (the aquarium hitman) but I was told at a pet store it was my pictus catfish making my fish disappear, so I traded them in and fish continued to disappear. So, I have a new tank for my other fish and he gets the old tank all to himself! We may add a large pleco and something else later. Basically, the fish is an excellent fish to have. Put him in a low traffic area, because they will freak if you startle them by walking by. I thought he was going to jump out of the water once! Make sure you put him with fish his size or bigger than him because if they fit in his mouth, he will eat them!
I have a Colombian shark about 15 cm long. He stays in a cave in the corner of the tank and only comes out when all the lights are off. He seems to be extremely aggressive and even chases around an Oscar I have about twice the size of him. He's very territorial. If any dare to swim by his cave they're in for a little surprise as he darts out and attacks them. Definitely a fun fish to watch, I would recommend him to anyone whose looking for an exciting fish to liven up the tank.
I have one of these Columbian sharks. I originally purchased two, but one died within 24 hours of being introduced to my tank. The other, once acclimated to the tank, has been very very active and flashy! It likes to play in the air bubble curtain that I have in the back of my tank. It'll do loops in it, circle around the tank, and go back and do a few more loops for good measure. It also swims upside down while skimming the top of the tank and loves bloodworms. I have to be careful not to give it too much or it zips around the tank for hours with its belly hanging a bit. It eats quickly and gulps, making a huge mess and thoroughly enjoying itself. I know these guys tend to like it dark, but mine doesn't seem to care. Any movement at all excites it, so we try to keep it quiet in its corner. Its name, most appropriately, is Jaws. :)
I have had a Silvertip Shark in my 280 liter aquarium tank for 2 years. I would not recommend this fish for a community tank with other fish that are smaller than 3 cm long. Mine ate my 12 neon tetras at night. If you have fish larger than 3 cm in your community aquarium, I would recommend this species, for they are active, non-aggressive, and interesting to watch. By the way, they love frozen foods, such as brine shrimp.
I used to have 3 of these cats. They were beautiful! Raised from 8 cm to about 30 cm maybe longer. They used to stand on their tailfins all three side by side and sway with the current. They were in freshwater. I used to feed them bloodworms, goldfish (10 gone in 30 seconds), and sometimes a little bit of cheese. They were very friendly and would swim back and fourth through my open hand if I held it under water. I had them for a couple of years...a visiting child put dishwashing soap into my tank and by them time I found out it was too late for them, none survived. That was 10 years ago and I have stored my tank away all this time. Nowadays 10 years later I set up my tank and purchased 5 silver tip cats and 2 pictus cats. Their new home is 380 liters and I hope to have them for many years to come.