Name: Hexanematichthys seemanni
Origin: California to Peru
The store where I bought mine had them named "Black Finned Sharks". He likes to hang out right behind the Red Bellied Pacu when he eats. And he seems to use the Pacu for a body guard from the "Red Devil Cichlids". Those two (pacu and the shark) are real good team mates!
Just an anecdote really! My Silver Shark inhabits the bottom of a 270 liter Tetra tank...with Silver Dollars, White Skirt Tetras and "red, white & blue" Tetras. I chose the smallest Silver Shark in the tank as they will grow quite large. I realize now that he was the smallest because he wasn't getting his fair share of food at the LFS. Immediately upon arrival in his new home he fell into a spirulina tablet that had slipped down the side of the tank and didn't come out until his belly was the size of a marble. He's never touched spirulina since! However, he will pick up a sinking pellet in his mouth and remove it from the front of the tank and the White Skirts that nibble on it and hide it in the darker substrate to eat at his leisure later. He never seems to rest and his antics are highly amusing.
Colombian Sharks are definitely one of my all time favourite fishes for aquariums. They have a powerful and dominating look to them even though they are a rather friendly fish. In the past, I've had the hardest time finding the right conditions for my aquarium to suit this fish. Don't get me wrong, this catfish is certainly a keeper but it does require a bit of maintenance to keep alive more so than other fish. I have found that Columbian Sharks prefer temperatures of close to 27°C and they like a little aquarium salt in their water. If the water is too cold, their immune system will slowly degenerate. This fish can exist in fresh water aquariums for a time but they are naturally brackish and enjoy a little salt. Try to keep them in groups of 3 or more and don't mix them with small fish like neon tetras cause they get big and they are natural predators as well. With a large enough tank, preferably 300 liters or bigger, these are a very desirable fish to keep in a community.
The female Colombian I have is a huge, thick, and mean little devil. She likes to bite and attempt to rip me to shreds well attempting to clean the tank. I have to wear puncture proof gloves and she tries to get me then too. The male loves to fly across the front of the tank with his barbs sticking out of the water, she was afraid to follow him at first but now all you see is 2 Colombians with tummies on the glass at the top darting along. They love to steal food from my Balas and love brine shrimp pellets. It rocks when the female eats pellets, she thrashes and chews and the pellet is usually swallowed whole. And recently she ate two of my Cherry Barbs whole. No more of those in my tank. The male is pretty calm. But in the morning, anyone who walks past that tank and the female throws a fit. They also love to break the Tiger Barbs up when they are swimming in a little colony.
This is my favourite fish. It looks really funny when it sticks its feelers out and searches for food. Sometimes when they want to eat off the top they swim upside down with their feelers facing up.
For almost 6 months now, I've been taking care of 4 Colombian Sharks together with a shoal of 15 Monos (Sabae and Argenteus) and a Ruby Scat. They were very small when I bought them. The sharks are now 13 cm long and they are growing quite fast. I give them bloodworms, mysis, cichlid flakes and special food for Discus fish. Occasionally they also get dried flakes for marine fish. They seem very healthy and I think, a good deal of their good condition is the fact that I keep them in almost seawater. When I bought them, they were kept in freshwater, but the salesman advised me to get them used to water close to the density of the sea. And when I changed water of my aquarium, I added more salt every time. The density is now 1.022. The Monos and the Scat are also in very good shape and I can now grow seaweed (Caulerpa species) in my tank. The sharks are very active, and you can hear them make a drumming noise, when it's quiet in the room where my tank is! I can recommend Colombian sharks to everyone, as long as you have a huge tank. I now have a tank which is in fact too small, but within a few months they will move to my new 760 liter tank. I cannot wait to see them swim in their new environment, growing out to the size of 40 to 50 cm they can get, if treated properly. So, if you want an attractive fish, with a beautiful silver colour and a pleasant character, Go for it!