columbian sharks

Question
hi Chris, i have a 33 gal. with 2 Columbian sharks (8-10 cm), 4 clown loaches (4-5cm), 2 khuli loaches, and 1 common pleco (12cm) i also had 1 crown tail betta until a week ago. it has been set up for about 9 months, with an aqua clear 70 filter, i do 25% water changes about every 4-5 weeks , the ph is 7.5 and the ammonia and nitrite are 0. first let me just say im not really familiar with columbians my boyfriend bought me 4 of them from walmart when i set up this tank, 2 of them died with in a week but these 2 hung on pretty well until about a week ago. i noticed that 1 of my sharks had a very round distended belly, it looked like it had swallowed a large marble, at the time i also noticed my betta was gone and assumed the shark had eaten it and thats why his belly was swollen. however a week later his belly is still swollen and it seems to be getting bigger and starting to spread its now about 3 cm long and kind of egg shaped with the round end at the head and the point towards the anal fin. im not sure what to do about this. the shark is still active and swims fine, seems to be eating alright. ive tryed researching on my and found 1 site that said bettas are toxic to other fish???? but that doesn't sound right. and the only other thing i can think of is it might be "pregnant" and ready to lay her eggs. i hope you can help me with this. thanks, Monica.

Answer
Hi Monica;

Your betta was probably eaten but they aren't toxic to other fish. He should have been digested  by now though. Your Columbian is very unlikely to be full of eggs because they have to be pretty large in order to breed. Considering he had a big enough appetite to eat betta already, I think he just gets most of the food. I used to have large catfish that would just gorge themselves and have round bellies all the time if I didn't monitor their feeding. As long as he is still swimming around and acting fine he's probably okay. He may eat your khullis if he can catch them and the other fish next as he grows. Colombians hunt at night so look every morning and see if anyone's gone missing.

Colombian sharks also need salt in their water, especially to be able to breed. They have not been bred in captivity however. They develop fatal skin conditions without salt in their water. However, your other fish can't tolerate much salt on a long-term basis. Columbians require salt in even higher concentrations as they grow larger too. They also grow to be over a foot long. In my opinion, they should not be sold as pets. Fish stores either don't know or don't tell their customers what kind of care and what size tank these guys eventually need. They really need a 125 gallon tank or larger with some salt in the water. Otherwise, if yours survive and grow bigger, they may eat all their tank mates and soon be the only fish you have left.... and still need a bigger tank.  Yikes!

Good luck...

At Your Service;
Chris Robbins