Black Ghost Knife Fish Irritating Tankmates

I have a 12-13 inch Black Ghost Knife Fish in a 125 gallon with young koi and angel fish. He does not cause any damage or attacks them. However, I notice that the fish are attentively avoiding him. The knife is very confident and swims everywhere around the tank. Earlier today, my ghost knife fish approached one of the koi. Immediately, the koi swam away but experienced a rapid head movement, similar to a seizure however maintained control in swimming. I am assuming this is due to the electric field.

Is the electric field health threatening/damaging for the other fish? I like to use the tank as a temporary holding facility for baby koi to grow for the pond.

Thanks for the help!

 

That's strange. I've never heard of another fish being affected by the electric field of a BGK. Are koi fish also electroreceptive? I've only heard instances of other BGKs being affected by more dominant BGKs.

BGKs are more active at night. Maybe the koi fish had a scare because it was asleep? BGKs do eat small fish when they grow larger.

 

I read that BGK can affect other fish on FAQs on Black Ghost Knifefish, Apteronotus (Sternarchus) albifrons, Systems. 1/15/10

The koi was awake because I had just fed them and the BGK. The koi and angelfish are about 7 inches, never had injuries or torn fins.

 

Sorry for the late reply.

Hmm. I wish the FAQ went over how it irritates other fish. BGKs can be housed with other large non-aggressive fish with few problems.

I'm no expert, but the koi fish sounds large enough to withstand a weak electric field. Since it's a grow out tank, did the koi fish grow from a way smaller size to 7 inches in the tank with the BGK? Maybe the electric field affected its development? Even then, in a 125G, there's ample space to avoid the electric field...

Another guide I read suggested corydoras in the tank although they never mentioned how corydoras acted around the BGK.

At this point, it's going to have to be an educated guess. I'd watch to see if the seizure-like movement occurs again when the BGK is near. If it does, the koi should be quarantined and watched to see if it still occurs. Your parameters are perfect if you're keeping a BGK, so the only factors left are temp, angelfish, and the electric field.

Sorry I couldn't help much; I would conclude it's the electric field if the seizure-like movements occur only when the BGK is near. Otherwise, your tank sounds like it has plenty of space for the koi to avoid the electric field for the most part.

 

Out of curiosity, does you BGK have a nice large private cave where he can hide?

 

I have heard of BGK electric field bothering other fish.

Be careful, there have been cases of owners BGKs biting out the eyes of other fish at night.

They will of course consume small fish whole.

Normal max size in captivity is 18". Larger in the wild.

 

The reason I asked if he has a hiding spot is that I find it strange that he is out and about all the time harassing the tank mates. BGks are nocturnal fish, they spend the daytime hiding in the dark. So I am thinking, if the fish doesn't have a place to go during the day, he is stressed and taking it out on the others.

My 14 inch BGK has a HUGE cave that his entire body can fit in (and then some). As a result, he spends his daytime hours relaxing in there and only comes out to eat, or when the lights are off. I bet he would also harass his tank mates if he had nowhere to hide during the day. So I am just theorizing.

Side note....angels should not be kept with koi. The koi require significantly cooler water. In fact, the koi shouldn't be kept with any tropical fish, and technically should be in a pond. That fish should be rehomed asap if you want to keep tropical fish in your tank.

 

Thanks for the replies.

I realized that the discussed koi has a minor cut under his lip. The electric field was not aggravating him. A piece of food must have touched the cut and caused the pain reaction from the koi.

 

BGK's electric field is not used to electrocute prey like the way electric eels use them. It's rather used like a radar to ping it's prey's position. The pulse is very weak and shouldn't harm even the tiniest fish/invert. But some fish might be extra sensitive to it thus showing signs of discomfort. Not an expert on cold water fish but perhaps Kois are sensitive?