Animal Stories - Black Ghost Knife Fish

Animal-World Information about: Black Ghost Knife Fish

The Black Ghost Knifefish is the most well known species of knife fish in the aquarium industry!
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Kyle - 2010-02-21
I have received lots of comments regarding my post on BGKs. And although the inch per gallon rule doesn't apply to large fish, my knifefish isn't that big. He's only five inches or so. Secondly, he has a large home to move into. Once my BGK is big enough, he has a 200 gallon tank with 3 tiger oscars to move into. I'm just growing him in a smaller tank until he can live with oscars without being a snack. And if you keep on top of your water changes, you can push the rule to the limit and have healthy and happy fish. I clean my tank every saturday morning and I usually do a 20-25% water change. And lastly bottom feeders like pleco contribute 75% less waste than any other fish so they practically don't count towards the inch per gallon rule. Because of this a 10" pleco counts for about 2.5-3" of space. Because of this many people say they just don't count. Do you even know how to tell when a pleco is too long for the tank? If a pleco is at the top of the tank and his length is 2/3 the length of the glass then he is too long. Many people don't know that. Thank you Calvin for your support. Its finally nice to talk to some one who actually knows what they're talking about (unlike J and Z). To give you a brief summary of my 44 G tank, it isn't your standard rectangular tank. Its a custom made corner unit (explaining the unusual size). My BGK has a cave that looks like the Roman Colosseum. He usually spends the most of his time during the day in his little hideaway, but during feeding time, he rushes out to gobble down a small chunk of frozen bloodworm. He spends his nights swimming in all sorts of weird patterns. My pH is about 7.4. in my set up. I would also like to hear about your unique sounding setup. I look forward to hearing back from you.

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  • Becka - 2010-10-09
    Hi Kyle, I've just been reading your posts and you seem to know what you're doing. My partner recently set up our aquarium but we are TOTAL novices.
    We've got 5 neons (ghost fish ate one), 2 glow tetras, 2 angelfish, 2 balloon mollies, a longfin fighter fish (who's now recooping in a breeder tank after our BGKF blew one of his eyes out) and our blessed little BGKF who's around 5 inches too.

    We're in New Zealand (South Island) so the water here is about as close to neutral as it gets and super clean.We only have a 50 gallon tank though. We knew when we bought the fish we'd eventually have to upgrade the tank, but after reading all these posts I'm worried our tank is already overcrowded?

    We already have all the fish, and upgrading the tank right now is difficult because our town just had a massive earthquake.... erm any ideas?
  • Lisa - 2010-12-09
    Kyle - You are SO terribly wrong about the plecos. Plecos are one of the heaviest waste producers in a tank. They poo ALL the time.
    So no, a pleco is NOT a low waste producer, they're actually pretty bad.

    And I would still be hesitant to add your BGK to a tank with 3 large? oscars, even if the BGK is a decent size. Because it's narrow, it could still end up as lunch for the oscars.
  • Anita - 2011-02-21
    I agree with Lisa. Plecos are huge waste producers. I have several, trust me. My big guy in my 125 gal is the messiest fish I've ever had, and that's saying something considering some of the fish I've kept. I think when you're referring to your inch per gallon rule with bottom feeders you're thinking of things like loachs and catfish. Cory cats aren't bad with waste and my clown loaches and botia's aren't bad with waste either. And even then, I still don't agree. Any person I've ever talked to with serious experience has told me that bottom feeders count just the same.
  • Anthony powell - 2011-05-01
    I totally agree with the comments regarding the plecos. I originally had 2 plecs but the waste produced by them was that bad I reduced it to one thinking that would be better. Nope didn't make a difference at all. I'm sure the other plec produced more waste just to spite me cuz I got rid of his mate. So I got rid of that one too. In summary. Plec = lots of waste.
  • david - 2011-06-12
    Plecostomus (I believe we are talking about Glyptopterichthys gibbiceps) is a very large waste producer. A Plecostomus by itself will require a thirty gallon tank. Therefore, if you have a 55 gallon, the Plecostomus alone will take up 30 gallons of that tank. On a waste producing chart, G. Gibbiceps are right alongside Oscars. Trust me.
keesha edward - 2011-04-09
Hi there. My husband and myself purchased our two ghost knives about 3 years ago or so. They were tiny when we first bought them, about 2 inches long. They are now about 10 inches. T o our surprise last night we saw a ghost kinfe of about 3 inches swimming around. This came as a complete shock as we were not expecting them to have babies at all. In all the years we have had our tank none of our tropical fish have bred. Im not sure how big they are when they are born so perhaps this fella has been around for a while and we just have not noticed? We have a tank of about 580L. We very proud and quiet amazed that this has happened as I believe this is very unusual??

keesha edward
south africa

Vikki Fraser - 2011-03-15
Hello I hope someone can help I have a black ghost knife fish and am concerned that he is scared in my tank he is in with a red tailed shark and the shark will not leave him the red tail playing or being aggressive I am not sure also are you better feeding late at night so that the ghost knife fish is getting enough food?

cspruce427 - 2011-03-06
Most pics show jet black ghost knifefish, your pic shows a grayer fish like I just bought. Can you tell me why?

Anonymous - 2011-02-25
Hi, last night when feeding my black ghost knife fish I noticed he has a scratch on the top of his back! I'm kind of worried about him and was wondering if there is anything I can do for him? It's almost half an inch long and I have no idea how he could of gotten it. Is there anything I can do for him? Or will it just heal on its own?

Amy - 2010-08-04
I was wondering what is the smallest size of tank you can put a 4in BGK in? We had one and the guy @ the pet store said it would do fine in a 10g tank with 2 tiger barbs (I think that's what they're called) an angel fish a goldfish and a pleco and a molly. They also told us to feed it freeze-dried bloodworms. It wouldn't eat them and it died and I was wondering what we did wrong and how to correct it so if we get another one the same thing doesn't happen to it. Because obviously we did something wrong cause it died. Please any advice would be helpful. And if it was stupidity feel free to tell me that as well.

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  • janine - 2010-08-18
    Amy there may have been something wrong from the get go. Your bkgf may have had a problem b4 he got there. I have a bgkf and he has been doing wonderful and we have some of the WORST water in the country here to work with. That is WAY too many fish to put in a ten gal tank with a ghost fish unless you only mean to do it for a short while. We kept ours in a ten gal till he outgrew that and he lives with an upside down catfish. Now in a 20 gal tank and is too big for it! So, you can't give him too many neighbors. They are scaleless which is one thing you need to remember, can't medicate the water for them as you would for others and watch their skin for any breaks in color or smoothness to let ya know if you need to pay attention to water quality or tankmate fights and such. Injuries, parasites or fungus. We really delight in our black ghost knife fish, he loves to frolick in his tank which he seems to be a watchdog over. :) Our knife fish is over ten inches long now, chases that catfish around when the catfish pokes him as he invades his cave. It's just all so funny. He barks at the catfishes house sooooooooooooo funny. But we are blessed by him. Try again sweetheart, k? But DO be prepared to get a bigger house for him and DO give him a log or cave and some deco to hide in, k? I would choose peaceable tankmates for your black ghost. No barbs! Meaning none of those barbs on the fish because a skin break can mean sick or loss of the black. We pray for ours. He a happy happy fish and I am soooo glad we bought him.! All the best and feel free to ask anything.
  • Ashlee - 2010-08-22
    BGK's need like 100 gallons. Always do plenty of research before you buy. That person at the petstore has no idea what they're talking about.
  • Anita - 2011-01-05
    Amy, don't take this the wrong way but what are you doing with an angel, 2 barbs, a goldfish, a pleco and molly in a 10 gallon? That is a majorly over crowded tank! Also, goldfish should not be a part of that group at all. Pick tropical fish or goldfish. Also, your angel and your pleco should both be in bigger tanks. That's cramping them.
    One, BGK's need a lot of room. I didn't even think about getting my first one until I had a 60 gal to put him in and I put him there knowing that there was a good chance I was going to have to move him into a larger tank in the future. Second, most fish don't seem to like freeze dried food all that well. They will eat it, but they prefer frozen or live. You have to make sure your BGK is getting enough good food and freeze dried wasn't going to do the trick. Mine personally loves his frozen blood worms. He also gets omega one flakes, frozen brine shrimp, frozen mysis shrimp, and sometimes live worms and shrimp.
    My advice: don't get another BGK until you have a much bigger tank and are willing to spend the extra money to buy frozen or live often.
  • Anonymous - 2011-02-13
    10 gallon way too SMALL! feed live food!
dave - 2011-02-12
What are good tank mates for BGK?

Andre - 2010-06-25
I just recently bought 2 BGK from petsmart is there any given advice to make sure that these beautiful creatures will live a long happy life?

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  • LasColinasCichlids - 2011-01-13
    First of all, you should only keep ONE BGK in a tank (also no other fish similar to him, such as other knifes, eels...).

    BGK need around a 50+ gallon tank when they get bigger as a minimum. I currently have mine in a 29 gallon, but he is only 3 inches long and is only housed with two small cichlids.

    Make sure your tank has been fully cycled and that there is no ammonia and the pH level is between 6.8 - 7.4 Temp should be between 78 and 82 degrees F.

    These beautiful creatures are nocturnal, so they hide during the daytime in dark caves and plants, and come out at night to feed and explore. They live on insect larvae (or however you spell it) in the wild...I feed my BGK, "Sparky" freeze-dried bloodworms, which he loves. I will be adding shrimp to his diet as well. I also provide him with flaked and pellet food that he once in a while will munch on.

    My advice is to return one of the BGK fish to your petsmart, and then find the employee that allowed you to purchase two for the same tank and smack them for me!

    I don't know what tank size you have, but you will need a pretty large one soon depending upon on fast your BGK will grow...I keep referring to you as only have ONE BGK in hopes that you will return one.

    BGK have a faint electrical charge and use something similar to sonar to navigate their environment and search for food. Another BGK (or similar made fishes such as eels, clown knifes, african brown knifes...) will interrupt their sonar ways and can cause your beloved fish to not act right and lead to stress. In the wild it is different because they have the entire Amazon River to swim through and can avoid one another, but sticking two in a tank, and they cant get far enough away. And as BGK get older, they become aggressive with other BGK unless they are in the hands of an experianced breeder/wholesaler.

    Any fish small enough to fit in the BGK's mouth, will probably end up there. They general do not bother other tank mates as long as they dont bother them. Remember, the BGK doesnt have scales and is highly affected by most medications you may put in your tank. Water conditioners, pH Balancers, and StressZyme are okay...but most other things can kill them!

    A lot of people have a lot to say about how big these guys get. It all depends on the tank you keep them in and what else is in the tank. Don't get me wrong, my BGK will NOT stay in a 29 gallon, but I will keep him in a 60 gallon when it comes time...which I should have a good year or two until it is completely needed. In captivity they general reach around 12". Some max out at 9-10" if kept confined (not nice!), and others kept in VERY large tanks of 125gallons+ can reach up to 18-20"!

    Hope this helps. If you need more info, you can find me on tropicalfishkeeping dot com and I am LasColinasCichlids. That is also my tag on youtube with my aquarium videos.
Kimberly - 2010-11-21

I just purchased 3 black ghost knife fish and 2 silver tipped sharks for my 45 gallon aquarium. I purchased the fish at PetSmart and was told to add water conditioner to the tank. I did so following the exact directions on the bottle and acclimated my fish to the tank leaving them in the bag and putting the bags in the tank for approximately 40 minutes for the temps to adjust. About 30 minutes after I introduced them to the tank they started dying off. The temperature of the tank is 82-84 degrees Farenheit, and the pH level is 7.6 which according to this site is the appropriate level and temps for both kinds of fish. I now have one silver tip shark surviving. Could someone please tell me or give me any suggestions as to how or why these fish could have died so quickly? I think it may just have been the fish from PetSmart, but I've purchased other fish from there that have lasted years. There were no other fish in the tank when I introduced these new guys to the aquarium and the water was fresh with everything rinsed off in warm water. The filter had been running for over 12 hours to make sure everything was clean and ready for these new fish. I just don't understand so any help would be greatly appreciated!

Thank you,

Kim from Glen Burnie, MD

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  • Enrikus - 2010-12-21
    Water is too bad.
    *ph around 7 (6.7-7.3) is best.
    *make sure your tap water is hardness or softness. make medium water softness and hardness.
    *Degress is ok but better between 80-82
    *black ghost knife need 125 gallons up+
    *filters run 24hour. make sure ammonia and nitrite to 0. don't worry about nitrate between 1-2ppm is fine. water change can help low nitrate.
    *tap water have chlorine, add carbon in filters.

    Hope that helps you.
  • jessica - 2011-01-03
    I disagree with a lot of the people on fish set ups. I don't honestly believe the tank has to be over 100 gallons for a Knife fish. Your tank set up sounds almost perfect. I agree with the last comment though and that you should make so minor adjustments to temperature and pH levels. I think where you went wrong is: you shouldn't have bought so many fish to start out a new tank and you did it a little too early. It's probably best to wait 24 hours. My 30 gallon tank has been running empty for about a week now and I just put fish (guppies; because they are a hardy breed) in it today. I have done some research on the Black Knife fish because I really liked them when I saw one in the store. They do say that you should have a 50 gallon tank at least, but in reality any fish (as well as any reptile) will only grow as big as the tank they are in will allow them. As for the 'Clean and Ready' thing, there are a couple cycles the tank has to go through before the fish can be added. You did the right thing by putting in the water conditioner, but you should have waited a day or so after putting the treatment in for it to work properly. Next go round, (if you decide to go with Black Knife Fish again) I would recommend letting the tank run empty for a couple days. Put the treatment in it again if you are using new water. Test the pH levels and all other things you feel like you should test and wait another day or so to make sure it stays sustained. Then only put one or two fish in at a time. Also, I have read that you shouldn't try to feed them for the first 24 hours, because most wont even eat and usually it will stress them out in their environment. Hope this helps. Good luck next time.
Heather - 2010-12-09
Our BGK has been doing well since we got him in May, but now I'm getting worried. He recently came out of a growth spurt and now will barely eat and sleeps a lot. Of course, I've been panicking lately when I find him asleep because he sometimes doesn't respond or move when I touch him. (We hand feed ours and he loves to be petted.) I'm trying to figure out if this is normal behavior or if something could be wrong.