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FAQs on Black Ghost Knifefish, Apteronotus (Sternarchus) albifrons, Behavior

Related Articles: New World Knifefishes, GymnarchusNotopterids/Clown KnifefishesElectrogenic Fishes,

Related FAQs: Knifefish Behavior, BGK FAQs 1, BGK FAQs 2, & FAQs on: BGK ID, BGK Compatibility, BGK Selection, BGK Systems, BGK Feeding, BGK Disease, BGK Reproduction, & Knifefishes 1, Knifefishes 2, Knifefish Identification, Knifefish Behavior, Knifefish Compatibility, Knifefish Selection, Knifefish Systems, Knifefish Feeding, Knifefish Disease, Knifefish Reproduction, Electrogenic Fishes, Notopterid Knifefishes (Clowns...),


black ghost knife fish, hlth./beh.  11/15/11
My black ghost knife fish has been happily living in my tank af 2 years.
The other day he started twirling in a vertical stance. Days later he is still in a vertical position. It is as if his floating bladder is haywire. He can't go lay on the bottom as normal and I don't think he can get anything to eat.
Is there any hope or treatment? Or is he going to starve to death? Any cure for the unbalance?
thanks for any help,
<Need some information on his aquarium, Jerome. For example, how big is the tank? What is the water chemistry and temperature? What are the water quality statistics? Have you used any medication recently? This sort of "twirling" usually means two things: an acute reaction to some poison in the water (e.g., copper, formalin, ammonia) or else the fish is so sick it's lost motor control. In the first scenario, multiple water changes to dilute the toxins can, should help. In the second scenario, the future is bleak without a good idea of why the fish is sick. Cheers, Neale.>

BGK behaviour change  11/14/11
Hey Crew,
I've had my Black Ghost Knife (named Spock) for a year now.. Pretty much exactly..
He/She is my special little buddy.. Currently living in a 55 gallon cube with 2 Discus, a Bristlenose Cat, an albino Rainbow Shark, a Pakistani Loach and 3 Clown Loaches.. I control feeding with all of my fish through hand feeding, they are all very well trained..
<I can imagine so! Otherwise the BGK couldn't be here>
Originally my BGK (Black Ghost Knife) would come to the surface to feed, but when he moved to a bigger cave in my tank, he would stop coming - this didn't bother me that much because I can still hand-feed him/her and even if somebody else feeds, the food seems to circulate close to his residence so he gets enough to get by! All very good stuff..
<Mmm, I'd be making/using a "feeding tool" of some sort, to deliver foods down/next to the cave opening>
I've started observing him more & more at night enjoying watching him explore the tank during his time of the day (or night in this case)..
However, today... during the middle of the day, with ALL the lights on - Spock is head up on the surface skimming the surface.. He (I'm not sur on it's gender as of yet, but it's just easier to say he) is not hungry, as he didn't eat any food I just put in and I do not think that it is a lack of oxygen because nothing in the tank has changed.
<Mmm, not too odd behavior. Apteronotids "do" such things at times>
Other possible reasons that I've ruled out:
- Sickness: Throughout my 1 year of caring for Spock, he hasn't been sick once and has no evident signs of being sick now (i.e.: no white spots on body or around gills, no lack of appetite [he ate yesterday], etc).
- Bullying: Nobody in the tank bothers him.. He is in fact the boss - nobody is allowed to be in his tunnel, he shoos them away.
- Chemical imbalance: Again, nothing has changed - when I get home I'm going to do a 10-20% water change.
Any explanations for a complete sudden change in behaviour???
<Maybe a dissolved gas issue; but again, doubtful... Discus/Symphysodon of size will have more trouble w/ this issue. Perhaps just a look/see>
<And you, Bob Fenner>

Black Ghost Behaving Oddly... poisoned  - 2/9/11
Hi Guys.
<And gals Marcel>
Does anyone know why my Black Ghost is behaving like this? It's going around and around on broad daylight. Normally it stays hidden in the plants or under some rock and only comes out when it's dark. But now, it's going around in circles.
<Sounds like some sort of metal presence... either decor, perhaps the heater, maybe a thermometer or other ferrous metal in contact w/ the water. This, and/or some other toxin/irritant>
It seems to have a scratch or peeled coating on the side of its body.
It was recently hit by a bad case of the Ich. It has only been 4 days since he was cleared of white spots. I treated the white spot breakout with Mebendazole, Metronidazole, salt and heated water successfully. The Black Ghost was still healthy after the treatment and then I had a 50% water change and added half a dose of Angel Drops StressOut. And then it started acting like this.
<... Angel Drops? This line from the PI?: http://geocities.ws/angeldropstrading/
doesn't list ingredients. I would NOT use>
All the other fishes seems to be acting normally. It has been 2 days since the water change and Black Ghost acting this way. I just made another 50% water change today.
<I would add carbon>
Watch the video here: http://www.singleshutter.com/index61.htm
<And you, Bob Fenner>

Black Ghost Knife fish and Bichir are lonely   8/18/10
I have been investigating your forums and information and I find your expertise quite useful.
<Only "quite"?>
I have a particular question regarding my current fish tank. I have a Senegal Bichir (4 in.) and a Black Ghost Knife fish (4.5 in.) in a 30 gal tank, too small for them in the long run for sure, however they are doing wonderfully right now.
<"For now" being the operating phrase. Whilst the Senegal Bichir might be kept in a 30 gallon tank indefinitely, the Apteronotus needs a much larger tank, and soon. Do understand that relatively few specimens survive into middle age, and they die prematurely PRECISELY because they're kept in the wrong environment. People promise themselves they'll buy a bigger tank when the time comes, in ignorance of the fact Apteronotus come from oxygen-rich, relatively cool fast-water habitats around rapids and waterfalls. They have very little tolerance for stagnant water conditions and high nitrate levels. To keep this species in a tank smaller than 55 gallons is, to be frank, dangerous.>
The BGK is very active, even during the day, swimming back and fourth and all over the place especially during feeding times.
<What they do in small tanks.>
The Bichir is the "ruler" of the tank and he goes where he wants with not much of a care in the world (with the exception of a log inhabited by the BGK). Right now the tank seems quite sparse for inhabitants I am looking for possible tank mates that will fit my plans in the long run.
<Least of your problems. Neither of these species needs tankmates, and indeed adding catfish or loaches would be foolish. A school of midwater characins such as Congo Tetras or Bleeding Heart Tetras would make the most sense.>
I plan on expanding to a 75 gallon tank within the next year or so, which makes it important that I choose fish that will work together in a tank of that size. I had a Corydoras Catfish for a while, however I think that the BGK picked on him too much and the Cory didn't make it possibly because he was the little one in the tank.
<Correct. Corydoras are inappropriate to this aquarium.>
Currently I am looking at different tank mate possibilities including an Oscar,
<No. Much too messy. Even in 75 gallons you'd be providing barely adequate conditions for an Oscar and a Bichir, and the poor Apteronotus would eventually die from the poor conditions.>
<No. Too much competition for food. Small Loricariids like a Bristlenose might be okay though.>
<There's really no suitable Loach that you'd keep singly. Most are gregarious, and in sufficient numbers a school of Yo-yo or Clown Loaches would be far too much competition for the Knifefish and Bichir.>
or an Angel fish,
<Requires completely different conditions: still water, much warmer.
Remember, you're keeping Apteronotus albifrons at a MAXIMUM temperature of 24 C/75 F, and anything warmer will soon kill it. The Bichir will be fine at that, as will most midwater characins. Likewise, water turnover needs to be at least 8 times the volume of the tank in turnover per hour. For a 75 gallon tank, that's 75 x 8 = 600 gallons/hour. That's a big-ass filter, and Angels will not like the current produced.>
however I am not sure what would work out best and if I could get more than one of those choices for the tank.
<I think you need to do more reading. Understand virtually everyone who buys Apteronotus albifrons kills it within a couple of years. When was the last time you saw a specimen 10 years old and 50 cm/20 inches long?
Paradoxically, what this species needs to survive is very well known, and has been for decades. German aquarists for example have maintained this species for more than 16 years! So why is their track record elsewhere so dismal? Because people assume they're "community fish". They are not. They need very specific conditions.>
I would like to have a number of smaller (7-8 in.) fish as opposed to 4 large (over 12 in) fish in one tank, but I am not sure what the best route is for my tank.
<You certainly could add a school of dither fish like characins that will encourage both the Bichir and the Knifefish to swim about in the open.
Surface swimmers like Giant Danios would also be good. Anything else would be foolish unless chosen extremely carefully. As for catfish, I'd look at either Ancistrus spp. or small whiptails such as Rineloricaria that could be kept in small groups without undue competition. Anything else would be daft.>
Do you have any suggestions on fish species that would work out well for my situation?
Thanks for any and all help,
<Hope this helps. Cheers, Neale.>

Black ghost fish shyness   1/26/10
Hello Crew, and thank you for the great information you've given me so far.
<Glad to help.>
(As you probably know by now) I have a 125 US Gallon tank with a 5" Black ghost knife, six silver dollars, a leopard Ctenopoma, two Botia Kubotai, a large Pleco and two Kuhli loaches. I realize they are nocturnal, and my black ghost tends to stay inside it's driftwood most of the daytime, coming out once and a while to move to a new piece.
<Yes. Quite normal.>
Recently, I have viewed multiple videos showing Black ghost knife fish swimming around tanks with high lighting, and was wondering if there was any way to train mine to come out more often?
<Not really. If the fish feels secure, and the aquarium is peaceful and has lots of shade, and if there are plenty of small dither fish swimming around the surface, yes, he'll come out. But if the tank is too rough and tumble for his liking, or if the dither fish are much bigger than he is, so seem more like predators, and if there's too much light, then no, he'll hide by day. Simple as that.>
They really are fascinating fish, and I was hoping I could see more of mine without turning the lights off (plus, feeding with the lights on is more convenient). Thanks!
<Welcome to the world of nocturnal fish. Some of my catfish take years to settle down before they risk daytime excursions. Some catfish never do this, no matter what. Try installing a red or "moonlight" lamp that comes on at night. Adding more floating plants instead of bottom plants, and darkening the water using peat granulate or similar can also help. Cheers, Neale.>

Listless Black Ghost Knife  5/10/09
Hi Guys
I have read through your site (which is fantastic btw) and have been unable to find anything similar to what I am experiencing.
I have had 2 black ghost knife fish in a 500 litre tank (with a variety of other fish, catfish, loaches etc) for about 6 weeks. They are both around 10cm's and very friendly and social. The other day I noticed one (Fred) laying totally flat (no movement at all) on the gravel inside one of the ornaments. I freaked and lifted the ornament thinking he was dead only to have him swim away and continue behaving normally. Today he was listless with his tail dragging on the bottom of the tank and can barely swim at all.
<Do be careful keeping multiple Apteronotus albifrons; like all electric fish, they tend to "jam" one another when in close proximity. The dominant specimen actually "bullies" the weaker specimens, forcing them to use less
favourable frequencies. In extreme situations -- as when you have just two specimens in a relatively small volume of water -- the dominant specimen may batter the other specimen to such a degree that it doesn't feed or act
normally. Now, while I'd expect 500 l (130 US gal.) to be adequate for two specimens, you never really know for sure. Apteronotus albifrons is one of those fish best kept either singly or in groups of six or more specimens,
so that bullying isn't likely going to be a problem.>
I quarantined him straight away and currently have him in a guppy breeding cage to keep him off the bottom of the tank - he is not moving at all and I don't know what to do - especially since it is now 8.30 on a Sunday night
so no pet shops open!
<First thing you do is check the water quality and water chemistry.>
I do about an 80ltr water change every 2-3 weeks and I've checked the water with a master kit and all of the levels are within good range with no ammonia or nitrate/nitrite issues.
<Good; also consider oxygenation and possible introduction of copper (e.g., with medications) or other toxins (e.g., paint fumes) that might stress these highly sensitive fish.>
They are fed tropical flakes, frozen bloodworms, dried shrimp and a frozen tropical meat mix - alternated over the week and small amounts a couple of times a day. Ginger, the other ghostie seems fine, as do the other fish but
I am very concerned as he has no obvious injuries, no white spots or coatings and is obviously very sick.
<My gut feeling is this is was initially a social, rather than environmental, problem, and if you moved to its own tank, the other specimen would pep up, given good conditions and a healthy diet. But do consider the other factors mentioned as well.>
Please please help!
<Good luck, Neale.>

Re: Listless Black Ghost Knife  5/10/09
Hi Neale
Thank you for responding so quickly.
<No problem.>
Unfortunately he died very shortly after I emailed you. One strange thing, it appears as those his eyes have disappeared.
<Likely bitten out post-mortem; for whatever reason, these tasty morsels seem to go first! Eyes are also among the first things damaged when fish fight, so again, think carefully about social behaviour issues whenever you
see this symptom.>
There's no wounds around them or anywhere else that I can see. So I don't know if that's a result of bullying or what they normally look like once dead?
I will keep a very close eye on the rest of tank over the next couple of days.
<Wise; would suggest you keep one electric fish per aquarium in future, unless you have a specifically gregarious species, such as Eigenmannia, and purchase a school of them (6+) together.>
Thank you very much for your help.
<Cheers, Neale.>

BGK playing dead?  4/4/09
have had a BGK for almost a month now, introducing it to a tank that previously and still contains 2 angels and a Pleco...i had a Gourami, not sure as to what species as i am totally new to this , it mysteriously
died...maybe overfed cuz it ate EVERYTHING. Then introduced a FW flounder
<Hard to keep>
4 platies 3 of which were pregnant, and a single Kuhli loach (i know i need more, but the store i got him from only had 2 and i didn't know much about them, and they don't get more till this Monday and they are absolutely awesome fish XD).
Yes i understand the BGK is definitely not a beginner fish, but its been perfectly normal, and I've learned so much from this site...only problem I've had with my BGK is its trick which is discomforting..."playing dead" or taking a nap, this started just under a week ago and has become more common idk if its a problem or not i just don't like it. I will live with it if it is not a problem though. I know it is nocturnal and usually is
seen feeding only at night
<What they do>
and it has a "Ghost house" tube to hide in, but i will move that out of constant light, another fine fishy fact i learned from your wonderful FAQs.
He usually eats live brine shrimp and halved cubes of frozen (by the time i get them to him thawed XD) bloodworms and maybe my first pregnant platy =/. Unfortunately seeing as this is my first tank the only info i can give is that it is a 30 gal tank and is usually above 75 F, and usually crystal clear but not so recently. Please respond with the best of your knowledge as always, Ken
<The "playing dead" behavior is normal for freshwater Knives... Bob Fenner> 

Strange BGK behaviour   8/6/08 Hello, I have a young BGK (about 4cm long) that is exhibiting strange behaviour. I'm Australian, so please forgive my metric measurements. <Not at all! I for one prefer metric measurements...> I have a 160L tank, the water temperature is 27 degrees Celsius and the PH is approximately 7.2. <Long term this tank is way too small for Apteronotus albifrons, though right now there's no harm, and won't be until the thing gets to around ~20 cm.> There are 8 Neons, one dwarf Gourami, one flame Gourami, one bristle nose cat fish and two snails. <Hmm... long term the Neons will of course be at risk of being eaten...> The knife fish appears to be rubbing itself against objects such as flat rocks and plants in what I would describe as a fish that appears to be infected with Ichthyophthirius multifilius. <Certainly possible, especially if new fish have been added to the system. Treating with heat/salt isn't a bad idea (raise the temp to ~28-30 to speed up the life cycle, and raise salinity to 1 gramme salt/litre, though add the salty water in stages across a few days so as not to shock the fish. http://www.wetwebmedia.com/FWSubWebIndex/fwich.htm Apteronotus albifrons is sensitive to some medications, so I wouldn't necessarily go with standard copper/formalin treatments.> However, there are no physical manifestations of this disease and the fish has a healthy appetite for it's diet of blood worms and does not show any other signs of weakness, immobility or discolouration. <Sometimes Ick and Velvet go for the gills before the skin/fins, so not seeing the white spots doesn't always mean much. Still, if the fish is infected you should see the white spots appearing eventually. The salt treatment won't do any harm. I'd also check the water quality/chemistry -- fish "flash" when irritated by ammonia/nitrite/pH changes, and Apteronotus is much more sensitive than the other species you have. If the other fish don't show any symptoms that would suggest Ick or velvet, I'd definitely be worrying about environmental issues.> All other fish appear healthy, happy and disease free. I owned a BGK about 7 years ago, but I do not recall it behaving in this manner. Any advice would be appreciated. I hope I'm not being too paranoid. <Ah, no, paranoia with this species is well placed. Extremely sensitive, and one of the more difficult to keep fish in the hobby.> Thanking you in advance, Janine <Cheers, Neale.>

Re: Strange BGK behaviour   8/6/08 Hi Neale, <Janine,> Thank you very much for your advice and quick reply. I was thinking about initiating the salt/heat treatment as I don't like introducing chemicals, but I have never done this before so I wasn't really sure how to go about it. Hopefully I've caught it early enough. <Fingers crossed!> Thanks again, Janine. <Most welcome. Cheers, Neale.>

Ghost knife, BGK beh., sys.    3/3/08 I have had a 40 gallon freshwater aquarium for several years, and until recently the tank was home to a few Oscars who eventually out grew the tank and now reside in a friend's outdoor Koi pond. This past Christmas 12/07 we decided to re-establish the tank with two silver dollars and one incredibly elusive ghost knife. The tank contains your basic under gravel filter, bio wheel, plenty of colorful plastic plants and a long plastic tube, guess who lives in the tube. When I purchased the ghost knife from the pet store he was in a tank with several other ghost knifes and no real shelter, he was swimming around the tank, front wards, backwards and performing all sorts of tricks. Now that the ghost knife has a place to hide he never comes out of his tube. I love to tell friends about this mysterious looking fish, however when they ask to see him I can only reply with ummm sorry he's still hiding. Any suggestions on how my ghost knife can overcome his shyness? <Apteronotus is only active in dark, shady aquaria. You need a soft substrate for digging, lots of rocks, and real or plastic plants that reach up to the surface of the aquarium and produce lots of shade. Use LOTS of floating plants (Indian Fern is ideal). What you do not want is brightly coloured gravel, bizarrely coloured plants, or bright light. Sounds and vibrations must be minimised, so don't put the tank near slamming doors or loud TV sets. Bob F just wrote a piece on setting up an African-themed aquarium, and the photo of the tank shown there is precisely what you need for Apteronotus, so have a read: http://www.wetwebmedia.com/FWSubWebIndex/fwlvstksel.htm Apteronotus live in major river systems and expect excellent water quality and lots of water movement. I'd be aiming for NOT LESS than 6 times the volume of the tank in turnover per hour. These are NOT easy fish to keep, and when kept poorly become shy, and often die.> I also wanted to know if adding aquarium salt when doing water changes was harmful to the ghost knife? <Yes.> I know with other fish that I have had, I have added approximately 1 teaspoon of aquarium salt for every 10 gallons, however I recently read that ghost knifes are not particularly found of chemicals such as prime coat and aquarium salt. <Indeed. The addition of Prime Coat and aquarium salt is unnecessary in a properly run aquarium. Instead focus on filtration and water quality. 50% weekly water changes and nitrates below 20 mg/l, and of course zero ammonia and nitrite, are what you are aiming for. Cheers, Neale.>

Freshwater fish electro-sense question I recently bought an elephant fish. today my girlfriend surprised me with a black ghost knife. They are both about 3in and are in a 34 gallon tank with separate very good hiding spots. Will there 'electro-senses' clash? <There have been some studies on these electromagnetic fields generated by these fish but not much in the popular aquarium literature. But I am sure that they are aware of each other.> also how sensitive are they to salt? <These fish come from clean warm acidic water and have become very sensitive to salt.-Chuck> I use a little less then the recommended dose of aquarium salt(1tbsp per 5 gallon). tank also includes 6 glass cats and a blue lobster. thanks for your time. -Zac  

Ghost Knife Turned cream I have had my beautiful Ghost for over 8 months.  He's only about 5 inches long.  Recently I have noticed, that he has turned a very pale shade of light tan. <be sure to check to see if his skin is turning the color, or does it appear to have a "dust" like coloration to his body.  It might be Oodinium (otherwise known as velvet). The visible symptom of this disease is a fine grey-gold to whitish 'dust' on the body of the fish. Fish will  usually show very rapid gill movement during this time. The disease is caused by a protozoan parasite, and may be triggered by exposure to ammonia and nitrite,  or excessive nitrate levels. That is if it appears to be something on the skin.  I've never heard of a ghost changing his color before.  Have you checked his water parameters lately?  Make sure that the ammonia levels aren't that high.  and be sure to keep up on the water changes.  If the fish isn't showing any signs of stress or sickness then I'm not sure what is the best course of action to take.  I wouldn't want to add a medicine to the water and stress it out if it's not needed.> Nothing has changed in the tank-no new fish added, etc., so I don't know why he would be stressed.  He still bobs to the top to eat.  Have you ever heard of this? <I haven't heard of this happening with a ghost knife, I would keep a close eye on him and make sure if you start to see any problems, or if the fish starts rubbing itself on objects in the tank to move it to another tank and start medicating it accordingly.> Ren in Montana <Good Luck with the fish. -Magnus>

Off-colored Ghost Knife and Oscars with Angels - 02/22/2004 Magnus... <Sabrina, today, hope all is well> Thought I would update you on my ghost who lost his color. I put him in my 5gal guppies tank.  Thought that would be best - no one to intimidate him.  Of course, he loved the old car for his home, and as expected, the baby guppies all disappeared.  Had to make a decision of sacrifice to hopefully keep him alive.  I noticed a bit of black coming back (due to fresh "sea food" I'm sure...), <And you'll surely have more baby guppies in the future, no worries.  Good that they have contributed to your ghost's well-being, a worthy cause, IMO.> but he has outgrown the little tank, <Heh, to be expected!> so I moved him to the 38gal.  This tank consists of Parrots, Tiger Barbs, and a handful of misc.  The red tail shark is probably the most aggressive, but lives in harmony with the others usually.  Once in awhile he'll chase the barbs around.  So far the ghost has found an ornament to hide in and seems to being doing okay. <IMO, all of these are too aggressive as tank mates - do keep an eye on him, watch closely for splits in his fins or any other signs of distress.> Another question....I have a 60gal octagon with two Oscars, two tins, <Hmm?  Ahh, tinfoil barbs, yes?> two fire mouth cichlids and two angels and a silver dollar.  All is well with the combination at this point, but as the Oscars grow (one is about 6"), do you think the angels will be okay?   <Not at all, not in this size/shape tank - I would consider all tankmates grossly at risk of harassing/harming one another as they "grow up" - the Oscars will likely require a tank of their own, if they're getting on well, they've likely paired.  Removing them to their own space will give you some wiggle room for the rest, and the Tinfoils are the next biggest worry - topping out at about fourteen inches.  Fortunately, they are durable, and slow growers - I would remove them with the Oscars.  A tank that is big on surface area (er, not a hex/octagon/tall tank) will do best for the four.> One angel is quite large, the other only about 2 1/2 inches.  I know there is not always a rule to go by, but do you think I should move the angels? <The Oscars and Tinfoils will need a larger tank in the long run.... not so much larger in gallonage as in usable space.> FYI-my "herd" has gone down in numbers.  I have been very blessed to have had 6 adoptions in the past two weeks.   <Wonderful!!> Down to 13 dogs-seems so quiet.   <Sounds like you're doing quite well.> Thumbs up to your girlfriend for helping the shelters and rescues-wish she was here! Have a wonderful day.  Ren <You, too.  Wishing you well,  -Sabrina>

Black Ghost Knife habits Good day, I am writing to ask about the black ghost's behavior. I notice that sometimes it lays on its side in the Mondo grass I have in my tank.  Is it 'sleeping'?  Or is it sick?  I have never had a black ghost until my brother bought one for my birthday the other day. any answers would be appreciated. < The black ghost is really a cool fish. Unfortunately it is nocturnal and is rarely seen during daylight hours. If you really want to see him out and about then you can turn off the aquarium light and feed the tank some black worms or live brine shrimp. Just use the room light to watch him. In bright light they will hide in logs or caves until dusk when they come out to feed. They get big, up to 18 inches but got to be up there as one of the strangest aquarium fish.-Chuck> Thank you! Eric

Training a black ghost knife fish  9/22/05 Dear Mr.  Fenner, I have a black ghost knife fish that I have had for a month.  He is now about 7" long and very healthy.  He eats flakes in the morning and at  night, occasionally I give him some freeze-dried Tubifex worms.  What I  would like to know is how you teach them to eat out of your hand. He seems to be  a smart one he figured out the flakes were edible on his own.  If you know  how to do this I would really appreciate it. Thanks for your  help, MDM <Try feeding small amounts of meatier foods, more frequently, particularly just with some light on outside the tank (not in... too bright). Takes time, patience. Bob Fenner>

FW algae and Apteronotus skin Hi, In my 29 gallon tank there are re-brownish specs on everything. My water parameters are fine and I do weekly water changes and cleaning. what do you think it is? <Almost undoubtedly algal colonies... take a read on WWM re> Also I have a Black Ghost Knife for about 10 months now and since November he has shown a weird green/brown gel-like coating over him. I thought it was ick but wouldn't have died by now if that was the case. Do you know what it is and how to treat it? thanks. <This is probably the animals skin itself... and your good vision. The species is "quite slimy" in good health. Bob Fenner>

FW algae and Apteronotus skin, II Bob, thank you for the response I just wanted to add that my knifefish's slime is a little whitish-gray when the aquarium light is on, does that make a difference? <Actually, yes... as stated, you have excellent vision, observation> I mean when I go to the pet shop all the ones are pure jet black. Jahner <These are more stressed... Bob Fenner>

BGK suddenly shy  11/12/07 Hello Crew, I've had a BGK for 8 months now. He lives in a 55 gallon tank with 2 clown loaches, 3 discus, 2 rams, and a golden nugget Plec, with loads and loads of plants. I do weekly water changes, and water conditions are almost perfect. ammonia 0, nitrite 0, nitrate trace. People always comment on how crystal clear my water looks. He's been very healthy and happy, and growing slowly. There are several hiding places for him but he has taken up home with the 2 clown loaches in a black tube. <Predictably> The three of them swim about looking for food during the day as well as when the lights go out. As soon as I drop food in, those three are the first on the scene playing with each other and eating as fast as they can, its so cute to watch. <Ditto> But in the last 3 weeks or so, the BGK has stopped coming out. He just stays in the tube wiggling about. At feeding time only the loaches come out. I'm very careful with over feeding so the food I put in is always all gone within ten minutes. So I'm 99.9% sure the BGK hasn't eaten in 3 weeks!! <Mmm, is eating something, assuredly... Perhaps you have other food... live worms and such, living in the gravel at this point> Is it normal for these fish to suddenly change their behavior? <Does happen> Today, I fed my discus live bloodworm as a treat, one worm landed in front of the hiding tube and the BGK stuck his head out ate it and went back in. My question is, how could a friendly full of life BGK suddenly become a scaredy cat? there has been no changes, no new tank mates, no change in feeding schedules. My tank is always in view, and he never comes out, day or night. Can there be a chance of illness with him? What can I do? thanking you in advanced Freddie <If I had to guess... I'd say that the most likely possibility is that your Discus are getting larger, perhaps showing a bit of aggression toward this Apteronotid... Do try to spend a bit more time in front of the tank to observe... If two do pair off, there may be trouble for all the other fishes here. I might try some cultured black worms (Tubificids) to urge this Knife's return to feeding. Bob Fenner>

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