How to train your Black Ghost
(Updated 2024) A detailed guide on hand-raising Black Ghost Knifefish in a freshwater aquarium
The Black Ghost Knifefish (Apteronotus albifrons) is one of the most unique freshwater fish you can own. From its physical appearance to behaviour, this fish amazes in many ways. In fact, this weakly-electric fish has an uncanny behavioural resemblance to a dog. A well-trained Ghost will rush to meet you when you put your hand in its tank. It will eat from your hand and even lay on it. The Ghost can be a truly friendly and playful creature.
But in order to bring out the best in our Ghosts, we need to carefully design their environment. We need to condition their behaviour. We need to earn their trust. If any of these aspects is missed, we will end up with an introvert Ghost who stays in perpetual hiding.
In this article, I’m going to share my experience in raising Black Ghosts so that they are extrovert. In short, I’m going to teach you how to be a good Ghost owner.
Note: This is going to be a very long and detailed piece. Grab a cup of coffee and read it at ease — or bookmark it for a later time.
Basic knowledge download
Before we get started, let’s get up to speed on established knowledge of the Black Ghost. The following links will aid in this…
The rest of this article will assume that you are well acquainted with the information in the above links, and will discuss deeper matters.
I also encourage you to do more research on your own. You will come across cool stuff like how scientists are creating underwater robots (GhostBots) that mimic the Ghost’s movement and how Ghosts communicate using electricity.
Okay, now let’s get started. The training of your Ghost will consist of two parts: Environmental conditioning and Behavioural conditioning.
Environmental conditioning
Before we get our Ghosts, we need to have the correct aquarium setup running. This will largely influence the success of the behaviour conditioning that follows. If you already have an aquarium, make it match the below requirements.
Aquarium
Ghosts grow large, to 24 inches (60 cm). We will be starting with the smallest size we can find, i.e. around 2 inches (5 cm). And if we follow everything in this article, they will grow to their maximum size in about 2 years time. Their lifespan will be about 20+ years. Also we will ideally start with not just one, but four Ghosts (more on that later).
Keeping the above in mind, we will ideally need a 500 litre (150 gallon) tank. Alternatively we can start with a smaller sized tank, with the intention to scale up later. The smallest size here should be a 200 litre (50 gallon) tank. Keep in mind that in a small tank the Ghost will not grow to its full size and its lifespan may be cut short due to the confined space. Also remember that larger the tank, lesser the maintenance and more stable the water parameters. Ghosts are scale-less fish, hence they are way more reactive to water contamination.
Having a low maintenance tank will also aid us greatly once the honeymoon period gets over and we realize the long-term commitment an aquarium requires. A mature 500 litre heavily planted tank can handle a bi-monthly 33% water change (though a 33% weekly change is recommended). Obtaining this convenience will be reckoned as the best decision you ever made. Smaller tanks and sparsely planted setups will require more frequent water changes, ranging from 1–3 times a week.
Aquascape
Our tank needs to be a densely planted tank with ample of hiding spots, consisting of driftwood. This will allow the Ghost to feel secure enough to hang out in the open. Ghosts do not like barren layouts. A jungle tank with a comfortable driftwood den will make the Ghosts feel safe. Ironically, the presence of these hiding spots will encourage the Ghosts to stay out in the open more often. Apart from driftwood, we can also add ceramic caves that aesthetically blend into the scape.
A heavily planted tank needs strong lighting. But Black Ghosts do not like light. Sounds like a contradiction? Actually we can get Ghosts to coexist with partial regions of strong lighting, however for this they need to be very young. The Ghosts in my current aquarium are exposed to strong lighting of 40 lumens per litre, and they still come out in the open. A key design element here is to have 1/3 of our aquarium well shaded by plants. Consider using floating plants like Amazon Frogbit to achieve this.
Next, we will design to make the Ghosts comfortable in coming up to the water surface. Being weak of sight, Black Ghosts always need some physical element present within their electric field. This makes them feel secure. As a result Ghosts are averse to venture into the open water, including the water surface. A simple remedy here is to have tall plants. Plants tall enough to reach the surface help the Ghosts to confidently swim to the top; e.g. Jungle Val (Vallisneria gigantea), Ambulia (Limnophila Aquatica).
In creating the jungle scape, we will need a good substrate (like ADA Amazonia, Fluval Stratum, or organic potting soil), correct lighting, filtration (external canister preferred), and a periodic column fertilization schedule (optional). CO2 injection can be omitted, since we want our water parameters to be as stable as possible. CO2 can be naturally created within the tank via organic decay of substrate (like ADA Amazonia) or you can simply opt for liquid carbon products (E.g. Continuum Flora•Viv Prolifera). While most micronutrients are present in tap water, it is always recommended to additionally dose Iron. Choose a good source of Chelated Iron to keep plants healthy.
It is good to put in some dry terrestrial leaves in the aquarium; like Almond leaves, Oak leaves, Mango leaves, and Maple leaves. The gradual decomposition of these leaves has three main benefits:
- They add beneficial Humic substances that positively contribute to the health of fish and plants.
- Increase the microbial community (esp. fungi and invertebrates) within the tank that serves as natural food for the fish.
- The breakdown of the leaves slowly releases macronutrients for the plants.
The decomposition of these leaves will also release tannic acid in the water, making it tea-colored. This does not cause any harm to the fish generally. Just make sure not to overdose. Add a single intact dry leaf to the tank every week till the colour becomes slightly brown. After that only add leaves when the water color starts to get clear. No need to remove the decomposed leaves. You can alternatively add ready preparations of Humic Acid from garden stores to the aquarium. A good dosage here is adding 5ml of a 12% Humic Acid solution to 200L of water, 1–2 times a week. During all this make sure there is adequate oxygen in the aquarium by causing the filter outlet to agitate the water surface and also installing an airstone.
It is common to find advise against having airstones in planted aquariums, since they reduce the carbon dioxide availability to plants. You will also find planted tank experts saying that they don’t provide any external oxygenation at all in their tanks (i.e. relying only on photosynthesis by plants) and that their setups are doing just fine. Now it is important to note that this advise works great for small fish. Ghosts, on the other hand, grow big in size and this increases their oxygen requirement. I have had a personal tragedy where an unexpected spike in the plant’s oxygen intake at night resulted in oxygen depletion that only affected the biggest ghost of my tank; resulting it in jumping out of the water and dying. From the very beginning please mentally establish what is the highest priority for you — Ghosts or plants. If it is the Ghosts, then don’t compromise on their oxygen requirement. That is why it is strongly suggested to have an airstone running 24x7 in a Ghost aquarium while avoiding CO2 injections. This will mean slower plant growth and limited plant variety in our tank, but we need to accept that from the start. Do not infatuate on making a your Ghost tank into a fancy Takashi Amano inspired aquascape. It is really not worth to have your mature Ghost die in exchange for faster plant growth. Always keeping an airstone running or use another method to maintain strong surface agitation. You may have other hobbyists advising you to remove the airstone; never do that. Furthermore, the plants described below will grow very well with the recommended substrates and airstone.
If you are new to planted aquariums, then go for easy plants like Amazon Sword, Cabomba, Water Wisteria, Water Sprite, Vallisneria, Dwarf Sagittaria, Anubias, Ambulia, and Cryptocorne. Also note that, while they are carnivores, some Ghosts like to chew on soft plant stems. This means plants like the Water Lily may not survive with them. There are certain plants that the Ghosts have a general spite towards and they will constantly rip them out to get rid of them altogether. As Ghosts grow, their tolerance for new changes in their territory reduces. This includes introduction of new fish and plants. So you may find the ghosts actively ripping our certain new plants in their environment. Plant your aquatic flora deep into the substrate to maximise the chances of their survival.
Another tip is to have plenty of Amazon Frogbits growing in the shaded region of the tank. Matured roots of the Frogbits provide a significant buffer to the aquarium’s biological filtration. This will further help keep water parameters stable and reduce maintenance. Ghost tanks tend to have high Nitrate levels (40-80ppm) because of their excretions, so having a nitrate-hog plant like the Amazon Frogbit is strongly recommended. Frogbits also provide a shaded region for the Ghosts to escape from the direct light. Just make sure the Frogbits are placed in a region where the water is calm with minimal surface agitation. If you have a population explosion of Frogbit, simply periodically give the extra ones away (free money!) or toss them in your terrestrial plant pots (free fertilizer!).
Tank mates
Now we need to select the right co-inhabitants of the aquarium. These will consist of species that positively influence the Ghosts as well as the aquascape.
Ghosts can be aggressive between themselves, but they are otherwise quite timid. Due to this we need to avoid other aggressive and territorial fish, like cichlids. The exception here is the Discus fish; they are in fact the perfect companions for Ghosts. The Black Ghost and Discus are both scale-less fish, and so need almost identical care.
Avoid herbivorous fish like the Goldfish. They will destroy all the plants. Avoid rainbow sharks, red-tailed sharks, and other dark-tone territorial fish. Rainbow/Red-tailed sharks will be at constant war with Ghosts.
As a clean-up crew, keep a school of a dozen Corydoras (E.g. Sterba’s Corydoras). These scavengers will take care of any uneaten food at the bottom. But make sure to give them their fair share of daily feeding. Another good addition to the maintenance crew is the Siamese Algae Eater.
Malaysian Trumpet Snails (MTS) are good for keeping the substrate clean and free of food debris. Their conical shell also does a good job of turning the soil as they move. This neutralises any anaerobic spots that may develop in the substrate. MTS also eat the faeces of fish. Black Ghosts don’t poop as often as Goldfish, but the size of their single excrement quite large. So it is good to have someone around to take care it. Another fun fact is that the Ghosts excrete from what seems to be their neck.
Coming back to MTS. Aquarium-keepers often frown upon MTS as unsightly beings that overpopulate the aquarium. However their population is observed to explode when there is abundance of uneaten fish food. Feeding how much your fish can finish in 2–3 minutes and keeping Corydoras is a good solution for this. And anyway, you don’t have to ever worry about a snail problem in a Ghost tank because Ghosts like to eat adult snails. Ghosts have a powerful jaw that breaks open the shell and lets them slurp up the snail from the inside (like a Balut). It should be difficult to find an adult MTS in an established Ghost tank.
Suitable tankmates for Ghosts are mainly medium-sized non-aggressive fish. This includes Discus, Angelfish, Gouramis, Siamese Algae Eaters, Congo Tetras, Catfish, Pleco, Mollies, Swordtails, and Guppies.
From my experience, small Black Ghosts get used to living with the smaller fish as they grow. But once they have grown, they either only tolerate the exact fish they grew up with (i.e. they will spare the small fish that are there since the Ghosts were also small, but will eat any newly introduced small fish of the same species) or will switch to hunting all small fish indiscriminately. As the Ghosts grow, they will develop opportunistic hunting traits, particularly towards small fish and shrimp.
So the small fish in your tank should mainly consist of Guppies, Mollies, and other fast multiplying livebearers. With adequate foliage and hiding space you will have a stable Guppy population that also acts as free live feed for the Ghosts. Don’t buy expensive Guppies however.
Same goes for Shrimp. The Ghosts in my smaller tank have wiped out the entire shrimp population. But the shrimp in my larger 1000L aquarium are alive and reproducing despite the ghosts because of the sheer number of convenient hiding places all around. But you don’t see them out in the open always.
There may instances of the Ghosts occasionally nipping and biting other medium-sized fish, mostly accidentally on being agitated or startled. Sometimes the inflicted wound can be dangerous. So always keep ointments around to treat any wounded fish.
Behavioural conditioning
Now that we have our aquarium up and running properly, let’s focus on the acquisition and training of our conversation’s subject.
Selection
Before we go out and buy the Black Ghosts, it is strongly recommended to have a new aquarium running for 1–2 months as per the environmental conditioning discussion. This will provide ample of time of the tank to cycle, water parameters to stabilise, and the smaller fish and shrimp to have comfortably established their own territories and social hierarchies. This will minimize the chaos caused when the Ghosts are introduced.
Now let’s go hunting for our Ghosts at fish stores. Search for a store that is selling small sized Ghosts, ideally about 2 inches (5 cm) long. These Ghosts are big enough to be identified as healthy and small enough to accept training and avoid social conflicts among themselves. Avoid larger Ghosts.
Purchase four or more Ghosts (based on your tank size). Never purchase two Ghosts. Four is the ideal number. Let us discuss why.
Black Ghosts maintain a strong social order within themselves. This hierarchy will be established in the first month of keeping them together in our aquarium. In this period you will see them often spar with each other. When sparring, they are seen opening their jaw to its full capacity. And boy, can they open it really wide! Anyway, by the end of all the sparring there will be a single dominant Ghost. This Ghost will be the most assertive and eventually largest in size. The Ghosts assert their dominance not only physically but also via their electric fields. You will notice other Ghosts fleeing as soon as they sense the dominant Ghost coming around them, even when it’s still out of their weak sight. This social behaviour is the reason why we need to have at least four Ghosts.
If we keep just two of them, then the dominant Ghost will constantly assault the weaker one — physically and electrically. The continuous stress of this will lead the submissive Ghost to remain stunted in size. You will see that it will hardly increase in size, while the dominant Ghost will grow huge — even though both are getting ample of nutrition. And finally after a few months, the dominant Ghost will actively murder the submissive one. This phenomenon is also seen in other fish (like Discus), but there the assault is not so extreme. So the submissive discus fish still survive. In Ghosts, the assault is lethal. That’s why we often find on the Internet advice to keep only a single Ghost. However the key here is to get them small and NOT to keep them as a pair. If we keep them in larger groups, their aggression dilutes to a safe level and they are found to be social with each other even as they grow up.
Hence the magic number four is drawn. Four Ghosts will let the aggression of the dominant Ghost be spread evenly among the others. The lowest-ranking fourth Ghost will be relatively stunted but quite healthy and safe otherwise. The second and third Ghosts will grow large, but not as large as the Alpha (usually a female). These two will probably share the same rank — Beta. In case of three Ghosts, the third Ghost may not be able to take the aggression of its two superiors. More than four Ghosts can also be purchased safely, as long as their tank is calculated to be spacious enough for all of them. Remember, for four Ghosts we will need 160–500 litre (40–130 gallon) tank. The bigger the tank, the bigger they’ll grow.
Right, so based on the above select your Four Horsemen. Refer online to see what a healthy Ghost is like. Make sure that the tails of the Ghosts are intact. The Ghosts transmit electric signals via their tails. Without its tail, a Ghost is pretty much doomed.
On a side note, while the tail is used for transmission — the rest of the Ghost’s body is capable of receiving signals. This helps the Ghosts in navigating their way through electrolocation. This is often demonstrated when a food particle drifts near a Ghost’s abdomen and the Ghost immediately identifies it and retracts to eat it (more info on this here). The reception ability is strongest around a Ghost’s head. In larger Ghosts we can observe dimples scattered around the head to finely receive signals and quickly pass it to its brain. These are called Electroreceptors.
After selecting and purchasing the Ghosts we take them to their new home. Also pick up the food mentioned in the Feeding section of this article. Introduce the Black Ghosts into the aquarium following the standard protocol for scaleless fish. Do this at time when you know you can observe them for the next 3–5 hours at least. As a universal rule, we always introduce a new entity (flora, fauna, solid, chemical) in an aquarium at a time when we can easily observe its behaviour/effects for the next 3–5 hours. Never introduce any new variable in the tank just before going to bed or out.
Feeding
Now that our Ghosts are well settled in the tank, let’s discuss their feeding plan. Like in the training of any animal, food plays an essential role in the Ghost’s training. It is the incentive that motivates, morphs, and binds them to the desired behaviour.
We need to be ready with the following fish food at the time of introducing the Ghosts in the aquarium:
1. Sinking-type: Hikari Sinking Wafers (nutrition review) / or / Hikari Sinking Carnivore Pellets (nutrition review)
2. Floating-type: Freeze Dried Bloodworms / or / Hikari Cichlid Excel floating mini pellet (nutrition review)
3. Handfeeding-type: Freeze dried Tubifex worms
Note: Hikari brand food are suggested in this article because of my consistent positive experience with them and because they are commonly found in fish stores. However food of other brands with similar properties can also be substituted.
Start using the above food to feed other fishes much before introducing the Ghosts. Do not feed any type of live worms in the aquarium. Forever.
While the Ghosts are young, we need to feed them with the aim to:
- Make them know when it is feeding time.
- Make them come to the surface.
- Make them accustomed to be hand fed.
- Make them disinterested in eating other smaller inhabitants.
- Keep them healthy.
The feeding time needs to be set to twice a day — morning and night. In the morning feed the fish between 7–10 am, earlier the better. At night feed them between 8–11 pm, and shut the lights only after the fish are done eating. All the fish in the tank are fed in these two slots only. Once a week, do not feed the fish for 24 hours. This helps the fish have a healthy digestive system and will keep them from falling sick.
At the beginning of every feeding session, we need to communicate to the fish that it’s food time. Develop your signature style for this; like tapping on the glass in a certain way, snapping fingers over the water surface. This is a classical conditioning technique that will get the fish to the surface and eventually interact positively with humans (more on this here). The fish will not respond to this initially, but they will do so once the technique is kept up for a month. This conditioning will trigger the Ghosts to come to the surface at your command, even when you do not intend to feed them.
Now to the actual feeding. We first feed the fish freeze-dried bloodworms and floating pellets. These do not sink and stimulate the Ghosts to come to the surface. Bloodworms should be an instant hit with all your fish. Also feed them a high-quality floating pellet, like Hikari Cichlid Excel (Floating mini pellet), that does not cloud the water, is small enough to be eaten whole by young Ghosts, and is liked by all fish including Ghosts and Discus. Cichlid Excel is also rich in plant matter that helps keep a healthy digestive system. Ghosts will always prefer Bloodworms over Cichlid Excel, so its a good idea to mix the two to regulary have them consume plant matter as well. Otherwise, a heavy diet of bloodworms may cause digestive issues. Ghosts have a packed abdomen, so they don’t often survive minor digestive disorders. If the Ghosts find the mini pellets of Cichlid Excel too large, then go for a good quality floating micro pellet. Avoid slowly sinking food, like Tetrabits and Biogold, at this early stage —you can use them later after training is done. We specifically need floating pellets. The Ghosts will eventually learn to sniff the presence of the worms/pellets and inversely skim across the surface to gobble them up. Feed an amount that all your fish can finish completely in 2–3 minutes.
Sometimes the Ghosts resist coming to the surface because they are not used to the intense light exposure. To overcome this, dim the lights or switch them off altogether. This will make them comfortable in swimming to the surface. Once they start surface feeding then gradually increase the light intensity during feeding time.
There is information online that discourages feeding floating food to fish because they can cause fish to swallow too much air and kill themselves. I’ve never come across practical incidents of anyone facing this issue. None of my fish have ever been affected in this manner either. So in the absence of proper validation of this condition, I continue to promote the usage of floating pellets.
After about 2–3 minutes of putting in the floating pellets have passed, we then put in 1–2 sinking pellets (Hikari Sinking Wafers or Hikari Sinking Carnivore Pellets). The sinking pellets are required for various reasons:
- These pellets are the Ghost’s food source till they are confident enough to do surface feeding.
- They contain bulk of nutrition required for them to grow.
- They are fed upon by bottom dwelling fish, like catfish.
- When the Ghosts feed on these, they throw off smaller bits of the pellets in the water column that are fed upon by the smaller fish.
Increase the number of pellets as the Ghosts grow, making sure all of them get a chance to feed. Once the dominant Ghost hits 8–10 inches in size, it will likely devour all the pellets by itself. When this starts to occur, switch to Hikari Massivore Delight (nutrition review). These pellets will be large enough to force the alpha Ghost to share them with everyone else. These pellets will also support the Ghosts in their next level of growth spurt. Remember to monitor your nitrate levels as the Ghost grows and keep Amazon Frogbits handy (other any other nitrate-hog plant like Hornwort, Water Hyacinth, Hydrilla etc).
When the Ghosts are new, feed them floating and sinking pellets in every meal. Once they learn to confidently feed on floating pellets, then feed them exclusively floating pellets in the mornings and floating + sinking pellets at night. We need to make sure the Ghost’s tummies are full at night, so that they are not inclined to go hunting when the lights go off. Fish like Mollies sleep near the bottom at night, in full range of a Black Ghost. And Ghosts like to wander around the tank at night while everyone else is asleep. This means that the fish will be completely vulnerable to a Ghost at this time. By feeding the Ghost well at night, we minimize the chances of a fatality.
Twice a week, feed the Ghosts Tubifex worms (while feeding dried blood worms daily). Toss a small piece on the surface if the Ghosts have learnt surface feeding. If not, press the piece on the glass near the substrate level. Tubifex worms are a bonus food that is occasionally given. It will also play a crucial role in the hand training of the Ghosts.
Hand training
Finally, we come to the core training part. Whew!
After the Ghosts have been introduced in the tank, periodically keep putting your hand in the tank, maybe just to fidget with the scape or plants. This will get them acquainted to your scent. You can try gently approaching them as well. Some Ghosts are extremely curious and they may come near quickly. Others may prefer to run away. That is of no matter now. Continue doing this along with the feeding training.
After a few weeks, the feeding training should be complete and our Ghosts will be actively coming to the surface whenever we snap our fingers (or perform the apt behaviour trigger). In this period the Ghosts would have also developed an appetite for Tubifex worms. Now we simply take a shot at feeding the Ghosts with Tubifex worms in our hand. The Ghosts should respond positively in no time. Remember to grip the worms well because Ghosts can latch and pull very well.
Hand-feed the Ghosts a few times a week at least to keep reinforcing this behaviour. Soon they will like to hang around your hand even after the food is over. From then on they will start come to your hand whenever you put it in the tank and perform the trigger move. In this way the Ghosts can be trained to interact with humans.
Most of the times “give me food” will be primarily reason for the Ghosts to seek your hand. However there will be times when the Ghost will hang around you out of sheer curiosity. In such times, the Ghost will try to size you up by touching you specifically with its tail, rubbing its abdomen against you, and sniffing across your skin surface. Such variety of interactions makes it stand out from other fish and make it resemble a dog; them moving their fins like a dog’s ears further adds to this. But of course, the bond between a dog and its master cannot be completely equated with a Ghost. However you can still develop a special bond with a Black Ghost that is strong enough to make you miss them when you are away and tear you apart when they eventually pass away. You will realize that these guys are really special and totally worth the investment.
Once they start readily interacting with you, consider inserting your hand once a day (say when you return from work) and play with them for a few minutes. This will further strengthen your bond and relationship for years to come. Ghosts tend to shy away as they age, so it is important that you invest in interacting with them. Otherwise you will find that a Ghost that was very friendly is suddenly extremely shy.
Discipline
Before we close, there remains a small but important topic of disciplining the trained Black Ghosts.
Once the Ghosts start actively interacting, they may start pecking on our hand and arm. It is common for fish to do this and is harmless by fish like discus, mollies, goldfish, and guppies. Even the pecks of small Black Ghosts are hardly felt. However as the Ghosts grow their pecks start to sting. It is not a good idea to let an 18-inch Ghost take peck at you, albeit in a friendly manner. So to avoid this we do a simple exercise early on to communicate to the Ghost that pecking is not welcome.
Around the time the Ghosts hit 5–6 inches, we start deterring them from pecking. Whenever they do peck, we lightly push them away by flicking our finger on the centre of their body. Be careful to be gentle and to aim at the centre of their body. Stay away from the head, gills, and tail. The Ghost will run away into hiding after we do this a few times. Soon it will be hesitant to come near the hand altogether, but will eventually come near during hand-feeding sessions. Often we can observe the Ghost trying to resist its urge to peck on the hand. If it pecks again, repeat the same drill. It will eventually learn to avoid pecking the hand altogether.
Closing
So there you have it, a detailed explanation on training your Black Ghosts. I hope this article will help you successfully raise and train a friendly pack that keeps you company for years. :-D
I also look forward to hearing your experience with them. Please do share them in the comments below. Videos and images are also welcome. I will try to update this article periodically based on the new information we gather together about keeping these extremely unique critters.
All the best!
Miscellaneous information
Below are some more points that didn’t fit in the flow of the article.
- The region around the gills of a Ghost can appear to be white in low light. This is normal.
- The white streak on their forehead can sometimes turn reddish in color. This is also normal and its sudden occurrence may indicate that the Ghost is in heat.
- Ghosts like their siesta. They are often found laying motionless on their side on the floor. They may also lodge themselves in an odd position. In such cases they may look dead but in fact are simply dozing. Do not touch or disturb them at such times. Else they will get the fright of their life and will scramble to their hiding spot and stay there for days or weeks.
