Post by dinosauria101 on Feb 28, 2019 2:08:24 GMT 5
Pictus Catfish - Pimelodus pictus
A newly introduced individual exploring the tank. Image taken by me.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Siluriformes
Family: Pimelodidae
Genus: Pimelodus
Species: Pimelodus pictus Steindachner, 1876
Description:
Usually just called pictus catfish and occasionally polka-dot or angelicus catfish. Easily recognizable in stores regardless of market name thanks to its characteristic combination of black spots against silver and black-edged fins, which also make it easy to distinguish from other species of pictus catfish such as 4-line, white line, and ornate pictus catfish.
Among these spotted individuals two morphs are currently known to exist. Although fish of different sizes cannot be compared due to the pattern changing with age, differences between fish of the same size are noted as the more common morph having smaller and more numerous spots with the other, rarer morph having larger and fewer spots.
A widespread belief that the smaller spotted individuals come from Colombia and the larger ones from Peru may not necessarily be true: in a purchase I have made of 5 individuals from a Colombian shipment, 3 have small spots while 2 have larger spots. I believe, unless this shipment was caught close to the international border where intermixing could plausibly happen to an extent, this is possible evidence for both morphs being found in both countries beyond mere border regions.
Although I personally have never seen an adult outside the size range of 120-150mm, total range of adult size is reported as up to 180mm for some individuals from fishkeepers I have spoken to. Size-related variation between individuals has been assumed to come back to the 2 different morph, with the common belief being that the small spotted morph grows larger.
Growth rate has also been variously reported as being slow to fast, and may have as much variation depending on temperature and morph as it would the usual variables of tank size and water quality. I have found from observing my own fish that morph type may play a role: my 5 fish were all at nearly identical purchase sizes yet the 2 large spotted fish have both grown faster and to a larger present size than the 3 small spotted fish - in spite of their apparently smaller adult size.
Appropriate Tank Size:
I find that due to its activity level and required space needed to extend its body-length whiskers (barbels), the appropriate tank size for pictus catfish is a footprint (length and width) of at least 1800mm by 450mm. This may seem overkill, but in smaller tanks it has been both my experience and my hearing from other keepers that the fish become less active and possibly stunted in smaller tanks due to lack of sufficient exercise space.
The majority of commercially available tanks this size are usually between 473 to 568 liters in volume - considerably larger than the 208-284 liter volume of the commonly-cited 1200mm x 300-450mm sizes. As such tanks are so large compared to the latter, more commonly kept size, their volume is intimidating for many a hobbyist, anda number of hobbyists also may be concerned about the ability of their floorboards to support such a heavy tank.
However, these fears can be mitigated by choosing a shallower custom-built tank. Unlike deeper-bodied open water aquarium fish which need relatively tall tanks to account for their size and desired position in the water column, the bottom swimming habits of pictus catfish mean height does not matter as much as length or width.
Although I have never kept mine in a shallower tank than 550mm, based on their desired swimming areas I feel comfortable recommending 300mm as the cutoff for the appropriate tank height - they do not go above this, generally. Therefore, if high tank volume or weight is a concern and custom built tanks are an option, a custom built 243 liter aquarium of 1800mm x 450mm x 300mm would be an appropriate starting point for keeping pictus catfish (although this does not take into account any other desired fish, which depending on the species may not do well in such a shallow tank).
Acquiring your Fish:
It has been reported by other fishkeepers that this species is sensitive to whitespot (ich) and its cure, and although I have never seen an individual with the disease, I believe this reported sensitivity mandates appropriate caution in choosing whitespot-free fish: ie, not buying from a shipment with any infected individuals. However, 2 of the fish I purchased had what may have been internal parasites due to their bellies getting flat abnormally fast after feeding, which flubendazole appeared to cure.
Either way, as with all fish, a lengthy quarantine of at least 3 months in a well-maintained, low-stress quarantine setup would be well-advised. Furthermore, because these fish are wild-caught, they may also come in with either undernourishment issues or additional diseases not forewarned above - all of which a quarantine setup is the ideal place to fix.
Appropriate caution must also be exercised when transporting the fish for any reason: as is the case for many catfish, their pectoral and dorsal fins have sharp spines. The ends are sufficiently sharp to be capable of puncturing plastic transportation bags (I have witnessed such firsthand while purchasing this species), and although not life-threatening, a sting from these spines will throb, swell, and hurt excruciatingly for several hours thanks to the venom within the spine mucus (because of this, I would recommend avoiding direct handling if at all possible).
Furthermore, the serrations on the spine will almost always get snagged in a net, which attempting to remove can be dangerous to the fish. Although my own removal attempt has not caused any trouble to the stuck fish beyond a slightly beaten up pectoral fin, I have heard of cases where either the whole fin had to be ripped off or the net cut off with some still left around the spine, both of which ended in the death of the fish due to infection.
Ultimately, the safe way to catch and transport these fish is with non-snaggable catching equipment (such as a clean long-handle mesh strainer) into a solid non-puncturable vessel (such as a bucket). As alluded to, however, pet stores will often use risky standard nets and bags. I would recommend bringing your own catching equipment (that can fit in the store's tank) and transportation vessel for them to use in order to minimize risk.
Required Setup and Maintenance:
Once the fish have been quarantined and found to be in good health, they can of course be moved to a permanent home.
Water chemistry requirements may be somewhat ambiguous. I have seen recommendations for up to 268 mg/l of hardness, but have also seen a recommendation - explicitly stated to be from the keeper's experience - that the fish fare poorly in hard water and that hardness shouldn't be higher than 178 mg/l or so.
Because my water is only 137 mg/l hardness I can neither vouch for or against these recommendations, but I would advocate the potential need for caution if your water is harder than 178 mg/l: as with reported variations in size and growth rate, differences between morphs may play a role in tolerance of hard water.
Water quality needs to be kept high at all times or the fish will have stunted growth and its associated health problems together with barbel loss. NO3 should not be allowed to exceed 5 mg/l: consequently, weekly water replacements (with dechlorinator if needed) that keep the NO3 at or under 5 mg/l are necessary, with a precise routine that will vary from tank to tank.
Temperature should be slightly colder than the average tropical tank. I have found recommendations from other keepers to be within ranges of 20-26 Celsius as opposed to the 24-28 Celsius range most tropical tanks are heated to, and my own experience is broadly in accord with this: I have had fish live within this whole range of temperatures for several months to years appearing to do well on all accounts.
This slightly colder temperature also means that a heater may not be required for all fishkeepers outside tropical climates, depending on ambient room temperature.
I have found that - at least compared to substrate-free, low-flow setups with less decor - this species requires more environmental complexity to thrive. Specifically, I believe the difference between getting the fish to thrive or not comes down to inclusion of the following in said environment:
-Fine, smooth sand substrate: for example, I have had success with silica pool filter sand. This is preferable to rougher choices such as play sand/gravel/plant soil because its smooth texture will not wear down the long, sensitive barbels of the fish, as well as to a lack of substrate which seems to make the fish continually on edge (likely due to its difference to the natural habitat of the fish).
Additionally, sand with a brownish color is best because it again bears more resemblance to the fish's habitat. I have seen reports of this species wash out on lighter sand as well as darken up on darker sand, neither of which are desirable because of the long-term stress of the attempted tone change compared to being matched with their natural habitat color.
-A mix of hiding spaces and open spaces. Although most individuals of this species spend most of their time out in the open, they need to feel sufficiently secure to do so: by having a number of hiding spaces alongside their required open swimming spaces, they know that there is plenty of safe space for them to go if they want to, and therefore become more active.
Easily available at any pet store that sells fish, synthetic hides/logs are an ideal way to provide the desired hiding space. Attached are images of my 2 tanks with this species for examples of what I find to be working.
-Strong current, although with spots to rest. As might be expected from its slightly colder than average temperature requirements, this is a riverine species and therefore needs replication in the aquarium of such an environment.
From my observations, providing such flow increases the activity levels of the fish. They may possibly be compelled to swim against the current as they would in nature, and therefore be more active than if there was no current to swim against.
A specific product I can recommend to create the flow required is the Sicce Voyager 4. This powerhead creates 6000 liters per hour linear flow: I have found this amount is needed to create the sufficient amount of flow in my 473 liter aquarium, but will need to be upscaled appropriately for more voluminous tanks.
Ideal positioning would be near the surface and on a slight upward angle to create oxygenating surface agitation while simultaneously providing undertow at the bottom for the catfish.
-Possibly subdued lighting. Technically I have not had to use this in my pictus catfish setups (I have noticed no difference in daytime activity in my experiments with different lighting), but it is reported by multiple keepers as a necessity for good daytime activity, therefore it should be at least noted as a possible requirement.
Optional additions that some keepers may want for the aesthetic value are driftwood, smooth rocks, and plants: I have all of these with my catfish and although I haven't seen the catfish make use of them, they do no harm to the catfish.
The only plants I have kept with these fish are fake plastic plants, but live plants that can handle the current, colder water, and possibly subdued lighting needed by the fish have been reported as safe additions by other keepers.
Feeding:
Carnivorous and not picky at all. I have found all the following meaty foods to be eaten without hesitation:
-Sinking carnivore granules
-Thawed frozen bloodworms
-Thawed frozen brine shrimp
-Thawed frozen mysis shrimp
-Thawed frozen sliced krill
-Thawed frozen tubifex worms of an appropriately large size
-Thawed frozen mussels
-Thawed frozen calamari
-Live earthworms
-Lawn grubs
-Crickets and grasshoppers
-Superworms
My recommendation would be a pellet staple as part of a varied diet including as many of these items as available (of course, with appropriate precautions taken for collection of live food). Take care not to overfeed as this species will eat enough at one time to greatly bulge its stomach if fed enough to do so - in fact, adults only need to be fed every few days.
Behavior and Tank Mates:
My experience with the behavior of these fish has been that they will spend most of their day visible and somewhat stationarily swimming against the current, but will have occasional greater bursts of speed back and forth across the length of the tank that will cause them to hit the decor and injure themselves if space is insufficient (hence necessitating their need for such a large tank). However, if very small individuals between 30-70mm in length are purchased they are likely to spend much of their time hiding during the day - this has been my experience with individuals this size, and I suspect those particular individuals will become more active as they get larger, which is more in line with the above described active behavior of my 80-100mm individuals.
It is a commonly held belief that this species is a schooling fish which should always be kept in a group of at least 5, however numerous anecdotal reports also exist of individuals purchased together as a school splitting apart, holding a territory in their tank, and being sufficiently intolerant of conspecifics within it to fight them away. My experience with 2 different purchases of 5 has shown both to be the case in both groups at varying times - in fact, it has also been reported from keepers besides myself that the schooling and splitting can vary over time!
At present I would not feel comfortable assigning a cause or set of causes to such variable and contradictory behavior given the numerous differences in the various tank setups it has been reported from. Unless further observations reveal possible causes, the average fishkeeper can do little more than be aware of the possibility and would be best advised to buy at least 5 in the event that the fish need the company.
The first rule of choosing fish that can go with your pictus catfish: don't get anything that they could eat! Thankfully most sources sufficiently stress this, but there are a notable minority I have seen which downplay its importance by marking these fish off as smaller-mouthed scavengers.
This is, unfortunately, misinformation. They may look like they have small mouths and act as scavengers, but their mouths open to a far larger size than when closed and any fish that fits will eventually becomes food in the closed system of an aquarium - giving this species a well-earned reputation for devouring bite-size species of livebearers, tetras, danios, and barbs.
The converse is also true: although pictus catfish may be predatory, they should not be kept with any fish large enough to eat them given their small size (for example, larger species of predatory pimelodid catfish that are also popular in the aquarium). Besides the risk to the fish, I have found that this species is most active when it is one of the largest species in the tank - probably thanks to instinctual fear of larger relatives that would eat it in the wild.
Besides the obvious of appropriately-sized fish, another appropriate consideration would be fish that can handle both the environment and the catfish. Specifically, this means they would have to come from similarly cooler, flowing water, and also be unstressed by the activity and barbels of the catfish.
The latter means slower-moving popular fish such as goldfish or cichlids would be inadvisable as tank mates, and as the latter are also more aggressive fish their exclusion from a pictus catfish tank is merited further despite their popularity.
Species I have found to work, or have been told work by multiple keepers, are as follows:
-Smallscale archerfish (found to work). These fish also enjoy current and slightly colder water, and as they live at the top of the tank they are always out of the way of the catfish.
Just be aware that both fish will have to be purchased at the same size if the archerfish aren't to eat the catfish. I almost had a trio of newly introduced 30-40mm specimens eaten by my existing 100mm archerfish (thankfully I could catch them out of the tank in time, and learned my lesson with no losses).
-Chalceus. Works for the same reason as the archerfish.
-Botia loaches that prefer slightly colder temperatures (found to work). Works for the same reasons as the above.
-Insectivorous, non-nippy sharks and barbs too large to eat (such as roseline sharks, found to work). Same again as above and they may also have a dither fish effect.
-Other species of carnivorous catfish that match environmental needs: for example, some Synodontis catfish, some doradid catfish, some plecos, some North American catfish, and some bagrid catfish.
-Possible: Pumpkinseed sunfish. I have seen this species in the wild in similar conditions to P. pictus and intend to try it as a tank mate for my P. pictus - whether it works, or not, will be reported when it is tried.
Extra Information:
There is a 2016 study[1], claiming the pectoral fins of this species are touch-sensitive and useful for navigating on the bottom of water bodies, but I have always observed my P. pictus holding their pectoral fins up off the substrate - only ever unintentionally touching the bottom with them.
The difference may have to do with the fact that the fish in the study were only in very small holding tanks that were bare, not in an appropriately sized and decorated tank.
Reference:
[1] Hardy, Steinworth, and Hale (2016). "Touch sensation by pectoral fins of the catfish Pimelodus pictus". Proceedings of the Royal Society B. royalsocietypublishing.org/doi/10.1098/rspb.2015.2652#d1e913
A newly introduced individual exploring the tank. Image taken by me.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Siluriformes
Family: Pimelodidae
Genus: Pimelodus
Species: Pimelodus pictus Steindachner, 1876
Description:
Usually just called pictus catfish and occasionally polka-dot or angelicus catfish. Easily recognizable in stores regardless of market name thanks to its characteristic combination of black spots against silver and black-edged fins, which also make it easy to distinguish from other species of pictus catfish such as 4-line, white line, and ornate pictus catfish.
Among these spotted individuals two morphs are currently known to exist. Although fish of different sizes cannot be compared due to the pattern changing with age, differences between fish of the same size are noted as the more common morph having smaller and more numerous spots with the other, rarer morph having larger and fewer spots.
A widespread belief that the smaller spotted individuals come from Colombia and the larger ones from Peru may not necessarily be true: in a purchase I have made of 5 individuals from a Colombian shipment, 3 have small spots while 2 have larger spots. I believe, unless this shipment was caught close to the international border where intermixing could plausibly happen to an extent, this is possible evidence for both morphs being found in both countries beyond mere border regions.
Although I personally have never seen an adult outside the size range of 120-150mm, total range of adult size is reported as up to 180mm for some individuals from fishkeepers I have spoken to. Size-related variation between individuals has been assumed to come back to the 2 different morph, with the common belief being that the small spotted morph grows larger.
Growth rate has also been variously reported as being slow to fast, and may have as much variation depending on temperature and morph as it would the usual variables of tank size and water quality. I have found from observing my own fish that morph type may play a role: my 5 fish were all at nearly identical purchase sizes yet the 2 large spotted fish have both grown faster and to a larger present size than the 3 small spotted fish - in spite of their apparently smaller adult size.
Appropriate Tank Size:
I find that due to its activity level and required space needed to extend its body-length whiskers (barbels), the appropriate tank size for pictus catfish is a footprint (length and width) of at least 1800mm by 450mm. This may seem overkill, but in smaller tanks it has been both my experience and my hearing from other keepers that the fish become less active and possibly stunted in smaller tanks due to lack of sufficient exercise space.
The majority of commercially available tanks this size are usually between 473 to 568 liters in volume - considerably larger than the 208-284 liter volume of the commonly-cited 1200mm x 300-450mm sizes. As such tanks are so large compared to the latter, more commonly kept size, their volume is intimidating for many a hobbyist, anda number of hobbyists also may be concerned about the ability of their floorboards to support such a heavy tank.
However, these fears can be mitigated by choosing a shallower custom-built tank. Unlike deeper-bodied open water aquarium fish which need relatively tall tanks to account for their size and desired position in the water column, the bottom swimming habits of pictus catfish mean height does not matter as much as length or width.
Although I have never kept mine in a shallower tank than 550mm, based on their desired swimming areas I feel comfortable recommending 300mm as the cutoff for the appropriate tank height - they do not go above this, generally. Therefore, if high tank volume or weight is a concern and custom built tanks are an option, a custom built 243 liter aquarium of 1800mm x 450mm x 300mm would be an appropriate starting point for keeping pictus catfish (although this does not take into account any other desired fish, which depending on the species may not do well in such a shallow tank).
Acquiring your Fish:
It has been reported by other fishkeepers that this species is sensitive to whitespot (ich) and its cure, and although I have never seen an individual with the disease, I believe this reported sensitivity mandates appropriate caution in choosing whitespot-free fish: ie, not buying from a shipment with any infected individuals. However, 2 of the fish I purchased had what may have been internal parasites due to their bellies getting flat abnormally fast after feeding, which flubendazole appeared to cure.
Either way, as with all fish, a lengthy quarantine of at least 3 months in a well-maintained, low-stress quarantine setup would be well-advised. Furthermore, because these fish are wild-caught, they may also come in with either undernourishment issues or additional diseases not forewarned above - all of which a quarantine setup is the ideal place to fix.
Appropriate caution must also be exercised when transporting the fish for any reason: as is the case for many catfish, their pectoral and dorsal fins have sharp spines. The ends are sufficiently sharp to be capable of puncturing plastic transportation bags (I have witnessed such firsthand while purchasing this species), and although not life-threatening, a sting from these spines will throb, swell, and hurt excruciatingly for several hours thanks to the venom within the spine mucus (because of this, I would recommend avoiding direct handling if at all possible).
Furthermore, the serrations on the spine will almost always get snagged in a net, which attempting to remove can be dangerous to the fish. Although my own removal attempt has not caused any trouble to the stuck fish beyond a slightly beaten up pectoral fin, I have heard of cases where either the whole fin had to be ripped off or the net cut off with some still left around the spine, both of which ended in the death of the fish due to infection.
Ultimately, the safe way to catch and transport these fish is with non-snaggable catching equipment (such as a clean long-handle mesh strainer) into a solid non-puncturable vessel (such as a bucket). As alluded to, however, pet stores will often use risky standard nets and bags. I would recommend bringing your own catching equipment (that can fit in the store's tank) and transportation vessel for them to use in order to minimize risk.
Required Setup and Maintenance:
Once the fish have been quarantined and found to be in good health, they can of course be moved to a permanent home.
Water chemistry requirements may be somewhat ambiguous. I have seen recommendations for up to 268 mg/l of hardness, but have also seen a recommendation - explicitly stated to be from the keeper's experience - that the fish fare poorly in hard water and that hardness shouldn't be higher than 178 mg/l or so.
Because my water is only 137 mg/l hardness I can neither vouch for or against these recommendations, but I would advocate the potential need for caution if your water is harder than 178 mg/l: as with reported variations in size and growth rate, differences between morphs may play a role in tolerance of hard water.
Water quality needs to be kept high at all times or the fish will have stunted growth and its associated health problems together with barbel loss. NO3 should not be allowed to exceed 5 mg/l: consequently, weekly water replacements (with dechlorinator if needed) that keep the NO3 at or under 5 mg/l are necessary, with a precise routine that will vary from tank to tank.
Temperature should be slightly colder than the average tropical tank. I have found recommendations from other keepers to be within ranges of 20-26 Celsius as opposed to the 24-28 Celsius range most tropical tanks are heated to, and my own experience is broadly in accord with this: I have had fish live within this whole range of temperatures for several months to years appearing to do well on all accounts.
This slightly colder temperature also means that a heater may not be required for all fishkeepers outside tropical climates, depending on ambient room temperature.
I have found that - at least compared to substrate-free, low-flow setups with less decor - this species requires more environmental complexity to thrive. Specifically, I believe the difference between getting the fish to thrive or not comes down to inclusion of the following in said environment:
-Fine, smooth sand substrate: for example, I have had success with silica pool filter sand. This is preferable to rougher choices such as play sand/gravel/plant soil because its smooth texture will not wear down the long, sensitive barbels of the fish, as well as to a lack of substrate which seems to make the fish continually on edge (likely due to its difference to the natural habitat of the fish).
Additionally, sand with a brownish color is best because it again bears more resemblance to the fish's habitat. I have seen reports of this species wash out on lighter sand as well as darken up on darker sand, neither of which are desirable because of the long-term stress of the attempted tone change compared to being matched with their natural habitat color.
-A mix of hiding spaces and open spaces. Although most individuals of this species spend most of their time out in the open, they need to feel sufficiently secure to do so: by having a number of hiding spaces alongside their required open swimming spaces, they know that there is plenty of safe space for them to go if they want to, and therefore become more active.
Easily available at any pet store that sells fish, synthetic hides/logs are an ideal way to provide the desired hiding space. Attached are images of my 2 tanks with this species for examples of what I find to be working.
-Strong current, although with spots to rest. As might be expected from its slightly colder than average temperature requirements, this is a riverine species and therefore needs replication in the aquarium of such an environment.
From my observations, providing such flow increases the activity levels of the fish. They may possibly be compelled to swim against the current as they would in nature, and therefore be more active than if there was no current to swim against.
A specific product I can recommend to create the flow required is the Sicce Voyager 4. This powerhead creates 6000 liters per hour linear flow: I have found this amount is needed to create the sufficient amount of flow in my 473 liter aquarium, but will need to be upscaled appropriately for more voluminous tanks.
Ideal positioning would be near the surface and on a slight upward angle to create oxygenating surface agitation while simultaneously providing undertow at the bottom for the catfish.
-Possibly subdued lighting. Technically I have not had to use this in my pictus catfish setups (I have noticed no difference in daytime activity in my experiments with different lighting), but it is reported by multiple keepers as a necessity for good daytime activity, therefore it should be at least noted as a possible requirement.
Optional additions that some keepers may want for the aesthetic value are driftwood, smooth rocks, and plants: I have all of these with my catfish and although I haven't seen the catfish make use of them, they do no harm to the catfish.
The only plants I have kept with these fish are fake plastic plants, but live plants that can handle the current, colder water, and possibly subdued lighting needed by the fish have been reported as safe additions by other keepers.
Feeding:
Carnivorous and not picky at all. I have found all the following meaty foods to be eaten without hesitation:
-Sinking carnivore granules
-Thawed frozen bloodworms
-Thawed frozen brine shrimp
-Thawed frozen mysis shrimp
-Thawed frozen sliced krill
-Thawed frozen tubifex worms of an appropriately large size
-Thawed frozen mussels
-Thawed frozen calamari
-Live earthworms
-Lawn grubs
-Crickets and grasshoppers
-Superworms
My recommendation would be a pellet staple as part of a varied diet including as many of these items as available (of course, with appropriate precautions taken for collection of live food). Take care not to overfeed as this species will eat enough at one time to greatly bulge its stomach if fed enough to do so - in fact, adults only need to be fed every few days.
Behavior and Tank Mates:
My experience with the behavior of these fish has been that they will spend most of their day visible and somewhat stationarily swimming against the current, but will have occasional greater bursts of speed back and forth across the length of the tank that will cause them to hit the decor and injure themselves if space is insufficient (hence necessitating their need for such a large tank). However, if very small individuals between 30-70mm in length are purchased they are likely to spend much of their time hiding during the day - this has been my experience with individuals this size, and I suspect those particular individuals will become more active as they get larger, which is more in line with the above described active behavior of my 80-100mm individuals.
It is a commonly held belief that this species is a schooling fish which should always be kept in a group of at least 5, however numerous anecdotal reports also exist of individuals purchased together as a school splitting apart, holding a territory in their tank, and being sufficiently intolerant of conspecifics within it to fight them away. My experience with 2 different purchases of 5 has shown both to be the case in both groups at varying times - in fact, it has also been reported from keepers besides myself that the schooling and splitting can vary over time!
At present I would not feel comfortable assigning a cause or set of causes to such variable and contradictory behavior given the numerous differences in the various tank setups it has been reported from. Unless further observations reveal possible causes, the average fishkeeper can do little more than be aware of the possibility and would be best advised to buy at least 5 in the event that the fish need the company.
The first rule of choosing fish that can go with your pictus catfish: don't get anything that they could eat! Thankfully most sources sufficiently stress this, but there are a notable minority I have seen which downplay its importance by marking these fish off as smaller-mouthed scavengers.
This is, unfortunately, misinformation. They may look like they have small mouths and act as scavengers, but their mouths open to a far larger size than when closed and any fish that fits will eventually becomes food in the closed system of an aquarium - giving this species a well-earned reputation for devouring bite-size species of livebearers, tetras, danios, and barbs.
The converse is also true: although pictus catfish may be predatory, they should not be kept with any fish large enough to eat them given their small size (for example, larger species of predatory pimelodid catfish that are also popular in the aquarium). Besides the risk to the fish, I have found that this species is most active when it is one of the largest species in the tank - probably thanks to instinctual fear of larger relatives that would eat it in the wild.
Besides the obvious of appropriately-sized fish, another appropriate consideration would be fish that can handle both the environment and the catfish. Specifically, this means they would have to come from similarly cooler, flowing water, and also be unstressed by the activity and barbels of the catfish.
The latter means slower-moving popular fish such as goldfish or cichlids would be inadvisable as tank mates, and as the latter are also more aggressive fish their exclusion from a pictus catfish tank is merited further despite their popularity.
Species I have found to work, or have been told work by multiple keepers, are as follows:
-Smallscale archerfish (found to work). These fish also enjoy current and slightly colder water, and as they live at the top of the tank they are always out of the way of the catfish.
Just be aware that both fish will have to be purchased at the same size if the archerfish aren't to eat the catfish. I almost had a trio of newly introduced 30-40mm specimens eaten by my existing 100mm archerfish (thankfully I could catch them out of the tank in time, and learned my lesson with no losses).
-Chalceus. Works for the same reason as the archerfish.
-Botia loaches that prefer slightly colder temperatures (found to work). Works for the same reasons as the above.
-Insectivorous, non-nippy sharks and barbs too large to eat (such as roseline sharks, found to work). Same again as above and they may also have a dither fish effect.
-Other species of carnivorous catfish that match environmental needs: for example, some Synodontis catfish, some doradid catfish, some plecos, some North American catfish, and some bagrid catfish.
-Possible: Pumpkinseed sunfish. I have seen this species in the wild in similar conditions to P. pictus and intend to try it as a tank mate for my P. pictus - whether it works, or not, will be reported when it is tried.
Extra Information:
There is a 2016 study[1], claiming the pectoral fins of this species are touch-sensitive and useful for navigating on the bottom of water bodies, but I have always observed my P. pictus holding their pectoral fins up off the substrate - only ever unintentionally touching the bottom with them.
The difference may have to do with the fact that the fish in the study were only in very small holding tanks that were bare, not in an appropriately sized and decorated tank.
Reference:
[1] Hardy, Steinworth, and Hale (2016). "Touch sensation by pectoral fins of the catfish Pimelodus pictus". Proceedings of the Royal Society B. royalsocietypublishing.org/doi/10.1098/rspb.2015.2652#d1e913
