Article © Shane Linder, uploaded January 01, 2002.
On this page we will finish up our tour of the bagrids with a look at the genus most commonly imported for the aquarium trade. The genus Mystus (Scopoli 1777) is a diverse group of fishes that can be found as far west as Turkey and as far east as the island of Borneo. From north to south the genus ranges from the icy waters of Siberia to the steaming jungles of Java. The majority of Mystus, however, are found from India to peninsular Southeast Asia. Nearly all of the Mystus catfishes make an excellent addition to the tropical aquarium. They are very active, yet peaceful, and all Mystus catfish are very hardy.
Before we get started, it is necessary to discuss the taxonomy of Mystus as it is in a complete state of disarray. There is even confusion over what the name Mystus means. According to Innes Mystus is derived from the Latin mystax meaning "whiskers" (although in my Innes edition (1966) the photo is not a Mystus, but a South American Pimelodid). Axelrod's Handbook of Tropical Aquarium Fishes states that Mystus means "mystic". Innes was actually closer to the truth. Mystus was first used by Belon in 1553 to describe all fishes having barbels. As you will see though, Axelrod's definition may be a more accurate description of these fishes.
In the past, many Mystus species were described without reference to important quantitative data such as gill raker and vertebral counts. Add to this the fact that many species lack a holotype (A fish chosen as "the" representative of the species. All later finds are compared to this single fish to see if they are the same species). To compound the problem, the genus has been through 220 years of taxonomic changes and revisions. All of this causes quite a bit of confusion, but it gets even worse! There are two schools of thought on what fishes should be included in Mystus. Many Asian authors follow Mo's splitting of the genus into Mystus and Hemibagrus. Western authors, for the most part, do not follow Mo's revision. So what is the problem?
In 1994, Tyson Roberts restricted Mystus to eight species. If you follow Roberts, (Roberts does not accept Hemibagrus) that leaves over 50 species of Bagridae without a genus! This series on Bagrids follows Mo's revision. For consistency, we shall continue to follow Mo, but will also accept Robert's definition of Mystus since nearly all authors agree that Mystus, as presently understood, is poorly defined. This leaves Mystus in a state similar to that of the American cichlid genus "Cichlasoma". The eight accepted Mystus species, according to Roberts, are: M. pelusius (Turkey, Syria, Iraq, Iran), M. bleekeri (Pakistan, India, Bangladesh), M. cavasius (Pakistan, India, Burma, Nepal, Sri Lanka, Thailand), M. rufescens (Burma), M. albolineatus (Thailand, Cambodia), M. bocourti (Thailand, Cambodia), M. rhegma (Thailand, Cambodia), and M. singaringan (Malaysia, Indonesia). This breaks the old Mystus into Hemibagrus (about 28 species), Mystus sensu stricto (eight species), and leaves the remaining 23 as "Mystus" since they have yet to be assigned to their future genera.
OK, now you are wondering, "How does all this complicated taxonomy affect me as a hobbyist?" The answer is that it affects you in many important ways. If you want to answer important questions like, "How big will this fish get?", or "What water chemistry should this fish be kept in?" you need to at least be able to find out what species you are keeping! Let's take a look at some of the more commonly imported Mystus and "Mystus" catfishes.
Perhaps the most commonly imported "Mystus" is the Asian two spot catfish (aka, Asian clown catfish, pink pim, twin spot catfish). Before discussing the captive care of this beautiful catfish, lets look at its taxonomic history. This fish presents an excellent example of how taxonomic complications can be a problem for the hobbyist. The Asian two spot was first described as M. bimaculatus by Volz (1904). In 1913 Weber and de Beaufort placed M. bimaculatus as a junior synonym to M. micracanthus. It is likely that Weber and de Beaufort confused the triangular caudal peduncle spot of M. bimaculatus with the similar spot on M. micracanthus. This mistake was to become the source of many problems for the hobbyist.
In 1840, Valenciennes described a new Mystus and named it M. nigriceps. However, the holotype for M. nigriceps later turned out to be a specimen of the fish normally identified as M. micracanthus. Therefore M. micracanthus (Bleeker 1846) is a junior synonym of M. nigriceps (Valenciennes 1840) since the name M. nigriceps pre-dates M. micracanthus. Smith (1945) treated M. nigriceps as a junior synonym of M. cavasius. The "lumping" of M. nigriceps and M. cavasius was again formalized by Dutt et al (1982). Are you confused? Here is the synopsis. If we accept all of these changes then: bimaculatus = micracanthus, micracanthus = nigriceps, and nigriceps = cavasius. Therefore the Asian two spot is properly M. cavasius. Never mind that the Asian two spot looks very different than these other catfishes and comes from a very different habitat. Until this taxonomic nightmare is sorted out, I think hobbyists should refer to the two spot as "Mystus" bimaculatus. Although this is not a valid scientific name, it clears up any confusion that may be caused by using the fish's proper scientific name.
Now lets look at the problems that this has caused for hobbyists. All current aquarium books refer to the two spot catfish as "M." micracanthus. I believe that this problem must have started with Asian exporters. These fish pass through many hands between local fisherman who catch the fish and the final exporter. Imagine this: the exporter receives these fish and dutifully attempts to identify them for export. Having an older book, he identifies these fish as "M." micracanthus. He has never met the peoples that caught these fish originally so he looks down the page for some mention of the fish's habitat. The book mentions that "M." micracanthus is found in brackish waters. The importer then boxes these fish up with other Asian brackish fishes such as gobies and puffers and ships them off.
The problem is that the two spot is not a brackish fish. "M." micracanthus is only found in blackwater swamps. The fact that so many survive importation and holding in brackish tanks is a testament to their hardiness. A friend of mine, Ng Heok Hee, has collected these fish in their natural habitat in Sumatra. The water is coffee-colored from tannins and the pH is very low (around 4-5). The substrate of these swamps is normally very peaty. Heok Hee notes that collectors must be careful entering the water because it is so acidic that it causes open cuts to sting. The captive care of "M." micracanthus should reflect their natural habitat. When kept under these conditions, the fish turn a beautiful deep red-brown. They can be kept with other blackwater fishes from West Africa, South America, and Asia. They are diurnal and thus can be enjoyed even when the tank lights are on. Although they are certainly capable of eating small fishes, I have never seen them do so. In fact, I once placed a dozen 1/4" kribs (Pelvicachromis pulcher) in a tank with four three inch "M." micracanthus. Two months later all twelve kribs were one inch long and very happy.
Another commonly imported "Mystus" is the pearl catfish ("M." armatus). This fish comes from India, Burma, and Bangladesh and reaches a length of just over five inches. Reports of this species from Pakistan and Sumatra are suspect. The pearl catfish, unlike most Mystus, exhibits high intraspecific aggression. This can be curbed by providing numerous hiding places and keeping one male with three or more females. Interestingly, the dominant fish is not always the male. In one of my set ups the male dominates the tank. In another tank, it is the largest female that rules the tank. Missing barbels, torn dorsal and adipose fins, and serious scratches are all the norm. Amazingly though, I have never seen even a seriously wounded "M." armatus succumb to any infection. These fish will not only fight with each other, but will eat any other fish that they can fit into their mouth.
"M." armatus is also the only "Mystus" catfish for which there exists a published spawning report (Garside, 1985) that did not involve the use of hormones. Male "M." armatus, like all other Mystus, possess a distinct genital papilla just fore of the anal fin. Three females and one male were placed in a heavily planted tank (including floating plants) with a pH of 6.8 and 3-4 DH. A large bog log had been added recently and the water was stained brown. No filtration or aeration was used. A 25% water change that evening dropped the tank's temperature from 76F to 70F. The fish spawned that night scattering thousands of eggs throughout the aquarium. The vast majority of eggs were lost to fungus (unfertilized?). The fry were raised on brine shrimp and hard boiled egg yolk. Garside (1987) later wrote that the key to spawning these fish is large scale water changes, planting large quantities of Indian fern, and violent aeration (although this last condition seems to contradict his earlier report). He theorized that all three conditions provided simultaneously trigger spawning by recreating monsoon-type conditions. Interestingly, Rao and Chattopadhyay considered the genital papilla of the male as a diagnostic characteristic for this species. It is likely that the holotype is a male and this led them to believe that all "M." armatus could be identified by what they referred to as an "anal papilla".
Last, but not least, are the various striped "Mystus" catfishes. Until recently these were all treated as a single species "Mystus" vittatus. Roberts (1992) separated the Southeast Asian striped species from "M." vittatus. Of the four Southeast Asian striped "Mystus", only one species, "M." mysticetus, is commonly imported. This fish is diurnal and very active. It may eat smaller tankmates. These fish reach a maximum length of four inches and do best in neutral to slightly soft acidic water. They are active swimmers and seem to do better in larger tanks where they can move about freely.
While Roberts' (1992) revision of the Southeast Asian striped catfishes made their identification much easier, no one has yet to revise all the striped Indian species that fall under "M." vittatus. At least two of these are imported with some frequency. One is the true Indian "M." vittatus. In order for Roberts to sort out the Southeast Asian species he had to first define the true Indian "M." vittatus, and his fish is imported. "M." vittatus is somewhat nocturnal but will venture out frequently in a heavily planted tank. They reach a maximum size of about three inches and are not particularly predatory. One interesting note is that according to Bhatt "M." vittatus reach breeding maturity in their first year of life. After having raised many of these fish from around 1/2 inch to maturity, I can say that Bhatt must have interpreted their life cycles incorrectly. The sexually mature fish that he measured in August were not fish that had hatched the previous August, but must have been from the year before and thus had reached sexual maturity in their second year of life. Because Bhatt believed these fish mature so fast he noted that their life span was only 2-3 years. I believe that these fish do not reach maturity until their second year and their life span must be much longer. My oldest specimen is five years old and going strong.
The final striped Indian "Mystus" is an undescribed dwarf species. These fish look superficially very similar to their larger cousin "M." vittatus. One simple way to tell them from juvenile "M." vittatus is to look at the adipose fin. In the dwarf "Mystus"" it is very short while that of "M." vittatus is greater than the width of the dorsal fin. After three years, my dwarves have only reached a length of just over one inch. They are happiest in schools and do not do well when kept alone. Their behavior is quite different from most other "Mystus". The entire group will roam the tank in a manner similar to a school of Corydoras. When frightened they all attempt to hide under the same piece of cover. Most "Mystus" species each stake out their own cave and each individual retreats only to its own lair. Like most "Mystus", these catfish seem to prefer a heavily planted tank with neutral to slightly soft and acidic water. Although they are undescribed, I would like to suggest the name "Mystus cf. vittatus dwarf" for use in the hobby to avoid confusion until they are properly described.
This brings our brief tour of Bagridae to a close. I have certainly only scraped the surface of this large and fascinating family about which so little is known to the hobby. On the next page we switch gears and look at the care and spawning of those oh-so-ugly, but lovable, frog-mouthed catfishes of the family Chacidae.
Do not read this if you have had your fill of taxonomy! I do fill obligated to finish answering questions from the last page though. I was asked why M. singaringan and M. rhegma were not included in Mo's revision of Bagridae. M. singaringan (Bleeker 1846) has been referred to by most authors since 1864 as M. nigriceps. Since the original description of M. nigriceps was based on the species known as M. micracanthus, M. micracanthus became M. nigriceps (see above). What was to become of the catfish known as M. nigriceps since M. micracanthus had taken its name? It turns out that this fish (the ex-nigriceps) had been described as M. macronemus, M. singaringan, and M. heterurus. Roberts (1994), as first revisor, selected the name M. singaringan.
M. rhegma was described by Fowler in 1935. Mo did not include this species as it appears that he never consulted any of Fowler's works (they are not listed in the bibliography). Mo also left out, not including species described after 1991, "M." atrifasciatus (Fowler 1937), "M." argentivittatus (Regan, 1905), "M." olvillii (Gunther 1874), "M." hovmoelleri (Smith 1931), "M." mica (Gronow 1970), and "M." trachacanthus (Valenciennes 1839). bagrid taxonomy is a far more time consuming hobby than bagrid husbandry!
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