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Related FAQs: Marine Catfishes

Related Articles: Ariid Marine Catfishes, Freshwater Catfish Families

/The Conscientious Marine Aquarist

Mostly Marine & Venomus: Catfishes of the  Family Plotosidae

Bob Fenner

  Plotosus lineatus

Only a pet-fish tenderfoot considers catfishes as "bottom sucking scavengers". Aquarists in the know are aware that the living catfish Order Siluriiformes is overstuffed with bizarre species that engage in all manner of lifestyles. From tiny half inchers to several hundred pounds, some are lowly cleaner-uppers, others top predators. There are even parasitic catfishes; by some definitions, ones that are parasitic on humans!

Can you name a body of freshwater that doesn't include them? Catfishes are found worldwide in tropical to temperate freshwaters. But did you know there are saltwater catfishes too? There are; some are sold as brackish to tolerant-of-hard-alkaline freshwater specimens. Don't try putting these cats on clean up detail; they are not scavengers and will do poorly left to survive on leftovers or recyclables. What's more these fishes are extremely venomous, and will render a nasty poisonous puncture if handled carelessly.

Classification: Taxonomy, Relation With Other Groups

There are several freshwater catfish families with members possessing venom-bearing spines in their dorsal and pectoral fins; and even another principally marine family, the Ariidae, besides our subject group. Having been punctured by the worst of them over my thirty years in the trade, the Plotosids are number one in the hurt department. They look so beautiful and unassuming, but these cats are to be reckoned with. Both Burgess and Nelson state that their stings might be fatal.

The eel-tail, coral, stinging or Tandan catfishes, family Plotosidae ("ploh-toe-sih-dee") are aptly named ("plotos" means swimmers). Their tapered bodies with pointed or bluntly rounded tails are almost in constant undulating motion. Nelson notes some thirty two species in nine genera, about half fresh, half marine. Freshwater species hail from Australia and New Guinea only.

Euristhmus lepturus (Gunther 1864), the Long-tailed Catfish. Indo-West Pacific. Northern Australia, New Guinea. To eighteen inches in length. This one in the Singapore Aquarium's exhibit of Dangerous/Venomous Fishes.

Plotosus lineatus (Thunberg 1787), the Striped Eel Catfish. Indo-Pacific; Red Sea to Micronesia. Only tropical reef catfish species. To a foot in length. Dangerously venomous. Keep hands clear when netting, moving. This group in captivity.

Natural Range Found in the Indian Ocean and western Pacific to Australia, New Guinea and the Philippines. Found in the Indian Ocean and western Pacific to Australia, New Guinea and the Philippines. Here's a "marauding school" of Plotosus scouring the inshore sands in the Philippines.

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Size: 

Most individuals offered are ten to fifteen centimeters (four to six inches) in overall length. The species offered to the retail rarely exceed a foot in captivity, though some are recorded exceeding a yard in the wild.

Selection: General to Specific

This is actually a relatively easy group to sort through for viable specimens. Being naked (as opposed to armored, all catfishes lacking scales) the plotosids take a real beating if handled and shipped without care. Take a close look at potential buys; are their whiskers intact, all about the same length? Are the eyes clear and bright? Any puncture, scrape or red marks on the body? Any of these symptoms on any of the individual cats in the system is cause for concern and a signal to let them by.

Collecting Your Own 

Can be done, with care, if you're in the area. When small, these can be hand netted right out of a group. Utilize either a very fine or coarse mesh net to avoid entangling. If one gets caught in the net, clip it out with a tool. I'm not joking; do not touch plotosid cats with your hands, gloved or not. Their pungent dorsal and pectoral spines are supported by poison-generating epidermal tissue that packs a powerful sting. More about this below.

Environmental: Conditions

Not picky animals as far as water make-up goes, coral cats appreciate strong current and hiding spaces.

Habitat 

Broken to mixed bottoms, sand/gravel and coral/rock rubble. Often seen aggregated in flanks or balls on sandy bottoms; spawners lay eggs amongst rocks.

Chemical/Physical 

A good quality salt mix (pre-mixed for a day before use) of a consistent high or low range salinity is fine. Keep your eye on pH shift with the heavy feeding that goes with these fishes.

Biology/Other

The issue of envenomation. Speaking from first hand experience..., you do not want to suffer these fishes painful stings. Pain is immediate and excruciating. My last bout occurred while "putting away" a large incoming Philippine shipment. A carelessly dropped cat poked me under the fingernail while I tried to scoop it up with a net on the receiving table. Knowing what would ensue I told my cohorts to keep an eye on me, wrote down the name of the fish (Plotosus lineatus) in case I lost consciousness, and rushed off to the bathroom to soak the wound site in as warm/hot water as I could stand. Quickly heating the proteinaceous poison goes a long way to denaturing it; changing its structure, therefore reducing pain. If you get jabbed, I strongly suggest you do all the above and additionally be ready to make a trip for professional attention. I obviously survived, with just localized pain and swelling, and a great deal of angst.

One other interesting behavior mention; their sound production. These cats hum or buzz loud enough to be heard outside the aquarium. Listen closely when feeding.

Filtration

Need not be elaborate. However, the more circulation, the better. Need not be elaborate. However, the more circulation, the better.

Display 

The smaller species offered are only happy in a small group. Buy a small, odd number (3,5,7...) and introduce all at once. The freshwater members can be successfully kept singly.

Behavior:

Territoriality

The larger members of the family may be testy toward members of their own kind as they grow bigger. all will gladly swallow other organisms small enough to fit in their mouths. Other fishes knowingly give the plotosid cats wide berth. The larger members of the family may be testy toward members of their own kind as they grow bigger. all will gladly swallow other organisms small enough to fit in their mouths. Other fishes knowingly give the plotosid cats wide berth.

Introduction/Acclimation

Any technique works with these fishes. Big wholesalers check and ameliorate pH and salinity differences going from shipping to placing in their systems.

Predator/Prey Relations

Coral cats are non-specific invertebrate predators. Marine forms focus on interstitial (between substrate) fauna (i.e. various worm groups, crustacea, mollusks...). Freshwater varieties more insect- and piscivorous.

Other large fish-eating predators leave these catfishes alone; even when/where the species natural ranges don't overlap. Perhaps they recognize the folly of swallowing something with three stout venomous spines sticking out at oblique angles.

Reproduction, Sexual Differentiation/Growing Your Own:

Spawning records for P. lineatus state that this species spawns during the summer months, males constructing nests in shallow, rocky areas. The eggs are small 3-3.5 millimeter in diameter and guarded by the male for about ten days. Some Japanese public aquaria report captive spawning success for this species, feeding the newly yolk-absorbed young on freshly hatched brine shrimp.

Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes

All foods, pellet, frozen, fresh, flake are accepted greedily by healthy specimens. I suggest twice daily feedings, at least once with defrosted frozen food that can be easily be placed in a given open area on the bottom. They grow quickly when well fed and fade away just as fast if starved.

Disease: Infectious, Parasitic, Nutritional, Genetic, Social

Plotosid catfishes are unfortunately quite susceptible to the common parasitic scourges of marine aquaria, and doubly unfortunate in their intolerance to common aquarium therapeutics. Just like your experiences with "naked" freshwater cats, you will want to look to them first for signs of fish disease in the system and treat very carefully. Avoid copper and malachite containing treatments in favor of freshwater dips, lowering salinities (gradually... as long as other tankmates are euryhaline) and more novel modes (e.g. Quinacrine and other Quinone compounds).

Summary:

Provided you start with a clean, parasite-free grouping of the smaller Plotosus or a good individual of a larger species, stinging cats are a breeze to keep. Just keep metal and dye medications and your hands away from them. They're cute and comical appearing but deadly as Lionfishes to touch.

Bibliography/Further Reading:

Burgess, Warren E. 1989. An Atlas of Freshwater and Marine Catfishes, A Preliminary Survey of the Order Siluriiformes. T.F.H. Publications, Inc. NJ.

Fenner, Bob 1992. The Candiru, Vampire Fish. FAMA 12/92.

Jackson, Lee. 1995. An Australian eel catfish, Neosilurus ater. FAMA 9/95.

Nelson, Joseph S. 1994. Fishes of the World, 3rd. ed. Wiley & Sons, Inc. New York. p152-3,

Walker, Braz. 1982. The Australian glass catfish, Tandanus obscurus. FAMA 2/82.

  

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