(4) Predatory Fishes

NOTE:

To a greater or lesser extent, all these fish eat other fishes and should only be combined with other fishes with care. Also, many require live food, at least until they can be weaned onto a substitute. Prospective owners should ensure they can supply the appropriate foods before buying any of these fishes.

(4a) Garpike (Lepisosteus spp. and Atractosteus spp.)

Garpikes are large, predatory fishes but are well suited to aquarium life. They are essentially peaceful and pretty inactive so long as they are kept with suitable tankmates. A garpike can only eat animals they can swallow easily. Consequently narrow, smooth fishes like minnows and livebearers are likely targets. Deep bodies fishes (like perch or cichlids) are ignored if they are too big; as are spiny fish like catfish. For example, a small garpike below 45 cms (18 inches) long is perfectly safe with medium sized cichlids (like convicts Cichlasoma nigrofasciatum). Adults, which can range from 60 to 300 cms (2 to 12 feet) mix well with large catfish like channel catfish (Ictalurus spp.), big but peaceful cichlids like the jaguar cichlid (Cichlasoma managuense). Garpike also mix well in moderately brackish water aquaria, where they coexist happily with monos, scats, Arius catfishes, archers and large sleeper gobies.

The alligator garpike Atractosteus tristoechus is the largest garpike, growing up to 300 cms (12 feet) in the wild. Of all the garpikes, this is the species most frequently seen in brackishwater, and also enters marine water. The other garpikes are freshwater fishes that occasionally enter brackishwater. The alligator garpike cannot really be recommended as an aquarium fish because of its size.

The spotted garpike Lepisosteus oculatus can tolerate marine conditions briefly, but should be kept in freshwater or brackishwater conditions with a salinity below about one-half that of seawater (specific gravity below 1.010). It is a much smaller animal, rarely exceeding 40 to 50 cms (16 to 20 inches) in captivity. One of prettiest of the garpikes, it has a lovely brassy or silvery body with bold brown markings. The slender or longnose garpike (Lepisosteus osseus) is somewhat longer but less bulky in shape and has distinctive, needle-like jaws. Keep in the same way as other garpike, but young individuals appreciate smaller morsels than the other gars, such as bloodworms and mealworms (insect larvae).

Some fishkeepers recommend moving gars kept in brackishwater into freshwater periodically (once a year or so). This seems to be good for the gar, keeps diseases and parasites to a minimum, and may even trigger spawning (thanks to Rod Harper for this).

(4b) Columbian Shark Catfishes (Arius seemani)

Columbian shark catfishes are among the most desirable of all aquarium fishes. They are big, powerful looking animals with sleek silver bodies and active natures. Although distinctly predatory, they are not aggressive and on the contrary, can be bullied by fishes like cichlids. Arius seemani (sometimes, incorrectly referred to as Arius jordani) lives in fresh and brackishwaters, and sometimes enters the sea. In aquaria hard, alkaline water is critical, as is a powerful filter and good oxygenation. A specific gravity of 1.005 to 1.015 is about right, with regular fluctuations within this range being beneficial to health. They need a big, roomy tank with a powerful motorised filter.

Some Arius have been bred in captivity, but not this species. This is presumably because of some missing trigger, but what that is is not known. The small size of Arius seemani should mean that captive breeding is possible. Both sexes reach about 30 cms (12 inches) in length, but females are noticeably stockier and develop swollen pelvic fins when mature. Many Arius mate in summertime at sea, and being a mouthbrooder the male carries the few large eggs until they hatch, depositing the young fish in rivers.

Arius appreciate a dark aquarium with a definite current. Decorate the tank with a thin layer of sand or gravel for burrowing in, with large rounded boulders to make caves and lairs. Keep in schools of three or more. Small specimens are adaptable, but above 12 cms (4 inches) they become distinctly restless, perhaps feeling some migratory drive. Fluctuations in salinity and strong water turnover are essential at this stage to settle the fishes down. Compared with other catfishes, these fish are not nocturnal and swim constantly, often into a part of the tank with a steady flow.

Shark catfishes are so named because of their powerful, sleek shape. They swim gracefully, something not easily appreciated in a small tank. Arius seemani has venom glands in the base of the dorsal fins, and should therefore be handled with care. Arius seemani also possess glands in the mouth capable of secreting anticoagulants, which they use when hunting. More obvious to the aquarist are the continual drumming noises they make. These are possibly used for echolocation and for communication between fishes in the school.

A local name for Arius fishes in South America is crucifix fish. When cleaned and suitably painted, the skull of this fish is sold as curio. On the underside a crucifixion scene can be imagined, and on the dorsal surface a bishop raising his arms in a blessing.

The name of the genus, Arius, signifies that the fish is 'of the war-god Ares' not altogether unfitting considering their impressive adaptations to the predatory lifestyle! All in all these are fascinating fishes.

(4c) Sleeper Gobies (family Eleotridae)

Although similar to the gobies, sleepers lack the fused pelvic fins (the "sucker" on the belly). The commonest sleeper goby traded, Dormitator maculatus, is sold as a pretty little fish that barely hints at the 25 cms plus (over 10 inches) monster it can potentially become. It is essentially a predatory fish, but will accept chopped up mollusc and crustacean meats as well as fresh white fish. It is found along the entire east coast of tropical South and Central America in brackish and marine water. Occasionally it enters freshwater, but it is much healthier in water that has some salt added.

 When small the colouration is rather plain, with an overall pale brass coloured body with dark bands on either flank. With age a colourful pattern of red and blue spots develop, which the fish seem to be able to adjust. Like many sleepers, the eye tends to have a "glassy" look, as if the fish is unconscious. Hence the name?

 Another predatory sleeper is the crazy fish Butis butis. Growing to around 15 cms (6 inches) this fish is rather more territorial than the common sleeper. It is handsome if sombre, being various shades of mottled brown in colour looking rather like a bullrout. Basically nocturnal this fish will feed on any invertebrate or fish it can overpower. Found in fresh, brackish and salt water it will adapt to most conditions although some salt is recommended (specific gravity 1.005 to 1.015). This fish gets its common name for its habit of perching upside down beneath overhanging rocks or pieces of wood, and sometimes in midwater.

(4d) Siamese Tiger Fish (Datnoides spp. )

There are two similar species imported, Datnoides microlepis and Datnoides quadrifasciatus. Both reach about 30 cms (12 inches). Similar in form to snappers, they have basically silvery white, with black stripes when young, tinting to brown or brass when older. The mouth is large and capable of swallowing fishes of about one-quarter their size.

These are peaceful but predatory fishes best kept among their own kind in a fair sized (over 90 cm, 36 inches) tank. A specific gravity from 1.002 to 1.005 suits them well, with thick plantings of Vallisneria and bamboo stems in which to lurk. While they ignore flake or pellet foods, they can be weaned off live fishes and shrimp and on to earthworms, bloodworms, raw meat including liver, and frozen crustacean and mollusc foods.

(4e) Ropefishes (Erpetoichthys calabaricus)

The ropefish or reedfish, Erpetoichthys calabaricus, is a relative of the better known bichirs (Polypterus spp.). It is a very elongate fish, with heavy scales like a garpike, and a series of small dorsal fins along the back. The pectoral fins are small, and the pectoral fins are absent. They can grow to 90 cms (3 feet) in length, but remain long and eel-like.

Ropefishes are essentially freshwater fish and do not need salt. They prefer soft or neutral waters, and only moderate hardness. They are common in the low salinity parts of the Niger delta. Keep these fishes in a community of other African fishes too large to be eaten and they do well; a specific gravity below 1.005 will allow the tank to be well planted.

Although not yet bred in captivity, they are distinctly social and should be kept in a small school (3 to 6 individuals) with plenty or rocks and caves. They are very good at escaping from tanks, and even into filters, so care should be taken to ensure the fishes are secure.

(4f) Freshwater Moray Eel (Echidna rhodochilus)

Although traded as freshwater fishes, these are brackishwater fishes best kept with other hardy brackish water fish like monos and scats, and can adapt to marine conditions as well. A specific gravity range of about 1.005 to 1.010 is acceptable for long term health. As with other moray eels, these fish are predators, enjoying small fish and crustaceans, but they are otherwise peaceful. A lair of some sort is needed, such as a flowerpot or cave built from rocks. Providing they have adequate space, morays are tolerant of one another.

Morays may need to be trained to accept dead food. One way is to attach food items to cotton thread and dangle this in front of the eel, rather as if you were fishing with rod and line. Move the bait about a bit, and the moray will generally catch on. If the moray refuses dead food for a while, earthworms and river shrimps make good treats.

(4g) Bullrouts (Nothestes robusta)

The bullrout is rarely imported and has little to recommend it as an aquarium fish. Besides being inactive during the day and highly predatory, it has venomous spines in the dorsal fin.

The bullrout is variable in colour and pattern, but usually shades of brown. It grows to about 30 cms (12 inches). It is found in fresh, brackish and marine waters around Australia and will adapt to most water conditions. A specific gravity of about 1.010 is adequate. Although it prefers live foods (worms, fish and shrimp) it can be weaned onto chunks of meat and frozen foods.

(4h) Flatfishes and Soles (Achiurus spp. and Brachirus spp. )

Flatfishes are only rarely available and do not make easy fishes for the aquarium. The main problem is feeding, since they are exclusively carnivores, and only really thrive on live foods like bloodworms. With time, they can adapt to pellets or flakes, but will need live foods initially. Even once feeding, they are slow moving, and may not compete with more active fish.

All flatfishes appreciate a soft, open substrate such as sand. They burrow most of time, and some species are nocturnal (bear this in mind when feeding). A few flat stones can be added, but plants are unnecessary. Flatfishes are very adaptable to different salinities (a specific gravity range of 1.005 to 1.010) but demand excellent filtration and plenty of oxygen.

(4i) Spiny Eels (family Mastacembelidae)

Spiny eels are small to large eel-like fishes from Africa and tropical Asia which spend most of the day buried in leaf litter and sand, emerging at night to hunt for worms, small fish and crustaceans. A few species regularly turn up in aquarium stores. All require similar conditions: a well filtered aquarium with a soft substrate, quiet tankmates, and a good supply of live or frozen foods. Properly cared for they prove to be easy to tame and friendly. Spiny eels appreciate warm water (up to 82 degrees-C), a neutral pH and moderate hardness, with a little salt (a specific gravity of 1.002 to 1.005).

The larger species, such as the tyre-track eel (Mastacembalus armatus) and the fire eel (Mastacembalus erythrotaenia) reach 75 to 100 cms (up to 3 feet), are essentially solitary when mature, and need spacious aquaria. Adults readily eat small fishes.

Smaller species, like the 30 cm (12 inch) peacock eel Macrognathus aculeatus are less difficult to keep and can be combined with other fishes.