#tankbusters

Warlord No. 49, cover dated 30 August 1975 with Tankbusters art by Jeff Bevan.

Usually they are described as 'living fossils' and as not having evolved very much - as though they were relictual. Rather the pressures of natural selection have stabilised these creatures, as rather perfect at what they do. The same applies to other ancient animals such as horseshoe crabs, tadpole shrimp, and lungfishes. As opposed to so-called living fossils that have no ancient, similar fossil relatives - such as the echidna; or that differ in important ways from what is known or sometimes assumed about their ancestors - such as the tuatara, the coelacanth, and the vampire squid; and those that are completely modern, such as the Komodo dragon.

The name 'garfish' is derived from an old, Germanic word meaning a spear, and it first applied to an unrelated needlefish, Belone. It is customary to refer to lepisosteids as 'garpikes' to distinguish them from their namesake; but of course, they are not related to the true pikes or esocids, either. Nor are they close allies of the pine characins, the ctenolucids, that are often called gars and appear in the aquarium yrade. All of the belonids, the ctenolucids, and the esocids belong to the main clade or 'family' of fishes, called the teleosts or true finfishes. The gar(pike) clade is related to the teleosts, but their last common ancestry with them is ancient indeed, and garpikes retain traits inferable for ancestral teleosts.

Garpikes are visually striking for their dense scales, which have a different composition from those of typical fishes; the latter have ledd hardened scales. One primitive trait of garfishes is that they can breathe air, although they are obligatorily aquatic. This is because the swim bladder of typical fishes - which is now used as their flotation device - is evolved from a lung, and not the other way around. Unlike gouramis, for example, the garpikes never had to invent a way to breathe air again, because they had never lost their ancestral ability to do so. Another ancient trait of the garpikes is that their tails are vertically asymmetrical. Although not to the same degree as in sharks, their vertebral column extends into the upper portion of their tail fin. Thus they have 'heterocercal' tails, unlike the 'homocercal' tails of most fishes.

Zoologists have traditionally considered garpikes to be members of a grouping named holosteans, that was considered, along with the bowfin, as a sort of primitive grade ancestral to the ordinary fishes, which are called teleosts. For decades zoologists have debated wether the bowfin is closer to the teleosts or to the garpikes; the name of Holostei refers only to the hypothesis that garpikes and bowfins are closely related. All the three clades together comprise the neopterygians, which are the only fishes in the original Pisces. (But the garpikes were misassigned as members of a teleost genus!)

Ancient members of the garfish group occupied broader niches during the Mesozoic, including well known shellfish crushers with deep bodies. Because of their bony scales, these fish are well known from he dorts of fossil beds that yield dinosaurs such as Iguanodon. However recognisable, almost modern type garpikes first appeared in the later Jurassic, and coeval with giant sauropod dinosaurs, plated stegosaurs, fierce allosaurs: flying pterodactyls; marine plesiosaurs and ichthyosaurs; and the once astonishing Archaeopteryx - which is now no longer the 'first bird', nor the most primitive. But during the same period of time that separates us from Archaeopteryx, the garpikes have changed little - a situation that is known as 'bradytely'.

Nowadays the garpikes have a Nearctic distribution that extends out into the Antillean archipelago; the latter is usually considered to be of a South American character, in most respects. But even during the Cenozoic, the garpikes had a wider distribution; for example they were fossilized in Germany, at the famous Messel Pit locality. It isn't really clear why this clade flourishes in North America, but went extinct on other continents

Garpikes have a similar superficial resemblance to the crocodile family, as they have massive scales, long toothy jaws, and a similar niche of hunting from a lurking position. Compared to true pikes, the garpikes have very rigid bodies, and this helps them to 'pass' for wood. Indeed they show a preference, in the wild, for associating themselves with tangles of wood in shallow water.

There a few species of garpikes and all of them are similar, although of course they differ among themselves in their precise niche, and their potential lengths. They are no longer traded as commonly as they used to be in Europe, and I have even seen small alligator gars offered for sale in the past. But probably the smallest of the living species, is the shortnose gar (Lepisosteus platostomus) from the Mississippi and Missouri river basins.

L. platostomus typically grow to about 60 centimeters to 24 inches long; but the species may grow to nearly half as long again. This is a species from backwaters and flow moving waters, where it waits near the water surface and hunts fish, amphibians, and insects. This species ambushes terrestrial prey from the water surface, and also functions as a scavenger. It is known to consume more amphibian and terrestrial arthropods as prey than other gar species sharing the dame habitat. Gars seize their prey using a sideways swipe of their heads during the lunge forwards, unlike similarly shaped teleosts which strike directly head on.

Shortnose gars inhabit seasonal climates with a cold season, but begin to spawn when the water temperature reaches 16 to 21 degrees centigrade. From this it may be seen that they are fine in what aquarists call a 'coldwater tank'; one that is unheated at a living g room temperature of 18 to 22 degrees. The species naturally experiences summer temperatures, that are equivalent to our 'tropical' tanks. They are unfussy about the water chemistry and can be thought to prefer broadly circumneutral waters. in the aquarium they should be given tangled wood to lurk around, and tall stem plants to hide among.

Garpikes are obligate carnivores that seize upon small fishes and similar prey animals. However, their gape is not extraordinary, and their craniofacial skeleton limits the size of the prey that they can take. Despite the usual folklore surrounding predatory fishes, gars will accept defrosted, meaty foods. And big, deep bodied tankmates should not be at risk; nor should those with diameters wider than that of the gar. Their conical teeth are plainly optimized for snapping at smaller prey,and as they occupy the upper water column they are easily compatible with many other big fishes. The problem is that even though it is a 'small' gar, even L. platostomus requires a large tank indeed, or an indoor pool.

Other than their differences in average sizes, the physical differences between the Chinese species in this complex are minimal. The recognition of several species that were formerly A. davidianus is widely accepted, but it is based on genetic phylogeography, forcing the recognition of important barriers to historical gene flow. It's still not sure how many species exist in the species complex per this criterion

The A. davidianus species complex is distributed in eastern, central, and southern China. A very similar related species, A. japonicus, is indigenous to Japan. There are a number of other Chinese species described other than A. davidianus, but they are all very similar animals. It is thought that all Chinese giant salamanders are capable of producing fertile offspring together, and similarly when crossed with the Japanese species.

Indeed introduced Chinese salamanders in Japan have hybridized with the native salamanders there. It is geographical boundaries that maintain all these animals as genetically distinct, and it's still unknown how many species of Andrias there are in Asia. The holotype populations of A. davidianus is native to waters of the Yangtze River basin. Other commonly recognized species in this complex are native to the Guandong, Jiangxi and Anhui regions of China.

The habitat of Asian giant salamanders is circumneutral upland streams with forest cover. Within these streams they fo not travel far from crevices between rocks, and caves in the riverbank where they lurk. These salamanders are primarily nocturnal and have a limited sense of vision, mainly detecting prey by sensing nearby changes in the water pressure that are caused by living animals and other moving objects.

Today the genus Andrias are referred to as the Asian giant salamanders, because they are today restricted to China and Japan. In the geological past species of Andrias were present in North America and Europe as well. It seems that they disappear from the European fossil recordwhen the climate cooled, as the Earth entered the Quarternary ice age. The youngest Western Palaearctic Andrias fossils are from the late Pliocene of the Caucasus region.

The famous discovery of a meter long fossil Andrias sp. in Germany, during the early 18th century, was initially misidentified as a fossilized human child, and described as 'homo diluvi testis'. At that time, living Andrias were unknown to Europeans, and although the identity of the fossil was soon suggested to be a salamander, it was not at first identified with its Asian cousins.

The nearest living relatives of Asian giant salamanders, today, are the hellbenders, Cryptobranchs, which are similar animals present in the eastern states of the USA. Some people think that there might be an unknown species of similar salamander, in the Trinity Alps of California. It has akso been suggested, though it is unconvincing, that tazelwurm sightings from Europe refer to an extant European Andrias species.

Asian giant salamanders and hellbenders form a clade called the cryptobranchids. Cryptobranchids seem to appear in the Palaeocene epoch, and the presence of the hellbender in eastern North America is a mystery, presumably involving prehistoric land bridges. Both Andrias and Cryptobranchus are slow moving bottom walkers, and suction feeding ambush predators.

Their skin has a folded and baggy appearance, because this increases its respiratory surface area exposed to the water. Although adult cryptobranchids have paedomorphic traits, which is common in aquatic salamanders, they do not have the external gill structures retained by so many other paedomorphic salamanders.

Asian giant salamanders are the largest amphibians in the world, and no fossil salamanders are known to be larger than are Andrias sp. The largest fossil salamanders are from Miocene strata, and they were themselves a species of Andrias, A. matthewi, growing to 230 centimeters. Andrias subsequently became extinct in North America

Chinese giant salamanders from South China are the largest, but they are now regarded as a different species from the archetypal A. davidianus. It is unlikely that their captive care would be significantly different. Some prehistoric stem amphibians were much larger, up to about 5 or 6 meters long, but their physiologies would not have resembled those of frogs or salamanders.

Unlike frogs, salamander size is not affected by seasonality in either precipitation or temperature. Yet neither major clade of amphibians, despite their diversity of species, has achieved the great body sizes that sharks, fishes, reptiles, and mammals have attained. Salamanders and frogs are thought to be limited in size by their method of gas exchange, which is across their hides.

A. davidianus is a subtropical amphibian, its optimal growth occurs occuring in water with a temperature of 15 to 21 degrees centigrade. Their feeding behavior was inhibited by water temperature lower than 8 or higher than 25 degrees, so high temperatures ought to be avoided. At low temperatures the adult salamanders become temporarily inactive for the wintertime, when the rivers run cold. Thus this species is unsuitable for tropical tanks, but it's temperature range matches that of an unheated but inhabited house in a climate such as that of Great Britain.

A. davidianus does not actually demand the sort of very cool water temperatures some people mistakenly believe they do, but a high dissolved oxygen content is important to them. The flow of the water should be vigorous enough to be visible at the water surface. Allowing the water to cascade down from the filter is one way to increase its dissolved oxygen content. The water should also be clear and well filtered. Normally it is said that the wild streams where giant salamanders live, have a pH of 6 to 7. However the pH in sampled stream habitats may also be as high as 7.7.

Their natural habitat of Asian giant salamanders has large boulders and a substrate of gravel. Therefore this species is well suited to inhabit a mountain stream biotope tank. Unfortunately they are predators of other motile animals, and able to ingest quite large prey. I have never heard of this animal being displayed in a mixed exhibit, other than in the moats of zoo enclosures. Needless to say these salamanders grow too large for most home aquariums

Sometimes it is said that these salamanders will drown if the water surface is not low enough for them.. Though they do breathe atmospheric air, they capable capable of swimming to the water surface to breathe. When they are stressed in the wild, these salamanders are known to retreat into the deeper water, so their water level does not need to be shallow, as long as they might access air.

T. semifasciata is a shark of the shallow depths along western North America. It is gregarious by nature, and large schools of leopard sharks are often encountered in bays, lagoons, and estuaries. This species is associated with both sandy and muddy bottoms, and rockier areas near kelp beds and rocky reefs. It is present in estuaries where the salinity approaches that of seawater, and the temperature there is stable, making these environments suitable for the gravid females and newborns. This species is reported from areas where the salinity is as low as around 20 ppt, or a specific gravity of 1.015, and rarely even 14 ppt, though salinities below 18 ppt are known not to be well tolerated by this species when it is for prolonged periods.

T. semifasciata is one of the so-called triakid sharks, although in reality the 'triakids' are merely a semi-natural or paraphyletic grouping, within the group of sharks known as carcharhiniforms. That is to say, Triakis and other so-called 'triakids' may be no more closely related to one another, than they are to the requiem sharks, the hammerhread sharks, or the tiger shark.

Wild T. semifasciata fortunately have wide environmental tolerances, and they can experience summer temperatures of 24 to 26 degrees centigrade, but not on a permanent, year round basis. A study of their metabolism found them adapted to tolerate temperatures of around 24 degrees, which befits their foraging in warm, very shallow environments during the summer months. Juvenile T. semifasciata, at least, prefer a cooler ambient water temperature of 17 or 18 degrees centigrade.

Mature individuals were found to prefer temperatures of 22 to 24 degrees, when they are aggregating in the summer and autumn seasons. At these higher temperatures, T. semifasciata are better able to metabolize their food, which is why they congregate and forage for benthic prey nearshore, during warm hours of the day. Sympatric rays with similar foraging habits must retreat to cooler depths, so that they may thermoregulate properly.

Even tropical marine aquaria have trouble with overheating in temperate summers, so temperate marines will also suffer in the heat. Unless the aquarist wishes to invest in an expensive chilling system, the tank or pool needs to be maintained in a cool, well insulated, and probably air conditioned room. The aquarium decor should not clutter their roving space, so as to become an obstacle, and the filtration needs to be of an extremely high capacity.

With that said, if the basic requirements for this shark are met, it proves very hardy in public and private settings. This is why the species is now a popular species in zoo exhibit, often in simulated kelp forests with artificial fronds, far distant from their native range in the North Pacific. Unlike some sharks, T. semifasciata is quite non-aggressive, and not prone to attempt predation on tankmates of large size, which contributes to its appeal.

T.semifasciata requires a tank or pool with a footprint at least 6 times by 4 times its own length. Accommodating juveniles of this species is therefore feasible, but sadly, the adults need more space than the entire ground plan of many homes. On the plus side, their teeth belong to a piercing guild, useful for seizing relatively small prey moreso than ripping flesh. This is why T. semifasciata will not hurt large fish or elasmobranchs, though matters of size are relative, and their natural diet upon maturity includes fishes up to a size of 50 centimeters, or 20 inches, including flatfishes and surfperches. This is about 1/3 of their own length.

Adult sterlet can grow to around 90 to 125 centimeters, or 36 to 50 inches long, but a more typical length would be 40 centimeters or 16 inches. This species are active bottom rovers, requiring an aquarium or pond that is at least six times by four times their own total length. Although they are thus too huge for most aquariums, they are considered a small sturgeon species, as the largest sturgeon weigh in excess of a metric ton. Sturgeons have no close living relatives excepting the paddlefishes, which share their superficial similarity to sharks, not least because of the structure of their tails. In fact this asymmetrical tail morphology - upkinked and sporting the caudal fin underneath - was seen in the most recent, Palaeozoic common ancestor of the sharks and true finfishes.

Sturgeon and paddlefishes are an ancient sister branch to the mainline of finfish evolution, lacking many of the traits that are common to typical fishes known as teleosts, and retaining anatomical curiosities as are seen in ancient fossils. One peculiarity of sturgeons is their impressive bony plates. These can be sharp to touch, especially in younger sturgeon, and have obviously evolved as armor to protect them from predators. As a group, the sturgeons are famous for migrating between their freshwater spawning grounds and the sea, but not all species make such journeys, and even among the those that do so, may exist landlocked breeding populations, which inhabit freshwater year round.

Riverine A. ruthenus is among those species that is never found in the sea, although it is known to migrate downriver to overwinter, before returning upstream in spring to spawn on gravel beds. They do not seem to spawn on softer substrates. Wild A. ruthenus are inhabitants of temperate, alkaline freshwaters, more specifically large rivers and their tributaries, from the drainages of the Danube to the Yenesei. Data on their water temperature tolerances is inconsistent in the scientific literature. One source says that their optimal ambient temperature, is 13 to 16 centigrade, and the seasonal rise of temperature to 13 degrees triggers their spawning. But another says their growth is optimal, at 18 to 22 degrees.

Gymnarchus niloticus, the aba, is a magnificent, tankbusting bonytongue fish with an African distribution. It is recorded from the basins of the Nile, Senegal, Gambia, Volta, Niger and Chad, for which reason peer reviewed literature has claimed it's pH tolerances, are 6.5 to 8.0. However the species is also collected from the shallows of the alkaline Lake Turkana, suggesting a still wider ability to flourish, where the pH is at least 8.6. There the surface temperature of the shallows, gets as high as 27 to 29 degrees centigrade. Gymnarchus grows to almost 170 centimeters, or 68 inches long, and the weight record is 18.5 kilos. Such a large and spectacular fish is suited only to the largest home aquaria, or to heated, indoor ponds. Phonetically speaking, it's closest relatives are the African radiation of fishes, called mormyrids. With these the and shares remarkable electrosensory abilities, but the kinship is by now distant. There is only one species in the genus Gymnarchus. The aba is such an unusual looking animal, that it is difficult to mistake it for any other species within its wide geographical range.

The aba is an air breathing fish dwelling in marginal vegetation and swamps. There the pair bonding fish constructs its nests, which may be about 100 centimetres in diameter, during the season of the innundation. It's diet is mobile prey and primarily other, smaller fishes, but also arthropods and annelids. Juveniles begin as insectivorous, as you might expect, before maturing with size and age, into the adult, carnivorous niche. These prey it locates just as it navigates, relying on a good 'sixth sense' of electroception, an ability shared with its mormyrid relatives. Gymnarchus generates electrical fields using a large organ that runs along most of its length, and this ability is so useful, that the fish can swim backwards as easily as it swims ahead, sending objects as disturbances to its own self-generated electrical field. The unusual mode of swimming employed by this fish is like the Old and New World kbifefishes, but involves the graceful undulation of its dorsal fin, rather than an anal fin. It has completely lost the paired fins of its hypothetical ancestors.