Goliath tigerfish

Goliath tigerfish habitat is unusual for a predator of its size and it explains most of what the fish is.

THE HABITAT IS FAST, TURBULENT, OXYGEN-RICH WATER. The Congo basin's rapids, cataracts and fast main-channel water are where this fish lives, along with the deep clear water of Lake Tanganyika. Most large freshwater predators — pike, wels, large catfish — are ambush hunters of slower water. This one hunts in the parts of a river system that other large fish avoid.

THE BODY FOLLOWS FROM IT. Heavy shoulder musculature, a powerful caudal peduncle and a deep body are the anatomy of a fish holding and hunting in current rather than lying in wait in it.

THE CONGO IS A VERY LARGE AND VERY POORLY DOCUMENTED SYSTEM, and that matters to what can honestly be said here. It is the deepest river in the world, it carries an enormous discharge, its rapids have isolated fish populations from one another in ways that are still being described, and a great deal of its ichthyology is incomplete. Statements about this species' distribution and abundance rest on a thinner base than equivalent statements about a European fish.

LAKE TANGANYIKA IS A DIFFERENT ENVIRONMENT AGAIN — an ancient, deep rift lake with its own extraordinary endemic fauna — and the species' presence there is a separate proposition from its presence in the river.

AND THE FLOOD PULSE ORGANISES THE YEAR. Rising water distributes fish into flooded margins; falling water concentrates them into channels and rapids. That cycle rather than temperature is what a tropical river's fish respond to, and it is the reason expedition fishing here is planned around water level.

Goliath tigerfish size claims need handling carefully, because this is a species about which a great deal is asserted and comparatively little is recorded.

ROD-CAUGHT FISH ARE COMMONLY 5 TO 20 KILOGRAMS at 70 to 110 centimetres, which is already an extremely large predatory characin.

OVER 30 KILOGRAMS IS A VERY LARGE FISH, and reported maxima exceed 50 kilograms and 130 centimetres.

THOSE TOP FIGURES REST ON FEW DOCUMENTED INDIVIDUALS. Unlike a European or North American species with decades of survey data and an active record-keeping culture, goliath tigerfish is caught rarely, in remote places, by small numbers of people. The maxima in the literature should be read as the edge of what has been recorded rather than as a well-sampled upper bound.

GROWTH IS SLOW AND LIFE IS LONG relative to most characins, which is the usual arrangement for a large apex predator and means a very large fish is an old one.

AND THE SPECIES SITS AT LEAST CONCERN on the global assessment, which is a statement about the range as a whole rather than about any particular reach of river. Local pressure from netting and from habitat change is a different question from the global one, and in a basin this poorly surveyed the difference matters.

THE PRACTICAL POINT FOR AN ANGLER is that a very large Hydrocynus from the Congo basin is this species, and a very large one from the Zambezi is not — which is a range statement doing identification work, and is why the identification block says plainly that range is supporting evidence rather than proof.

This is one of only two species in this sprint's handling batch where the danger runs towards the angler, and the mechanism is worth being precise about because the usual toothy-fish precautions are not quite sufficient.

THE TEETH ARE SET IN SOCKETS AND INTERLOCK OUTSIDE THE CLOSED MOUTH. That is not a description of a fish with sharp teeth; it is a description of a mouth that is dangerous when it is shut. There is no safe position around the head, no gap to put a hand through, and no equivalent of a bass's or a pike's lower-jaw grip.

WHICH MEANS CONTROL IS ESTABLISHED AWAY FROM THE HEAD ENTIRELY. A firm grip across the body well behind the gill covers, with the fish supported horizontally and the head pointed away from everybody in the boat. Long pliers or a de-hooking tool, never fingers. Gloves. And a second person, because a large goliath is more than one person can hold and unhook at once — the same conclusion the conger record reaches by a different route.

CUTTING THE TRACE IS FREQUENTLY THE RIGHT ANSWER. A hook left in a fish that will be returned costs a hook; a hand in that mouth costs considerably more. Where the fish is going back, the decision should be made quickly rather than after several attempts.

AND THE FISH IS STRONG ENOUGH TO MOVE WHILE IT IS BEING WORKED ON, which is what turns a controlled situation into an uncontrolled one. Everything about the handling assumes a sudden violent movement rather than hoping against it.

THE WELFARE SIDE IS ALSO REAL AND IS EASILY LOST BEHIND THE DRAMA. This is a large fish caught in warm water, and warm water holds less oxygen while a hard-fought fish needs more. A goliath that has been played to exhaustion recovers slowly, and the recovery is where the mortality is. Support it horizontally, keep it in the water as much as possible, keep air exposure to seconds, and hold it upright facing into any current until it leaves under its own power.

A VERTICAL HOLD BY THE JAW IS NOT AVAILABLE HERE for the obvious reason, and it would be wrong anyway: a heavy fish held vertically is carrying its own weight on its spine.

The Congo basin does not have seasons in the temperate sense, and describing this fish's year by month would be close to meaningless. It has a flood pulse instead, and the flood pulse organises everything.

WHAT A FLOOD PULSE IS. A large tropical river system rises and falls annually with the rainfall of an enormous catchment, and the rise inundates floodplain, forest and marginal ground that is dry for the rest of the year. That inundation is the most productive event in the system: terrestrial material enters the water, invertebrates and small fish explode in the warm shallow flooded ground, and everything that eats them follows.

ON RISING WATER, THE FISH DISPERSE. Predators spread out into the flooded areas after the prey, which is a period of abundance and of very poor fishing — the fish are spread across an area many times the size of the dry-season channel and there is more food than any lure competes with.

SPAWNING FITS INTO THE RISE. Like most large tropical river fish, this species moves into flooded margins and tributaries as levels rise and spawns there, timing reproduction so that the young hatch into the most productive conditions the year offers. The details for this species are less well documented than for its southern relatives, and the record says so rather than borrowing them.

ON FALLING WATER, THE SYSTEM CONCENTRATES. As levels drop, fish are forced out of the floodplain and back into channels, rapids and permanent water. Prey and predators are compressed into a fraction of the space, the water clears, and the fishery becomes practical. That is the window, and it is a hydrological condition rather than a date.

WHICH IS WHY THE RAPIDS MATTER SO MUCH. Goliath tigerfish hunt in fast turbulent water where their speed and muscle give them the advantage, and the rapids and cataracts of the lower Congo are the ground the species is associated with. On falling water those become the concentration points as well as the hunting ground.

THE PRACTICAL CONSEQUENCE FOR ANYBODY PLANNING is that the question is not which month but what the river is doing, that the answer differs between tributaries within the same basin, and that a wet year and a dry one produce different fisheries in the same calendar window.