Forktail lates

Identifying it

The literature holds on to two characters, and one of them named the fish: small scales, and a tail fin notched in juveniles. The notch shallows out with age, which leaves part of the identification resting on a feature that erases itself — awkward for anybody sorting adults.

The outline is fusiform and compressed, the build of an open-water swimmer. Size separates it better: maturity comes at around 51 cm, and growth continues well past it.

Breeding

What is known amounts to three lines, and each one is a surprise in an open-water fish. Spawning is thought to happen in vegetated areas, which means near the shore, where the adult no longer lives. The breeders pair off two by two rather than spawning as a crowd. The eggs are laid and abandoned.

A pelagic predator that returns to the littoral to breed depends on two habitats instead of one, and there is no reason for the two to deteriorate at the same rate.

The water it needs

The fish lives in one lake, and inside that lake it changes worlds once and for good. Up to 18 cm it occupies a defined inshore habitat close to the edge. Past that length it moves out into the surface layer of open water and does not come back down.

Its boundary with rivers is exact. Young fish will sit off a river mouth — the Malagarasi delta holds them — but they do not enter the river. It is a line the species approaches without ever crossing.

What it eats

One diet, one layer of water: clupeids — the lake's sardines — and, to a lesser degree, Luciolates. Nothing else, at no point in adult life.

That narrowness chains the predator to its prey. Where the shoals move it moves; where they collapse it has nothing to fall back on. A fish that eats four things absorbs the loss of one of them. This one has nothing behind it.

How to catch it

It is taken on handlines in open water, and the search follows from the diet: what has to be found is the sardine shoal, not the fish. Once adult it holds where they are, in the offshore surface layer, and nowhere else.

Handling raises no particular difficulty, since nothing about the animal is dangerous to a person. What needs settling before the take is what happens to the catch, because the stock is in poor condition and a decision improvised at the moment of unhooking always goes the wrong way.

Conservation

The predator is caught by the fishery that targets its food. As an adult it lives in the offshore surface layer and eats sardines, and that layer and those sardines are exactly what the lake's industrial fishery works. It shares the hour, the place and the depth of what it eats, and it comes up in the same gear whether or not anyone is looking for it.

That is the only cause the 2025 review retains for its decline. Not pollution, not a dam, not an introduced competitor: exploitation, and nothing besides.

Add to it what a closed lake implies. The population has no outside source — Tanganyika is not restocked from a neighbouring basin — and the fish does not breed below half a metre. An individual returned to the water weighs more here than the same gesture would weigh in a river.

Other names

English has no vernacular for this fish, so it presses the genus into service as one: it is a lates, and a qualifier does the rest of the work. Forktail lates is what the catalogue carries; German Gabelschwanz-Lates and French capitaine à queue fourchue make the same choice, and all three describe the tail.

The awkwardness is that the tail they describe belongs to a juvenile. The notch is clear on a young fish and fades afterwards, so the name fits the animal caught near the shore rather than the one hauled up from open water. The scientific name went the other way and took the scales.