Most of the freshwater fishes in our aquariums are either catfishes, carps, characins, or perches such as cichlids and toothcarps. However there are more unusual fishes either regularly or sporadically encountered in the aquarium trade; the herrings are not usually among them, and fer herrings are freshwater fish. So there are reasons why Denticeps clupeoides, the denticle herring from West Africa, is worthy of zoological commentary. The denticle herring is distinguished from other herimgs by the remarkable presence of its namesake denticles - these being numerous small teeth on the surface of its head. These structures truly are teeth and do not merely bear a resemblance to teeth, and they resemble the oral teeth of the animal in their shape and size, although they are not used by the fish in biting. Some other true fishes also possess teeth outside of their mouths, but it is an exceptional characteristic nonetheless. Despite being found only in rivers, it is a true herring, and it is also an ancient offshoot of the other modern herrings that retains certain ancient traits that would have been present in ancestral herrings. Despite all of these points of interest, D. clupeoides is an unassuming size, no longer than 15 centimeters or 6 inches, and not usually longer than around 8 centimeters or 3 inches, and it is not visually dazzling.
Although only D. clupeoides is recognised today, the denticle herrings as an evolutionary line are ancient sisters to all other modern herrings, called the clupeoid herrings, which include the anchovies, sprats, shads, pilchards, and sardinellas - all varieties of herring. Although we usually think of herrings as marine fishes, the clupeoid herrings have colonised rivers more than once around the world, over the course of their evolution. The modern denticle herring almost certainly descends from a marine ancestor that colonised up freshwater rivers; there are no denticle herrings recognised among the fossil record of any continent excepting Africa. In all this little African fish is to the herrings, what the Australasian monotremes are to mammals; what the Asian tarsier is to the monkeys; and what the New Zealand tuatara is to lizards. It is not that Denticeps is unchanged from a known ancient ancestor - it is not truly a 'living fossil'; but that it is a phylogenetic outsider among its evolutionary line, one that has some ancient traits its relatives have modified or lost, during the same geological timescale since their ancient ancestor.
The denticle herring is indigenous to the lowland rivers of the Guinean region of Africa, such as the Oueme and the Mungo. It forms schoals in the midstream of the river, where the current is strong. This oxygen demand makes the denticle herring difficult to transport, and they need good oxygen levels and water flow if they are to survive and thrive in the aquarium. Once in the aquarium they are peaceful to other fishes and apt to cohabit with other species. Denticle herring possess numerous pointed and conical teeth suited to siezing small arthropod prey, as well as some gill rakers appropriate for filter feeding behaviors. In the aquarium they are observed to be unfussy feeders, although they are observed to be reluctant to feed from the bottom of the aquarium. This means that dentical herrings should share aquarium space well with bottom swimming fish like catfishes and loaches. Naturally they should be accommodated with numbers of conspecifics, and as they are active, powerful swimmers, they require much unobstructed swimming space. In addition to their requirement for space. and for high oxygen levels and water flow, these riverine herrings like soft water with a pH that is between around 6 and 7, and a temperature between 25 and 29 degrees, based on the water parameters of their habitats of origin.
