Page 17 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

DIVERSITY 15

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km ) of sea water, compared to one species for every 3 ⁄2 cubic New species are constantly being discovered.
miles (15 km ) of fresh water. The diversity of freshwater The Red Dwarf Pencilfish (Nannostomus
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fish relative to the size of their habitat is due to the ease with mortenthaleri) was first collected as recently
as 2000 from the Rio Nanay near the town
which groups of fish can become separated and geographically of Albarenga, Peru.
isolated in rivers and pools, compared with the sea.
Geography and species formation
There is no better example of diversification and species
formation than Lake Malawi in Africa’s Great Rift Valley.
Created about two million years ago by a geological fault, the
365-mile- (584-km-) long lake is today home to more than 1,600
species of cichlids—more than occur in all of the rest of
Africa. It is thought that all these cichlids developed from just
one or two ancestral species, which entered the lake at the
time it was formed. The early lake cichlids adapted to the also diversified in their breeding habits, some species scattering
entire range of different habitats that they encountered in their eggs, others displaying a long period of parental care.
the lake. Some became predators; others plant eaters. Some By dividing up the biological “niches” available in the lake,
became restricted to the shoreline; others occupied the depths the cichlids were able to explode in number, without directly
of the lake. Some grew to large sizes; others diminished. They competing with one another for limited resources.

BODY SHAPES
Fish occur in a wide range of different shapes, which usually relate to shape may, however, change with age. The discus, for example, has
their lifestyle. Surface-dwelling fish, for example, have flattened backs a compact body when young; it attains its flattened shape only at
and upturned mouths so that they can grab floating food. Body several months of age.
Tubular body shape
Obviously flattened
body; propulsion
provided by the
Tall, flattened body; so-called “wings”
barring helps to break
up the fish’s outline
Propulsive power comes Narrow, tubular,
from body, rather than wormlike body lacks
fin, movements caudal, pelvic, and Tail assists
anal fins movement

A Spotted Moray Eel (Gymnothorax A discus slips through dense weed to A Pipefish (Syngnathoides sp.) drifts Flatfish spend their lives on or near
moringa) hides in its lair. The body shape escape a predator. Its tall, narrow shape in a bed of sea grass, perfectly the substrate. They have asymmetrical
of this hunter means it can hide away in is typical of species that live in slow- camouflaged by its shape and color. bodies, with both eyes on the same side
caves or under rocks, from where it can moving waters. Fast currents would It even holds its body at a slight angle of the head. They are able to burrow into
ambush prey. make swimming difficult for this fish. to accurately mimic the sea grass. the substrate, hiding most of the body.

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