Page 16 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

14 INTRODUCTION TO FISHKEEPING

Diversity
Africa
Lake Malawi
Fish have colonized almost every aquatic environment
on the planet. Blackfin Icefish inhabit the freezing depths South
of the Antarctic Ocean, while Desert Pupfish thrive at Atlantic
Ocean
over 104°F (40°C) in pools in the Nevada Desert.
The huge diversity of fish habitats worldwide has driven
the evolution of the countless shapes, sizes, and colors
that make fish so fascinating to keep.

The observed diversity in the appearance of fish is the
product of millions of years of evolution. Imperceptibly, the
forces of natural selection have shaped every fish’s external
form, internal anatomy, and behavior to deal with the
challenges of its own very particular environment; in the
process, they have created thousands of living species of fish in Lake Malawi is home to many species
the world’s seas and fresh waters. Most species are created by of cichlids. The species (of which a
geographical separation; this occurs when one population of selection is shown below) have highly
localized distributions in the lake, and
fish becomes fragmented into two or more smaller groups. many have color variants.
Natural selection works on each group in slightly
different ways and changes them so that if
members of both groups meet again, they are
too different to interbreed. By definition, a new
species has been created. Maylandia zebra M. zebra (Blue morph) M. zebra (Cobalt blue morph)
Of the 25,000 living species of fish, about 60 (Orange blotch morph)
percent are marine—a surprisingly low proportion
given the extent of the world’s oceans compared
to its fresh waters. This is equivalent to one
species for every 24,000 cubic miles (100,000 M. lombardoi (Yellow morph) M. lombardoi (Blue morph) P. elongatus

Coral reefs are highly varied habitats Mangrove forests, where fresh- and The Amazon is the world’s largest Human activity has damaged or
—they have been called the tropical saltwater habitats merge, are the river, measured by volume. Seasonal reduced many natural fish habitats.
rain forests of the seas. They are areas natural home of a number of flooding of this vital fish habitat Some species, however, benefit from
of extremely high species diversity, aquarium species, such as enriches the water with food and acts agriculture, spreading into drainage
for both fish and invertebrates. mudskippers and Archer Fish. as a trigger for breeding. ditches and paddy fields.

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