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<p>Fish originated over 480 million years ago. Fish evolved in fresh water and spread to the seas at a much later period. Fish are the dominant free swimming animals of the seas with a body designed for ease of movement. This ability to move about easily without relying on water currents to carry them about has enabled fishes to exploit most parts of the world’s oceans. Fish are a very important food source for many nations. Fish can see smell touch feel and taste and they have developed some new senses such as electroreception. Fish can sense light chemicals vibrations and electricity. In general fishes are cold blooded. They derive their body heat from their environment and conform to its temperature. The circulation of blood in fish is simple. Their hearts only has two chambers unlike us. This is because the fish heart only pumps blood in one direction. Detailed coverage of environmental aspects relating to fish biology is a key feature of this book. It is of great use to students and individuals in fish biology fisheries aquaculture and environmental sciences.</p>
