Fish are vertebrate animals living in fresh-or sea-water. They are poikilothermic and reproduce by laying eggs. Fish are streamlined in their shape,their bodies are covered with scales, they possess fins and breathe by means of gills.
POIKILOTHERMIC. An animal whose body temperature varies with that of its surrounding is said to be POIKILOTHERMIC. The temperature of such an animal is usually a few degrees above that of its environment, but a rise or fall in the temperature of the air or water in which it lives will produce a corresponding change in the animal's body temperature.
Since the speed of most chemical changes that take place in living organisms is increased by a rise in temperature, it follows that the rate of activity of a poikilothermic animal will depend to a large extent on the surrounding temperature. Some animals may,at a low temperature, be reduced to a state of torpor, while high temperatures may lead to vigorous activity. The popular term "cold- blooded " is unsatisfactory since it conveys the impression of a constant temperature; for example, fish living in "warm" tropical seas would according to popular definition, be correspondingly "warm- blooded"
