13.2 Lesson 13.2: Fishes
Lesson Objectives
- List the general traits of fish.
- Describe the features of jawless fish.
- List the general features of the cartilaginous fish.
- Describe the features of bony fish and the significance of this superclass.
- List some of the reasons why fish are important.
Check Your Understanding
- What are the unique characteristics of vertebrates?
- What are the two main groups of vertebrates?
Introduction
So what exactly is a fish? You probably think the answer is obvious. You may say that a
fish is an animal that swims in the ocean or a lake. But there is lots more to fish than that.
Fish are aquatic vertebrates, which through evolution became a dominant form of sea life
and eventually branched to create land vertebrates. They have a number of characteristic
traits and are classified into two major groups: jawless and jawed fish. Jawed fish are further
divided into those with bones and those with just cartilage. Fish, in general, are important
in many ways to humans - economically, recreationally and culturally. Perhaps you can think
of some of these ways?
Characteristics of Fish
Fish are vertebrates that are typically ectothermic, are covered with scales, have jaws and
have two sets of paired fins and several unpaired fins. A typical fish has a streamlined body
that allows it to swim rapidly, extracts oxygen from the water using gills or an accessory
breathing organ to enable it to breathe atmospheric oxygen, and lays eggs that are fertilized
internally or externally (Figure13.5). Fish range in size from the 16 m (51 ft) whale shark
to the 8 mm (just over ¼ of an inch) stout infantfish.
Traits of a typical fish include:
- Vertebrate
- Ectothermic
- Scales