External Structure of a Bony Fish

SCIENCE CONCEPT:

The external structure of most bony fish is covered with scales. The scales are covered with a slimy substance that helps fish move through the water.

STUDENT OBJECTIVE:

The student will label and color the parts of a typical bony fish. They will also write a short description of the functions of the parts of the bony fish.

OVERVIEW:

The students will gain a greater appreciation and understanding of the abilities and functions of a bony fish as it moves through the water.

PREPARATION TIME:

20 minutes.

LESSON TIME:

25 minutes.

TEACHER PREP:

Locate and reproduce a large picture of the external structure of a typical bony fish. Then make enough copies for each of your students.

WORDS TO KNOW:

scales

operculum

fins: dorsal, caudal, anal, pectoral, & ventral fins

gills

secreted

stability

propulsion

steering

braking

displacing

TEACHER TEXT:

Fish have several different ways of dealing with friction drag and thus achieving more laminar flow over their bodies while swimming. Many fast swimmers are covered with a slimy mucous layer secreted from glands beneath their scales. The long-chained slime molecules help stabilize the water into laminar flow. In barracuda, for example, the slime layer reduces drag by at least 60%!

Fish fins can be placed into two categories. Median (vertical) fins originate along the midline of the body and include the dorsal fins on the back, the caudal or tail fin, and the anal fin on the bottom, just behind the vent or anus. Paired fins are on the sides of the body and include the pectoral fins just behind the head and the pelvic or ventral fins located below and behind the pectorals. Fish use this combination of fins for stability, propulsion, steering and braking.

The caudal or tail fin is the main source of propulsion for most fish. Fish tails come in different forms depending on the lifestyle of the fish. The main job of the tail is displacing the necessary amount of water needed with each tail stroke in order to move the fish. A broad tai is useful for fish who need to make quick starts from a stand-still. Long narrow tails are more efficient for fast, long-distance swimmers.

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Last modified: Sat Aug 23 14:04:12 PDT 1997