Main Points:
Video Lesson (19 mins)
Classroom Activities:
- Habitat requirements of salmonids are further examined - particularly shelter
- The need for shelter by both free swimming fish and developing eggs is considered
- An experiment shows the value of covering eggs with gravel
- The small size of fish eggs is related to their hatching early in development and the existence of the alevin life stage
- Developing fish quickly outgrow the egg shell and eggs hatch at a very early stage
- Hatchling "alevin" still have a large yolk sac
- Alevin continue their development while living off their yolk sac. They do not require food.
- Observation of the alevin shows
- Well developed eye
- Working fins
- Breathing (mouth opening/closing and gill covers moving)
- Heart beating
- Blood vessels
- Oil droplets in the yolk (energy source for alevin)
- Blood vessels going from body to yolk sac
- Alevin move very little to conserve energy and use it for growth
- In nature, they remain hidden in the gravel at the bottom of the stream during this stage of their life
Video Lesson (19 mins)
Classroom Activities: