68 10.2 More on Fish

Adaptations for survival

Schooling provides several benefits:

• Protection: 1000 small fish might look like one large fish to a potential predator
• Food gathering: if one fish finds food, all know about it soon
• Mating: a fish doesn’t have to travel far to find the “fish next door”
• Most schools consist of fish of the same species, age, and size

Color

• Colors in a fish may be used as a means of species identification
• Or, it may be defensive in purpose, serving as a kind of camouflage
• Cryptic coloration
  • Allows a fish to blend with its surroundings, as in this seahorse

Countershading

• Notice how the skate has a dark dorsal surface and a light colored ventral surface
• When it’s swimming, a predator above looking down will see the dark surface, which blends in with the bottom
• A predator swimming below, looking up, will see the lighter surface that seems to blend in with the surface

Lateral line system

• The lateral line system consists of  a line of cells  along the side of a fish and often around the head with hair-like elements that project above the skin surface
• These hairs act like sonar and are sensitive to low level acoustic vibrations  (sound waves) used by water currents of fish or other marine life
• It’s used in an active way – the fish sets up vibrations in the water and listens for the reflected waves
• The sensitivity of the lateral line system increases with depth

Gills

• The gill membrane assists with gas exchange with the surrounding water
• Water taken in through the mouth is expelled through the gill slit and passes over the gills, which extract dissolved oxygen from the water
• The gill rakers shown are tiny hairs that extract plankton from the water
• Other specialized cells help to maintain osmotic balance