Zoology 10th Edition by Stephen Miller,John Harley

Exercise 12

Fishes use fins and body-wall muscles in locomotion. Most modern fishes are predators, although some are filter feeders or herbivores. Fishes have a heart that develops from four embryological chambers. Blood circulates from the heart through gills to body tissues. Blood returns to the heart in the venous system. Gas exchange occurs through a countercurrent exchange mechanism at the gills. Pneumatic sacs are modified to form either lungs or swim bladders. Olfaction, vision, equilibrium and balance, water movement (lateral line sense), and electroreception are important sensory modalities for fishes. The nephron is the functional unit of the fish kidney, which functions in excretion and water regulation. Other osmoregulatory mechanisms include saltabsorbing or salt-secreting tissues in gills, kidneys, or rectal glands. These mechanisms either conserve water and excrete excess salt (most marine fishes) or excrete excess water and conserve ions (freshwater fishes). Mating of fishes occurs in large schools or as individual pairs of fishes. Most fishes are oviparous with little or no parental care of young.
How are each of the following processes or structures helpful in explaining why a fish is fishlike: countercurrent exchange mechanism, left atrium, pneumatic sacs, and lateral-line system?