Question

Why do sticklebacks have spines on their pelvis and back?

Answer 1

Answer:

Marine fish have prominent spines, presumably to deter predators, but the freshwater fish have only small ones, if any at all. That's probably because their new environment was short of the minerals needed to make the spines, which made spine-building consume too much of the fishes' energy to be worthwhile.

Explanation:

Answer 2

Answer:

Marine fish have prominent spines, presumably to deter predators, but the freshwater fish have only small ones, if any at all. That's probably because their new environment was short of the minerals needed to make the spines, which made spine-building consume too much of the fishes' energy to be worthwhile.