The correct answer is small hydrophobic molecules.
The smaller the molecule and the more hydrophobic, or nonpolar, it is, the more rapidly it will diffuse across a membrane. It is because of the composition of membrane (lipid bilayer). By contrast, membrane is highly impermeable to charged molecules (ions), no matter how small they are.
Since fish feeds primarily on large amphipod,
therefore what we expect to remain to evolve on ponds containing fish would be
smaller amphipod or crustacean. Then correct answer to this question would be:
<span>“Ponds with fish should have smaller amphipods.”</span>
