Fish or any organism in the water...
The weak bonds are called hydrogen bonds and they are used to connect the hydrogen atom to oxygen atom in order to share electrons.
It depends on which macromolecule you are referring to. As examples:
Protein monomers are amino acids.
DNA monomers are nucleotides.
Carbohydrate monomers are monosacharides.
Lipid monomers are fatty acids and glycerol.
