Well... apart from protecting the fish from predatory attack, it also protects it from the harsh chemicals in the ocean. One in particular is Mercury which is a naturally occurring liquid metal and very detrimental to human health. According to the E.P.A, (Environment Protection Agency), human fetuses exposed to this poisonous chemical “may be at an increased risk of poor performance on neuro-behavioral tasks, such as those measuring attention, fine motor function, language skills, visual-spatial abilities and verbal memory.”
Fully developed humans are also not immune to these damaging effects and because of this, It has been advised by various medical practitioners to desist from eating fish or any sea creatures without scales protecting its skin (such as Catfish, shrimps etc) because without it, the mercury gets absorbed by the fish's skin, which eventually ends up in us.
Pretty enlightening fact about what we eat and its effects..Now you know and you're welcome :-)