In the Marvel Cinematic Universe, in order to cause Terrigenesis to occur an object called a Diviner is used to find out who is and who isn't Inhuman. This object kills anyone that comes in contact with it who isn't an Inhuman.
Contained inside the Diviner are Terrigen Crystals. Once the Diviner is opened inside an Inhuman temple, the Terrigen Crystals release the Terrigen Mists. It is the Terrigen Mists that cause latent Inhumans to transform.
In Agents of SHIELD season 2;
We learn that Jiaying has been creating her own artifical Terrigen Crystals. Due to the fact that they are artificial, and Jiaying has been unable to perfect the process of creating them, they are imbued with shards of metal from The Diviner.
These particular crystals are therefore lethal for non-Inhuman characters to touch thanks to the presence of the the metal from The Diviner. However, it seems safe to assume that regular Terrigen Crystals (and the Terrigen Mist they produce) would be safe for regular humans to touch.
In the second season finale;
Skye uses her powers to knock a Quinjet full of these fake crystals into the sea.
We later see that the fake crystals appear to be reacting with the sea water, releasing their Terrigen Mists into a nearby school of fish while the deadly Diviner shards sink to the bottom of the ocean.
I would imagine that if any fish had have come in contact with a shard from The Diviner, they would have died just as non-Inhumans do.
Edit: My theory about the seperation of the Diviner metal and the Terrigen crystals in the sea has since been confirmed by Agents of SHIELD in the season 3 episode "Laws of Nature".