In the climax of S2E22 of Agents of SHIELD;
Skye pushes a Quinjet containing Terrigen Crystals created by Jiaying into the ocean.
We go on to see that a school of fish come in contact with the crystals, and are later caught and converted into Fish Oil Pills.
But every non-Inhuman we have seen come into contact with Terrigen Crystals has been killed. Why didn't the fish die?
It’s coming into contact with the Diviner metal that seems to be deadly, not the crystals within. When Jiaying’s hybrid crystals fell into the sea, only the crystal part dissolved into the water.
This seems to be confirmed in the first episode of season 3. When discussing the crystals at the bottom of the ocean, Bobbi explains that (a) there’s a lethal and non-lethal component, and (b) they were separated when released into the ocean.
The good news, if you want to call it that, is the deadly metallic element sank to the bottom. So the chemical contaminating the fishlife isn't deadly to humans… just game-changing for Inhumans.
Anybody that took a trip to the seabed would presumably come into contact with the metal and suffer similar effects. I have no idea what would happen to the fish, because I don’t know whether the Diviner tries to judge or just ignores fish. Perhaps it petrifies them, perhaps it does nothing.
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".
They might not have died because they were not humans and had a different reaction towards the divine. And I am not sure but maybe it is true that there was no mist. Always the most comes when the divine is active. It happened twice. Trip died only when the mist came. Gonzalez died because the mist came in action. But in this case there was no mist just an affect so maybe these are the two reasons that the fish did not die and the reaction was less and maybe it was underwater.
