Spikefish

Spikefish World is an underwater magitech steampunk setting where pufferfish-like creatures cover the ocean surface with waves of Spikefish, preventing traditional ships from sailing the ocean blue, instead relying on Crawlers, massive cities that walk across the ocean floor during Spikefish season when the ocean surface is covered in Spikefish. Did I mention Spikefish also bring magic into this world by excreting magical waste which harbors bright lively underwater reefs filled with strange and mystical sea life. Also in large quantities sometimes that waste goes magically nuclear, sometimes resulting in fantastical magic and rifts to otherworldly places, but often it leads to magical cancers.

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The Spikefish changed everything, drove humanity to the seas; sharp barbs ended the age of sail leaving only punctured wooden hull; their toxins poisoned the wells and the earth became a wasteland. Some say they were simply a natural phenomena, some say these spiked devils were a punishment for our sins, perhaps they are guardian angels protecting the Earth from us. We believe they are simply a part of our lives now.

— Minerva's Weavers

Spikefish get their name from being covered in razor sharp barbs. While they seem innocuous to a Terran their barbs are sharp enough to puncture wood and erode metal, and their toxins can kill an adult with enough exposure. Individually they are relatively harmless but in large swarms that cover the ocean surface in several feet of Spikefish prevent ships from sailing, makes shorelines inhospitable, and poisons many land based water sources.

Spikefish Season

I can't tell you where Spikefish come from, they simply are.

— Instituite d'Arcanum

There no known instance of Spikefish mating, nor do autopsy reveal they have reproductive organs or means to reproduce. Instead during Spikefish season fully grown Spikefish come out of the ocean floor where they then float to the surface.
Spikefish season occurs once a year randomly on a global scale where it lasts for a few days from randomized spawning areas of the ocean floor. Investigation into these spawning areas reveal nothing of note from the area. Afterwards the Spikefish season continues for roughly 6-10 months, during which the Spikefish excrete magical waste that provides life and magic to the ocean bottom.

The Flood

Full article for The Flood

The Flood was the end for some, a revival for sometime, and the birth of a new era

— Endless Warlord

The Flood was a gradual change, the end of colonialism. As Spikefish began to flood the ocean surface with several feet of Spikefish on the ocean surface, sailing ship travel became impossible as even the toughest metal hulls would eventually be worn away and punctured by the waves of Spikefish. The world found itself isolated from each other as the seas were filled with Spikefish. Many civilizations collapsed as they no longer had access to essential resources from their harbors. The Spikefish's toxins also poisoned the shoreline and decimated the fishing industry leading to mass starvation across many much of the world. Soon the only safe place was underneath the ocean surface. And thanks to Sobek Enterprises civilization continued.

Arcanum

Full Article on Arcanum

While the process is rather messy, the results are astounding

— Minerva's Acolyte

The ending of Spikefish season is signified by magical anomalies and extreme weather as high concentrations of Spikefish waste often causes mutations and cancers which kill off Spikefish. Surviving Spikefish often cannibalize the corpses and it's waste, leading to further magical chain reactions until a majority of Spikefish experience similar fates.
The end result of this magical chain reaction is Arcanum, a magically dense source of arcane power useful as fuel or catalysts for intricate rituals.
Feeding Arcanum to a Spikefish results in a more dense, less stable Arcanum. Eventually Arcanum will become so unstable it'll instantly destabilize. Destabilization can cause a variety of unusual events; from most likely to least likely explosions, cancers, magical anomalies, mutations, or rifts to an otherworldly area are most common results.

A rare picture of a lone Spikefish

Behavior

Incredibly passive with no sense of survival instincts aside from filter feeding anything that floats into their mouths.

Diet

An oddity is that Spikefish do not require sustenance to survive.

Lifecycle

Spikefish do not seem to age or grow and are biologically immortal

Reproduction

No known accounts of reproductive behavior have been noted. See main article for further details.

Autospy

An autospy of a Spikefish seem to reveal nothing about Spikefish anatomy and only raises further questions. A bisection reveals Spikefish have no internal organs, simply a large water filled space. The only known organs Spikefish have are it's skin, barbs, mouth, teeth, and eyes; no further discernible features have been found.