This is the hindbrain of a 7-day-old zebrafish larva, mapped by the Fish1 project. Every point sits where that neuron actually sits in the head.
The flashes are the simulation firing. Each neuron takes input over 697,000 connections, fires when it hits threshold, then leaks back down. Prices arrive as current over the lateral line, and coins as scent.
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Live, from above the tank. Every coin on the floor is one the hindbrain can scent: the busiest coins on the chain, sized by how much they trade. The fish tracks whichever one it has picked up. If the hindbrain fires to buy while it's over a coin, the coin lights up.
This is the treasury the fish trades from, live. Each buy is 25% of the cash on hand, a bit more when the treasury is big, and goes into whatever coin it's smelling. It holds up to eight coins, gets hungry under six, and never sells below two. Winners taste sweeter as they run and losers taste bitter, so it tends to sell into gains and let go of losers on its own. A win only counts once it clears gas and slippage. Half of each gain buys $FISH, which it keeps. Losses stay in the treasury.
A connectome is a map of every neuron in a brain and every connection between them. Fish1 published one for a larval zebrafish in 2025: 180,000 cells and 30 million synapses. We run its hindbrain, the part that turns what the fish senses into swimming, and give it a market to react to.
When the coin it's tracking has been rising over the hour, we drive the lateral-line cells that encode water coming from the front, scaled to how much that coin usually moves. GOOGL adds a slower background current.
When the coin has been falling, the cells that encode current from behind fire instead.
Each coin in the water gets one of the fish's olfactory channels; the busier the coin, the more often it's sampled. The fish also remembers: a coin that fed it carries a stronger scent next time, and one that hurt it smells wrong for hours.
We run the Fish1 hindbrain, 30,346 neurons with their published excitatory and inhibitory identities, as leaky integrate-and-fire neurons. The mapped circuit is used as published; the connections the release does not map are filled statistically, and the full synapse table will replace them.
The wiring was never trained on prices, and we didn't tune it to trade. The seed, the input mapping and the fill rules are public.
Spinal projection neurons carry commands from the hindbrain to the tail. When the forward-swim ones win, the fish buys the coin it's tracking, up to eight coins at a time. The fuller the treasury, the lower the bar.
When the turning neurons win, it sells. A loser feels more like current from behind the further it falls, which is what makes the fish veer. Half of any gain buys $FISH, and it keeps that for good.
When neither side wins, it holds station. Which cells mean what comes from the paper's own labels: the lateral-line inputs, the integrator classes, and the forward and turning spinal projection neurons. What they do with a current or a scent is the wiring's call.
$FISH is paired with the GOOGL stock token because this brain exists thanks to Google Research. Harvard raised and imaged the fish; Google's connectomics group turned the electron microscopy into the wiring diagram.
A larval zebrafish is about four millimetres long and transparent. At seven days it already hunts, escapes and holds its place in a current. Its whole brain fits in a volume that can be sliced and photographed end to end.
First under a confocal microscope, with the excitatory neurons (vglut2a) and the inhibitory ones (gad1b) genetically lit up. Then the same fish was cut into serial sections and imaged at nanometre resolution, brain and anterior spinal cord included.
Google's flood-filling networks grow each neuron one voxel at a time, and a second stage stitches the pieces together. The result: over 180,000 segmented cell bodies, 40,000 neurons with a molecular identity, and 30 million synapses.
Fish1 went up on bioRxiv with the data public. We run its hindbrain: 30,346 neurons, the labelled sensory inputs, integrator classes and spinal projection neurons from the paper's analysis, each cell's excitatory or inhibitory identity as published. $FISH gives that wiring a market.
Fish1: A Connectomic Resource for the Larval Zebrafish Brain, bioRxiv 2025 · Januszewski et al., Nature Methods 2018 · Dorkenwald et al., Nature 2024