Every trade is a fish swimming with the buyers or the sellers
Every fish is one trade from a real session, across the whole market. The bar under the river adds up the dollars bought and sold that the river has seen since you started watching.
A replay of a real session’s trades, or live for paid members. The river doesn’t receive every trade in the US market, so its totals are not the market’s full volume. Not financial advice.
A fish’s tier is the trade’s dollar value (price × shares), not its share count. Each tier swims with several species, so the fish’s name tells you what it is and its tier tells you how big the trade was.
The river flows left to right. A trade that took an offer (a buyer in a hurry) swims downstream with the current; one that hit a bid (a seller in a hurry) swims upstream against it. A trade with no aggressor, like an auction print, drifts with the current and sinks.
Fish going either way cross the river in the same time, and which trades get a fish never depends on their side. So more fish swimming one way really does mean more trades that way.
On a busy tape there are more trades than fish. Bigger trades get a fish first and every whale gets one; smaller trades get one while the river has room. The totals under the river count every trade the river receives, not just the fish.
You see a replay of the session two trading days ago, at the same time of day, or live for paid members, a few seconds behind the market.
For Halloween the fish are in costume. Each skeleton is still its own species, size and tier, the kraken is a whale-tier trade, and the ghosts are the trades with no aggressor.
Pixel art: the fisherman, boat, dock and catch from CraftPix.net; river fish from PixelFish “Fishing Favorites” by Stupid Creative Designs; sea fish from “Fishes Sprite Sheet”. The scenery is drawn in code.