CORE MECHANICS
Dropping
Aim moves along the top of the tank; a tap releases the next fish (previewed in the HUD) into the release zone. There's a short cooldown between drops (0.35s) so you can't machine-gun the tank. On drop, the fish performs a persona-seeded "acclimation swim" — it bolts and darts, tail beating, steering toward a wandering heading and trailing golden bubbles for the first moments before settling into normal behavior.
Merging
When two fish of the same tier touch (and neither is the max species), they merge at their midpoint into the next species up. Merging:
- pays pearls (scaled by the new tier and any combo),
- can trigger a mutation in the offspring (see Mutations & Traits),
- plays that species' merge cue and a burst of particles,
- counts toward the goal (two Leviathans → Cosmic Whale).
Combos: merges within 2.5s of each other chain, multiplying pearls (up to ×3) and escalating the show (COMBO / MEGA COMBO callouts).
Tank capacity
The tank holds a limited number of fish. Base capacity is 14; each capacity upgrade in the Reef Shop adds 2, up to a hard cap. When the tank is full the capacity label flashes red — you must merge to make room. Fry also spawn passively while there's space.
Two-plane depth
Fish live on one of two depth planes (front/back) with their own collision filter, so the reef reads as a real volume rather than a flat sheet. Fish cross planes, are z-ordered and dimmed by depth, and a smoothed depth-cross keeps it visually clean.
Underwater currents
A gentle ocean current — a slow baseline drift plus occasional gusts every 7–16s — nudges every non-spike, non-just-dropped fish slightly, so the whole tank breathes and eases like real water.
Physics
Bodies are sprite-hugging (collision shapes match the fish outline) on an inlined Matter.js engine. The step uses a clamped delta so behavior stays stable across refresh rates; current and drift forces are framerate-independent.
Winning & resetting
Raise two Leviathans and merge them → the Cosmic Whale is summoned → victory. After the celebration, the "YOU WON!" menu offers a fresh reef (lifetime Codex, achievements and stats survive the reset).