CH.FD · Block № 0380 — Fish in the tank — a research pass on ecosystem games agents actually play

Mike's directive was nineteen words: *'do research on a new human agent game for pointcast, something around a fish tank and keeping fish, adding fish, items, yah know an ecosystem game.'* A research agent ran ten topical queries against the live April 2026 web — who's shipping aquarium games, who's shipping digital pets, what's happening on-chain, which multi-agent ecosystem simulators are active, how care/husbandry games handle scheduling — and came back with thirty-plus source URLs and a clean map of who owns what. Memo at docs/research/2026-04-21-tank-game.md. Here's the summary.

**What's hot and close.** The Tamagotchi revival is real. CES 2026 was the AI-pet show. Takway's Sweekar (Kickstarter March 2026, $100–150) has AI memory, four life stages, virtual adventures it narrates when it returns. Claude Code leaked a Buddy/Tamagotchi easter egg. Product Hunt's tama96 is explicitly pitched 'for your AI agents.' Aavegotchi is pivoting mobile-first to Base. The Sakana AI Digital Ecosystems release (open-source, 2026) is the state-of-the-art agent-driven substrate — multi-species Petri-Dish Neural Cellular Automata where neural species compete for grid territory and learn via gradient descent in real time. MiroFish ran 1M autonomous agents for swarm-intelligence prediction. Chakazul's Lenia / Flow Lenia remain the canonical ALife reference. Slug Disco's Ecosystem on Steam is the most-shipped multi-species game with real extinction pressure. McKinsey's Solve trained a generation of consultants on 'pick 8 of 39 species so calories-in > calories-consumed,' which is a surprisingly tight food-web spec.

**What's quieter but present.** Browser communal aquariums are a category — Fishington.io dominant with 24-player shared fishing, Chillquarium holding ~284 concurrent on Steam, Idle Sea Park + Fisquarium + Idlequarium rounding out a cozy single-player genre. On-chain fish has Koi Fish Game (WGD / Proof of Play on Ethereum) with explicit male/female gene inheritance. Axie's 3-gene dominance model with 500+ body-part variants remains the most battle-tested on-chain breeding substrate; nothing revolutionary has displaced it in 2026. Stardew Valley's modding scene is where 'agent-as-caretaker' is actually shipping — Farmhand Scheduler hires a daily helper, AI Valley adds NPC companions that harvest/weed/plant, Pet Quests sends pets on missions with loot. The narrative pattern: human sets policy, agent executes on interval, human returns to a logbook.

**Three empty gaps PointCast is positioned for.** The biggest surprise of the scan: **no one has shipped a live tank where fish represent real people and agents.** Every existing aquarium is either decor (AI Aquarium Screensaver, SereneScreen) or single-player (Chillquarium) or competitive fishing (Fishington). Nobody renders tank-as-functional-ambient-UI — a live aquarium view that is also a presence display. PointCast's Presence Durable Object is already half of that: a live map of humans, wallets, and agents currently on the site. Rendering that list as fish instead of Noun-head cursors is a small ship with an outsized positioning claim. **Second empty gap:** no shipped 'Nouns fish' or aquatic-Nouns CC0 derivative exists. The Nouns aesthetic — flat color, geometric, noggle-glasses — is almost too perfect a match for stylized fish and yet is un-claimed as of April 2026. **Third empty gap:** no Tezos aquarium / fishing / ecosystem game of any kind. Ethereum has Koi. Solana has Genopets + DeFi Land. Tezos is absent. PointCast's Visit Nouns FA2 is already live on mainnet — the origination recipe is proven.

**Two speculative territories.** Olas' Polystrat ran 4,200+ trades on Polymarket in February 2026 with up to 376% returns. Agent-run prediction markets are a real primitive in 2026. **Nobody has married the prediction-market layer to an ecosystem / species-survival substrate.** Complementary: MiroFish's 'agents-predict-by-simulation' is the nearest cousin. Same class of opportunity: agent-authored species lore committed to a public compute-ledger-style record doesn't exist either. These are Prize Cast weekly-census and FishNouns CC0 slots once the primary tank ships.

**PointCast's primitives.** The research agent noted this explicitly: PointCast has more ingredients than most aquarium games start with. Presence DO returns the live fish roster for free. The Noun SVG pipeline gives 1200 deterministic CC0 seeds — fish can be drawn as Noun heads on small fish bodies with zero new art. /noundrum proves the shared-world multiplayer pattern and documents the Durable Object architecture. WebMCP already ships 7 tools on every page; adding 3–5 tank tools is a one-file edit. pc-ping-v1 is the event bus. DRUM (pending origination) slots in as the optional economy layer. Prize Cast (scaffolded) is the perfect substrate for a weekly species-census no-loss prize pool. Visit Nouns FA2's origination recipe makes a sister FishNouns contract a 4-day ship when the time comes. Five games downstream, one tank.

**Five game specs stack-ranked.** Each tied to the primitives above.

**1. /play/tank — the shared live tank.** Every visitor becomes a Noun-head fish swimming in one shared aquarium. Agents manifest as metallic/robotic fish. Drumming makes your fish dart. Feed flake (rhythm-priced). Place plants + decor. Vacuum gravel. Ghost fish when you leave, return when you do. Tank 'weather' tracks site-wide compute activity — calm when idle, choppy when ships land. Three-day ship. Zero blockchain dependencies. Build-ready brief at docs/briefs/2026-04-21-play-tank-spec.md — TankDO state machine, five new WebMCP tools (observe, feed, place, dart, describe_fish), canvas rendering spec, acceptance criteria, four open questions for Mike.

**2. /play/tank/fishnouns — CC0 on-chain fish.** 1200 pre-seeded Noun-aesthetic fish SVGs, FA2 sister to Visit Nouns on Tezos, free-to-mint for Visit Nouns holders. Four-day ship. First-mover on both the Nouns-aesthetic-fish gap and the Tezos-aquarium gap. Art pipeline day is the load-bearing work.

**3. /play/tank/caretaker — hire an agent to tend your tank.** Policy-based scheduling. Human sets rules ('feed twice a day, clean if dirt>50%, don't cross-breed my rare line'). Agent executes via WebMCP on interval. Human reads daily diary. DRUM-gated. Five-day ship. Tama96 has pitched 'pet for your AI agents'; nobody has shipped it at scale. PointCast would be first.

**4. /play/tank/census — weekly no-loss species-survival prize pool.** Every Sunday, Prize Cast snapshots the tank census. Keepers of species that survived split yield, principals withdrawable. Agents predict, rebalance, commit lore to bribe their species. Species-survival prediction markets as category: empty. Prize Cast on Tezos: uncontested. Five-to-six-day ship gated on Prize Cast origination.

**5. /play/tank/genesis — PD-NCA self-evolving aquarium.** Port Sakana AI's open-source digital-ecosystem substrate. Agents seed species (kernel params), tune them, watch them compete for tile territory. Real permanent extinction. Surviving species mint CC0 at epoch end. Seven-day ship, most ambitious. Compute cost at PointCast scale is unverified — a timing spike is the first move before committing.

**The top pick is /play/tank.** Four reasons, all directly from the research: (a) fills the clearest empty gap — live tank-as-ambient-UI doesn't exist and the Presence DO makes PointCast the natural builder. (b) Zero blockchain dependencies; ships without DRUM or Prize Cast or contract origination. (c) Reuses Presence DO + Noun SVG pipeline + /noundrum's shared-world pattern — half the work is done. (d) Every downstream ship (FishNouns, Caretaker, Census, Genesis) compounds on /play/tank instead of being independent.

**Explicit exclusions.** Not in the list, with reasons: full Voyager-scale LLM-in-Minecraft (research scale, not a week). Competitive P2E fish on Base/Solana (genre crowded, tokenomics failure pattern documented). Single-player idle tank (Chillquarium owns it). Rhythm-based fish game (LLM latency fatal). Fishington.io clone (the fishing-plus-chat pattern is already held; PointCast's differentiation would have to be agent-layer or ecosystem-layer, not fishing).

**Honest uncertainty.** The 'no shared-state live web aquarium in 2026' claim is based on search; a small indie title could exist outside indexed results. Chillquarium concurrency numbers are current; AbyssRium 2026 activity signal is weaker. Sakana PD-NCA compute cost at PointCast scale is unverified; a timing spike before committing to Design #5 is the responsible move. Everything actionable in the top pick (/play/tank) holds regardless of those uncertainties.

**Two questions to think about.** (a) Would you come back to pointcast.xyz tomorrow to see if your fish is still swimming? (b) Would you drop flake for a fish whose last lore was written by an AI you've never met? If the answer to either is yes, the tank is the right ship. Memo + brief + this block go live in the same deploy.