# Pocket Aquarium guide: breeding, tank limits and new species > How Pocket Aquarium works: pair two fish, wait for the egg, and use the 16% mutation rate to breed rare traits. Covers the 8-slot tank, the daily wanted poster and world-first species naming. Published 2026-10-06 by Glowbox · https://glowbox.dev/guides/pocket-aquarium-guide [[game:pocket-aquarium]] Pocket Aquarium is a small fish-breeding game in a browser tab. You keep a handful of fish, pair them, wait for an egg, and see what hatches. Fish are described by five genes, so every fish is a five-digit species code that is shared worldwide. There is nothing to rush: no timer, no score to protect, and no way to fail. You can close the tab and come back to the same tank. ## What you start with A new tank contains **3 fish** and nothing else. They are ordinary starter fish: common colours, common body shapes. The tank holds **8 slots**, and eggs share those slots with fish — one egg waiting to hatch uses one of your eight. Two eggs can be hatching at the same time. A third pairing is refused until one of them hatches, so if you are waiting, you are waiting. ## How breeding works 1. Tap a fish. A card appears with its name, rarity and traits. 2. Tap **Breed** on the card, then tap a second fish. An egg drops to the sand. 3. The first egg you ever breed hatches after about **6 seconds**. Every egg after that takes **20 seconds**. 4. When it hatches, you see the new fish. If the species is new to the world, you get a full field-guide card. While you wait for a partner, your chosen fish stays highlighted and the others slow down. ## The five genes Every fish is built from five separate traits, and each trait is inherited separately from one parent or the other: | Gene | Options | | --- | --- | | Body | Round, Slim, Puff, Long | | Fins | Fan, Veil, Spike, Ribbon | | Pattern | Plain, Stripes, Spots, Fade, Scales | | Main colour | Coral, Sunny, Mint, Sky, Lilac, Rose, Pearl, Opal | | Second colour | the same eight | That is **4 × 4 × 5 × 8 × 8 = 5120 possible combinations**, and each combination has its own five-digit code, like `21407`. Two players holding the same code are holding the same species, everywhere. ## Mutation is the whole game Offspring inherit each gene from one parent. But **each gene has a 16% chance to mutate**, which means most babies will differ from both parents somewhere. The second colour mutates at half that rate, 8%. Mutations are weighted: a mutation is more likely to land on a common trait than a rare one, with common options roughly four times as likely as the rarest. That still leaves plenty of room, because rarity is measured across all five genes at once. Every fish is scored out of 10 and labelled: - **Common** — score 0 or 1 - **Uncommon** — score 2 or 3 - **Rare** — score 4 or 5 - **Legendary** — score 6 or more A single rare gene gives Rare. Two rare genes — say a Puff body and a Scales pattern — puts you in Legendary territory. **The key rule: rare traits only ever arrive by mutation.** Breeding will never produce a Puff body or a Pearl colour from two fish that do not already have one. So the practical question is not "which pair should I choose" but "how do I keep rolling the dice". ## Getting further - **Keep a diverse tank.** With only 3 fish you keep re-breeding the same small gene pool. Filling the extra slots with different colours and shapes gives you more different mutation outcomes to work with. - **Cross carriers of different rare traits.** If one fish has a Puff body and another has Ribbon fins, each has a 50% chance of passing its own trait, so about **1 in 4** of those eggs carry both. That is far better than waiting for two rare mutations to land at once. - **Watch the second colour.** Colours cross between parents: a baby takes its main colour from one fish and its second colour from the other. Two-tone parents therefore produce much more colour variety than two identical fish. - **Do not rush to release.** Your field guide keeps a species record forever, even after the fish swims off to the sea. Releasing is a way to free a slot, not a penalty. ## Today's wanted poster A poster in the corner asks for a fish with **two specific traits**, drawn from the date so that everyone gets the same one. Breed a fish that matches both and the poster is answered. The first person worldwide to answer it has their name on it, and everyone after that is counted. The poster resets at **midnight UTC** and you get a new one each day. It is checked automatically the moment an egg hatches, so you do not have to submit anything. One detail worth knowing: the poster pool never asks for a Round body, Fan fins or a Plain pattern. Whatever it asks for, at least one part of the answer is something you cannot get by simply breeding your starter fish unchanged. ## Species names and the world field guide The first person to breed a species nobody has bred before **discovers** it. That first discovery triggers the naming step: the game writes a name, a Latin-style binomial, a short field-guide entry and one line about its habits. That record is then attached to the species code for everyone. If someone else breeds the same fish later, they see the name the first person gave it, plus a note that it has been bred a certain number of times worldwide. The same applies to the field guide tabs: Newest, Most bred, Wanted and Mine. You can also send a fish to a friend. The share link carries the five-digit species code, and whoever opens it can adopt a copy — once per species per player. If your tank is full when the link opens, the game tells you to make room first. ## Common sticking points - **"You need two fish to breed."** This is the message you get if you tap Breed with nothing selected. Select the first fish, then tap Breed on its card, then tap the second fish. - **"The tank is full."** You have 8 slots taken by fish and eggs combined. Eggs disappear when they hatch, so waiting is often the fix; otherwise release a fish. - **Waiting for eggs and doing nothing.** Eggs hatch on their own after 20 seconds. You do not need to keep the page in front of you, and the hatch is processed when you come back. - **Expecting to control the result.** You cannot pick the outcome. If you want a specific trait, keep breeding until mutation delivers it. ## How long does any of this take? There is no official figure for how long it takes to fill a field guide, and no claim here will give you one — it depends on how much you breed. What is knowable is the rhythm: about 20 seconds per egg after the first, two eggs at a time, and a tank that tops out at eight. ## FAQ **Can you lose in Pocket Aquarium?** No. There is no fail state, no timer and no energy system. The worst thing that can happen is a full tank, and you fix that by releasing a fish or waiting for an egg. **Why is my tank full when I only have a few fish?** Fish and eggs share a single limit of 8 slots. Two eggs waiting to hatch count as two slots, so a tank of 7 fish and 1 egg is full. **How do I get a Rare or Legendary fish?** Rare traits can only arrive through mutation, and each gene mutates on a 16% chance per egg. Keep diverse parents and breed in volume; two rare genes on one fish is what makes a Legendary. **Do I need to keep every fish?** No. Releasing a fish frees its slot and it swims off to the sea, but its species stays in your field guide permanently. You are not allowed to release down to fewer than two fish. **When does the wanted poster change?** At midnight UTC. Everyone gets the same two-trait poster that day, the first person to answer it is credited, and a new one appears the next day. ## FAQ **Can you lose in Pocket Aquarium?** No. There is no fail state, no timer and no energy. Fish keep swimming while you are away and eggs hatch on their own. **Why is my tank full when I only have a few fish?** Fish and eggs share one limit of 8. Two eggs waiting to hatch count as two of those slots. **How do I get a Rare or Legendary fish?** Rare body shapes, fin types, patterns and colours can only arrive through mutation. Each gene has a 16% chance to mutate on every egg. **Do I need to keep every fish?** No. You can release a fish back to the sea and it stays recorded in your field guide. You are not allowed to go below two fish. **When does the wanted poster change?** It resets at midnight UTC and asks for two specific traits. Everyone playing that day gets the same poster. ## Games in this article - [Pocket Aquarium](https://glowbox.dev/game/pocket-aquarium): Breed little fish, hatch eggs, and be the first in the world to discover a species nobody has seen before.