Part of the With What family
Pets With What
Group Guide

Aquatics

The animals that live inside a box of chemistry you run for them — and the group where the equipment is most of the keeping.
An aquarium is a life-support system, and the animal in it can never leave. Most of what goes wrong in fish keeping is the water, not the fish — stress, poor water quality, overcrowding and skipped quarantine sit under many of the diseases that follow.1 Get the tank right before the animal arrives and this is one of the calmest, longest-lived corners of pet keeping. Get it backwards — fish first, chemistry later — and the fish pays for the lesson.
At a glance — all aquatics
Lifespan
2–25+ years
Adult size
3 cm – 30 cm
Minimum tank
Bigger than the bowl — always
Water
Cold to tropical, all of it conditioned
Weekly upkeep
Water changes, weekly, forever
Diet
Less than you think — overfeeding fouls the water
Company
Shoals, pairs and strict loners — know which
With children
Watch, don’t touch
Tankmates
Compatibility is research, not luck
The tank is the pet. A filter takes four to six weeks to grow the bacteria that make water safe, so the tank is set up and cycled before the animal is bought — in that order, every time.2
Species  ·  8 listed
Every entry below is a species page with its own varieties, costs and honest warnings.
Angelfish
  • Tall tank needed
  • Cichlid manners
  • Eats small fish
The elegant one — which is still a cichlid, with a cichlid’s opinions about neighbours.
Axolotl
  • Cold water only
  • Never handled
  • 10+ year commitment
A smiling amphibian that must stay cool, stay wet, and never be handled.
Bristlenose Catfish
  • Algae help, not algae cure
  • Needs driftwood
  • Peaceful
The janitor myth made flesh — except it still needs feeding, housing and respect.
Corydoras
  • Shoal of 6+
  • Bottom dweller
  • Soft substrate
The armoured street-sweepers of the community tank — cheerful, busy, and never to be kept in ones or twos.
Goldfish
  • Decades, not months
  • No bowls
  • Cold water
Not a bowl fish. Never was. A big, long-lived carp that deserves the truth.
Guppy
  • Livebearer — they multiply
  • Beginner-friendly
  • Tropical
The easiest fish in the hobby, with one catch: the plural is automatic.
Neon Tetra
  • Shoal of 10+
  • Tropical
  • Peaceful
A living neon sign, sold by the dozen and best kept that way.
Siamese Fighting Fish
  • Males live alone
  • Heated tank — always
  • Interactive
A gorgeous, intelligent loner sold in a cup — the cup is the scandal, not the fish.
The three things that kill aquarium animals

Sources

  1. Disorders and Diseases of Fish. MSD Veterinary Manual 2026. Accessed 2026-09-05. International MSD Veterinary Manual Many of the disorders and diseases that occur in fish are the result of stress, poor water quality, overcrowding, and failure to quarantine. New tank syndrome is ammonia accumulating when fish are added before the biological filter works, typically in the first one to three weeks. Ich (white spot) is a common protozoal infestation whose fast reproduction is what makes it deadly.
  2. Providing a Home for Fish. MSD Veterinary Manual 2026. Accessed 2026-09-05. International MSD Veterinary Manual Prolonged ammonia exposure is highly toxic to fish; bacteria convert ammonia to nitrite (also toxic) and then to nitrate, and those bacterial colonies take four to six weeks to establish on their own. Stock gradually so the colonies grow with the waste.

Every source here was checked, not recalled. Where this page makes a health statement and no source appears against it, that is not an oversight we have hidden — it means the claim is not yet sourced, and the build reports how many are in that state.

Availability, registration and keeping requirements differ from place to place. Check the rules where you live before you commit to any animal — we describe animals, not law.