Pufferfish

The mbu puffer reaches 26 inches (67 cm) and lists a 396 gallon (1,500 liter) tank, the fahaka 18 inches (45 cm) in 119 gallons (450 liters). On the marine side the map, guineafowl and stars-and-stripes puffers pass 20 inches (50 cm) and want 180 gallons (680 liters) and up, and even the dogface and porcupine puffers need 150 gallons (570 liters) or more. They are sold as coin-sized babies with faces that make people buy them. Read the adult size first.

Three rows straddle the water types. The figure eight puffer is happy in fresh or light brackish water, stays around 3 inches (8 cm) and is one of the few marked social. The green spotted puffer is sold from freshwater tanks and is a brackish fish that wants full marine salinity as an adult, which is most of why it is rated difficult. The Ceylon puffer sits alongside it. If you plan to keep either, plan the salt from the start.

A puffer's beak grows for life and is worn down by crushing shells, so a diet of soft frozen food leaves it overgrown and the fish unable to eat. Feed snails, unshelled shrimp, mussels and cockles regularly. The Amazon puffer is the famous case: its teeth outgrow a soft diet fast enough that keepers trim them, and that plus its need for a shoal and a mature tank earns it the difficult rating.

The big Arothron and Diodon puffers are not reef safe. They eat snails, crabs, shrimp and whatever coral takes their fancy, so they belong in a fish-only tank. The small tobies, the valentini and the blue-spotted toby, are marked caution instead: they mostly behave in a reef but nip clams, small inverts and the fins of slow tank mates.