Fish

Oscars, sailfin catfish and pacus that outgrew the tank:

these are the fish most often looking for a new home, because each one arrives the size of a coin and never stops growing. A common sailfin catfish passes 30 centimetres, an oscar gets close to that, and a pacu grows several times bigger than anything a living-room tank can hold. Convicts are the other regular: a pair breeds so readily that its owner ends up with fry to give away every few weeks. All of them belong under aquarium fish; koi and goldfish from a garden pond go to pond fish, and the glass, filters and heaters are bought and sold in aquariums and aquarium accessories.

A community tank, a cichlid tank or a pond:

which one a fish needs depends on its adult size and temper, not on the size it is today. Central American cichlids, convicts, firemouths and the Jack Dempsey, a native of the same Atlantic-slope rivers, hold territory and will harry or eat guppies and tetras, so they live with their own kind or alone. Goldfish belong with goldfish: they make a lot of waste for their size and like cooler water than tropical fish, which is why so many end up in a pond. Koi need a pond, not a tank; one adult wants more water than most aquariums hold.

Armoured catfish loose in Guatemala’s rivers:

they are what happens when a fish that grew too big is let go instead of passed on. Sailfin catfish released from aquariums now live wild in Guatemalan rivers, and pacus have turned up too. Lake Atitlán shows how long that kind of damage lasts: the black bass put into the lake for anglers were one of the reasons the poc, a grebe found nowhere else, died out. A fish you can no longer keep goes to another keeper, never into a river, a lake or the drain.

Fins, gills and appetite in a fish looking for a home:

tell you more about its health than any description. Fins should be held open, not clamped against the body or frayed at the edges; white specks like grains of salt are ich, which spreads to every fish in your tank. A fish gasping at the surface with its gills working hard, hanging in a corner or with a hollow belly is either ill or living in bad water. Ask the owner to feed them while you watch: a healthy fish eats straight away. Even then, a newcomer is safest in a spare tank for a couple of weeks before it joins your own fish.

A whole tank handed over with its fish:

is the easiest move for them, as long as the filter travels wet. The sponge or media in a running filter carries the bacteria that break down waste; let it dry out on the way and the tank starts from zero, which is when transferred fish die. Carry it in a bucket of the tank’s own water. The fish travel in sealed bags, about a third water and two thirds air, inside a cooler so they stay dark and at an even temperature. At home, float the bags for a quarter of an hour before letting the fish out.

Listing fish, a pond clear-out or the tank they lived in:

name the species as precisely as you can, common sailfin catfish or bristlenose, convict or Jack Dempsey, and give each fish’s size now in centimetres, measured against the glass. Say how many there are, which sex if you know, what they share a tank with and what they eat. Explain why they are moving on: “outgrew a 200-litre tank” is exactly what someone with a bigger one wants to read. Then agree how they will travel. Someone collecting fry in Villa Nueva needs bags and a cooler; a pond of koi leaving a house in Chimaltenango needs large tubs, an air pump and two people.