The greatest difficulty in keeping mandarins is their feeding requirements: in the wild, mandarins subsist on a diet consisting almost entirely of microscopic live marine crustaceans and tiny marine worms. In order to sustain themselves on such small prey, they must hunt continuously. By the time most pet mandarins reach their eventual owners, they have spent weeks in holding and transport with nothing to eat, and are often in very bad shape.
A common misconception is that mandarinfishes only take live foods, which would suggest that they only eat foods that move. On the contrary, having watched mandarinfishes hunt, I have observed that even when catching live prey, they tend to strike stationary targets. The reason why most conventional fish foods are rejected by mandarins is not because they are not live, but because of their size. The preferred food particle size for mandarinfishes is 1/5 to 1/2 of a millimeter, which is about the size of a speck of dust, or the period at the end of this sentence. Live marine crustaceans larger than this tend to be ignored, as my mandarins would hunt live copepods exclusively while passing up the much fatter amphipods in my aquarium.
Mandarinfish foods spreadsheet:
Frozen brine shrimp (5mm) | Frozen mysis shrimp (5mm) | Deshelled brine shrimp eggs (0.25 mm) | Wild copepods (0.5 mm) | Capelin roe (sushi fish eggs) (2mm) | Dry foods (flake, new life spectrum pellets) | Refrigerated Arctic copepods (non-frozen, 2mm) | Notes | |
Green mandarin, 4 inch male, (store bought, poor condition, very skinny) | yes | no | - | no | - | no | no | Died within 24 hours of purchase from general poor health |
Spotted mandarin, 1.5 inch male (ORA tank-raised) | no | no | - | no | - | no | no | Starved after 3 weeks. Ate nothing, didn’t know how to catch wild copepods. |
Spotted mandarin, 2 inch female (wild) | yes | yes | - | yes | - | no | no | Did great, but suffocated due to aquarium power outage |
Spotted mandarin, 1.5 inch male (wild) | no | no | yes | yes | yes | no | no | Doing great, now extremely fat |
Spotted mandarin, 1.5 inch female (wild) | no | no | yes | yes | no | no | no | Doing great, now very fat |
