Work with the clock, not against it
A nocturnal fish is not being difficult; its eyes, feeding instincts and sense of safety are all wired for darkness, and no training will turn it into a daytime performer. What training can do is relocate the night shift. If the food reliably appears in one visible place at one predictable moment, most nocturnal catfish, loaches and plecos will come to that place in front of you — on their schedule, but on your stage.
Pick one stage and never move it
Choose a feeding station at the front corner of the tank: a small glass or ceramic dish sunk into the substrate, or a swept-bare patch of gravel or sand. A dish is better — it keeps sinking pellets, wafers and frozen foods in one visible spot instead of scattering into the decor where the fish feeds hidden. Put the station somewhere you can sit and watch comfortably, a little to one side of the fish's favourite daytime hiding place, so the journey to dinner is short on the first nights.
Feed at lights-out, watch in near-dark
Drop the food in as the tank lights go off, and watch in dimness: a low blue 'moonlight' LED, or simply the room's ambient light with the tank light off. Let your own eyes adjust for a few minutes. Never blast a phone torch or camera flash into the tank — a sudden beam sends nocturnal fish bolting and teaches them the feeding station is dangerous. Viewed in low light, most species emerge within ten to twenty minutes at first, and faster as the routine beds in.
Condition a dinner bell
Run the identical sequence every night: room lights low, tank lights off, one soft tap on the rim or the feeding tongs appearing above the station, then food down into the dish. Fish learn place and cue astonishingly well — nocturnal species navigate by smell and vibration, and the tap-plus-scent combination becomes a dinner bell. Expect the first week to look like failure, with food eaten only after you leave; by the third or fourth week most individuals are waiting near the station before the food lands.
Beat the daytime competition
The usual reason a nocturnal fish 'never eats' is that faster tankmates eat first. Feed the daytime fish their own meal shortly before lights-out so they are less frantic, and for very shy species use a pipette or tongs to place food directly into the dish — or, in the first weeks, right at the entrance of the fish's hide, gradually shifting the drop point toward the dish. Remove uneaten food the next morning so the station stays clean and the water stays honest. If a fish that had learned the routine stops emerging at night or stops eating altogether, test the water first and then seek an aquatic veterinarian's advice, because appetite loss at night is often the first visible symptom of a problem. Keep the nightly sequence unbroken by sharing it in KinsLe, where Care Teams can assign the lights-out feed to whoever is home, every feed closed with a timestamp.