Shy fish are not being difficult; they are running the survival maths of a prey animal in a glass box. Every decorating choice that lowers their sense of exposure — cover within reach, broken sight-lines, softened light — pays you back in fish that come out, feed confidently and show their real colours.
Block the See-Through Effect First
An uncovered back pane makes a tank feel like open water overlooked from all sides. Fit a plain dark background to the outside of the back glass and the fish instantly treat that whole side as a wall rather than a window. Plant the back and both ends more densely than the front, so the tank has a sheltered rear corridor running its full length. Fish that know they are one flick from that corridor will cruise the open front far more boldly than fish in a bare tank with a single ornament in the middle.
Provide More Hides Than There Are Fish
Caves, coconut shells, hollow wood, rock piles with gaps and dense plant thickets are the furniture of confidence — but only if there is enough to go round. A single prized cave creates a competition the shyest fish always loses. Scatter several hides of different sizes along the back and ends, with entrances facing different directions, so every fish can claim one and a chased fish always has a second door to dive through. Bottom-dwellers want their shelter on the substrate; mid-water fish shelter in planting, so give each layer its own cover rather than decorating only the floor.
Break Up Sight-Lines and Soften the Light
A shy fish crossing an open tank feels watched the whole way. Tall plants, a leaning piece of wood or a rock stack placed mid-tank divide the space into rooms, letting fish move in short hops between cover instead of one long exposed dash — and the same breaks interrupt a dominant fish's line of sight, which settles squabbles as well as nerves. Overhead, floating plants or tall growth reaching the surface diffuse the light, removing the hard shadows from above that read to a small fish as a heron arriving. Bright, bare and shadowless is the most frightening combination of all.
Help Confidence With Placement and Routine
Where the tank sits matters as much as what is in it: a spot beside a slamming door or in the middle of the household's busiest walkway undoes good decorating. Put the tank where people pass at a distance and approach from the front in view of the fish, feed at the front glass at the same times each day, and let the fish learn that the big shape arriving means food, not danger. Schooling species also draw courage from numbers, so a shy school kept at a proper group size will always out-behave the same fish kept as a pair.
The layout only protects the fish while it stays where you built it, and a well-meaning tidy during a water change can demolish a shy fish's whole map in a minute. A photo and a few notes shared on the tank's Family Sharing page in KinsLe tell everyone who cleans or feeds exactly which cave, thicket and wood pile are load-bearing for the fish's confidence.