Bagging: water, air and darkness
The bag is the fish's whole world for the journey, so build it properly. Use strong, purpose-made fish bags, filled about one-third with water from the fish's own tank and two-thirds with air, which carries the oxygen the journey consumes. Bag fish individually if they are large, territorial or spiny, and in small compatible groups if they are tiny schooling species, because a bag of mixed tempers arrives with casualties. Double-bag everything, the second bag inverted so the corners of the first cannot trap a fish, seal both, and pack the bags upright and snug in a dark insulated box or cool bag. Darkness is not packaging detail; it is sedation, keeping the fish calm and still for hours.
The day before: empty stomachs, calm water
Stop feeding from the day before travel. A fed fish in a small bag produces waste into water that is never filtered or changed, and ammonia in a sealed bag is the main killer on long journeys, ahead of temperature and ahead of oxygen. A partial water change the day before bagging gives the tank water the fish travel in the cleanest possible start. Catch the fish with a soft net or a jug, never chase them around the tank until they are exhausted; a fish that goes into the bag already stressed spends the journey recovering instead of resting. Bag the most nervous species first while the tank is still calm and fully set up.
In the car: steady temperature, no sliding
The box rides in the cabin, wedged so it cannot slide, tip or be crushed by luggage, and out of direct sun through the windows. Keep the cabin temperature steady and comfortable; the insulated box smooths the small swings, but a car parked in full sun or heated to tropical levels defeats it. Drive the journey as one leg if you can. The bags, properly filled, carry fish safely for many hours, and opening them at a service station to check does more harm, in lost air, light shock and sloshing, than leaving them sealed and dark. Resist the peek; it is for you, not for them.
Arrival: temperature first, then patience
At the destination, the order reverses the packing. Set the receiving tank up and running first, or at minimum a prepared holding container with conditioned water at the right temperature, before the box is opened. Float each sealed bag on the surface until temperatures match, then open, add small amounts of the new water over several minutes, and net the fish gently into their tank, keeping the bag water out of it. Lights off, no food until the next day, and no rearranging around them while they settle. A fish that hides for the first evening after a long journey is behaving normally, not reporting a problem.
Records that travel better than memory
On a long move, the details that matter at the far end are easy to scramble: which species were grouped, what temperature each tank ran at, who eats what. A KinsLe Pet Passport holds each fish's identity, group and routine in one portable packet, so the tank you rebuild after hours on the road matches the community that left home, and nothing depends on a tired driver's memory at midnight in a new house.