The last hour decides the first month

A marine ornamental fish can survive a flawless collection, conditioning, packing and flight, and still be lost in its first hour in your facility if acclimation is rushed. Acclimation is the controlled process of moving a fish from the chemistry of its shipping bag into the chemistry of your system without shocking it. This professional protocol from Bluefields Aquatics is written for importers and aquarium stores receiving boxes of marine fish, and it is the natural companion to our guides on shipping stress and quarantine.

Before you open a single box

Prepare the room first. Dim the lights — a fish that has spent a day in a dark bag is dazzled and panicked by bright light, and panic costs oxygen and triggers injury. Have your acclimation containers, clean saltwater, airline tubing and test kit ready before the courier arrives, so that no fish waits longer than it must. Check the water temperature of your receiving system; it should be close to standard tropical marine values and stable.

Open the boxes calmly and in order. Note the condition of each bag as you go: clear water and upright fish are good signs, while cloudy water, strong ammonia smell or fish lying on their sides indicate a hard journey and a fish that needs extra care.

Temperature first

The first variable to equalise is temperature, because it changes fastest and stresses fish most immediately. Float the sealed, unopened bags in your receiving water, out of direct light, for fifteen to thirty minutes until the temperatures match. Do not skip this even if the bag feels warm — a sudden temperature shift of a few degrees can be enough to kill an already-tired fish.

Then pH and the drip

Once temperature is matched, the chemistry must be equalised gradually. The classic professional method is the drip acclimation: open the bag, pour the fish and its water into a clean container, and use airline tubing with a loose knot or a valve to drip system water in slowly, roughly two to four drips per second, over thirty to sixty minutes until the original water has been diluted several times over. This gives the fish time to adjust to differences in pH, salinity and hardness between the bag and your system.

There is one important caveat unique to long-haul marine shipments. The water in a sealed bag often has a low pH from accumulated carbon dioxide, and that low pH keeps toxic ammonia in its less harmful form. The moment you open the bag and oxygen rushes in, the pH rises and the ammonia becomes far more toxic. Work efficiently: do not leave fish sitting in opened bag water, and never drip so slowly that the fish marinates in rising-pH bag water for hours. Speed and gentleness must be balanced.

Moving the fish

When acclimation is complete, net the fish out and place it into your system — do not pour bag water into your tanks. Bag water can carry ammonia, medication residue and potential pathogens, and there is no reason to introduce it. For a busy import operation this also protects your biosecurity, keeping each incoming batch from contaminating your holding water.

New arrivals should go into a dimly lit, quiet quarantine system rather than straight onto a sales floor or into a display. This is where the link to quarantine becomes critical: the acclimation ends and the observation period begins.

The first 48 hours

Resist the urge to feed immediately. Most marine fish should be left to settle for several hours, sometimes overnight, before the first small feeding. A fish that eats within the first day or two is a fish that has travelled well; one that hides and refuses food needs close watching. Keep lighting low, keep the system stable, and disturb the fish as little as possible. Many losses in the days after import are not caused by the journey at all but by overhandling, bright light and premature feeding in the first 48 hours.

Reading trouble early

Watch for rapid gilling, clamped fins, loss of colour, or fish resting on the bottom — these are the signs of shipping stress that our separate guide covers in detail. Catching them early lets you adjust temperature, oxygenation or salinity before a recoverable fish becomes a loss. A fish that arrived in good condition will usually reward patient acclimation by colouring up and feeding within a day or two.

Acclimation is a shared responsibility

At Bluefields we pack to give every fish the best possible chance, and we plan routes to keep transit short, but the final hour belongs to you. An importer who acclimates carefully will see the low DOA we work so hard to deliver carried right through to healthy, feeding fish on the sales floor. To start a relationship with an exporter who supports you at every stage, request our stocklist or contact our team.

Building an acclimation routine for regular shipments

If you import marine fish regularly, acclimation should become a documented routine rather than an improvised scramble each time a box lands. A repeatable process protects your fish and frees you to handle volume without sacrificing care. Establish a fixed sequence: prepare the room and dim the lights, lay out clean containers and tubing, open and inspect boxes in order, float for temperature, drip for chemistry, net into quarantine, and record the condition of each batch. Keeping brief notes on how each shipment arrived — water clarity, fish condition, any losses — builds a picture over time of which routes and which species travel best, and gives you concrete feedback to share with your exporter. Train every staff member who might receive a shipment to the same standard, because a single rushed acclimation by an untrained hand can undo a perfect shipment. Stage your space so that incoming fish move smoothly from box to acclimation container to quarantine tank without bottlenecks, and never let a fish wait in opened bag water while you deal with something else. The investment in a documented routine pays off in consistency: the same low losses shipment after shipment, regardless of who is on duty. It also makes scaling possible, because a process that lives only in one person’s head cannot grow with your business. Pair this routine with a disciplined quarantine system and an eye for early shipping stress, and you have the receiving end of a reliable import operation.

Frequently Asked Questions

How do I acclimate newly imported marine fish?

Dim the lights, then float the sealed bags in your receiving water for 15 to 30 minutes to match temperature. Open the bags into clean containers and drip system water in slowly over 30 to 60 minutes to equalise pH and salinity. Then net the fish out — never pour bag water into your system — and place them into a dim, quiet quarantine tank. Leave them to settle for several hours before the first small feeding.

Should I pour the bag water into my tank?

No. Bag water can carry ammonia, medication residue and potential pathogens, and there is nothing in it worth keeping. Always net the fish out and discard the bag water. This also protects your biosecurity, keeping each incoming batch from contaminating your holding water — important for any store or wholesaler receiving regular shipments.

Why shouldn’t I feed new arrivals immediately?

A fish that has just endured a long flight is stressed and not ready to digest food, and uneaten food fouls the water it is trying to recover in. Most marine fish should be left to settle for several hours, sometimes overnight, before a first small feeding. A fish that eats within the first day or two has travelled well; many post-import losses come from overfeeding, bright light and overhandling in the first 48 hours.

Why does bag water pH matter during acclimation?

Sealed-bag water often has a low pH from accumulated carbon dioxide, and that low pH keeps toxic ammonia in a less harmful form. The moment you open the bag, oxygen rushes in, pH rises, and the ammonia becomes far more toxic. So work efficiently: do not leave fish marinating in opened bag water, and balance a gentle drip against the need to move fish into clean water before ammonia toxicity climbs.