Buckle up! After months (or maybe years) of long hours, vigilant care and much faith, your fish are ready for sale! Only one obstacle remains... the delivery.
It’s important to remember that a fish in transport is the same creature as the fish in a hatchery tank. It requires the same water quality to survive as it does in a culture tank. And, it will succumb to the same water quality as it will in a culture tank.
Of course there are extenuating circumstances... handling stress, sloshing stress, crowding, zero water exchange... but, these things do not change what the fish is. However, it should change the systems we provide the fish to survive. Some key concerns include the following:
• Why is there handling stress during a fish transfer? Perhaps the handling methods need to be changed to remove the stress.
• Why is there sloshing in the tank? A full tank will not slosh – perhaps the transfer tank design should change.
• Why is there zero water exchange? Perhaps a water exchange can happen en route? Or, the transport vehicle can be fitted with a zero water exchange treatment system.
We must remember that fish take in oxygen and release carbon dioxide. The CO2 decreases the pH. The fish release ammonia into the water. They release solids into the water. To successfully transfer fish, these factors have to be considered and mitigated if any parameter is likely to reach stress-inducing level.
Each of these parameters can be ‘treated’ or ‘mitigated’, but first, consider prevention. Consider how to prevent the degradation of water quality to the point of stressing the product. Here are several options:
• Lower stocking density: if feasible, this measure could prevent any issues from developing. If the added cost of two trips instead of one is nominal, perhaps this is the most effective measure.
• Lower temperature: at a lower temperature, fish respiration slows. If you have the time and equipment to do this, lower the temperature one degree/day until you reach the lowest safe temperature for your species prior to transport. Maintain the low temperature until reaching the destination and gradually increase the water temperature one degree/day back to the desired temperature.
• Stop feeding: the feasibility and methods here may be species-specific, but a fish that has not eaten for several days, will have lower respiration rates, lower rates of solids release and ammonia production. Therefore, water quality will be less affected.
• Better Handling: Handling of fish can be stressful to most species, and it is perhaps the most overlooked area in fish transport. Handling includes everything that happens to the fish from the time the transfer process begins until it ends. This may mean being chased around the tank, dipped out of water (multiple times), jostled, poked and prodded, water quality swings and extra hours in the transport box. All of this adds up to a very stressed animal. Transport time is when the staff needs all hands on deck, perhaps even some extra staff. Well thought out handling practices can be the greatest preventative measure contributing to a successful fish transfer.
If you think this is the section where the fish transfer systems engineering starts, go back to the section on prevention. Treatment is only necessary where we push and/or exceed the boundaries of biomass, temperature, feeding and handling. In reality, it may be necessary to some degree, certainly as risk management if nothing else. A list of common treatment areas includes:
• Oxygen: what happens to the oxygen level in your culture tank if the biomass is maxed out and the fish are stressed? The oxygen will drop just as fast in a transport tank with the same stocking density. Supplemental oxygen is possibly the single most important ingredient to a successful transport. A gas bottle with a ceramic diffuser is a highly mobile and cost-eff
ective oxygen supply system.
• Carbon dioxide and pH: the respiration of fish releases carbon dioxide causing pH to drop. A pH buffer additive can help to control this during transport where a CO2 degasser is not feasible. Degassing via aeration can be a cost-effective treatment method during longer transfers where a gas-powered blower can be used.
• Ammonia: establishing a biofilter on a transport vehicle is likely not feasible (please correct the author if this is wrong). There are products that ‘lock’ ammonia into non-toxic forms that allow fish to survive with higher than normal ammonia levels in the water.
Even the most in-depth system needs to be monitored during transport. Oxygen, temperature, pH are quick to measure at any given time. Oxygen is the main parameter to be concerned with unless the transfer is more than a couple of hours in length (some exceptions may apply). Periodically check that oxygen is still being applied to the tanks, aeration equipment is operational, and any other equipment is doing as it is supposed to.
4. Final considerations
So, you have covered all the bases for a successful fish transfer. But, you’re still assuming some things that shouldn’t necessarily be taken for granted. For instance:
• Transport vehicle: what is your backup plan if the vehicle breaks down?
• Rules of the road:
- Is the transport vehicle over its maximum weight?
- Is the vehicle over the maximum weight of any of the roads you plan to use?
- Do you have someone traveling with the shipment who knows how to monitor and react to water quality parameters or equipment failures?
• How long will it take to clear customs?
• Will adverse weather add to the length of the trip and can the fish handle the extension?
• Conscientiousness and tracking: mishaps such as forgetting the pH buffer in one of the transport boxes is a preventable ‘accident’. Create written procedures and checklists for your specific transport plan so quality control is firmly in place.
• Arrival/Unloading: A well-executed transfer can be sabotaged in the unloading phase if the same considerations have not been made to unloading as they have been to loading. Again, think about how to introduce the fish to their new home without causing them undue stress from rough handling, temperature shock or other factors.
As with most topics in aquaculture, fish transfers are so varied in terms of species, weather, duration, method, and value that it is difficult to give specifics in an article like this. Transfers have been successfully made by truck or boat with full RAS systems including tanks, and temperature control, by plane with no treatment system, and likely every variation in-between. The considerations described above should help you make the balance between risk and costs in your future fish transfers.
Philip Nickerson, B.Eng. is the Technical Manager and Engineer for Scotia Halibut Limited in Nova Scotia, Canada. He also owns and operates an aquaculture design and operations company – Aqua Production Systems Incorporated. To continue discussions from the article, contact him at: firstname.lastname@example.org