Aquaponics · Animal husbandry and production biology

Fish rearing in aquaponics

Sustainable fish production does not come about through the highest possible stocking, but rather through an environment that is suitable for the fish species, controlled feeding, reliable water treatment and sufficient reserves for disturbances.

Animal welfare before maximum stockingBiomass instead of quantityFeed load as a basis for calculationPlan for emergency ventilation

Clearly determine the production goal

1. What raising fish means in aquaponics

The fish area is an independent animal husbandry system within the overall facility. It must also function reliably when plants absorb fewer nutrients, pumps fail or a plant module is temporarily out of operation. Fish provide nutrients for plants through food and metabolism; However, they are not interchangeable “nutrient generators”.

Posture goal

Healthy animals with species-specific behavior, growth and low avoidable stress.

Production target

Predictable biomass increase with documented feeding, water quality and mortality.

System goal

A feed load that biofilters, oxygenation and crop production can handle permanently.

Key decision: Fish species, temperature range and production goal are determined before tank size, stocking and plant area.

Biology before market price

2. Match fish species and location

No one type is universally “the best type of aquaponics.” The decisive factors are temperature, oxygen requirements, water chemistry, social behavior, growth, available young fish, food, legal situation and sales. Hot water types may require heating energy; Cold water species usually have high requirements for oxygen and cooling.

2. Match fish species and location
Test field	Key question	Planning sequence
Temperature	Does the species-specific area match the location and crop production?	An honest assessment of heating, cooling and seasonal operation.
Oxygen	Does reserve remain even at night and at maximum biomass?	Design ventilation according to peak load and failure event.
behavior	Is the species territorial, flock-forming, ground-oriented, or sensitive to handling?	Adjust tank shape, structure, sorting and group size.
Law and market	Can the species be kept, transported, slaughtered and marketed?	Clarify permits and marketing channels before stocking.

No species list replaces a site inspection. Target areas are always species-specific and must also be assessed according to life stage, origin and husbandry system.

Quantity is not a sufficient key figure

3. Plan stocking based on biomass and system capacity

A hundred young fish can form a low initial biomass and overload the system a few months later. Therefore, current weight, expected final weight, feed quantity, oxygen requirement, TAN production, solids accumulation and hydraulic limits are considered together.

Number of pieces × average weight→Biomass→daily feed load→O₂, filter and discharge requirements

Conservative entry

Start with a low load, set up a measuring routine and only increase it if water quality, behavior and filter performance remain stable.

Growth reserve

Tank, biofilter and ventilation are tested for the highest expected biomass before harvest or sorting - not just for the initial stocking.

Classification of the FAO guideline: The FAO specifies a maximum of around 20 kg of fish per 1,000 liters for the units described in its small-scale installation manual. This is not a universal standard and replaces neither species-specific animal welfare assessment nor proof of real system capacity.

Lining is the central material input

4. Measure, observe and balance feeding

Feed determines growth, oxygen consumption, nitrogen load, solids production and a large part of the operating costs. The daily ration is adapted to species, biomass, size, temperature, health status and actual feed intake.

Before feeding

Check temperature, oxygen, behavior and technology. If the values are abnormal, first clarify the cause.

During feeding

Feed in portions, monitor intake and avoid leaving food permanently in the tank or filter.

After feeding

document quantity; Assess leftovers, feces, oxygen depletion, and unusual behavior.

Warning signal: Sudden refusal to feed is not a reason to make the food more attractive, but to check water quality, oxygen, temperature, stress and illness.

Interpret measured values together

5. Water quality is habitat

5. Water quality is habitat
Measurand	Meaning	Operational response
Oxygen	respiration of fish and biofilm; Demand increases with biomass, feeding and temperature.	Ventilate continuously, protect against peak loads and power outages.
Temperature	Influences metabolism, feed intake, oxygen solubility and NH₃ content.	Keep changes slow and stick to species-specific range.
pH	Affects fish, biofilters, plants and the NH₄⁺/NH₃ ratio.	Do not correct in isolation; Evaluate alkalinity and temperature.
TAN / NH₃	TAN includes ammonium and ammonia; NH₃ is significantly more toxic.	Limit feeding and stocking, check biofilters as well as pH, temperature and oxygen.
Nitrite	May affect oxygen transport in fish.	resolve cause; Only use countermeasures specific to the species and professionally.
Nitrate	End product of aerobic nitrification and plant nutrient.	Evaluate plant intake, water changes or further treatment.

A single value does not describe safe operation. Measurement methods, units, sampling times and trends must be documented.

Practically observe animal welfare

6. Behavior and body condition as an early warning system

Unobtrusive

Species-specific swimming style, even distribution, controlled food intake and intact skin and fins.

Needs clarification

Chafing, secretion, unusual dark or light coloring, frantic swimming, conspicuous gills or repeated gasping for air.

Act immediately

Several animals with respiratory distress, loss of balance, acute mortality or sudden refusal to feed.

Stocking density does not work alone. Water quality, group composition, current, feeding, handling, disease and retreat options can increase or weaken their effect.

Dimension technology according to animal load

7. Tank, flow, aeration and solids discharge

Tank geometry: must allow for uniform mixing, controllable flow and complete visual inspection.
Inlets and outlets: Secure against suction, jumping and dead zones.
Solids discharge: Remove droppings and leftover food promptly without constantly stressing the animals.
Ventilation: think independently of the water pump; Provide critical components with alarms and reserves.
Materials: Food and animal compatible, cleanable and suitable for the operating conditions.

Planning rule: The system must function at the maximum intended biomass - and allow enough time for an orderly response to a failure.

Onset is a stressful event

8. Young fish, quarantine and acclimatization

Document origin, health status, type and number of items.
Provide quarantine area with separate equipment and controllable waterway.
Gradually adjust temperature and water chemistry; Avoid unnecessary exposure to air.
Only use when biofilter capacity and emergency technology are verifiably available.
In the first few days, closely check behavior, mortality, feed intake and water parameters.

New animals, transport water, nets, hands and equipment can transmit pathogens. “Clear water” is not proof of health.

Treat causes instead of symptoms

9. Health, biosecurity and medication use

If there are any abnormalities, water quality, oxygen, temperature, technology, feeding, injuries and recent changes are checked first. A reliable diagnosis belongs in expert hands.

Biosecurity

Define visitor and equipment routes, quarantine, cleaning, dead fish management and proof of origin.

Treatment

Medicines, salt and disinfectants can affect fish, biofilters, plants and food safety. Only use in a legally and technically coordinated manner.

Do not treat on suspicion: An untested dosage can mask symptoms, damage the biofilter and promote residues or resistance.

Secure critical functions

10. Incidents and emergency plan

10. Incidents and emergency plan
event	First priority	Prevention
Power failure	Maintain oxygen supply and stop feeding.	Test UPS, generator or independent emergency ventilation regularly.
Pump failure	Secure tank ventilation, check waterways and overflow.	Maintain a spare pump, alarm and easily accessible barriers.
Oxygen drop	Additional ventilation, root cause check, feeding break.	Sensor or fixed measurement routine and reserve power.
TAN/nitrite increase	Reduce or stop feeding, check biofilter and flow.	Increase load slowly, document trends, do not clean filters in an uncontrolled manner.
Leak or overflow	Limit water loss and secure fish stocks.	Emergency volume, dry running protection and defined overflows.

Data makes operations controllable

11. Growth, feed utilization and inventory management

Regular spot checks enable the biomass to be estimated and thus adapted feeding. At least stocking, origin, amount of feed, sample weights, mortality, treatment, water parameters, technical malfunctions and harvest are recorded.

Biomass

Number of pieces × resilient average weight; Update mortality and withdrawals.

Growth

Don't just look at averages: large spread can indicate sorting, food access or health.

Feed utilization

Derive only from documented feed and reliable biomass change; Consider losses and harvest.

Protect food and animals until the end

12. Sorting, transporting and harvesting

Every handling must be justified and prepared. Equipment, personnel, water, oxygen and target containers must be ready before animals are captured. Sorting and transport take place as quickly as possible, quietly and with a suitable stocking density.

Only plan feeding breaks specific to the species and for the intended process.
Minimize air exposure, temperature change and mechanical injury.
Carry out slaughter and stunning in accordance with applicable law and appropriate methods.
Document cold chain, hygiene, traceability and waiting times.

Application note: Keeping, transport, stunning, slaughtering and marketing must be coordinated with the veterinary authority, food control and applicable law.

Comprehensible technical basis

13. Specialist sources

Somerville, C. et al. (2014): Small-scale aquaponic food production, FAO Fisheries and Aquaculture Technical Paper 589.
FAO: A guide to recirculation aquaculture.
EFSA: Fish welfare – scientific assessments and EU framework.
EFSA AHAW Panel (2008): Welfare aspects of husbandry systems for farmed trout.
FAO Technical Workshop (2016): Advancing aquaponics: technical and policy considerations.

Limit of validity: Guideline values must always be adapted to the fish species, life stage, stocking, feed, water source, measurement method, animal welfare, food safety and applicable law.