Recirculating Aquaculture Energy-Feed Balance Calculator
This calculator helps you explore how feed, energy, water, and basic economics interact in an intensive recirculating aquaculture system (RAS). By adjusting stocking density, feed conversion ratio (FCR), survival, and energy loads, you can quickly see how these choices affect cost per kilogram of fish produced and overall net margin.
Use the default values as a starting point, then adapt them to match your tanks, species, climate, and local energy or water prices. The tool is best used for comparing scenarios side by side rather than trying to predict an exact profit figure for a specific farm.
How the calculator thinks about your RAS
The model works on a per-cycle basis. You enter a grow-out length in days, average daily feed and energy use, and basic prices. The calculator then estimates total biomass produced, feed required, energy and water consumption, operating cost, and finally expresses everything on a per-kilogram-of-harvest basis.
At a high level, it uses these steps:
- Estimate total harvest biomass from system volume, stocking density, and survival rate.
- Use the feed conversion ratio (FCR) to relate biomass growth to feed input.
- Scale daily energy loads (pumps, aeration, heating/cooling) and water exchange over the grow-out cycle.
- Combine feed, energy, water, labor, and mortality disposal into an operating cost for the cycle.
- Convert totals into per-kilogram metrics: energy per kg, feed per kg, cost per kg, net margin per kg, and water use per kg.
Core formulas (simplified)
The exact implementation can vary, but the core relationships are straightforward. A simplified way to think about the biomass side is:
If you know the feed conversion ratio, the total feed required per cycle to achieve that harvest can be expressed as:
Energy and water are scaled over time. For example, if you treat pump and aeration power as operating continuously:
Dividing by harvest biomass converts these into per-kilogram results (for example, energy per kg or water use per kg). Operating cost per kilogram and net margin per kilogram follow naturally from multiplying quantities by unit prices and subtracting costs from harvest revenue.
How to interpret the outputs
The results panel shows several key indicators. They are intended as planning metrics and for comparing “what if” scenarios.
- Energy per kg harvest — Total electrical and thermal energy divided by kilograms of fish harvested. Lower values generally indicate more energy-efficient production, but extremely low values may assume unrealistically low aeration or heating.
- Feed per kg harvest — Effectively your realized FCR. Lower values mean more efficient growth and less feed cost per unit of fish, within biological limits for your species and system.
- Operating cost per kg — Sum of feed, energy, water, labor, and disposal costs divided by kilograms of harvest. This is a useful benchmark when comparing to your expected farm-gate price.
- Net margin per kg — Harvest revenue minus operating costs, expressed per kilogram. Positive values indicate that, under the assumptions entered, the system is covering operating costs and generating margin before capital and financing.
- Water use per kg — Makeup water required for daily exchange divided by harvest biomass. Recirculating systems typically target much lower water use per kg than flow-through systems.
Typical indicative ranges (these are not strict limits):
- Stocking density: 20–60 kg/m³ for many intensive finfish RAS, depending on species and system design.
- FCR: 1.1–1.6 for well-managed systems using high-quality feeds for many species; higher values indicate poorer feed efficiency.
- Survival rate: 85–98% is often achievable in stable, well-managed grow-out systems; significantly lower survival erodes margin quickly.
Worked example: medium-scale warmwater RAS
Suppose you run a 150 m³ warmwater system stocked at 40 kg/m³, with a survival rate of 92% and an FCR of 1.25. You operate for a 180-day grow-out. Pumps and filtration draw 18 kW, aeration and oxygenation draw 12 kW, and you use 80 kWh per day for heating and cooling. Electricity costs $0.11/kWh.
At the end of the cycle, your harvest biomass is roughly:
150 m³ × 40 kg/m³ × 0.92 ≈ 5,520 kg.
With an FCR of 1.25, total feed to support this growth is around 6,900 kg. If feed costs $1.85/kg, feed alone represents roughly $12,765 over the cycle. When you add energy, water, labor, and disposal costs, the calculator aggregates these into a total operating cost and then divides by 5,520 kg to report operating cost per kg.
If your farm-gate price is $7.80/kg, the tool computes total revenue (≈ $43,000 in this example) and net margin per kg. You can then test scenarios such as slightly lower stocking density with better FCR, or higher aeration loads that improve survival, and see how these shifts impact cost and margin.
Comparing scenarios and benchmarks
A common use of this calculator is to compare a less intensive scenario with a more intensive one. The table below illustrates, in qualitative terms, how increasing intensity typically changes your indicators.
| Parameter | Lower-intensity RAS | Higher-intensity RAS |
|---|---|---|
| Stocking density | 20–30 kg/m³ | 40–60 kg/m³ |
| Typical FCR | 1.3–1.7 (more variable) | 1.1–1.4 (with tight control) |
| Energy per kg harvest | Lower total energy, but moderate per kg | Higher total energy, often similar or slightly lower per kg if efficient |
| Water use per kg | Moderate exchange, moderate per kg | Often lower per kg with optimized filtration and reuse |
| Operating cost per kg | Lower fixed costs but less kg to spread them over | Higher energy and equipment load, but more kg to distribute costs |
| Net margin per kg | Can be stable but sensitive to price shocks | Can be higher if technical performance is strong; more sensitive to failures |
To use the tool in this way, change one or two variables at a time (for example, stocking density and aeration power) and record the outputs using the CSV download. Comparing runs side by side helps you understand which levers have the biggest impact on your cost and margin.
Assumptions and limitations
The calculator intentionally simplifies many aspects of RAS design and biology. Keep the following in mind when interpreting the results:
- The system assumes a roughly constant average biomass and stocking density over the grow-out period, which does not fully capture growth curves or grading events.
- Daily feed and energy inputs are treated as averages for the whole cycle; real systems will ramp up feed and energy as fish grow.
- Survival rate is applied uniformly across the cycle, without modeling specific mortality events or disease outbreaks.
- Water exchange is assumed to scale linearly with the percentage entered and system volume.
- Only major operating costs are included (feed, energy, water, labor, and basic mortality disposal). Infrastructure depreciation, financing, insurance, health treatments, broodstock, and equipment replacement are not covered.
- Results are expressed in nominal currency terms; inflation, tax, and interest are outside the scope of the model.
Because of these simplifications, you should treat the outputs as approximate planning figures and use them mainly for comparing alternative designs, technology choices, or management strategies rather than as a full business plan.
Who can use this tool?
This calculator is designed for farm owners, RAS designers, consultants, and students who want a quick way to link biological performance (FCR, survival, stocking) with operating costs (energy, water, labor) and expected harvest revenue. It can complement more detailed engineering models or financial spreadsheets by giving a fast view of the trade-offs involved in running an intensive recirculating aquaculture system.
Make recirculating aquaculture profitable without guessing the energy bill
Recirculating aquaculture systems (RAS) promise local, year-round seafood with minimal water use. They also carry serious energy loads: pumps, drum filters, biofilters, ultraviolet sterilizers, oxygen cones, and climate controls hum around the clock. Feed remains the largest single expense, but electricity and labor compete closely for second place. This calculator links the biological and mechanical halves of a RAS so you can evaluate whether stocking density, feed conversion, and pump sizing align with your financial targets.
The input block begins with biomass. Enter the total water volume across tanks and sumps, then choose a stocking density. Intensive RAS operations often target 40 kg of fish per cubic meter, though species like tilapia tolerate higher levels. Feed conversion ratio (FCR) captures how efficiently feed becomes fish: a value of 1.25 means 1.25 kg of feed yields 1 kg of growth. Grow-out cycle length controls how long pumps and staff run before harvest; multi-batch systems can adjust the cycle length to mimic continuous harvest.
Daily feed offered ties the biology to operations. Multiplying daily feed by cycle length gives total feed input. Survival rate determines how much of that feed becomes harvestable biomass versus mortalities that require disposal. Harvest price per kilogram reflects your market: premium salmon fetches $8–10/kg, while catfish may sell for $4–5/kg. Feed cost per kilogram is sensitive to protein content; inflation has pushed high-protein diets above $2/kg in some regions.
Mechanical inputs capture electricity demand. Pumps and filtration loads include mechanical filters, degassers, and recirculation pumps. Aeration load accounts for blowers or liquid oxygen systems. Daily heating or cooling energy covers heat pumps, chillers, or immersion heaters needed to maintain optimal water temperature. Multiplying these loads by energy cost per kilowatt-hour reveals daily utility expenses.
Water exchange stays low in RAS, but any percentage of makeup water multiplies across the entire volume. For a 150 m³ system, a 1.5 percent exchange uses 2.25 m³ per day. Enter the cost of water and wastewater discharge. Labor cost per day reflects technician wages and supervisory overhead. Disposal cost per kilogram of mortalities covers rendering or composting fees along with labor for removal.
The math balances inputs and outputs. Let be daily feed (kg), the cycle length (days), the feed conversion ratio, and the survival rate. Total harvestable biomass equals:
Mortalities total . Energy consumption combines continuous loads and daily heating energy:
Here and represent pump and aeration loads in kilowatts, while is daily heating/cooling energy. Water use equals system volume times exchange percentage times cycle length. Operating costs sum feed, energy, water, labor, and mortality disposal. Net revenue equals harvest biomass times price. The calculator outputs energy per kilogram , feed per kilogram , operating cost per kilogram, and resulting margin.
The results panel summarizes these metrics with plain language, including total revenue, total operating cost, and EBITDA-style margin. It also notes whether daily feed input aligns with FCR-based growth; if feed exceeds what biomass can consume at the chosen density, the tool warns you about potential waste and water-quality risks.
The scenario table presents three cases. “Baseline” mirrors your inputs. “Energy squeeze” assumes utility rates jump 30 percent and heating demand rises 20 percent during winter. “Feed optimization” lowers FCR by 10 percent through diet upgrades but increases feed cost by 12 percent to reflect premium ingredients. Each scenario lists energy per kilogram, feed per kilogram, operating cost per kilogram, margin, and water use.
Consider the default numbers: 150 m³ at 40 kg/m³ targets 6,000 kg of biomass. Feeding 120 kg/day over 180 days delivers 21,600 kg of feed. With a 1.25 FCR and 92 percent survival, harvestable biomass reaches about 15,897 kg. Mortalities total roughly 1,381 kg. Pumps and aeration draw 30 kW combined, consuming 129,600 kWh across the cycle; heating adds 14,400 kWh. At $0.11/kWh, energy costs about $15,840. Feed costs $39,000, water roughly $270, labor $46,800, and mortality disposal about $829. Total operating cost is near $102,739. Selling 15,897 kg at $7.80/kg yields $124,003 in revenue, leaving $21,264 in gross margin. Energy intensity is 9.06 kWh per kilogram of harvest, and feed use is 1.36 kg per kilogram after accounting for mortalities.
The comparison table below recaps these figures:
| Scenario | Energy (kWh/kg) | Feed (kg/kg) | Operating Cost ($/kg) | Margin ($/kg) | Water Use (L/kg) |
|---|---|---|---|---|---|
| Baseline | 9.1 | 1.36 | $6.46 | $1.34 | 17 |
| Energy squeeze | 11.2 | 1.36 | $6.98 | $0.82 | 17 |
| Feed optimization | 9.1 | 1.23 | $6.38 | $1.42 | 17 |
Winter energy spikes erode margin dramatically, while better feed efficiency recovers profits even with pricier diets. The calculator also shows water use at 17 liters per kilogram—far lower than flow-through systems—reinforcing the sustainability case when pitching investors.
Limitations: the model assumes constant stocking density throughout the cycle, ignoring early-stage tanks and grading events. Adjust the daily feed input if you stagger cohorts or use split-pond systems. Energy loads are treated as steady, but actual operations may throttle pumps or oxygen at night. Incorporate duty cycles if you have telemetry data. Finally, the calculator omits capital expenses, depreciation, and financing costs.
Use the CSV export to align feed suppliers, electricians, and bankers. When feed prices climb, input new costs and share the updated margin with investors. If utility companies propose demand charges, simulate higher energy costs to justify installing variable frequency drives or waste-heat recovery. The goal is to answer “How low can we let margin fall before stocking a second species or renegotiating power rates?” With this calculator, you have data ready before the next planning meeting.