S4ag Aquaculture

---
name: s4ag-aquaculture
description: "Set up, stock, or manage a fish pond, tank, crayfish system, or aquaponics unit. Use when the user says anything like 'fish pond', 'trout tank', 'aquaponics', 'crayfish', 'water quality fish', 'fish production', or 'integrate fish with plants'."
allowed-tools: [Read]
---

# Aquaculture

Small-scale aquaculture is a high-value protein and fertility system that most farms can support. A well-managed pond, tank, or aquaponics unit produces food, generates biological fertility for the rest of the farm, and integrates naturally into any water-harvesting design. Your first decision is not which fish to grow — it is what kind of system fits your land, climate, water supply, and management capacity. Get the system match right and the fish largely look after themselves. Get it wrong and you will be managing a slow-motion emergency.

**How this skill works:** Each sub-tool pauses at a **Checkpoint** to confirm the assumptions it is about to build on before producing output. A recommendation built on a wrong assumption wastes time and money — confirm the checkpoint before acting. Each sub-tool ends with **Next steps** — the skills worth running once you have acted on this one.

---

## Expert Lineage

*The thinkers whose frameworks underpin this skill — and what they specifically discovered that changes how you farm.*

**Murray Hallam — Practical Aquaponics**
Hallam documented that the key failure mode in small-scale aquaponics is not fish disease or plant deficiency — it is mismatched fish-to-plant ratios leading to ammonia spikes that crash the bacterial nitrification cycle. His most actionable finding: start with fewer fish than you think you need, and add incrementally as the system matures. A system cycled for 4–6 weeks before fish are added survives; one that isn't rarely does.

**Nick Savidov — Nutrient Dynamics in Aquaponics**
Savidov's Alberta Agriculture research demonstrated that plants grown in aquaponic systems develop larger, more complex root systems than hydroponically grown equivalents, and that the microbial community on those roots — not just dissolved nutrients — is responsible for the productivity difference. His finding: aquaponics is not hydroponics with fish; it is a biological ecosystem where the bacteria are as important as the fish.

**Will Allen — Systems Integration**
Allen's Growing Power operation in Milwaukee demonstrated that aquaponics integrated with compost systems and soil-based growing outperforms either approach alone. His contribution: the effluent from fish tanks is not waste to be managed — it is a biological inoculant loaded with bacteria, bioavailable nutrients, and organic carbon. Pump it to soil beds and it functions as a live fertility input that soil farmers pay large sums to approximate.

**James Rakocy — Recirculating Aquaponics Research**
Rakocy at the University of the Virgin Islands developed the UVI aquaponics system and the design ratios that practitioners still use: stocking density, feed rate, plant bed sizing, solids management. His key finding: solids removal is the most underestimated maintenance task — uneaten feed and fish waste accumulate on the bottom of tanks and, if not removed, generate hydrogen sulphide and crash the system. Build the solids management into the design from day one.

**Elaine Ingham — Water Biology**
Ingham's soil food web framework extends into aquatic systems. The nitrification cycle in aquaponics — ammonia converted to nitrite by Nitrosomonas, nitrite to nitrate by Nitrobacter — is a food web within the water, not just chemistry. Her insight: healthy diverse bacterial populations in the water and on every surface in the system (media, tank walls, pipes) buffer against ammonia spikes better than any chemical intervention. Biological stability is achieved through diversity and biomass, not through chemistry.

**Peter Moodie — Pond-Based Polyculture**
Moodie's work on integrated pond systems in temperate climates demonstrated that combining species at multiple trophic levels — surface feeders, mid-water feeders, bottom-feeders, algae consumers — significantly increases total biomass production per hectare compared to monoculture ponds. His finding: in pond polyculture, each species' waste becomes another species' food, mimicking a natural lake ecosystem and reducing the need for external feed inputs.

---

## Which tool fits

| You need to... | Tool |
|---|---|
| Choose between pond, tank, or aquaponics | system-selection |
| Diagnose or prevent water quality problems | water-quality |
| Plan feeding, reduce feed costs, or grow your own feed | feeding-and-nutrition |
| Design or troubleshoot an aquaponics system | aquaponics |
| Connect aquaculture to the rest of the farm | integrated-systems |

## Routing Decision

- **Starting from scratch and unsure which system fits** → system-selection
- **Have an existing system with fish health or algae problems** → water-quality
- **Feed costs are too high or fish growth is slow** → feeding-and-nutrition
- **Want to grow fish and plants together** → aquaponics
- **Want to use fish effluent for crops or link water systems** → integrated-systems
- **Unclear** → system-selection first; it identifies which other sub-tools apply

---

## System Selection

*Matches the aquaculture system type to the farm's land, water, climate, and management capacity.*

Before choosing a species, choose the right system. Species can be swapped out. Infrastructure is expensive to rebuild.

**The four system types:**

| System | Capital cost | Management intensity | Production type | Best for |
|---|---|---|---|---|
| Earth pond | Low–medium | Low | Fish only | Farms with suitable topography and water supply |
| Lined tank (outdoor) | Medium | Medium | Fish only | Limited land, urban/peri-urban, no suitable pond site |
| Recirculating aquaculture (RAS) | High | High | Fish, premium species | Small footprint, high-value species, year-round production |
| Aquaponics | Medium–high | High | Fish + plants | Integrating food production; maximising fertility use |

**Decision sequence — work through these in order:**

**1. Water supply.** How much water do you have access to, and how reliably?
- Earth pond requires significant initial fill volume; top-up from rainfall, spring, or stream.
- Tanks and RAS require ongoing water input but less than ponds per kg fish produced.
- Aquaponics is the most water-efficient — evaporation losses only after initial fill.

**2. Land and topography.** Is there a natural depression, clay-heavy area, or spring-fed hollow?
- Earth ponds are cheapest where topography helps — a hollow requiring minimal excavation.
- Flat or sloping land without natural hollows makes pond construction expensive.
- Tanks and aquaponics can go anywhere with a level surface.

**3. Climate.** What are the winter temperatures?
- Trout and perch tolerate near-freezing water; carp survive freeze-over in dormancy.
- Tilapia die below 15°C — not suitable for outdoor unheated systems in cold climates.
- RAS and indoor aquaponics can maintain temperature year-round but at energy cost.

**4. Management time.** Be honest.
- Earth ponds with the right species can require as little as 2–3 hours per week.
- Aquaponics and RAS require daily monitoring — ammonia and dissolved oxygen crises develop in hours, not days.
- If management time is constrained, a low-intensity pond system almost always outperforms a poorly managed intensive system.

**5. Production goal.** What are you trying to produce?
- Protein for the farm household → earth pond, low-intensity, carp or perch.
- Premium market fish (trout, barramundi) → RAS or cool-water pond.
- Fish + vegetables for market → aquaponics.
- Fertility for the farm → any system with effluent management (see integrated-systems).

**Species matching by system:**

| Species | System | Climate | Notes |
|---|---|---|---|
| Common carp | Earth pond | Cool–warm temperate | Hardy; tolerates poor water quality; good polyculture anchor |
| Rainbow trout | Earth pond / RAS | Cool (10–18°C water) | High oxygen requirement; premium market value |
| Perch | Earth pond / tank | Temperate | Good flavour; slower growth; suits low-intensity systems |
| Crayfish | Earth pond / channel | Temperate–cool | Very low management; good margin; needs clean cold water |
| Tilapia | Aquaponics / indoor tank | Warm (>22°C) | Fast growth; tolerates crowding; temperature-limited |
| Murray cod | RAS | Warm temperate | Premium; slow; requires high management |
| Duckweed-fed carp | Earth pond | Warm temperate | On-farm feed production; very low external inputs |

**Checkpoint — confirm before finalising:**
- What is the water supply source and reliable annual volume?
- What is the winter low temperature for air and available water?
- How many hours per week can you commit to aquaculture management?

Recommending an aquaponics or RAS system to a time-limited farmer, or a tilapia system to someone in a cold climate, produces a failing system.

**Output:**
```
SYSTEM SELECTION
Recommended system type: [earth pond / lined tank / RAS / aquaponics]
Primary species: [species]
Secondary/polyculture species: [species or none]

Rationale:
- Water: [supply assessment]
- Land/topography: [assessment]
- Climate: [suitability]
- Management fit: [hours per week required vs. available]
- Production goal match: [assessment]

What to do first:
1. [first action — site survey / water test / planning permission check]
2. [second action]

What this system cannot do: [limits to set expectations]
```

**Next steps:**
- Run **water-quality** (within this skill) to understand what monitoring the chosen system requires before stocking.
- `/s4ag-water` — if this system is part of a larger farm water design, map the water flows together.
- `/s4ag-earthworks` — earth pond siting and construction connects directly to keyline and water-harvesting design.

---

## Water Quality

*Measures, maintains, and diagnoses the parameters that keep fish alive and growing.*

Water quality is the single most important management variable in aquaculture. Everything else — feed, stocking density, species choice — is secondary. Fish die from water quality problems, not from feed deficiency. Plants stall in aquaponics from water quality problems. Learn to read the water before you need to react to a crisis.

**The six parameters and what they mean:**

| Parameter | Healthy range | Critical level | What goes wrong |
|---|---|---|---|
| Dissolved oxygen (DO) | >6 mg/L | <3 mg/L | Fish gasp at surface; lethal below 2 |
| pH | 6.5–8.0 | <6.0 or >9.0 | Stress at extremes; nitrification disrupted |
| Ammonia (NH3/NH4) | <0.5 mg/L total | >2 mg/L | Gill damage; immune suppression; death |
| Nitrite (NO2) | <0.1 mg/L | >0.5 mg/L | Brown blood disease; blocks oxygen uptake |
| Nitrate (NO3) | <50 mg/L | >200 mg/L | Chronic stress; important in closed systems |
| Temperature | Species-dependent | See table below | Stress; reduced immunity; spawning triggers |

**Temperature ranges by species:**

| Species | Optimal range | Stress threshold |
|---|---|---|
| Rainbow trout | 12–18°C | >22°C dangerous |
| Carp | 18–28°C | <8°C dormancy |
| Perch | 16–24°C | >28°C stress |
| Tilapia | 24–30°C | <18°C dangerous |
| Crayfish | 14–22°C | >28°C stress |

**The ammonia cycle — the most important thing to understand:**
Fish excrete ammonia from their gills continuously. In a new system, ammonia accumulates to toxic levels within days unless the nitrifying bacteria (Nitrosomonas, Nitrobacter) are established first. This is called "cycling" the system.

Cycling protocol:
1. Fill the system and run the pump for 2–3 days.
2. Add an ammonia source (pure ammonia solution to 2–4 mg/L, or a small number of fish).
3. Test ammonia and nitrite daily.
4. After 2–4 weeks, ammonia and nitrite will spike then drop as bacteria establish.
5. System is cycled when ammonia and nitrite both read zero within 24 hours of dosing.
6. Only then stock at full density.

*Skipping this step is the most common reason new aquaculture systems fail in the first month.*

**Diagnosing common problems:**

| Observation | Likely cause | Immediate action |
|---|---|---|
| Fish at surface gulping | Low DO | Add aeration immediately; check pump |
| Fish lethargic, off feed | High ammonia or low DO | Test both; water change if ammonia >2 |
| Gills pale or bloody | Nitrite toxicity | 0.5% salt addition buys time; water change |
| pH dropping steadily | Biofiltration acid production | Lime or bicarbonate buffer |
| Algae bloom (green water) | Excess nutrients + sunlight | Shade pond; reduce feed; increase plant load |
| Fish flashing, scratching | Parasites | Observe; salt treatment if confirmed |

**Monitoring schedule:**

| System type | DO | Ammonia/Nitrite | pH | Temperature |
|---|---|---|---|---|
| Earth pond | Weekly | Monthly | Monthly | Weekly |
| Outdoor tank | Twice weekly | Weekly | Weekly | Daily in extremes |
| RAS | Daily | Daily | Daily | Continuous |
| Aquaponics | Daily | Daily | Daily | Daily |

**Aeration:** In all systems except low-density ponds, aeration is not optional. Dissolved oxygen is the first variable to crash in a stressed system — a cheap air pump or paddlewheel aerator is cheap insurance against mass mortality.

**Checkpoint — confirm before finalising:**
- What system type are you monitoring (pond, tank, RAS, aquaponics)? Monitoring intensity differs substantially.
- Do you have a test kit capable of measuring ammonia, nitrite, and pH, or just a general strip test?
- Is this a new system (cycling phase) or an established system with an existing problem?

Recommending a monthly monitoring schedule to someone in the first month of a new system will produce dead fish.

**Output:**
```
WATER QUALITY ASSESSMENT
System type: [type]
Date of assessment: [date]

PARAMETER READINGS
Dissolved oxygen: [value mg/L] — [status]
pH: [value] — [status]
Total ammonia nitrogen: [value mg/L] — [status]
Nitrite: [value mg/L] — [status]
Nitrate: [value mg/L] — [status if measured]
Temperature: [value °C] — [status for species]

ISSUES IDENTIFIED
[parameter]: [problem description and urgency]

IMMEDIATE ACTIONS (do today)
1. [action]
2. [action if needed]

ONGOING MONITORING SCHEDULE
[parameter]: [frequency]
```

**Next steps:**
- Run **feeding-and-nutrition** (within this skill) — overfeeding is the most common cause of ammonia spikes and poor water quality.
- Run **aquaponics** (within this skill) if this is a coupled system — plant bed sizing directly affects water quality buffering.
- `/s4ag-water` — if water quality problems are linked to the source water, assess the water supply.

---

## Feeding and Nutrition

*Reduces feed costs, optimises fish growth, and builds toward on-farm feed self-sufficiency.*

Feed is usually the largest ongoing operating cost in aquaculture, and the most direct driver of water quality problems. Overfeeding kills fish through ammonia. Underfeeding slows growth and undermines the economic case. The target is not maximum feed — it is optimal conversion.

**Feed conversion ratio (FCR):** The mass of feed required to produce 1 kg of fish. A well-managed system should achieve:
- Trout: FCR 1.0–1.5
- Tilapia: FCR 1.5–2.0
- Carp: FCR 2.0–3.0 (lower with natural food supplementation)
- Crayfish: FCR 1.5–2.5

An FCR rising above these ranges means feed is being wasted (water quality problem), fish are stressed (health problem), or feed quality is poor.

**Feeding rate by temperature:**

Feed conversion and appetite both depend on water temperature.

| Temperature | Feeding rate (% body weight/day) |
|---|---|
| <10°C | 0.5–1% or skip |
| 10–15°C | 1–2% |
| 15–20°C | 2–3% |
| 20–25°C | 3–4% |
| >25°C | Reduce to 2–3% (stress threshold for many species) |

Never feed fish that are not actively eating — uneaten feed sinks, decays, and spikes ammonia. Do the 5-minute rule: add a small amount of feed; if it is not consumed in 5 minutes, stop feeding for that session.

**On-farm feed production:**

Replacing purchased pelleted feed with on-farm produced feed can reduce feed costs by 40–80% for the right system.

| Feed input | Suitable species | Production method | Notes |
|---|---|---|---|
| Duckweed (Lemna spp.) | Carp, tilapia, ducks-to-fish | Surface pond or channel | Up to 40% of diet replacement; high protein (~35%) |
| Black soldier fly larvae (BSFL) | Most species | Organic waste processing | Very high protein and fat; excellent FCR replacement |
| Earthworms | Perch, trout, crayfish | Vermicompost system | High quality; labour-intensive at scale |
| Algae (Spirulina, Chlorella) | Tilapia, carp | Open raceway | High setup cost; high protein value |
| Daphnia / water fleas | Fry and small fish | Small tank with algae | Excellent fry food; low cost to produce |
| Insects (crickets, mealworm) | All species | Feed bin system | Flexible; can use farm waste as substrate |

**Duckweed as a system component:**
Duckweed thrives on nutrient-rich water — including fish effluent. A duckweed growing channel fed with pond effluent closes the loop: fish waste grows duckweed; duckweed feeds fish; cleaned water returns to the pond. A 200m² duckweed bed can provide a meaningful proportion of the feed requirement for a 1-tonne pond.

**Supplementing with natural pond productivity:**
In earth ponds, natural food (phytoplankton, zooplankton, invertebrates, aquatic plants) can supply a substantial fraction of diet requirements. Encouraging this through:
- Low-level organic matter addition (manure, compost tea) to drive phytoplankton growth.
- Pond polyculture: carp at mid-depth consume zooplankton; surface feeders consume insects and algae; bottom-feeders consume detritus.
- Stocking density kept at or below the level the natural productivity can support — this dramatically reduces purchased feed requirements.

**Checkpoint — confirm before finalising:**
- What species are you feeding, and what water temperature is the system currently running at?
- Are you trying to reduce existing feed costs, or designing a new feeding programme from scratch?
- Do you have access to organic waste streams (food scraps, manure, crop residues) that could support BSFL or duckweed production?

Recommending a high-stocking-density intensive feeding programme to someone who wants to reduce purchased feed inputs points in exactly the wrong direction.

**Output:**
```
FEEDING PROGRAMME
Species: [species]
System type: [pond / tank / aquaponics]
Current water temperature: [°C]

DAILY FEED AMOUNT
Target feeding rate: [% body weight/day]
Estimated fish biomass: [kg]
Daily feed amount: [kg/day]
Feeding frequency: [times per day]

FCR TARGET: [value]

ON-FARM FEED SUBSTITUTION OPTIONS
[option]: [estimated diet replacement %] [production requirements]

FEED COST ESTIMATE
Current purchased feed: [$/£ per week]
With on-farm substitution: [$/£ per week]
Estimated saving: [%]

FEED QUALITY CHECK
Do not feed if: water temperature <10°C / fish not actively rising to feed / system under stress
```

**Next steps:**
- Run **integrated-systems** (within this skill) — duckweed and BSFL systems connect aquaculture to farm waste streams.
- `/s4ag-composting` — a worm system producing earthworms as fish feed is a composting system that earns.
- `/s4ag-seasons` — feeding rates change by season; build the temperature curve into the annual farm calendar.

---

## Aquaponics

*Designs and manages an integrated fish-plant production system.*

Aquaponics is a closed-loop production system: fish produce ammonia, bacteria convert it to nitrate, plants consume the nitrate, cleaned water returns to the fish. Done well, it produces more food per litre of water than almost any other system, uses no synthetic nutrients, and generates biological fertility for soil beds from its effluent. Done badly, it produces dead fish, sick plants, and frustration.

**System types:**

| Type | How it works | Best for | Drawbacks |
|---|---|---|---|
| Media bed | Gravel or clay pebble beds flood-and-drain; roots grow in media | Beginners; diverse crops; biological filtration included | Heavy; limited plant density |
| Deep water culture (DWC/raft) | Plants float on foam rafts over fish effluent | Lettuce, leafy greens; scalable | Separate biofilter needed; cold-sensitive |
| Nutrient film technique (NFT) | Thin film of water flows past bare roots in channels | Herbs, lettuce | Poor in high solids; clogs easily |
| Hybrid | Combination of the above | Maximising diversity and resilience | More complex to balance |

**For first systems:** Media bed is the most forgiving. It provides biological filtration in the same unit, tolerates variable stocking, and grows a wider range of crops than DWC.

**System sizing — the critical ratios:**

The most important relationship is fish biomass to plant bed area.

| System type | Ratio |
|---|---|
| Media bed | 0.5–1 kg fish per 5–10L of media |
| DWC | 1 kg fish per 1–2 m² of raft bed |
| Rakocy's UVI system guideline | 60–100g of fish feed/day per m² of raft bed |

**Start undersized on fish, not on plants.** You can always add more fish once the system is stable. You cannot recover from an ammonia crash caused by overstocking.

**Balancing the system:**

A balanced aquaponic system achieves three things simultaneously:
1. Ammonia is consumed by bacteria as fast as fish produce it.
2. Nitrate is consumed by plants as fast as bacteria produce it.
3. pH is stable in the 6.5–7.2 range where both fish physiology and plant nutrient availability are optimal.

Signs the system is out of balance:

| Signal | Interpretation |
|---|---|
| Ammonia rising despite established system | Overstocked, overfed, or biofiltration compromised |
| Nitrate accumulating faster than plants consume | Plant load too small; add more plant beds |
| pH dropping | Nitrification producing acid; add bicarbonate buffer |
| Yellow leaves on plants | Iron deficiency (common in alkaline aquaponics); chelated iron addition |
| Plants lush, fish growing slowly | Fish load too low for plant demand — add fish or reduce plant beds |

**Plant species selection for aquaponics:**

| Category | Species | Notes |
|---|---|---|
| Best performers | Lettuce, basil, spinach, Asian greens, watercress | Thriving in high-nitrate water |
| Good performers | Kale, chard, pak choi, spring onions | Adapt well |
| Moderate | Tomatoes, cucumbers, capsicum | Need higher fish density for nutrients |
| Challenging | Blueberries, strawberries | Prefer lower pH; need careful management |
| Avoid | Root vegetables (carrots, beets) | Don't suit media bed growing well |

**Solids management:**
This is the most neglected maintenance task. Uneaten feed and fish faeces accumulate in tank corners and pipe elbows. Build the following into system design:
- Swirl filter or settling tank before media beds — removes suspended solids before they accumulate.
- Weekly flushing of settleables.
- Solids discharged to compost or soil beds — this is some of the richest organic material in the system.

**Checkpoint — confirm before finalising:**
- What is the primary production goal — fish, plants, or both equally?
- Is this an indoor or outdoor system, and what temperature management is available?
- How experienced is the operator with water chemistry testing and daily monitoring?

Recommending a DWC raft system to someone who has never managed aquaponics before, or a tilapia-based system to someone in a cold climate without heating, creates a system that will fail.

**Output:**
```
AQUAPONICS SYSTEM DESIGN
System type: [media bed / DWC / NFT / hybrid]
Fish species: [species]
Plant species: [primary crops]
Location: [indoor / outdoor / greenhouse]

SIZING
Fish tank volume: [litres]
Target stocking density: [kg fish]
Plant bed area: [m²]
Estimated fish:plant ratio: [ratio]

CYCLING PLAN
Pre-stocking cycle period: [weeks]
Ammonia source during cycling: [method]
Target before stocking: ammonia 0 mg/L, nitrite 0 mg/L within 24hr of dosing

MONITORING SCHEDULE
Daily: DO, ammonia, nitrite, pH, temperature
Weekly: nitrate, plant health, fish behaviour and appetite
Monthly: full system audit, solids accumulation check

BALANCING ACTIONS
[current imbalance if any]: [corrective action]

EXPECTED PRODUCTION
Fish: [kg/year estimate]
Plants: [kg/week estimate at steady state]
```

**Next steps:**
- Run **water-quality** (within this skill) — aquaponics requires the most intensive water monitoring of any system type.
- Run **integrated-systems** (within this skill) to connect the system's effluent and solids to soil-based fertility.
- `/s4ag-controlled-environment` — if this is an indoor system, the CEA skill applies to the plant production side.

---

## Integrated Systems

*Connects aquaculture to other farm systems — irrigation, fertility, composting, and water infrastructure.*

Aquaculture is most valuable on a farm not as an isolated protein source but as a node in the farm's biological fertility cycle. Fish effluent is one of the most nutrient-dense and biologically active liquid fertilisers available. A pond or tank that discharges to a drain is wasting a major fertility resource. This sub-tool designs the connections between aquaculture and the rest of the farm.

**The fertility value of aquaculture effluent:**

Fish tank or pond water carries:
- Ammonia/ammonium nitrogen: bioavailable immediately to plants
- Bacteria: diverse populations similar to a diluted compost tea
- Phosphorus: released from fish waste as orthophosphate
- Trace minerals: accumulated from feed and fish metabolism
- Dissolved organic carbon: food web substrate for soil biology

Compared to purchased liquid fertilisers, aquaculture effluent is cheaper (it is a system byproduct), biologically active (soluble synthetics are not), and builds soil food web diversity rather than bypassing it.

**Applications by system type:**

| Source | Application method | Best use |
|---|---|---|
| Pond overflow | Gravity-fed irrigation to adjacent market garden | High-volume, low-labour fertility delivery |
| Tank effluent water changes | Bucket or pump to vegetable beds | High-nutrient targeted application |
| Aquaponics solids discharge | Compost pile addition or direct soil incorporation | Concentrated slow-release fertility |
| RAS concentrate | Dilute and irrigate; do not apply directly — too concentrated | Needs 1:10–1:20 dilution |
| Pond dredge sediment | Apply to heavy-feeding crop beds; annual pond clean | Rich in P and OM; excellent soil amendment |

**Connecting to farm water infrastructure:**

The simplest integration: position the aquaculture system upslope of the vegetable garden or orchard, and allow overflow or regular water changes to gravity-irrigate downslope. This requires:
- No pump energy for distribution.
- Regular monitoring of nutrient concentration (too much N too often will burn crops).
- A dilution buffer (rain water storage or clean water source) to regulate concentration.

For ponds integrated with earthworks: site the pond at the keyline point or slightly above, so that overflow distributes across the irrigated land via swales. This connects Yeomans' keyline design with aquaculture in a single water system — the pond stores water, produces fish, and distributes fertility.

**Duckweed-fish-soil loop:**

The most complete biological cycle for a small farm:
1. Fish tank effluent flows to a shallow duckweed growing channel.
2. Duckweed cleans the water by consuming nitrogen.
3. Duckweed harvested daily and fed back to fish (partial diet substitution).
4. Overflow from duckweed channel irrigates vegetable beds.
5. Vegetable bed runoff (with root exudates) returns to the system via a constructed wetland or biofilter.

This loop reduces purchased feed, eliminates effluent discharge as a waste problem, and delivers biological fertility to food crops in a closed cycle.

**Constructed wetland as biofilter:**

A shallow constructed wetland planted with reeds, iris, watercress, and other aquatic plants can polish aquaculture effluent before it reaches crops or waterways. Benefits:
- Removes suspended solids.
- Reduces nutrient peaks before application.
- Provides additional harvestable biomass (watercress, reeds for mulch).
- Creates habitat for beneficial insects and frogs.

Sizing guide: 1–2 m² of constructed wetland per 100L of daily effluent.

**Integrating with composting:**

Aquaculture solids (from tank clean-outs, swirl filters, pond dredging) are high-nitrogen amendments that activate a compost pile. They are best added to an active hot compost with a high-carbon material (straw, wood chips) to avoid anaerobic decomposition and odour. Ratio: 1 part aquaculture solids to 3–4 parts carbon material.

**Ingham lens — aquaculture effluent as inoculant:**

Aquaculture water carries a diverse bacterial community, particularly after a well-cycled system matures. Applied to soil, it functions similarly to aerated compost tea — a live bacterial inoculant that establishes populations in the rhizosphere. The effect is most pronounced on transplants and in soil recovering from heavy synthetic input use. Apply effluent to the root zone at transplanting time for a direct food web benefit.

**Checkpoint — confirm before finalising:**
- What is the destination for aquaculture effluent — vegetable garden, orchard, compost, or currently draining to waste?
- Is the aquaculture system upslope or downslope of the intended application area?
- What is the volume of effluent produced daily or weekly?

Recommending gravity-fed effluent irrigation to a system where the pond is downslope of the garden, or recommending full-strength RAS effluent application to vegetable beds, creates problems rather than solving them.

**Output:**
```
INTEGRATION PLAN
Aquaculture system: [type and location]
Application destination: [vegetable garden / orchard / compost / constructed wetland]
Topography: [upslope / downslope / level relative to destination]

EFFLUENT VOLUME
Daily effluent: [litres/day estimate]
Nutrient concentration: [high / medium / low — based on stocking density]

RECOMMENDED INTEGRATION METHOD
[method]: [description]
Dilution required: [yes/no — ratio if yes]
Application frequency: [daily / weekly / per water change]

CLOSED-LOOP DESIGN (if applicable)
[duckweed / constructed wetland / compost integration as relevant]

FIRST STEPS
1. [immediate action]
2. [second step]
3. [third step]

WHAT TO MONITOR
- [parameter]: [monitoring frequency]
```

**Next steps:**
- `/s4ag-water` — map the full farm water cycle to understand where aquaculture fits in the water-harvesting design.
- `/s4ag-composting` — use aquaculture solids as an activator in hot compost.
- `/s4ag-soil` — apply the Ingham lens to measure whether effluent application is building soil food web diversity.