Fish farming in ponds
A drainable earthen pond, manured from the farm's animals, grows fish without bought feed: site, species, water, stocking, feeding, daily care and harvest.
Home: Aquaculture, Level 2 · Forge, level 1 of 1 in its track. Serves 1 step.
A fish pond kills in three ways, all preventable. Children drown in it — drowning kills about 300,000 people a year, nearly a quarter of them under 5 (WHO) — so fence it and keep a rescue pole on the bank. Its fish die in one night when plankton uses up the oxygen before dawn, so walk the pond at sunrise. And its fish, eaten raw or undercooked, carry liver flukes that cause bile-duct cancer, so cook every fish through.
What it gives is protein from manure and water: a 400 m² pond stocked with 800 tilapia fingerlings is harvested at about 6 months (FAO). The step is fish ponds, with the reasons behind every number; the build is the drainable fish pond. Every figure here is from FAO's training manuals on pond construction and freshwater fish culture.
At a glance: the order of work
Each stage has a check. Do not move on until it passes.
| Stage | Do | Pass when |
|---|---|---|
| 1 · Make it safe | Fence, gate, rescue pole | No small child can reach the water without passing a shut gate |
| 2 · Choose the site | Slope, water by gravity, soil tests at every depth | Every test hole passes the squeeze and bottle tests |
| 3 · Build the pond | Levels, outlet pipe and monk first, rammed dikes, inlet, grass | It fills, holds its level and drains by gravity |
| 4 · Choose the fish | Log the noon water temperature | It sits inside the species' range all season |
| 5 · Prepare the water | Lime the dry bottom, fill, manure | The water is green and the Secchi disc reads 40–60 cm |
| 6 · Stock | Carry the fingerlings cool, match the water, release | The fish swim strongly the next morning |
| 7 · Run it | Dawn check, Secchi disc, manure and feed to the water | A reading in the notebook every day |
| 8 · Harvest and restart | Partial harvests, then drain; cook through; dry the bottom | The harvest is weighed and the bottom is cracked dry |
Part 1Before you build
Site and soil
Gravity in, gravity out, and soil that holds water (FAO, Site selection; Soil).
| Check | Good | Reject |
|---|---|---|
| Slope | 0.5–3 % | Over 5 %; dead-flat land makes drainable ponds dearer |
| Water | 2–5 l/s per hectare of pond, by gravity, taken upstream of sprayed fields | A source that fails in the dry season |
| Floods | Above the highest flood marks on trees and bridges | Ground the river reaches |
| Soil | Keeps the shape of your hand when squeezed; over 50 % silt and clay in the bottle test; sandy clay, silty clay loam or clay loam | Rock, gravel, sandstone, limestone, peat, termite mounds, big tree roots |
| Safety | Room for a fence on every side facing houses and paths | A pond children pass on their way to school |
Choose the fish by water temperature
Log the pond water at noon through the year, then choose fish that grow in it (FAO, Pond water quality). Fish that eat different foods can share a pond.
| Fish | Best for adults | Eats | Lowest dawn oxygen |
|---|---|---|---|
| Nile tilapia | 27–30 °C; in danger below 12 °C | Phytoplankton: thrives in manured green water | 2 mg/l |
| Common carp | 23–26 °C; survives 2–36 °C | Bottom animals | 3 mg/l |
| Grass carp | 23–28 °C | Water plants and cut grass | — |
| Silver carp | 23–28 °C | Phytoplankton | — |
| Bighead carp | 23–31 °C | Zooplankton | — |
| African catfish | 25–27 °C | Almost anything | about 1 mg/l: it breathes air |
Part 2Build it
The pond, in numbers
Start with one pond of 400 m², 20 × 20 m, and follow the drainable fish pond build. The numbers that decide whether it works (FAO, Pond construction):
- Depth: 0.8 m at the inlet to 1.0 m at the outlet, the bottom falling about 1 %; never under 0.5 m.
- Dikes on good clay soil: 1.53 m as built, settling to 1.30 m; crest 1.0 m; slopes 2:1 inside and 1.5:1 outside. On loamy soil: crest 1.3 m, slopes 2.5:1 and 2:1.
- Earth: in rammed layers 15–20 cm thick, moistened, over a cut-off trench of clay where the ground leaks.
- Outlet: floor at least 10 cm below the lowest point of the pond; the pipe falling at least 1 % to end 20 cm above the drain, with a concrete anti-seep collar.
- Inlet: screened, its floor 10 cm above the water, reaching 0.6–1 m out.
Outlet pipe by pond size (FAO, Outlet structures): 10–15 cm for 200–400 m², 15–20 cm for 400–1,000 m², 20–25 cm for 1,000–2,000 m², 25–30 cm for 2,000–5,000 m²; never under 10 cm behind a monk.
Part 3Run the pond
Read the water
Measure at sunrise, when oxygen and pH are lowest, and write every reading down (FAO).
| Measure | Aim for | Act when |
|---|---|---|
| Dawn behaviour | Fish calm, below the surface | Fish gulp at the surface, tadpoles crowd the edge, or the water smells of rotten eggs: stop feeding and manuring, let in fresh water, run bottom water out through the monk |
| Secchi disc, 09:00–15:00 | 40–60 cm | Under 40 cm: stop manuring. Under 25 cm: high risk of an oxygen crash, worst after 2–3 cloudy days. Over 60 cm: manure more |
| pH at sunrise | 6.5–8.5 | Most farmed fish die below 4.5 or at 11 and above; over 9 harms eggs and young fish |
| Total alkalinity | 25 mg/l or more | Under 25 mg/l a month or two after liming: lime again |
| Noon temperature | Inside the species' range | Under 20 °C: stop manuring and feed less |
Prepare the water and stock
- Lime the dry bottom of a new pond: 2,000 kg/ha of ground limestone on sandy soil to 4,000 kg/ha on heavy clay — 80–160 kg for 400 m² (FAO, Liming).
- Fill, and manure 10–15 days before stocking at 10–20 kg of manure dry matter per 100 m², so the water is green when the fish arrive.
- Carry the fingerlings in a clay pot, a bucket or a plastic bag, in clean water, cool and in the shade. If they gasp at the surface, change some of the water and aerate it (FAO handbook).
- Match the water: if the pond is much warmer or colder than the transport water, replace half of it with pond water and wait half an hour.
- Stock 2 tilapia of 5 cm or more per m²: 800 for a 20 × 20 m pond. Release them gently.
Manure and feed
Manure grows the plankton the fish eat; feed adds to it. Once or twice a week per 100 m² in a small tropical pond: 4.5 kg poultry droppings, 3 kg sheep or goat dung, 6 kg pig dung or 5 kg cattle dung; never more than 1.2 kg of dry matter per 100 m² a day in the tropics, 0.6 kg in cool climates (FAO, Fertilizing).
Rice or wheat bran for tilapia, per day (FAO handbook):
| Month | Per 100 m² | For a 400 m² pond |
|---|---|---|
| 1 | 360 g | 1.44 kg |
| 2 | 480 g | 1.92 kg |
| 3 | 720 g | 2.88 kg |
| 4 | 960 g | 3.84 kg |
| 5 | 1,200 g | 4.80 kg |
| 6 | 1,440 g | 5.76 kg |
Every day at the pond
From FAO's handbook for small fish farmers (FAO):
- Check the water level and the screens every day.
- Keep water weeds to no more than a quarter of the surface; cut the grass on the banks.
- Repair any leak at once with good soil.
- Keep away fish-eating animals: birds, frogs, turtles, rats and snakes.
- Keep cattle, buffalo, horses and donkeys off the banks, which they break down; goats and sheep may graze them.
- Do not bathe or wash clothes, dishes or pots in the pond, its source or its supply ditch.
- No big trees near the pond; cut branches that shade the water.
- Shut the gate behind you.
Part 4Harvest and restart
Harvest, cook, and start again
- From the fifth month, take a few big fish each week with a seine of 3–3.5 cm mesh, which lets the small ones escape. Harvest at about 6 months (FAO handbook).
- Stop feeding 2–3 days before draining. Drain early in the morning, slowly, lifting the monk's boards one row at a time so the fish follow the water to the catch basin.
- Take only what you can eat, sell or preserve; leave the rest for later partial harvests.
- Weigh the harvest and write it down, with the fish stocked, the manure and feed used and the months taken.
- Dry the bottom before refilling: 2–3 weeks in the tropics, 3–4 months in temperate climates. Dig out thick mud for the fields, and lime the dry bottom with a quarter of the new-pond dose.
Build the gear
Where to go next
This page covers what you are most likely to meet. It is not a field guide, and on identification that difference can kill you. These are the works that go further — chosen because they can be held offline.