Integrated Livestock-Fish Farming
Senior 3 · Agriculture
Integrated Livestock-Fish Farming
Lesson 4 of 4
25 min
Let's begin
A fish farmer's worst mornings begin with something wrong at the pond: fewer fish rising at feeding time, a kingfisher sitting on the post by the outlet, a few fish rubbing against the bottom, or dead fish floating at the edge. Most losses in small ponds come from three sources: animals that eat fish, diseases that spread when fish are stressed, and dirty or poorly drained ponds. MINAGRI's National Aquaculture Strategy (2023) lists better fish health and biosecurity, including care over diseases such as tilapia lake virus, among its aims. This lesson covers pond enemies, the common fish diseases, and the sanitation that prevents most of them.
Definition
Pond enemy: an animal that eats or competes with farmed fish, damages the pond or steals the harvest.
Predator: an animal that hunts and eats other animals, e.g. a kingfisher eating fingerlings.
Stress: a condition (poor water, crowding, rough handling, sudden temperature change) that weakens a fish's defences, so disease takes hold.
Pond sanitation: keeping the pond, its water, its equipment and its surroundings clean, so that pathogens and parasites cannot build up.
Liming: spreading lime on a pond bottom to reduce acidity and kill pathogens and pests.
| Enemy | Damage | Control |
|---|---|---|
| Fish-eating birds (kingfishers, herons, cormorants) | eat fingerlings and small fish | nets or lines of string over small ponds; scaring devices; deeper water at the edges; guard during harvest |
| Otters and monitor lizards | eat fish; burrow into dikes | fencing; guarding; repair burrows |
| Snakes and frogs | eat fry and fingerlings; frogs compete for food | screens; cut grass on dikes; remove frog eggs |
| Wild and predatory fish | eat fry and compete for food; wild tilapia breed and crowd the pond | screen the inlet; drain and dry the pond between cycles |
| Water insects (dragonfly nymphs, water beetles) | eat fry | fill the pond just before stocking; stock fingerlings rather than fry |
| Crabs and rats | burrow through dikes and cause leaks | regular dike inspection and repair; trapping |
| Thieves | steal fish, especially near harvest | fence; guard; ponds near the home |
Pathogens are present in most ponds; fish fall sick when stress lowers their defences. Watch for fish that stop feeding, swim slowly at the surface or at the edges, rub against the bottom ("flashing"), or show the signs in Figure 20.
Figure 20. Signs of disease to look for on a fish (drawn together for teaching; a sick fish usually shows only one or two).
| Disease | Cause | Signs | Prevention and control |
|---|---|---|---|
| White spot disease | a protozoan parasite (Ichthyophthirius) | tiny white spots like grains of salt on skin and fins; flashing | good water; quarantine new fish; treatment as advised by a fisheries officer |
| Fungal disease | water moulds (Saprolegnia) | white or grey cotton-wool patches, usually on wounds | handle fish gently; remove dead fish and uneaten feed |
| Bacterial ulcers and fin rot | bacteria (e.g. Aeromonas) | red sores, bleeding, frayed fins, swollen belly | avoid crowding and dirty water; antibiotics only on an expert's prescription |
| Fish lice and anchor worms | crustacean parasites | small flat lice or thread-like worms attached to the skin; red spots | screen the inlet; dry the pond between cycles; quarantine |
| Oxygen shortage (not an infection) | too much manure or fertiliser; algal bloom; hot, still weather | fish gasping at the surface at dawn; sudden deaths of the largest fish | stop manure and feed; add fresh water; stir the surface |
New viruses, such as tilapia lake virus, can arrive with live fish brought from elsewhere. Buy fingerlings only from certified hatcheries, and report unusual deaths to the district fisheries or veterinary officer.
Worked example 1: liming a drained pond
Problem. After harvest, a 400 m² pond is to be limed at 1,500 kg per hectare (a typical rate for an acid pond bottom). How much lime is needed?
Solution.
Answer: 60 kg of lime, spread evenly over the damp bottom, especially in the wet patches where the last fish and mud lay.
Worked example 2: counting losses
Problem. A farmer stocked 1,200 fingerlings and harvested 1,020 fish. (a) What percentage died or were lost? (b) If each lost fish would have reached 0.25 kg and sold at 3,000 Frw per kg (illustrative price), what income was lost?
Solution.
Answer: 15% were lost, worth about 135,000 Frw: a good reason to net the pond against birds and keep the water healthy.
Warning
Safety. Wear gloves and boots when handling lime: quicklime burns skin and eyes, so keep it away from your face and from children, and wash after use. Never eat fish found dead in a pond. Do not use antibiotics or other chemicals in a pond except as prescribed by a fisheries or veterinary officer.
Tip
Memory hook: "Screen it, net it, don't stress it, drain it, dry it, lime it."
This Is Aquaculture: "Disease Protection in Fish Farming: 3 Levels of Biosecurity in Aquaculture". Note the three levels of protection described and match each to a sanitation rule in this lesson.
Practice
Key points
Further reading
Sources and credits
Written by Ganzaa: the text, the tables, Figure 20 and the worked examples. The liming rate is a typical value and the fish price is illustrative.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
