Livestock: Fish and Bees
Senior 3 · Agriculture
Livestock: Fish and Bees
Lesson 1 of 4
25 min
Let's begin
Rwanda caught or farmed about 52,439 tonnes of fish in the 2024–25 financial year, and its hatcheries produced about 71.7 million fingerlings (young fish) for farmers (MINAGRI, Annual Report 2024–2025). Yet a farmer who digs a pond still faces a basic question: which fish should go into it? Rwanda is high and cool, and the most popular farmed fish in Africa, the Nile tilapia, prefers warm water. This lesson shows you how to recognise the main farmed species and how to choose between them.
Definition
Aquaculture (fish farming): rearing fish and other aquatic animals under control, in ponds, tanks or cages. Capture fisheries catch wild fish from lakes and rivers instead.
Fingerling: a young fish about the length of a finger, used to stock ponds and cages. Fry are younger still, just after hatching.
Hatchery: a farm that breeds fish and raises fry and fingerlings for sale.
Stocking density: the number of fish put into each square metre (ponds) or cubic metre (cages) of water.
Monoculture: rearing one species; polyculture: rearing two or more species together, so that each uses a different food in the pond.
Operculum: the bony flap that covers and protects the gills.
A farmer must recognise species and spot sick fish, so learn the parts in Figure 9. Fins steer and balance the fish; the caudal fin drives it forward. The lateral line is a row of sense organs that detect movement and vibration in the water. Water enters the mouth, passes over the gills, where oxygen is taken in, and leaves under the operculum.
Figure 9. External features of a bony fish, such as tilapia.
MINAGRI's National Aquaculture Strategy (2023) says Rwandan aquaculture depends mainly on the Nile tilapia, while the African catfish is growing in popularity and common carp is also farmed; rainbow trout might one day be farmed in the colder upland waters.
| Species | How to recognise it | Food | Strengths | Weaknesses |
|---|---|---|---|---|
| Nile tilapia (Oreochromis niloticus) | deep, flattened body; long dorsal fin, spiny in front; dark vertical stripes on the tail fin | omnivore: algae, plankton, bran, pellets | hardy; grows fast in warm water; easy to breed; highest price on the Rwandan market | breeds early and very often, so ponds overcrowd and fish stay small; grows slowly in cool water |
| African catfish (Clarias gariepinus) | long, scaleless body; flat, bony head; four pairs of whisker-like barbels; long dorsal and anal fins | omnivore and predator: insects, small fish, pellets | breathes air with an extra breathing organ, so it survives low oxygen; grows fast; eats surplus tilapia fry in polyculture | fry must be bred in a hatchery; young fish eat each other (cannibalism); lower price |
| Common carp (Cyprinus carpio) | large scales; two pairs of short barbels on the upper lip | bottom feeder: worms, insect larvae, plant matter | tolerates a wide range of temperatures, including cooler water; uses food on the pond bottom | stirs up mud, making water cloudy; many small bones; lower price |
| Rainbow trout (Oncorhynchus mykiss) | streamlined, spotted body with a pink band | carnivore: high-protein pellets | valuable; suits cold water | needs cold, clean, well-oxygenated, flowing water and costly feed; not yet farmed widely in Rwanda |
The small sardine of Lake Kivu, isambaza (Limnothrissa miodon), is important food, but it is caught wild by fishers, not farmed.
Ask these questions before stocking a pond or cage:
Rwanda's fish farms use two systems: earthen ponds, about 3,000 of them, mostly in the Eastern Province near the dams built for irrigating rice, and in the warmer south; and floating cages in lakes such as Kivu and Muhazi. In 2021 cages gave 55% of the country's farmed fish and ponds 45% (MINAGRI, 2023).
Worked example 1: comparing prices
Problem. MINAGRI's strategy (2023) reports a retail price for fresh tilapia of about US$4.37 per kg, 20% higher than carp and 30% higher than catfish. Find the price per kg of carp and catfish.
Solution. "20% higher than carp" means tilapia price carp price.
Answer: carp about US$3.64 and catfish about US$3.36 per kg. (A common mistake is to subtract 20% of 4.37, which gives US$3.50: wrong, because the 20% is of the carp price.)
Worked example 2: planning a harvest
Problem. A pond of 400 m² is stocked with mono-sex tilapia fingerlings at 3 per m² (a typical semi-intensive rate). If 80% survive and each reaches 250 g, what harvest can the farmer expect?
Solution.
Answer: about 240 kg of fish.
Warning
Common mistakes. (1) Stocking mixed-sex tilapia and getting thousands of tiny fish instead of a few big ones. (2) Stocking far more fish than the pond can feed and supply with oxygen. (3) Putting catfish fingerlings of very different sizes together: the big ones eat the small ones. (4) Releasing farmed species into rivers and lakes: they can harm wild fish.
Tip
Memory hook: "Tilapia for the market, catfish for low oxygen, carp for cool water, trout for cold streams."
Rwanda Agri: "Kivu Tilapia Farm, a successful story of fish farming in cages on Lake Kivu in Rwanda". Notice which species is farmed, how the cages are built and how the fish are fed.
Practice
Key points
Sources and credits
Written by Ganzaa: the text, the table, Figure 9 and the worked examples. The stocking rate and harvest weights are typical values.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
