Fish Health and Diseases – SS2 Livestock Farming Lesson Note (First Term)

A healthy fish swims actively, has clear eyes and shiny scales, and rushes to feed. A sick fish gasps at the surface, swims alone, rubs its body on the pond walls or shows marks such as white spots. Most diseases start when fish are stressed by dirty water, crowding or bad food.

Behavioural objectives

By the end of the lesson, students should be able to:

• Describe the signs of a healthy fish and of a sick fish.
• Name and describe fin and tail rot, white spot disease (Ich) and fungal infections.
• State four things that stress fish.
• List ways of preventing fish diseases in a pond.
• Describe simple first-aid treatments for sick fish.

How do you know your fish are sick?

A good fish farmer is like a doctor: you have to “listen” to your fish even though they can’t talk. Most diseases in a pond happen because the water is dirty, the fish are crowded, or the food is bad.

Signs of a healthy fish

• They swim actively and react quickly if you splash water.
• They have clear eyes and shiny scales.
• They rush to the surface when it is feeding time.

Signs of a sick fish

• Gasping: They stay at the surface “gulping” air (this means they can’t breathe).
• Isolation: A sick fish often swims alone in a corner while others stay together.
• Rubbing: They scratch their bodies against the pond walls.
• Physical marks: Look for white spots, bleeding fins, or a swollen belly.

What are the common fish diseases?

In Nigeria, these are the most common problems you will face in your pond (the “Big Three”).

1. Fin and tail rot (bacterial)

• What it looks like: The edges of the fins look ragged, torn, or “eaten away.” You might see white or red sores at the base of the tail.
• Cause: Usually caused by dirty water or “bullying” (fish biting each other).

2. Ich or white spot disease (parasitic)

• What it looks like: It looks like someone sprinkled salt or white sugar all over the fish’s body.
• Cause: A tiny parasite that attaches to the skin. It makes the fish very itchy.

3. Fungal infections

• What it looks like: White, cotton-like growths on the skin or mouth.
• Cause: Often happens after a fish has been handled roughly or wounded. The fungus grows on the wound like mould on bread.

Why do diseases start? (The stress factor)

Fish don’t just “wake up” sick. Disease usually happens when the fish is stressed.

Things that stress fish

1. Overcrowding: Putting 1,000 fish in a tank meant for 200. It is like living in a room with 50 people: everyone gets sick.
2. Bad water: High ammonia (from fish waste) or low oxygen.
3. Rough handling: Catching fish with rough nets or dropping them on the floor.
4. Temperature change: Moving fish from very cold water to very warm water too quickly.

How can fish diseases be prevented? (The “Clean House” rule)

It is much cheaper to prevent a disease than to treat it. Once a disease starts, you might lose half your fish before the medicine works.

• The quarantine rule: Never throw new fish straight into your main pond. Keep them in a separate “quarantine” tank for 14 days to see if they are sick.
• Water management: Change your water regularly. If it smells like rotten eggs, it is dangerous.
• Liming: As we learned in pond construction, lime helps kill germs in the soil before you start.
• Clean tools: Don’t use a net from a “sick” pond in a “healthy” pond without washing it with salt or disinfectant first.

What simple treatments and first aid can you give sick fish?

If your fish do get sick, don’t panic. Here is what to do:

1. Stop feeding: Sick fish don’t eat much. Food left in the water will rot and make the disease worse.
2. The salt bath: Common salt (non-iodised) is a useful medicine for fish. It kills many parasites and helps the fish breathe better. You can soak sick fish in a strong salt solution for a few minutes.
3. Antibiotics: For serious bacterial infections, you can mix special fish medicine into their feed.
4. Fresh water: Sometimes, just draining half the pond and refilling it with fresh, clean water is all the “medicine” they need to recover.

Teacher’s closing note: Most fish diseases start with poor management by the farmer. If you keep the water clean and don’t overfeed, your fish will stay healthy and grow big.

Evaluation

1. State four signs of a sick fish.
2. Describe how white spot disease (Ich) looks and what causes it.
3. List four things that stress fish.
4. Why should new fish be kept in a quarantine tank for 14 days?
5. Describe the salt bath and say how it helps sick fish.

Assignment

The observation test

Go to the school pond or a nearby farm. Watch the fish for 10 minutes, then answer these questions:

• Do you see any fish swimming upside down?
• Is there any fish “flashing” (turning sideways quickly to rub against the wall)?

Report your findings in your notebook.