Aquaculture – SS3 Agricultural Science Lesson Note (First Term)

Aquaculture, also called fish farming, is the rearing of selected species of fish, shrimps and other aquatic food organisms under controlled conditions.

Behavioural objectives

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

1. Define fish farming.
2. Explain some terms associated with fish farming.
3. State the importance of fish farming.
4. Highlight the conditions necessary for siting a fish pond.
5. Outline the classes of fish and give examples of each.
6. Discuss the processing and preservation of fish.

What is fish farming?

Fish farming (aquaculture) is the rearing of selected species of fish under scientifically controlled conditions in enclosed bodies of water.

• Where: ponds, tanks and other enclosed water, such as controlled parts of streams and rivers.
• What happens: the fish feed, grow and breed in the water.
• Purpose: the fish are harvested for food or for sale.
• Other products: shrimps and other aquatic food organisms are also produced.

What are the terms associated with fish farming?

Fish farming terms are the words used for fish stages, groups, places and tools.

Why is fish farming important?

Fish farming is important because it supplies food, income and raw materials.

• Food: fish is a source of protein for people and livestock.
• Cheaper protein: it makes protein available to more people at reduced cost.
• Waste recycling: animal dung from farms, factories and sewage systems can be used in ponds.
• By-products: fish can be processed into fish meal, fish oil, manure and skin.
• Employment and income: it provides jobs and earnings for many people.
• Land and water use: it ensures better use of land and water in the environment.
• Research and education: it is useful for research work and teaching.

What are the types of fish ponds?

There are three common types of fish pond: earthen, concrete and tank.

• Earthen pond: a pond dug into the soil, the cheapest type and common on Nigerian fish farms.
• Concrete pond: a pond built with cement and blocks, which lasts long and is easy to drain and clean.
• Tank: a plastic or fibreglass container used where land is small.

What conditions are necessary for siting a fish pond?

Siting a fish pond means choosing the best place to build it, and seven conditions guide the choice.

• Adequate water supply: the site needs clean water all year, free from pollution.
• Soil in the area: clay or clay-loam soil is best because it holds water and does not leak.
• Vegetation of the area: a site with few trees and little bush saves the cost of clearing.
• Topography of the area: a gently sloping, flood-free site makes filling and draining easy.
• Availability of fast-growing fishes: fingerlings of species such as catfish and tilapia should be easy to get.
• Availability of supplementary feedstuff: feed should be available to add to the natural food in the pond.
• Market and labour: buyers and workers should be within reach of the pond.

How are fishes classified?

Fishes are classified in two ways: by habitat and by body structure.

What is classification based on fish habitat?

Classification by habitat groups fishes into two: freshwater fishes and saltwater fishes.

• Freshwater fishes: they live in water that does not contain salt, such as ponds, streams, rivers and lakes. Examples: tilapia, carp, perch, trout and mudfish.
• Saltwater fishes: they live in water containing salt, such as lagoons, seas and oceans. Examples: salmon, mackerel, shark, rays and eels.

What is classification based on body structure?

Classification by body structure groups fishes into two: bony fishes and cartilaginous fishes.

Bony fishes

Bony fishes are fishes with skeletons made of true bone.

• Examples: tilapia, mudfish, carp, trout, catfish, salmon, perch and herring.
• Habitat: they are found in both freshwater and saltwater.

Cartilaginous fishes

Cartilaginous fishes are fishes with skeletons made of soft cartilage instead of bone.

• Examples: sharks, dogfish and rays.
• Habitat: the majority are found in salt water.

How do bony and cartilaginous fishes differ?

How is fish processed and preserved?

Harvested fish is either eaten, sold or preserved for future use.

What is fish processing?

Fish processing is the preparation of harvested fish for eating or storage.

1. Remove the scales.
2. Cut off the fins.
3. Remove the gut.
4. Remove the gills.
5. Wash the fish clean.
6. Cook or fry the fish for eating, or preserve it.

What are the by-products of fish processing?

• Fish meal: ground fish waste used to feed livestock.
• Fish scales: parts removed from the body during processing.
• Cod liver oil: oil taken from the liver of cod.
• Fish skin: the outer covering, which can be used to make leather.

What are the methods of preserving fish?

There are five common methods of preserving fish: salting, smoking, sun-drying, freezing and canning.

• Salting: salt is applied to the fish. It prevents the growth of spoilage organisms.
• Smoking: fish is dried over naked fire. It reduces the moisture content and improves taste and flavour.
• Sun-drying: fish is dried using heat from the sun. The fish can be stored for only a short time.
• Freezing: fish is kept in cold storage such as refrigerators and deep freezers. It can be stored for a very long time.
• Canning: processed fish is sealed in cans under special conditions for future use, for example sardines.

Evaluation

Students answer these questions in class:

1. Define fish farming.
2. Distinguish between fry and fingerlings.
3. State four conditions necessary for siting a fish pond.
4. Name the two ways of classifying fishes and give two examples of fishes in each group.
5. List the five methods of preserving fish.

Assignment

Differentiate between bony fishes and cartilaginous fishes, giving two examples of each.