Chapter 4: Harvest and process fish

Fish harvesting is a critical stage in fish farming that directly impacts the quality, yield, and profitability of aquaculture enterprises. For Agriculture and Extension professionals in Kenya, understanding efficient and sustainable harvesting methods is essential to support fish farmers in maximizing returns while preserving fish health and pond integrity. This chapter explores the tools and equipment used in harvesting, their appropriate applications, and the necessary maintenance practices to ensure longevity and effectiveness in Kenyan fish farming contexts.

4.1 Fish harvesting

Fish harvesting is the removal of fish from ponds, tanks, cages or open waters when they have reached market size. A good harvest is quick and gentle, because fish that are chased for hours, crushed or left to struggle lose scales, bruise and spoil sooner. The farmer therefore chooses the harvesting gear to match the species, the size of the unit and the number of fish to be taken, and keeps the gear in working order. In smallholder ponds the harvest may be done with one net and a few buckets, while a commercial farm may drain several ponds and use pumps, grading tables and scales. This topic covers the tools, equipment and materials used, how each is used and how each is kept in good condition, while the methods of harvesting are covered in the next topic.

4.1.1 Fish harvesting tools, equipment and materials

Harvesting tools fall into three groups: gear that catches the fish, equipment that moves and weighs them, and materials that keep them alive and clean until they reach the buyer. The table lists the common items. The specifications should be chosen to suit the species and the size of the unit and not copied from a standard figure.

4.1.1.1 Fishing nets

Nets are the main tool for harvesting from ponds, cages and lakes, and the type used depends on where the fish are. Seine nets are drawn across a drained or partly drained pond by two or more workers, while scoop nets and cast nets handle small numbers. Gill nets hold fish by the gills and are set in open water. The mesh size is chosen so that fish of market size are retained and smaller fish can pass through, and it is measured on the opened mesh. Trawl nets and purse seine nets are used in open waters and are taught under Fish harvesting methods.

• Seine nets: Used in ponds and shallow waters, the net has floats along the top edge and weights along the bottom, so that it hangs upright in the water. It is paid out around the fish and hauled to the pond edge with the floats kept at the surface and the lead line along the bottom. It can take many fish in one operation, but it needs several workers and careful handling to prevent injury.
• Scoop nets: A handled net with a soft mesh, used to lift fish from tanks and from the bag of a seine net. It limits handling and physical damage, but it is slow for large quantities.
• Cast nets: A net that opens as it is thrown, then sinks and closes. It is cheap and easy to use in small ponds and cages where fish gather near the surface, but it works only when fish are visible and concentrated, and it needs skill in throwing.
• Gill nets: Set in the water and left for a period, then lifted, which can injure fish, so they suit fish that will be processed rather than sold alive.
• Mesh size: A mesh that is too small catches fingerlings, and one that is too large lets market fish pass through.
• Materials: Nets are made from nylon or polyethylene twine, which is strong and does not rot as quickly as natural fibre.

4.1.1.2 Fishing traps

A trap catches fish that swim in through an entrance and find it hard to leave. Traps are cheap, can be made on the farm from local materials and work without constant attention, which makes them suitable for farmers with limited labour.

• Basket traps: Made from woven reeds, bamboo, wire or plastic, with a funnel-shaped entrance that fish can pass through but not return by.
• Baiting: Bait such as pieces of fish or food scraps draws fish into the trap and is renewed each time the trap is set.
• Setting: Place the trap on the bottom near cover, anchor it and tie it to a float or a rope at the water edge so that it can be found and lifted. Traps are useful where there are inlet and outlet channels or in natural water bodies.
• Checking: Lift the trap often, so that the fish are not left to die, and check it for damage.
• Selectivity: Use a trap of a size that suits the target fish, with a door or an escape opening for small fish. The size of fish taken is limited by the size of the trap.
• Cleaning: Remove mud, weed and old bait after each use and let the trap dry.

4.1.1.3 Longlines and handlines

Handlines and longlines catch fish on baited hooks. They injure fish less than gill nets when hooks are removed carefully, and they allow fish to be returned alive when they are too small. Longlines suit larger water bodies such as dams and lakes, where fish are caught over a wide area, while handlines suit single fish and small volumes.

• Handline: A single line with a hook and a sinker, held by hand or tied to a rod, used for taking a few fish at a time.
• Longline: A long mainline held by anchors and floats, with short branch lines carrying hooks, baited and set over a distance.
• Hooks: Select the hook size to suit the mouth of the target fish, and choose a type that does not damage the fish more than necessary.
• Bait: Use fresh bait that suits the species, and replace it when it is washed off or spoiled.
• Checking: Lift the line at set intervals and remove fish promptly.
• Safety: Handle hooks with care and store them in a box so that workers do not injure themselves.

Other harvesting equipment and materials

A harvest also needs equipment to handle, weigh and carry the fish. Landing baskets, buckets and crates keep fish clean and prevent crushing, and a scale gives the weight for sale and for farm records. Where ponds are large, a water pump lowers the water and brings the fish together so that fewer workers are needed. A fish pump uses a wide hose and a fine mesh filter to draw fish gently out of tanks and small ponds, which lowers handling and stress, though it needs a power source and regular servicing. Gumboots, gloves and, on lakes where cages are harvested, life jackets protect the workers. Aerated tanks or oxygenated bags are used to carry live fish to market.

4.1.2 Uses of harvesting tools, equipment and materials

Each item has a role in the harvest, and using it correctly keeps fish alive, reduces losses and speeds the work. The choice of tool depends on pond size, fish species, the scale of the harvest and the quality wanted by the buyer. The farmer matches the item to the stage of the harvest.

Uses of nets

Seine nets collect the fish into a smaller area, scoop nets lift them out, cast nets take fish from shallow open water and gill nets catch fish that swim into them. Used with skill, nets gather fish quickly and with little loss of scales, and they reduce the chance that fingerlings are taken with market fish.

Uses of traps

Traps are left in the water for a period and lifted when fish have entered. They suit species that hide or move at night, they take few fish at one time and they can be checked while other work goes on.

Uses of longlines and handlines

Longlines and handlines take fish on baited hooks. They are used to harvest fish in open water, and a handline is suitable for a quick sample to check the size and condition of fish before a larger harvest.

Uses of landing baskets

Landing baskets are used straight after netting to move fish from the water into holding containers. The smooth surface and short handling time reduce injuries, which keeps the fish fresh and keeps the price of the fish high.

Uses of pumps

A water pump lowers or drains the water in a pond so that the fish are concentrated and can be netted easily. It reduces the manual work of bailing, and it can supply water to holding tanks so that harvested fish can be kept alive until sale. A fish pump moves the fish themselves with little handling.

Uses of weighing scales

A scale gives the weight of each lot of fish, which is needed for sales, records and the calculation of the farm's production. Accurate weights prevent disputes between the farmer and the buyer.

Uses of buckets and crates

Buckets and crates hold fish during sorting, grading and transport. They must not be overfilled, because crowded fish run short of oxygen and die.

Selective and bulk harvesting

The farmer may take only part of the stock or all of it, and the tools differ. Selective harvesting uses scoop nets and traps to remove mature fish and leave smaller fish to grow, which suits ponds that supply a steady trickle to the market. Bulk harvesting uses seine nets, and cast nets in small units, to take a large quantity quickly, and it is done when the whole pond is harvested at the end of a cycle.

Care during harvesting and transport

Fish that are handled well fetch a better price. Keep the water oxygenated and disturb the pond as little as possible, because stressed fish use oxygen quickly. Transfer fish with scoop nets and landing baskets rather than by hand. Carry live fish in aerated tanks or oxygenated bags, and keep the fish shaded and cool.

Timing and species considerations

The time and the gear depend on the species and the market. Tilapia, catfish and trout differ in their behaviour and body shape, so each may need a different mesh size and technique. Harvest in the early morning or late afternoon, when the water is cooler and fish are less stressed. Adjust the harvest schedule to market demand so that fresh fish are supplied at a good price.

4.1.3 Maintenance of harvesting tools and equipment

Harvesting tools are used rarely but under pressure, so a broken net or pump on harvest day costs time and fish. In farms where money is limited, regular care also makes the equipment last longer. A simple routine after every harvest keeps it ready.

• Cleaning: Wash nets, baskets, buckets and traps with clean water after use to remove mud, algae and slime, and disinfect them if they will be used in another pond.
• Drying: Spread nets in the shade or dry them fully in the sun before folding them, because damp nets rot and grow mould, and long exposure to strong sun weakens the twine.
• Avoiding chemicals: Keep nets and metal parts away from harsh chemicals, fuel and oil, which weaken the fibres and corrode the metal.
• Inspection and repair: Check nets and traps for holes, tears and broken frames before and after each use, and mend small holes with twine and a netting needle before storage.
• Checking scales: Test scales with a known weight and adjust or replace them if they are wrong.
• Servicing pumps: Drain and flush the pump, check the hoses and seals, lubricate moving parts to prevent rust, and service the engine or motor according to the maker's instructions. Test pumps before the harvest day.
• Storage: Store gear in a dry, shaded, lockable room away from rodents, chemicals and fuel, with nets hung or folded loosely so that they do not tangle or stretch.
• Replacing worn parts: Replace worn hoses, floats, weights, hooks and handles before the next harvest, and keep spares of the items that fail most often.
• Training: Teach every worker how to handle and care for the equipment.

Chapter Summary

This chapter covers the essential aspects of fish harvesting, beginning with an overview of the various tools, equipment, and materials used in the process, including fishing nets, traps, and lines. It explains the specific uses of these harvesting implements and highlights the importance of proper maintenance to ensure their longevity and effectiveness. The chapter then explores different fish harvesting methods such as trawling, longlining, and purse seining, detailing how each technique operates and their suitability for various fishing environments. Fish processing is also addressed, emphasizing the steps necessary to prepare the catch for market or consumption. Finally, the chapter underscores the significance of keeping accurate fish records to monitor harvest quantities, track stock health, and support sustainable fish farming practices. Together, these topics provide a comprehensive understanding of the harvest phase in fish farming operations.