Grade 10 marine and fisheries technology – Production Systems Quiz

Extensive pond systems use low stocking densities and depend on natural food produced in the pond (plankton), commonly practised by small-scale farmers in Kenya. The other options describe intensive or different culture systems (intensive tank, RAS, marine cages).

Cage culture on Lake Victoria uses the lake's water, allowing farmers to grow fish without building ponds. It reduces land needed but still requires management and can have disease risks and feed inputs.

RAS filters and treats water so it can be reused, giving farmers control over water quality and reducing water use. It is not dependent on natural plankton and often has higher initial costs.

Polyculture involves raising multiple species (for example, tilapia and catfish) that occupy different ecological niches, improving resource use. Monoculture means a single species.

Broodstock are mature fish kept for reproduction; they supply eggs and sperm for hatcheries to produce fry and fingerlings.

Hatcheries produce fry and nurseries rear them to fingerling size, increasing survival and growth when stocked into ponds, cages, or tanks. They do not remove the need for pond management or feeding.

Stocking density refers to how many fish (or how much fish biomass) are stocked per unit area (pond) or volume (tank, cage). It affects growth, water quality, and disease risk.

Aerators (paddlewheels, diffusers) mechanically increase oxygen transfer into the water, raising dissolved oxygen, which is critical for fish health. Fertiliser may increase oxygen indirectly but can cause oxygen crashes at night.

Fertilisation (organic or inorganic) stimulates growth of phytoplankton and zooplankton, which serve as natural food for young fish, improving survival and reducing feed costs.

Biosecurity includes measures like quarantining new stock, disinfecting equipment, and limiting visitor access to prevent disease introduction and spread on farms.

Partial water exchange helps remove dissolved wastes (ammonia, nitrate) and refresh oxygen and other water quality parameters; it does not permanently stop algae or intentionally change temperature drastically.

FCR is the mass of feed given divided by the mass of fish weight gained. A lower FCR means more efficient feed use—important for farm profitability.

Monoculture involves one species; polyculture combines species that exploit different foods or niches. Whether yields differ depends on system design.

Nile tilapia is widely cultured in Kenyan freshwater systems, including Lake Victoria cages. Atlantic salmon, tuna, and barramundi are not native or commonly farmed in Kenyan freshwater cages.

Proper pond preparation includes draining/drying to expose predators and weeds, liming to adjust pH, and fertilising to build plankton before stocking. Immediate feeding without preparation is poor practice.

Carrying capacity is the limit of fish biomass that the system can sustain while maintaining acceptable water quality and fish health; exceeding it causes stress and disease.

IAA integrates fish farming with crops or livestock so nutrients from pond effluent or manure are recycled for crops, increasing farm efficiency and income—common in smallholder Kenyan systems.

Hatcheries spawn broodstock and rear eggs to fry and fingerling stage, supplying healthy seed for grow-out systems. Processing and storage are different facilities.

Clay soils have fine particles that retain water and reduce seepage, making them preferable for earthen pond construction. Sandy or gravelly soils allow leakage and are less suitable without liners.

Dissolved oxygen is vital for fish respiration; low DO can cause stress and mass mortality. Other parameters matter but DO is the most immediate life-or-death factor.

Raceways use flowing water through long channels to carry waste away and maintain oxygen; they are used for species like trout elsewhere. Ponds are more static, cages use open water, and RAS reuses water.

Coastal seaweed culture in Kenya commonly uses rope or long-line methods in shallow water where seaweed is tied to lines; deep-sea cages or freshwater hatcheries are not appropriate.

Abnormal behaviour (e.g., gasping at surface, erratic swimming), reduced feeding, and skin lesions indicate disease or poor water quality and should prompt immediate action.

Probiotics support beneficial microbes in fish guts and water, reducing disease risk and lowering antibiotic use, which helps prevent antibiotic resistance; they do not replace good hygiene entirely.

Harvesting by partial draining and seining is a standard, humane method for ponds. Using chemicals, explosives, or neglectful netting are illegal, unsafe, and harmful to the environment and human health.

Disease control measures include establishing buffer zones, disinfecting nets and tools, and buying seed from certified disease-free hatcheries. Sharing equipment and untreated water increases disease risk.

Uneaten feed and fish waste can accumulate under cages, degrading sediments and causing oxygen depletion and habitat change. Cage culture interacts with wild populations and can increase environmental risks if not managed.