Grade 10 marine and fisheries technology – Fundamentals of Marine and Freshwater Fisheries Quiz

A fishery includes the people, vessels, gear, and the area involved in catching or farming fish and processing them. It is broader than just a market or one tool.

Marine fisheries are in salty ocean or sea water, while freshwater fisheries are in lakes, rivers and ponds with low salinity. Salinity affects which species live there and how they manage water balance.

Bony fish (like tilapia, Nile perch, mackerel) have bones and many have a swim bladder to control buoyancy. Cartilaginous fish (sharks, rays) have cartilage and lack a swim bladder.

Fish use gills with thin membranes and many blood vessels; water flows over gill filaments and oxygen diffuses into the bloodstream while carbon dioxide diffuses out.

Freshwater fish are hyperosmotic to their environment, so they take in water and must excrete excess as dilute urine while conserving salts. Marine fish do the opposite.

Dissolved oxygen in water is what fish take up through their gills. Low DO (from pollution or eutrophication) reduces survival, growth and can lead to fish kills.

Primary producers convert sunlight into energy. In aquatic systems, phytoplankton and seagrasses are the main producers forming the base of the food web for fish and other organisms.

Herbivores eat primary producers (plants or phytoplankton), so they are primary consumers on the second trophic level, feeding on producers and supplying energy to higher levels.

Nile perch is a large predatory fish introduced to Lake Victoria and became a major commercial fishery species in Kenya and neighbouring countries.

Closed seasons protect spawning adults and their offspring so populations can reproduce and maintain sustainable stocks for future fishing.

Larger mesh allows juveniles to escape, reducing recruitment overfishing and helping sustain fish stocks by allowing young fish to reach maturity.

Pond culture involves constructed ponds on land, while cage culture uses floating or fixed cages in lakes, rivers or the sea to contain fish in natural water.

Fingerlings are juvenile fish large enough to be transferred to grow-out ponds or cages; they are stronger and have higher survival chances than fry.

FCR = feed given divided by weight gain. A lower FCR means more efficient feed use, important for cost and environmental impact.

Carrying capacity refers to the limit of organisms an environment can sustain with available food, oxygen and space before growth or health declines.

Bycatch includes unwanted species, protected animals, or undersized fish caught while targeting other species; it can harm biodiversity and fisheries sustainability.

CPUE shows how much is caught for a given effort (e.g., kg per net per day). Declining CPUE with constant effort suggests stock declines or overfishing.

When fish stocks are overfished, more effort yields less catch because fewer fish remain; this is a key indicator of declining stock health.

Mangroves offer sheltered, food-rich habitat where juvenile stages of many marine species grow, supporting coastal fishery productivity and biodiversity.

Fish are cold-blooded; their metabolic rate rises with temperature, increasing food and oxygen needs. Very high temperatures can cause stress or low oxygen problems.

When too many nutrients enter water bodies, phytoplankton blooms increase and later die, depleting oxygen and harming fish and other life—this is eutrophication.

Catch and effort data allow calculation of indices like CPUE, which help estimate stock trends and inform management decisions.

Anadromous fish (like salmon) spend most of their life in the sea but return to rivers to spawn. The opposite (freshwater to sea) is catadromous.

Small mesh nets trap fish of many sizes, increasing capture of juveniles and bycatch and reducing selectivity for target sizes or species.

KMFRI conducts scientific research, monitors fish stocks and habitats, and provides information and recommendations to support sustainable fisheries and aquaculture in Kenya.

Marine and freshwater fish face different salinity levels, so the key difference is how they osmoregulate (control salts and water in their bodies) to survive in salty seawater or in fresh water.

Nile tilapia is a native and widely farmed/harvested species in Kenya, common in Lake Victoria and many freshwater systems in the country.

Spawning is the act of releasing eggs (by females) and sperm (by males) into the water so fertilisation can occur.

Warmer water holds less dissolved oxygen than cold water; temperature changes therefore strongly influence oxygen levels available to fish.

An estuary is a transition zone where fresh river water and salty seawater mix, creating important habitats for many juvenile fish species.

Bycatch refers to species caught while targeting other fish; reducing bycatch helps protect ecosystems and valuable species.

Traps designed with escape gaps let small or unwanted organisms leave, making them more selective and causing less bycatch than destructive methods.

Tilapia commonly feed on algae and plant material and some small animals, placing them as primary consumers or omnivores in the food web.

Salinity (amount of salt in water) is usually reported in parts per thousand (ppt) in marine and estuarine studies.

Eutrophication is caused by excess nutrients (like fertiliser runoff), causing algal blooms that later decompose and reduce oxygen, harming fish.

Taking large numbers of adult, reproductive fish lowers the population's ability to replace itself and leads to declines.

Mangroves provide sheltered waters, food and protection for juvenile fish, making them crucial nursery grounds for many coastal species.

A fish stock refers to the number of fish of one species in a defined area and is the unit managers use to assess and set rules.

Carrying capacity is the highest population size that an ecosystem can sustain over time without degrading the habitat.

Closed seasons protect fish during spawning so adults can reproduce, helping maintain healthy future stocks.

Pollution can cause oxygen loss or toxins that lead to mass fish deaths and bad smells — visible signs of poor water quality.

Deep-water fish often have reduced or flexible gas bladders so they are not crushed by high pressure and can control buoyancy safely.

Bioaccumulation is when toxins concentrate inside fish tissues because they are taken up faster than they are eliminated, posing risks to fish and people who eat them.

Mangroves shelter young fish and trap nutrients, and their roots stabilise shorelines against erosion — both benefit fisheries and coastal communities.

Mark-recapture is a practical field method: by marking and later recapturing fish, you can estimate total population size mathematically.

Dagaa (Rastrineobola argentea) is the small pelagic fish from Lake Victoria widely caught, eaten and sold in Kenya.

Migration helps fish reach areas with abundant food or safe places to spawn, which increases survival of their offspring.

Secchi depth is a simple field test: the depth at which a disk disappears indicates water clarity and light penetration.

Like tree rings, otoliths and sometimes scales show annual growth rings that scientists use to determine a fish's age.

Nutrient pollution from agriculture and untreated sewage fuels algal growth; some blooms are toxic and reduce oxygen when they decay.