(Fisheries for the future) 8.3 AQUACULTURE

What are the requirements for the long term success of aquaculture projects?

Availability of stock Availability of clean water Availability of feed Efficiency of use of feed Availability of labour Disease management Availability of location Market demand Access to market Return of investment

Preparation of brood stock

Brood stock fish are selected from open water cages in the sea. Males and females that seem to be of strong genetic quality are selected. These are placed into freshwater tanks or cages in autumn for a period of about two months during which they are fed with high- protein food to increase egg and sperm production. Males are females are usually kept in separate tanks. In some highly intensive aquaculture projects, fish are brought into reproductive season by manipulating the hours of light or injecting the fish with hormones.

Aquaculture is usually carried out using one of three systems

Cages Ponds Indoor tanks

Stage of the salmon life cycle

Egg -> Alevin -> Fry -> Parr -> Smolt -> Adult

What are the requirements in order to produce fish and shellfish successfully?

Food source Oxygen Clean water Space Separation of ages and sizes Disease prevention

Environmental impacts of aquaculture

Habitat destruction Overexploitation of feedstocks Pollution Introduction of invasive species and cultured stock Spread of disease Competition for resources Reduction in the exploitation of native stocks

Positive outcomes of aquaculture

Increased employment opportunities - a successful business can provide higher incomes for local people and the opportunity to be trained. As a business grows, it employs more people, many of whom may move into the area and require housing and will also buy goods and services from local businesses. In areas with low wealth, the development of an aquaculture business that generates more money from exports can increase local wealth (raises the standard of living for local people). Improved infrastructure, such as increased road and rail links. In regions where malnutrition is high, the development of aquaculture ventures may offer a cheaper and more abundant source of food that is rich in protein.

Salmon Aquaculture- What are the key stages?

Preparation of brood stock Spawning Hatching

Minimising the negative effects of aquaculture

Reducing pollution Using resources sustainably Preventing escape Conserving habitats Minimising social impacts

Harvesting

Salmon are typically harvested after about two years of growing out in seawater. They are carefully moved into holding pens before being transported to a slaughter area where they are stunned, bled and processed. Some adults are retained as brood stock for the next generation of fish.

Negative outcomes of aquaculture

Some aquaculture ventures can cause more unemployment Local fishing industries can become less cost effective and unable compete with the lower prices of farmed products Less extensive farms may close because they can't compete Intensive farms may impact upon local fish stocks and so reduce the yield of fisheries Shortage of labour - other industries may suffer

Hatching

The trays of eggs are left in freshwater at a temperature of less than 10°C, usually in the dark. At the bottom of the trays are placed small stones or matting to recreate the conditions normally found in a 'redd' in the riverbed. The trays are monitored by staff and as soon as hatchlings, called alevins, are seen to move to the surface of the water, food is added to the surface.

Salmon Aquaculture

Uses both intensive and extensive methods

Growing out in seawater

When smolts reach a size of around 100 g, they are checked to see if they have become tolerant to seawater, and then transferred to open sea cages systems. The cages are large nets suspended into the sea, anchored to the seabed and with platforms around them so that workers can feed, inspect and harvest the fish. Several cages are often grouped together to make it easier to raise the fish. The natural water currents remove waste, maintain salinity and bring oxygen. Food is provided for the fish regularly and consists of high-protein pellets supplemented with fish oils. As Salmon is largely carnivorous, the food pellets tend to be produced from other fish catches. This can lead to overfishing of other species to provide food for the salmon. Feeding is now often automated and controlled to prevent overfeeding and pollution. The temperature of the water needs to be ideally between 6 and 16 degrees Celsius and the fish are usually stocked up to a density of about 20kg m-3. Fish are kept in cages according to age so that their sizes are similar. Antibiotics, pesticides, fungicides and other substances may be added to reduce the spread of disease and to give the salmon meat the characteristic pink colour, pigments are added to the food pellets.

Disease prevention

large numbers of a single species encourage the spread of disease, so methods of prevention and control must be used.

Cages:

organisms are placed into nets or cages within open, natural water The natural water flow flushes waste out of the cages and brings oxygen and some natural food into the cage. Molluscs such as mussels are often grown on free ropes in the water.

Ponds:

organisms are placed into specially dug outdoor ponds The ponds may be made out of a range of materials, such as earth or concrete, and may be totally or partially separated from natural water. In some cases, they are simply areas of coastal water separated by ditches. Raceway ponds are a particular type of shallow pond that extend over a large area and are often used for the production of shrimp.

b (ii) Use Fig. 4.1 to suggest the function of the paddle wheels

oxygenates / aerates the water ; ensures an even distribution of food / phytoplankton (for grouper) ; ensures an even distribution of nutrients (for phytoplankton) ;

Indoor tanks:

species are placed into plastic or metal indoor tanks They are isolated from natural water and water is pumped in. Waste water is passed through filtration systems.

Oxygen

the water must contain sufficient oxygen for respiration.

Food source

there must be sufficient food to maximise growth.

(c) The grouper are harvested and the water is removed from the pond. The mud at the bottom of the ponds is then ploughed, chlorinated and dried for 1 month before restocking with young grouper, called fingerlings. (i) Explain the benefit of treating and drying the mud at the bottom of the ponds, before restocking with grouper fingerlings.

to remove / kill any parasites so that they do not infect new stock / fingerlings ;

Clean water

waste must be removed before it becomes toxic.

(b) In Japan, as well as in many other countries, river beds are excavated to increase channel depth and dams are constructed to retain fresh water. Salmon hatcheries collect mature wild salmon to be used in aquaculture for breeding purposes. Suggest and explain how these activities have affected salmon numbers

wild salmon numbers will decline ; plus any 2 of: excavation of river bed destroys, salmon nests / redd / habitat / eggs / alevin OR removes, gravel required for nest / redd / hiding places for alevin / fry ; excavation release sediment so blocking gills ; water deeper, so oxygen concentration at river bed decreased (as greater distance between river bed and surface) / temperature too cold ; dam prevents migration / salmon reaching spawning area / juveniles / smolt reaching estuary / ocean ; collecting (wild) salmon reduces numbers breeding ;

Space

with more predatory species, there must be sufficient space to prevent cannibalism.

Separation of ages and sizes

with predatory species, smaller fish must be kept away from larger fish.

b (iii) Suggest why there is no need for the paddle wheels to operate 24 hours per day.

any 2 of: photosynthesis occurs during the day / not at night ; oxygen levels fall at night ; so paddles maintain sufficient oxygen (for grouper respiration) ;

Nursery tanks

When the alevins develop into small fish, called fry, they are transferred to larger tanks and fed more frequently. The fry are grown in enclosed systems with recirculating fresh water and conditions, such as temperature, can be manipulated to change growth rates. In the wild, salmon fry develop into larger freshwater fish, called Parr, that live in rivers. The parr live and feed in rivers for between six months and three years, after which they migrate to estuaries where they change into a smolt. Smolt gradually become adapted to the saline conditions of the ocean, and then migrate into the ocean to become adults where they live up to four years. In aquaculture, whrn fry become parr, they are placed into either larger tanks or placed into outdoor cages located in freshwater bodies. When the parr become smoly they may also be raised in large, encloused tanks or in lake cage systems.

Spawning

When the salmon are ready to breed, the females afd carefully taken from the water and 'stripped' of their eggs. The fish is held carefully, and light pressure applied to its abdomen so that the eggs are ejected into a bowl of water. A male fish is then taken and sperm (known as milt) is ejected onto the eggs by applying light pressure to the abdomen. The eggs are then left to fertilise, are disinfected and then placed into trays of clean freshwater. Unfertilised eggs are removed as they could cause bacteria to grow.

(a) Fig. 6.1 shows the stages in the life cycle of Pacific salmon. egg .................................... fry .................................... smolt--- adult Complete Fig. 6.1 with the names of the missing stages in the life cycle. [2

alevin parr

(d) (i) Conservation areas in Japanese rivers have been created to separate wild salmon from hatchery-produced salmon to prevent them breeding together. Suggest one reason for preventing the wild salmon from breeding with hatchery-produced salmon.

any 1 of: hatchery produced salmon could be inbred / have (harmful) mutations ; have a different, genotype / gene pool ; idea of: wild salmon genotype / gene pool / genetic diversity, is not altered

(ii) State two other disadvantages of releasing hatchery-produced salmon into the ocean.

any 2 of: idea of increased competition for food / breeding sites / mate ; easier for diseases / parasites, to spread ; poor swimmers ; less able to adapt to any change in named conditions ; more easily predated (as they are not used to predators) ; can alter food chains / webs ;

4 (a) The Cam Ranh area of central Vietnam is important for grouper aquaculture. Grouper are cultured in mud-lined ponds around the shores of small bays, where there are no rivers. Grouper grow best at temperatures of between 22°C and 23°C, in water with a salinity of 28‰ to 38‰ and a rich supply of phytoplankton. Suggest and explain two reasons why the lack of rivers make the water in this area suitable for grouper aquaculture.

any 2 of: no silt to reduce light penetration, so phytoplankton productivity high no freshwater to dilute seawater / keeps salinity high enough temperature remains stable / river water brings cooler water no water flow to remove phytoplankton / grouper eggs / grouper fry

(c) Farm-hatched fish are often released in large numbers, to help increase wild populations. Suggest and explain two advantages of rearing salmon in a hatchery, rather than relying on natural reproduction in the wild.

any 2 of: more offspring / eggs survive and there are no predators / salmon are constantly monitored ; increased chance of fertilization and eggs can be artificially fertilized ; optimum (named) conditions provided and faster growth / larger fish / more reliable supply of fish / more able to meet market demand ; easier to spot disease / fish can be vaccinated / given antibiotic and prevent disease / treat disease / less mortality ; selective breeding (over several generations) and faster growth / larger fish / more eggs / fry ; increased chance of breeding and mature salmon kept together

(b) Traditional farming methods involve several farmers, each having three or four ponds, which are 2500m2 in area. Each pond has gates on opposite sides to allow sea water to enter or leave the pond, depending on wind conditions and daily tides. More than 50% of water is exchanged each day. (i) Explain the advantages of having more than 50% of the water exchanged each day.

any 3 of: to remove waste products / faeces / carbon dioxide / toxins / pathogens ; which could be, toxic / decrease chance of, disease / algal blooms ; to renew oxygen ; for respiration which prevents suffocation ; to bring in food (for grouper) / nutrients for phytoplankton ; maintains, salinity / temperature / pH ; as grouper can only tolerate a small range of salinity / temperature / pH

4c (ii) In Vietnam, more hatcheries are being constructed to supply grouper fingerlings to farmers. Use the information in Table 4.1 to discuss the reasons for constructing more hatcheries.

any 4 of: 1) high demand for grouper fingerlings ; 2) too many wild-caught fingerlings are used ; 3) too few left to grow into adult grouper in the wild ; 4) less reproduction / less fingerlings / population decreases / unsustainable in future / less recruitment ; 5) less (adult) grouper for fishermen to catch ; 6) importing fingerlings from overseas is more costly 7) local production provides more jobs / economic benefit ; 8) more control on fingerling quality ; 9) supply of wild-caught fingerlings not guaranteed / fingerling supply from hatchery more guaranteed / can meet demand