Aquaculture

• SPECIES SELECTION

  Local conditions and species adaptation:

  Salmon thrive in cooler, whereas Tilapia in tropical. Marine species kept in coast
• SPECIES SELECTION

  Market demand:

  in MEDCs, popular species are carnivores (eg: salmon). In LEDCs, aquaculture species are herbivores(eg: tilapia) because they feed on naturally occuring plankton, vegetation and need less inputs
• SELECTION OF BREEDING ADULTS

  Desirable characteristics:

  • disease resistance
  • rapid growth rate
  • good appearance
• GENDER CONTROL

  The desirable gender depends on the species:

  • Rainbow trout: meat from females has better flavour. Some femals given male hormones so that they can fertilise eggs, producing only females
  • Tilapia: males more energy efficient and larger
• CONTROL OF PESTS AND DISEASES

  High stocking densities increase risk of disease spreading.

  • WATER FLOW: between tanks from younger and older fish reduces risk of spread from old and new stock
  • LOWER STOCKING DENSITY: reduces spread and collisions( which lead to infection)
  • PESTICIDES/BIOLOGICAL CONTROL: using wrasse for lice
  • Tanks with CIRCULATING CURRENTS: this avoids collisions
• NUTRITION

  Herbivorous fish can find natural food in lagoons( eg phytoplankton) . Carnivorous fish need artificial feed. More likely to find artificial control of feed in intensive systems.
• ABIOTIC FACTORS

  TEMPERATURE: depends on species. Warmer temps increase metabolic rate and growth but reduce dissolved oxygen.

  DISSOLVED OXYGEN: species with high requirement ( trout) need well aerated tanks especially if stock density high. (remove waste in tanks as this can cause deoxygenation)

  DAYLENGTH: affects reproduction. Salmon stop growing when they reach maturity. Long days with artificial lights delay maturity so they grow larger

  WATERFLOW: Make fish swim in same direction - avoid collision( better appearance and less infection risk) High waterflow makes muscular fish.
• EXTENSIVE OYSTER AQUACULTURE

  Low inputs. Oysters filter plankton from seawater.
• SHRIMP

  10% of worlds mangroves destroyed for shrimp farms

  In extensive, shrimps feed on naturally occurring plankton. In intensive, nutrients added to increase algae growth & food pellets added.

  Water exchanged to remove waste, & aeration prevents deoxygenation.
• INTENSIVE SALMON AQUACULTURE

  • desirable adult fish chosen (fast growth, shape, bright scales), stripped of eggs & milt, which are mixed to fertilize.
  • fertilized eggs raised in aerated freshwater tanks. Dead/ diseased are removed.
  • young fish are moved through a series of tanks & fed fish meal pellets.
  • after 12-18 months are moved to seawater. Continue to be fed on fish & plant meal pellets until harvest at 3-5kg.
• CONTROL OF LIMITING FACTORS

  • salmon are sensitive to low O2, so temperature mustn't be too high.
  • dissolved O2 levels kept high with water sprays/ weirs.
  • water flow rate kept high to make muscular fish.
  • pest & disease controlled by removing dead fish & using pesticides & antibiotics. Predators excluded/ killed.
  • light levels controlled to induce smoltification.
  • food chain controlled to increase efficiency. Fishmeal pellets from low value fish (anchovies, sandeels)-- similar to their natural food. Efficiency increased by adding lower trophic level foods (plants & veg oil).
• POLYCULTURE

  Produce food from multiple species at once. Productivity increased by rearing species together.

  Rearing predators can control smaller fish, enabling larger fish to grow more without competition.

  Bottom feeding fish disturb nutrient rich sediments increasing plant & phytoplankton growth.
• In this example, grass carp, common carp, bighead carp and silver carp can all be harvested and they all increase each other's yield. The common carp is a bottom-feeder and increases nutrient and therefore food availability for all. No 2 species compete for the same food. No artificial food pellets needed-- less input.

  
• INTEGRATED MULTI TROPHIC AQUACULTURE

  A polyculture system with species of different trophic levels.

  • Fed aquaculture: species given food.
  • Inorganic extractive aquaculture: species that absorb inorganic nutrients for growth (algae).
  • Organic extractive aquaculture: species that catch plankton (eg: filter feeding fish).
• AQUAPONICS

  Nutrient-rich water (that could lead to deoxygenation in aquaculture) from aquaculture is used in the hydroponics, & hydroponics drainage water retuned to aquaculture.

  • hydroponics species: leafy salad veg. (eg: lettuce).
  • aquaculture species: Tilapia, carp, catfish.

  
• CAN AQUACULTURE REPLACE FISHING?

  Trophic level efficiency:

  • raising herbivorous is very productive-- amount raise per unit area is high. Carnivorous fish more popular with customers & higher value.
  • Fish have higher food conversion ratios than other livestock, because of low Basal Metabolic Rates (don't use energy for support or warmth).
• CAN AQUACULTURE REPLACE FISHING?

  Food requirements:

  • Herbivorous may eat naturally occurring plants. Growth increased by adding plant nutrients. Supplementary feeding -- add plant material like crop waste.
  • Carnivorous fed on lower-value fish (eg: sandeels). Overfishing of sandeels has caused other species' decline. Fish meat produced may be less tasty when fed plant-based feeds instead.
• CAN AQUACULTURE REPLACE FISHING?

  Stock collection:

  Some species like Atlantic Blue Fin Tuna don't breed well in captivity, so young are caught at sea & raised in large cages. Tuna aquaculture can't continue without wild population.
• ENV IMPACTS - HABITAT LOSS

  • especially in mangroves

  Control:

  Careful site selection. Selection of non-tropical species.
• ENV IMPACT - PESTICIDE POLLUTION

  • may kill wildlife

  Control:

  Mechanical cleaning of cages & biological control with wrasse
• ENV IMPACT - ANTI BIOTIC RESISTANT BACTERIA DEVELOPING

  • may transfer to human pathogens

  Control:

  Lower stock densities allow lower antibiotic use.
• ENV IMPACT - LICE GENE IMPACTS

  • Lice can spread to wild populations. Hydrogen peroxide washes, pyrethroid pesticides are used to control lice.

  Control:

  Tanks should hold fish of only 1 age so no transfer of lice from old to young fish. Biological control w/ wrasse (however, can reduce wild wrasse pops., as they are caught & moved to fish farms). Mechanical removal (can cause stress to fish).
• ENV IMPACT - WILD GENE POOL

  • farm fish escape & breed w/ wild fish, producing disadvantageous traits (e.g.: bright colour).

  Control:

  Better cage designs. Eggs exposed to high pressure producing triploid (infertile) fish, which also grow faster
• ENV IMPACT - INTRO. ON NON INDIGEONOUS SPECIES

  • may colonise wild & become predators / competition.

  Control:

  Cultivation of species that can't breed in wild (eg: Japanese oysters find UK too cold to breed).
• ENV IMPACT: ORGANIC WASTE POLLUTION

  • faeces and surplus food cause deoxygenation

  Control:

  Preventing over-feeding. Cages located where currents disperse waste. Freshwater aquaculture systems with effluent treatment works. Planting bacteria in reed beds that absorb nutrients & break down OM.