aquaculture

• Aquaculture aims to maximise productivity
• Ways that aquaculture is controlled:

  1. Selection of species 
  2. Control of species 
  3. Control of abiotic factors 
  4. Control of biotic factors 
  5. The environmental impacts of fish farming 
  6. Minimising environmental impacts 
• Choosing a species to cultivate depends on their range of tolerance (temperature, quality of water, location of fish, salt/fresh water). It also depends on how the fish tastes (carnivorous fish) and ethics. 

  • Muscles 
  • Cod 
  • Oysters 
  • Mackerel 
  • Anchovies 
  • Tuna 
• Control of species includes selective breeding and genetic modification. This produces a fast growth rate, good taste, bright colours, tolerable texture and tolerance to disease/temps/salinity/pH. 
• An environmental impact may be escapee fish. Escaped fish may breed with native fish and be more susceptible to predation. They may also be less able to survive in the wild dur to lack of food. They could also outcompete, predate or carry diseases to native species.  
• Control of abiotic factor can use light to speed up smoltification, which means they are able to be transferred to salt water sooner. Fish farms are often found in tidal areas that bring food and remove waste, with good access. Mangroves are often cleared to make room for fisheries, this destroys habitat and removes a carbon sink. 
• Some abiotic factors that are controlled include: oxygen levels - high stocking density, so consume high levels of oxygen during aerobic respiration. Aeration is improved by pumps that use energy constantly. To be more sustainable, a reduction in stocking density, which reduces productivity - this implemented through multi-trophic systems by using plants and shellfish to remove DOM. 
• Another abiotic factor is temperature, unsuitable temperatures can reduce growth rates and reduce dissolved oxygen levels. Thermostatically controlled intensive systems - use energy. More suitable climates for location of farms. 
• Flow rate can be simulated artificial flows to produce muscle on fish, achieved by mechanical wave boards (energy), larger enclosures and tidal locations. 
• A biotic factor is food, some fish are herbivores some are carnivores. Carnivorous fish need animal tissue to eat, they are more likely to cannibalise each other. Energy is used to catch fish for farmed fish to eat, this can lead to overfishing and excess bycatch. Fish are the most efficient animal to produce  due to their low feed conversion ratio, they're also ectothermic (coldblooded) and most of the fish is edible. Excess food/excretion is decomposed leading to deoxygenation and eutrophication, it increases turbidity so less light penetrates. 
• Disease has to be controlled, so antibiotics are circulated around enclosures, it escapes into the environment causing pollution and antibiotic resistance. Pesticides are used to kill parasites (fish lice). Pesticides result in the death of non-target species and reduced biodiversity. 
• Predators are culled to prevent predation of valuable fish, this reduced biodiversity. 
• Uneaten food and excretion from fish can be pumped into natural bodies of water, this DOM is decomposed by bacteria and reduces the dissolved oxygen levels. Bacteria also convert ammonia into to NH4 which is nitrified and converted to NO2 and NO3 which leads to algal blooms and eutrophication.