Aquatics - Feeding Strategies

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What is different about fish diets?

  • More protein is required compared to other vertebrates
  • there are 10 Essential Amino Acids
  • Fat is important for carnivorous fish, but still not more than 8% is needed
  • Fish can lack access to carbohydrates and too much can deter growth
  • Carbohydrates in fish can aid digestion
  • Need vitamins and minerals for bonesteeth and scales
  • Found in water and in the diet
  • Only some fish need to drink
    • in freshwater fish, the salinity is lower in the water so freshwater flows in through their gills and when they eat
    • Chloride cells produce an enzyme that controls the flow of dissolved salts across cell membranes
    • Saltwater fish live in an area where the salinity outside their body is higher than the salt levels inside their body
      • Saltwater fish therefore have to drink water, but have to filter out the salt
      • Saltwater fish generally filter out salt in their kidneys but they also have chloride cells which pumps salts out of their bloodstream
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Diet Changes

Diet can change depending on age, breeding needs and the environment.

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Why is it important to get diets right?

  • to provide the best welfare
  • improved successes e.g., breeding
  • deficiencies can impair health directly or indirectly by making fish more susceptible to disease
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Herbivores/Browsers

  • often have pharyngeal teeth
  • Food spends a long time in the gut
  • have a long gut and little or no stomach
  • herbivores are known for grazing and browsing
  • feed on plant matter
  • e.g., parrotfish, angelfish, blennies, tangs
  • browsers feed on dicotyledonous plant material
    • feed on e.g., algae, aquatic plants, corals
    • browsers: e.g., sea slugs, sea urchins, parrot fish, manatees
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Carnivores/Insectivores

  • stomachs - digestive vat
  • usually have teeth but can be in different areas
    • edge (maxillary)
    • roof of the mouth (vomerine)
  • carnivores use active hunting, ambush hunting and scavenging
  • feed on animal matter
  • Carnivores: e.g., Red-bellied Piranha, Arowana, Butterfly Fish
  • insectivores are known for active hunting, ambush hunting and scavenging
    • feed on invertebrates
    • usually have maxillary or vomerine teeth
    • digestive vat stomach
    • e.g., Carp
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Omnivores

  • digestive system can vary
  • opportunistic
  • most aquatic species fall into this category, especially in desperate times
  • omnivores are known for scavenging, ambush and opportunistic feeding
  • feed on plant material and animal matter
  • e.g., goldfish, corys, plecos
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What can help you work out what to feed a fish?

  • mouth size
  • mouth shape
  • habitat
  • common family traits
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Types of Feeder

  • Terminal - middle feeders
    • pick material whilst it is in suspension before it settles on the substrate
    • e.g., angelfish, discus, cardinal tetra, tiger barb
  • Superior - surface feeders
    • take food that has fallen onto the surface of the water
    • mouth facing upwards
    • e.g., butterfly fish, glass catfish, siamese fighting fish
  • Inferior - bottom feeders
    • pick up particles of food that have settled on the substrate
    • are often scavengers
    • e.g., pleco, clown loach
  • Filter feeders
    • e.g., clams and anemones, herring (Clupeidae), Paddlefishes (Polyodontidae), Whale Sharks (Rhincodon)
    • long gill proccesses, called gill rakers, trap plankton while the fish is swimming through the water with its mouth open
    • take in mouthfuls of water and expel excess water e.g., through baleen
  • ambush
  • shoal feeding
  • grazing
  • scavenging
  • active hunting
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