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Basic Fish Biology
Biology of a Mussel
Biology of a Lobster
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Basic Fish Biology


  1. mouth: most fish have a conical mouth cavity with a relatively small opening in front and an expandable rear compartment to create suction for capturing food.
  2. nostrils: in most fish the nostrils are only used for smelling but not for respiration.
  3. eye: fish eyes are optical but are not capable of binocular vision because they are located on either side of the head.
  4. lateral line: a canal lined with sensory organs which detect vibrations and changes in temperature and pressure. The lateral line helps fish to maintain balance and maintain distance from other fish when schooling.
  5. first dorsal fin: the anterior fin on the dorsal surface of a fish which is used for balance.
  6. second dorsal fin: the posterior fin on the dorsal surface of a fish which is used for balance.
  7. caudal fin: the tail fin of a fish which is used for propulsion, steering, and balancing.
  8. caudal peduncle: a fish's "tail stem", the caudal peduncle is usually heavily muscled and is used for propulsion.
  9. anal fin: the unpaired fin located on the posterior ventral side of a fish and is used for swimming.
  10. pelvic (ventral) fins: a pair of fins located on the ventral surface of a fish.
  11. pectoral fin: one of a pair of fins located on either side of a fish behind the gills used for balancing and braking.
  12. gill cover / operculum: a protective cover over the gills.
  13. gills: gills absorb oxygen from the water as it passes into the mouth and out through the gill cavity. Gills also maintain salt balance and are excretory organs.
  • scales: scales provide protection and reduce friction for fish: two common types are ctenoid (small teeth on rear edge) and cycloid (smooth edged) scales.


  1. brain: the central point of a fish's nervous system.
  2. kidney: the kidney is part of a fish's excretory system and has immune function.
  3. vertebra: a fish's backbone used for structural support and for protecting the nerve chord.
  4. muscle segments: because fish require great strength to move through water, 40% to 60% of a fish's body weight is made up of large muscles called myotomes.
  5. gonads: the reproductive organs of a fish
  6. swim bladder: by altering the amount of gas in the swim bladder, a fish can adjust its buoyancy, and therefore its depth, in the water. (sharks and other cartilaginous fish do not have a swim bladder)
  7. intestine: an organ for digesting food.
  8. stomach: an organ for breaking down food.
  9. liver: an organ for detoxifying blood.
  10. heart: a two-chamber pump in a fish's circulatory system.
  11. gill rakers: a set of tooth-like structures which strain the water passing through the gills to prevent debris from entering the gills.