Aquatics - Anatomy - Revision Cards in Other Other

Fins and Locomotion

movement in water is less costly for fish than it is for terrestrial animals on land
- streamlined shape and mucoid secretions
  - mucoid secretions lubricate the body surface and reduce friction
buoyant properties of water contribute to the efficiency of movement
aquatic animals spend less energy supporting their bodies against gravity
fins and body wall push against the incompressible surrounding water
Specialised muscles arranged in a zigzag pattern
- these muscles extend posteriorly and anteriorly
  - the contraction of each muscle bundle affects a large portion of the body wall

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pectoral fin = steering
ventral/pelvic fin = balance, but is adapted in some species
anal/dorsal fin = balance
caudal fin = propulsion
- forked in some fast swimming fish (e.g., tuna and mackerel)
  - reduced surface area for turbulence that could interfere with forward movement
adipose
- only present in some species (e.g. trout and salmon)
- ichthyologists unsure of the purpose

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oxygen and carbon dioxide
made of filaments covered in lamellae
covered in operculum
Counter Current Mechanism - blood flows in the opposite direction to the water flow
- higher concentration gradient
some fish have lungs (e.g., mudskippers and lungfish)

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swim bladder - expandable sac
- fish can control the amount of air in the sac
- when gas is in the swim bladder of Osteichthyes the fish becomes less dense
  - when the swim bladder is deflated the fish will sink
cartilaginous fish have an oil-filled liver
- filled with squalene
- can't control the amount of oil in the liver
- the oil makes the fish less dense

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closed circulatory system
- evolution of lungs in fish paralleled by changes in the vertebrate circulatory system
  - associated with the loss of gills, delivery of blood to the lungs, and the separation of oxygenated and deoxygenated blood in the heart
vertebrate heart develops from four embryological enlargements of the ventral aorta
most fish have a single circulatory system
- a few fish have lungs (e.g. lungfish)
  - presence of lungs changes the pathway of circulation
  - circulation to gills continues but a separate artery has developed that branches off the aortic arch VI
    - pulmonary artery
  - blood returns to the heart via the pulmonary veins
  - atrium and ventricle potentially divided
    - less oxygenated blood prevented from mixing with oxygenated
  - spiral valve in the conus arteriosus helps direct blood from the right side of the heart to the remaining aortic arches
  - lungfish show distinction between the pulmonary circuit and the systematic circuit

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blood flows from the venous system through the thin-walled sinus venosus
from sinus venosus into thin-walled atrium
atrium to single ventricle
- the ventricle is the primary pumping structure
anterior to ventricle is the conus arteriosus
- connects to the ventral aorta
in teleosts, the conus arteriosus is replaced by an expansion of the ventral aorta (bulbus arteriosus)
ventral aorta to gills
efferent vessels collect oxygenated blood and deliver it to the dorsal aorta
blood is spread through the body before being returned to the heart by the venous system

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earliest fish thought to have been filter feeders and scavengers
- sifted through mud on the sea floor
- most likely to have contained decaying organic matter, annelids, molluscs and other bottom-dwelling invertebrates
fish have changed dramatically since then
- they are now efficient predators
- modern fish feed on invertebrates and other vertebrates
teeth of most fish are simple cone-shaped structures that are uniform in length (homodont condition)
- seated in a shallow depression at the summit of the jaw bone (acrodont condition) by a cement-like material
fish usually swallow prey whole
- teeth capture and hold prey
some teeth are modified to crush the shells of molluscs and the exoskeletons of arthropods
to capture prey, fish close their opercula and rapidly open their mouth
- causes a negative pressure
- pulls prey into the fish's mouth
some fish are filter feeders (e.g. herring, paddlefish, whale sharks)
- long gill processes (gill rakers) trap plankton while the fish swims with its mouth open
fish such as carp feed on a variety of plants and small mammals

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fish such as lampreys are ectoparasites for at least a portion of their lives
only a few fish are primarily herbivorous
fish stomachs (if they have one) store large and infrequent meals
carnivores have a large stomach and short gut
small intestine is the primary site for enzyme secretion and digestion
herbivorous fish have a small or no stomach
- long intestine
  - typically coiled
  - can be longer than the fish's body length
sharks and other elasmobranchs have a spiral valve in their intestines
bony fishes have out pockets on their intestines called pyloric ceca
pyloric ceca increase the absorptive and secretory surfaces

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