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Lecture

Mar 19-Fish II.docx

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Department
Biology (Sci)
Course
BIOL 305
Professor
Virginie Millien
Semester
Winter

Description
Fish II Locomotion: Swimming ­ As a fish you need to overcome drag and gravity ­ Fish live in a denser medium, so it takes much less energy to stay them off the  ground. However, without lift or buoyancy, you still sink ­ As you generate thrust to create that lift or buoyancy, you may create yaw, which  is a problem for going straight. Stabilization is done by the other fins ­ All swimming styles evolved from one ancestral form ­ Tail design: the bone position in the tail is what determines the shape (fin tissue  doesn’t matter) o Epicercal: good at generating lift o Hypocercal: No extant groups have these tails, but it is present in the fossil  record o Homocercal: very common because it is present in Teleostei Minimizing drag: When thrust is generated, you also generate drag. To minimize energy  expenditure in swimming, you need to reduce drag ­ Reducing viscous drag: Scales are parallel to the water current ­ Reducing turbulent drag: vortices generated at the tail use a bunch of energy that  could be going towards forward motion o Increasing aspect ratio (depth:length) of the caudal fin reduces turbulent  drag o Having a lower aspect ratio is good for certain life styles. It’s good for  generating energy in certain forms of movement and to turn quickly, eg. a  fish that needs quick busts of speed or to avoid obstacles may prefer a  lower aspect ratio ­ Reducing inertial drag: increased streamlining, optimal depth:width body ratio is  0.25 Generating lift: necessary to avoid sinking. If you only such your tail to generate lift, it’s  very inefficient and very energetically costly ­ Add an internal float o Oily liver: in sharks o Swim bladder: Compartments that contain air that they can let air in and  out  Physostomous swim bladder: • Swim bladder directly connected to the gut • These fish go up to the surface and gulp air to float and  burp it
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