How are animals selected to have certain forms
1.morphology, physiology, biochemistry - amount of swimming muscle
2.performance capacity - burst swimming speed
3.behaviour - escape or not
4.fitness - life or death (leads to selection)
what 2 things are there a balance between
- Some animals are fast and efficient survivors – but need lots of food + energy
- Other animals are slow – exist in a niche where less energy / food is required
what happens when fish move its body to swim and how can we deal with this
some of it becomes thinner – move less mass to generate thrust
- Thin parts become floppy – becomes ramified with cartilaginous rods that run through body wall and thin body tissue
-Part in body wall = basal
-Part in fin = radial
what are the cartilaginous rods called in the body and fin
-Part in body wall = basal
-Part in fin = radial
what are the cartilaginous ridges that run through fin and body wall in elasmobranchs called
Still have basal + radial
- Ceratotrichia = fin
- Batoids = substantionally longer basals
example of how radials change within different rays
- Ones that flap find like birds – radials extend considerably into fin itself
- Ones with more flexible fins – radials does not extend considerably into fin itself - gives more control at low speeds
what does the radial articulate with in Primitive bony fish e.g. sturgeon
- radial now articulates with lepidotrichia (bony fin rays) outside body, and basal inside body
- Radial and basal made of bony material not cartilage
fin structure in Advanced bony fish e.g. teleosts
- lepidotrichia = jointed – jointed fin rays
- Radial reduced to nub -> distal pterygiophores
- Basals = Inter and proximal pterygiophores
Explains why you have such different looking fins
what are radials called in Advanced bony fish e.g. teleosts
distal pterygiophores
what are basals called in Advanced bony fish e.g. teleosts
Inter and proximal pterygiophores
what gives bony fish much more control over their fins
Each fin ray has an associated muscle
what kind of muscles do Pterygiophores have
- erector + depressor muscles – moves fin up and down
- indicator muscles – move fins left and right
what can fin rays be ossified into in higher teleosts
Fin rays can be heavily ossified into spines in higher teleosts
why are spine structures useful in higher teleosts and what 2 kinds can you get
- useful to make yourself bigger so cannot fit in preys mouth (gape limitation)
- Can also have venomous spines – if do get eaten get spat back out
-Neural spine – goes upwards from vertical collumn
-Haemal spine - goes downwards from vertical collumn
what are fin characteristics in elasmobranchs and bony fishes
- Elasmobranchs = Rigid, inflexible, non-retractable primitive fins
- Bony fish = Very flexible, retractable fins supported by soft and spiny rays
2 categories we can group fins into
- median fins (Single fin on central body line)
- paired fins
5 different fin kinds
- dorsal
- anal
- pectoral
- pelvic
- caudal
caudal fins job and characteristics
- All about thrust – escaping
- Can be symmetrical or asymmetrical
-Bony fish usually have homocercal tail – reflects swim bladder – want to generate equal thrust when swimming
-Primitive bony fishes + sharks = heteroceral tail – elasmobranchs have much bigger upper lobes – creates lift by giving downwards thrust (lack swim bladder) - Can be highly decorative
what kind of caudal fins do elasmobranchs and bone fishes have and why
- Bony fish = homocercal tail – reflects swim bladder – want to generate equal thrust when swimming
- Primitive bony fishes + sharks = heteroceral tail – elasmobranchs have much bigger upper lobes – creates lift by giving downwards thrust (lack swim bladder)
what is Aspect ratio and its equation
Describes how much power that tail can generate
- Power to drag ratio of caudal fin depends on shape
- Problem with generating lots of power = generating lots of drag – more energy consuming
TAIL SPAN2 / TAIL AREA
describe a Low aspect ratio tail
BROAD, FLAT TAIL: lots of thrust, but high drag
- used for short burst of speed e.g. rounded, truncate, emarginate
- Seen in cod, salmon, pike
describe a high aspect ratio tail
THIN, NARROW TAIL: poor thrust, but little drag
- used for sustained swimming e.g. forked or lunate tail
- Seen in herring, mackerel and tuna
describe a Intermediate-low aspect ratio tail
great thrust + reduced drag
- allows salmon to overcome hydrodynamic obstacles (travel far + overcome waterfalls) to reach their spawning grounds
what is needed for Caudal fin swimming and how is this achievable
Flexible but non-compressible backbone
- Separately innervated blocks of muscle (myotomes - separated by myosepta) – each block can contract independantly
- Contraction of blocks on one side of body + and relaxation of blocks on opposite side will generate flexing of the body
