Fish I Flashcards
The evolution of fishes
What are fish
They are a grade not clade
Paraphyletic group
Name the three main extant groups of fish
Agnatha (cyclostomes)
Chondrichthyes
Osteichthyes (Actinopterygians, Sarcoptergyians)
What are the 2 extant jawless agnathans
Hagfish and lampreys
What are the 5 characteristics of agnathans
They are jawless fish so: jawless (obviously) absence of paired fins Presence of notochord in larvae and adults seven or more gill pouches 2 chambered heart
Provide a brief description of hagfishes (can draw diagram)
Many pairs of tidal gill pouches no jaws long thin bodies simple myotomes tail fin feature rasping tooth plates that move apart together to eat into dead fish
list three somewhat interesting features of hagfish
They are benthic marine scavengers that eat into dead fish
Can exude large quantities of mucus (myxine glutinosa)
In order to shed the slime produced, can tie body into knot that can move up and down the body
What are the archaic features of hagfish?
Clue: features from diagram included
They have a stiff fibre-sheathed notochord but no vertebrae
many pairs of tidal gill pouches
single nasal capsule
only ONE semi-circular canal in statocyst
myotomes not divided into D and V blocks
No pepsin or HCl in stomach
Segmental excretory funnels in trunk
no paired fins
long thin body
What are lampreys?
Surviving agnathans
Long and cylindrical marine fish with vertebral structures
they are ectoparasitic on other fishes - stick onto them by suction - they rasp the flesh of their prey with oral tooth plates
Describe gill ventilation in lampreys
The tidal ventilation of gill pouches allows the lamprey to remain attached and breathe while rasping away with muscular tongue - eating into prey
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What are the archaic features of lampreys
Cartilaginos incomplete vertebrae around the notochord
many pairs of tidal gill pouches
single nasal capsule
only TWO semi circular canal in statocyst
myotomes not divided into d and v blocks
no pepsin or hcl in stomach
segmental excretory glomeruli in trunk
no paired fins
long thin trunk
Describe the anadromous life cycle of lampreys
adults live in oceans or big lakes
ascend rivers or streams to breed. temperature triggered migration
males and females construct nest
females lay eggs that are fertilised by males
larvae differ dramatically from the parents. They leave the nest, and currents carry them downstream
larvae burrow themselves into mud and spend a few years as filter feeders
undergo metamorphosis
produces parasitic juvenile
Why was the evolution of jaws a major step in fish evolution
The change from agnathans to gnathostomes led to:
new feeding habits: herbivory, predation
ability to manipulate objects (build nests, grasp mates during mating, care for young etc)
How else are gnathostomes more derived than agnathans? (7 things)
A duplication of Hox gene complex
paired fins(that allow for increased manoeuvrability)
well developed lateral line
third semi circler Canal in inner ear (better 3D orientation
more complex vertebrae
ribs
two nostrils
Describe how the evolution of jaws may have come about
Why modify the gill arch and not cartilage surrounding mouth?
gnathostomes are active - high metabolic demands
derived feature -> powerful mechanism for pumping water over gills
the mandibular gill arch evolved into protojaws, playing a role in forceful ventilation.
pharynx can be filled and then emptied by spreading and compressing the rays of the arches
cranial nerves become associated with jaw (e.g. dogfish jaws)
Describe cells involved in the detection of fluid movement
see diagram!
neuromasts are basic displacement sensitive cells
they are excited by bending in one direction and inhibited in the opposite direction
Talk about the neuromasts
Present on surface of all fish
they are superficial: naked and set on surface along body
canal: set in formal canals opening to the outside
What is the difference between superficial and canal neuromasts
Canal neuromasts: low pass filter
different functions; high vs low frequency ?
What are statocysts and where are they located?
The craniate head contains paired statocysts in the inner ear
statoliths (ossicles) give up and down info
also displaced by acceleration
swirling in semi circular canals is caused by angular acceleration
hagfish have one semicircular canal
and lampreys have two
What do three paired canals allow for? (we have three paired canals)
Allow discrimination of rotational accelerations in yaw, pitch and roll axes as well as translational accelerations in any plane
Describe the early appearance of paired fins
Early Devonian fish acanthodian fish : Euthacantus had paired rows of spiny finlets between the pharynx and anus
in the related acanthodes, reduced to discrete paired pelvic and pectoral fins
Explain the locomotor function of fins
Increase manoeuvrability and stability
unpaired dorsal and anal fins control tendency to roll or yaw
paired pectoral and pelvic funs control pitch and act as brakes
non locomotor functions of fins?
Spiny fins are used in defence - can evolve to inject poison when combined with glandular secretions e.g. in lion fish
colourful fins used to send signals to potential mates, rivals, and predators.
What are the two forces acting on fish while swimming
Thrust and drag
There are different fish swimming modes
Body or caudal fin swimming (greater thrust and acceleration)
median or paired fish swimming (greater manoeuvrability)
describe anguilliform swimming (eel)
The travelling wave throughout the fish’s body pushes water backwards. the wave increases in amplitude as it is pushed backwards . the force generated (push) increases from head to tail as a result.
the equal and opposite reaction force to the push – the forces can be resolved into longitudinal thrust components and sideways components .
along the body , the thrust components summate, but the sideways components cancel out .
describe carangiform swimming (trout)
Amplitude of undulation is small at the head and large at the tail - therefore major forces are produced at or near the tail, and the middle parts of the body do not contribute much to thrust
what is vortex generation and shedding
swimming involves generation and shedding of vortices, forming a train
a vortex has mass and velocity – the ???
Thunniform swimming (tuna)
oscillation is largely confined to the tail (hinge at beginning of tail). The tail acts on a large volume of water
propeller efficiency - if the mass of water moved backwards by the fish exceeds that of the fish, water will move backwards slowly but the fish moves forwards more rapidly.
Tail acts on a large volume of water so propeller efficiency is high!
What are the main forms of drag?
Skin friction between fish and boundary layer (mucus, scale adaptations)
pressures formed in pushing water (fish shape)
energy lost in vortices formed around the fins
