Fish

Question 1

Are fish a clade?

Answer 1

No, they are paraphyletic.

Contains most recent common ancestor but not all of the descendants.

Question 2

Main extant groups of fish?

Answer 2

Agnathans - jawless hagfish and lamprey

Chondrichthyes

Osteichthyes - Actinopterygians and Sarcopterygians

Question 3

Describe the Agnathans?

Answer 3

• jawless
• no paired fins
• notochord in larvae and adults
• seven+ gill pouches
• two chambered heart

Question 4

Why are Hagfish vertebrates?

Answer 4

The embryos have a neural crest, 3 part brain, paired sense organs but with archaic features (single nasal capsule, no vertebrae)

Question 5

Why are Lampreys vertebrates?

Answer 5

Have 3 part brain, paired sense organs but with archaic features (single nasal capsule, and cartilaginous incomplete vertebrae around notochord. Show metamorphosis and move upstream to breed.

Question 6

Evolution of jaws?

Answer 6

Led to new behaviours: new feeding regimes (herbivory and predation) & ability to manipulate objects (build nests, grasp mates and care for young). It is thought that they evolved to aid gill ventilation. Gnathostomes are very active with high metabolic demands. The mandibular gill arch evolved into protojaws, playing role in forceful ventilation.

Question 7

What is the lateral line?

Answer 7

System of sense organs found in aquatic vertebrates used to detect movement, vibration and pressure gradients in the surrounding water

Question 8

What are statocysts?

Answer 8

Small organ of balance and orientation. Paired in the inner ear, displaced by acceleration. Three paired canals allow for detection of 3D movements

Question 9

What are paired fins?

Answer 9

Increased manoeuvrability

Question 10

What does duplication of the Hox gene complex allow?

Answer 10

Happens often with big evolutionary changes as allows for changes to be made to the copy. Involved with patterns of development

Question 11

What are neuromasts?

Answer 11

Basic displacement sensitive cells. Excited by bending in one direction and inhibited in the opposite direction. Present on the surface of all fishes. Detect fluid movements. As a fish swims, this creates a flow field around the fish so can detect interfering objects.

Question 12

Locomotor functions of fins?

Answer 12

increase manoeuvrability and stability
unpaired dorsal and anal fins control tendency to roll or yaw
paired pectoral and pelvin fins control pitch and act as brakes
more fins = more control

Question 13

Non locomotor function of fins?

Answer 13

spiny fins are used in defence – can evolve to inject poison when combined with glandular secretions
colourful fins can be used to send signals to potential mates, rivals and predators

Question 14

What forces act on fish?

Answer 14

thrust forwards
drag backwards
-body/caudal fin – greater thrust and acceleration (important when swimming long distances)
-median/paired fin – greater manoeuvrability (important in cluttered environments)

Question 15

How do eels swim?

Answer 15

Wave passes along body, increasing in amplitude. Generates a forwards push from the water. Sideways components roughly cancel out, but also moves forwards

Question 16

How do trout swim?

Answer 16

Amplitude of undulation is only large at the tail. Major forces are produced at the tail, and middle parts of body don’t contribute much to the thrust

Question 17

How do tuna swim?

Answer 17

Oscillation is confined to the tail, but acts on a large volume of water. If the mass of water moved backwards by the fish is far larger than that of the fish, the water moves backwards slowly whilst the fish moves forwards rapidly – efficient propeller

Question 18

How does vortex generation help fish swim?

Answer 18

Involves generation and shedding of vortices, forming a train. A vortex has mass and velocity so the fish swims.

Question 19

How does drag occur in fish?

Answer 19

• skin friction between fish and boundary layer
• pressures formed in pushing water
• energy lost in vortices formed around fins

Question 20

Problems with an aquatic existence?

Answer 20

dense medium for movement 
respiration 
depth regulation 
maintaining a stable internal environment within body 
regulating body temperature 
navigation through complex environments

Question 21

Describe bones, scales and skin in fish?

Answer 21

bony skeletal elements start as cartilage which gets calcified and vascularised
bony fish have ossified dermal elements – bony scales
over time, skeletons of bony fish, become thinner and more mobile
ray finned fish = bony fish

~early bony fish had thick interlocking ganoid scales
~late bony ray finned fish (teleosts) have thin and flexible bony scales

~advanced teleosts have ctenoid scales with drag reducing trailing edges (serrated edge)

~teleosts also appear silvery due to reflective layers in the skin under the scales, this composes of guanine/tissue sandwich. The light reflected interferes constructively, and reflects up to 90%

Question 22

Main features of Chondrichthyes?

Answer 22

Not vascularised
Skeletons of sharks use varying degrees of calcification, jaws may be heavily calcified and therefore rigid
Shark skin has crossed helices of collagen fibres, which provide a tough support for placement of scales and teeth
Sharks reduce drag with the shape of their scales, by altering the micro-turbulence over the skin surface

Question 23

How does respiration occur in fish?

Answer 23

Water is pumped in through the mouth and out though the gills
Pumping action of mouth and the opercular cavities creates positive pressure across gills so the respiratory current is only slightly interrupted in each pumping cycle
Back flow is prevented by a buccal flap valve
Water is sucked into the pharynx by lowering the floor of the mouth
Water flows through lamellae (large surface area), with counter current flow against the blood.
The blood flows in thin flat spaces, so the blood to water distance is quite small
Perpetual swimmers create a respiratory current by swimming with their mouths open, meaning that they must constantly swim in order to gain oxygen
Lung fish have lungs in order to supplement their low oxygen environment.

Question 24

How is bouyancy regulated in fish?

Answer 24

The teleost swim bladder is a gas filled part of the gut which regulates buoyancy
Can adjust gas volume to obtain neutral buoyancy, ascend or descend
In more primitive fish, the swim bladder connects to the gut and gas can be swallowed or burped out
In more derived fish, the swim bladder is regulated by uptake/secretion of O2 from a gas gland on the wall of the bladder. Lactate is pumped from the outgoing vessels into the incoming vessels, thus lowering the pH at the gas gland to around 6.3, allowing O2 to diffuse out of the blood
Chondrichthyes don’t have swim bladders but its fine because they stay on the bottom of the ocean
Many sharks are neutrally buoyant, achieved by a vast liver up to 25% of the body weight – mostly made of squalene, however this causes considerable hydrodynamic drag.
Quite a lot of fast swimming sharks use dynamic lift from pectoral fins, but if they stop they sink

Question 25

How does heat exchange occur in fish?

Answer 25

Many large fish have warm muscles, but this requires large body to minimise heat losses via conduction, and a heat exchanger system.
In typical fish, the muscles’ blood supply is along the mid-line, whilst in tuna and some sharks the muscles are supplied by vessels running just under the skin
Cold blood passing inwards exchanges heat with the outgoing blood from the centre

Question 26

How does reproduction occur in fish?

Answer 26

Majority of teleosts use external fertilisation, whilst a few fertilise internally and produce live young (guppies)
To ensure effective fertilisation, many fish congregate, make fertilisation pits, nests, etc. Elaborate courtship may occur.
The sea provides a rich alternative planktonic niche for fish larvae
All Chondrichthyes have internal fertilisation, where sperm is transferred to the female’s oviduct along one of the male’s pelvic claspers

Question 27

Feeding in Actinopterygians?

Answer 27

Piranha – omnivore
Swordfish – predator
Cichlid – parasites from catfish
Dwarf pygmy goby – plankton

Question 28

Feeding in Chondrichthyes?

Answer 28

Common predatory life
Great white shark – predator
Whale shark – filter feeder
Shark teeth – grow from pockets in the lower and upper jaws. Several rows of teeth could be in use at any one time, and teeth may get left in prey

Question 29

Adaptations to deep sea?

Answer 29

Angler fish, dragonfish and gulper eel
These fish are called Bathypelagic. They reside in the least studied habitat on Earth – the deep sea. 75% of the ocean is always dark
As all animals depend on photosynthesis, fish decrease in abundance, size and species diversity at depth.

Main issues – availability of food and the very high pressures
Adaptations – eye size correlates with depth (get bigger), photophores (used for finding mates), enormous jaws, small, with less dense bone and less skeletal muscle

Pelagic (live in water columns) and Benthic (live at bottom)

Anglerfish – predation using a lure (bioluminescent photobacteria), can distend jaws and stomach for eating. There also exists a very large sexual dimorphism. The males are parasitic and very tiny, but with well-developed olfactory organs which detect female pheromones. When mature, the male digestive system degenerates, the male bits the female and digests her skin. The male then releases sperm after female releases eggs.

Question 30

Adaptations to live in cold water?

Answer 30

Antarctic toothfish – have antifreeze glycoproteins which bind to small ice crystals to inhibit growth, as most damage is caused by the growing ice crystals. Convergent evolution of antifreeze in animals. As this is energetically expensive to produce, Winter flounder has a built in cycle of production controlled by growth hormone released from pituitary gland in tune with seasonal cues.

Question 31

Adaptations to live in caves?

Answer 31

Astyanax fasciatus – blind Mexican cave fish. Eyeless, with reduced pigmentation, increased taste bud number and larger jaws. Convergent evolution of reduced eyes and pigmentation.

Question 32

Why is it advantageous to lose eyes if you live in fish?

Answer 32

1. Adaptation to prevent disease/economical
2. Drift, mutations accumulated in genes required for eye formation due to relaxed selection
3. Evolutionary trade-off to allow development of other characters

Question 33

Navigational case studies?

Answer 33

Coral reef fish – Selection for ability to manoeuvre through complex 3D structures, and to be able to navigate by learning and remembering information from the surroundings.

Short range homing – Intertidal gobies, will only travel via the pools to the main pool at low tide, if had already travelled there at high tide. Can also learn that landmarks signal food presence.

Question 34

Magnetism in fish?

Answer 34

Salmon – migrate back to where they were born upstream in order to reproduce. This is due to imprints they leave on their outward journey during development. Nocturnal orientation of salmon guided by magnetic field shows a correlation between the magnetism and orientation of sockeye. It is thought this is due to iogenic magnetite found in nose of trout which react to magnetic fields. The torque placed on magnetite chains depolarises the nearby nerve cells.

Question 35

Electric fields in fish?

Answer 35

The fish creates an electric field by discharging an EOD pulse
The fish detects disruptions using electroreceptors on its skin surface
Can also passively sense bioelectric fields of prey and predators

Question 36

Problems with overfishing?

Answer 36

Modern netting techniques are so effective that there are strict quotas for staple food fish
Fishery management not always helped by the expectation for fresh fish at all times
Dumping of by-catch as well as fishing over quota, and illegally-catching species don’t help matters