Fish ecology

Question 1

What were the first vertebrates?

Answer 1

Fish

Question 2

Chondrichthyes

Answer 2

Sharks and rays

Question 3

Osteichthyes

Answer 3

Bony fish

Question 4

Fish vs fishes

Answer 4

Many individuals of one species = Fish

More than one species = fishes

Question 5

What is a fish?

Answer 5

Aquatic vertebrate with gills and with limbs in the shape of fins

Question 6

Gills

Answer 6

Extract oxygen from water
Counter current exchange
(blood goes in one direction and water goes in the other - makes them very efficient at getting oxygen from water)

Question 7

Vertebral Column of fish

Answer 7

Internal skeleton with a spine surrounding dorsal nerve cord
Brain is fully encased in skull or cranium made of cartilage or bone

Question 8

Nutritional deficiencies of fish

Answer 8

unable to synthesise the aromatic amino acids and must consume in diets

Question 9

Single loop circulation in fish

Answer 9

Blood is pumped from heart to gills
Then oxygenated and out to body
Heart has 4 chambers

Question 10

Characteristics of jawless early vertebrate fishes

Answer 10

Many lacked paired fins - not precise swimmers

Narrow mouths - filter feeders (e.g. algae)

Question 11

Evolution of the jaw in fish

Answer 11

Enlargement of gill arches

Development of muscles so gill arches can move

Anterior gill arches started to move and become shaped towards the jaw

Layer of scales around inner mouth - modified and became teeth

Bigger mouth that can open and close - can now pump water over the gills

teeth meant they could now grasp and hold prey

Powerful pharyngeal muscles
could suck in prey - ability to attack moving prey

Aided gill support and ventilation

Question 12

What is likely the key driver of selection for jaws in fishes

Answer 12

Efficiency in respiration

Question 13

Challenges of living in water?

Answer 13

Density - more energy required to move water for oxygen than land animals

Oxygen content:

• Fish must ventilate 10-30x the volume of water to get the same amount of O2 as terrestrial animals
• Respiration has a higher demand for energy

Viscosity - 18x more viscous than air

Aquatic animals need to be streamlined

Tidal ventilation is very difficult

Pressure effects - water is much denser - increasing pressure with increasing depth

Question 14

How challenges of living in water were overcome?

Answer 14

Swimmer bladder = buoyancy

• evolved gas-filled structures as buoyancy aids
• this meant a fish could sit in the water column and turn on it’s axis without sinking or moving forward (didn’t have to swim all the time to avoid sinking)
• May also be involved in, sound and pressure reception and respiratory function
• Bottom dwellers may have reduced or absent swimmer bladder

Question 15

2 main types of telosts (fish)

Answer 15

Physostomes (more primitive)

• swim bladder has connection to the oesophagus/ gut
• oral intake of air

Physoclists

• Swimmer bladder has no connection
• Release of gas from arterial blood passing by a gas gland

Question 16

Gills Anatomy

Answer 16

Delicate

Massive surface area

Exposed to environment

Most fish:
- 4 gill arches on each side of head
- operculum cavity
- depends on pumping
water across gills for oxygen 

Water comes in the mouth and then out the gills

Question 17

Gill filaments

Answer 17

lined by skin (epidermis)

contains cells which aid osmoregulation

rigid core

Question 18

Secondary lamellae in gills

Answer 18

semi-lunar folds over dorsal and ventral surfaces of primary lamellae

larger surface area than entire body of the fish!

loaded with capillaries

site of gas exchange and ammonia secretion

Question 19

Three functions of gills

Answer 19

1) Gas Exchange
- the gill is a system for bringing the blood haemoglobin into close contact with water
- oxygen is absorbed & carbon dioxide is released

2) Osmoregulation
- exchange of ions, particularly Na+ & Cl-

3) Waste Excretion
- ammonia is highly water soluble gas

Question 20

Fish ventilation when mouth is open:
Opercular chamber is -

Opercular valve is -

Answer 20

Opercular chamber expands (pressure negative)

Opercular valve is closed

Question 21

Fish ventilation when mouth is closed:
Buccal chamber is -

Opercular valve is -

Answer 21

Buccal chamber is contracting (pressure positive)

Opercular valve is open

Question 22

Ram ventilation in fish

Answer 22

Sharks are an example

• Keeps mouth open while swimming forward
• Only found in fast swimming fishes
• some fishes can use both types of ventilation

Question 23

2 subclasses of chondrichthyes

Answer 23

Elasmobranchii

• Sharks and rays
• Cartilaginous skeleton
• Ram ventilation

Holocephali

• Chimeras
• AKA ratfishes
• Little known about their biology

Question 24

Elasmobranchs

Answer 24

Most sharks have a streamlined body - swift body

Predatory carnivores

Short digestive tract with a spiral valve

Possess acute senses

Must swim or else they sink

distinctive rostrum overhangs the mouth

lack a swim bladder

oil-filled liver that reduces density but not enough to prevent sinking

placoid scales: small tooth like structures & give skin tough abrasive feel

Shark eggs are fertilized internally but embryos can develop in different ways:

• Oviparous: eggs hatch outside the mother’s body
• Ovoviviparous: the embryo develops within the uterus and is nourished by the egg yolk
• Viviparous: embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood

Question 25

Osteichthyes

Answer 25

Bony fish
- all have a bony endoskeleton

2 subclasses:
◦Actinopterygii: ray-finned fishes
◦Sarcopterygii: lobe-finned fishes

Question 26

Characteristics of Osteichthyes

Answer 26

Evolved in fresh water

Skeleton made of bone

Paired and median fins supported by dermal rays

Respiration mainly by gills

Gills covered by operculum

Commonly have swim bladder

Complex nervous, circulatory and excretory systems

Highly mobile fins that are supported by rays

Very thin scales

Lateral line system (series of sensory organs)

Question 27

Alien species

Answer 27

Exotic or feral - not native species

Question 28

Human assisted dispersal of alien fish species

Answer 28

Australia is an island - in order for fresh water fish to get here we have to bring them