Fish ecology Flashcards
What were the first vertebrates?
Fish
Chondrichthyes
Sharks and rays
Osteichthyes
Bony fish
Fish vs fishes
Many individuals of one species = Fish
More than one species = fishes
What is a fish?
Aquatic vertebrate with gills and with limbs in the shape of fins
Gills
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)
Vertebral Column of fish
Internal skeleton with a spine surrounding dorsal nerve cord
Brain is fully encased in skull or cranium made of cartilage or bone
Nutritional deficiencies of fish
unable to synthesise the aromatic amino acids and must consume in diets
Single loop circulation in fish
Blood is pumped from heart to gills
Then oxygenated and out to body
Heart has 4 chambers
Characteristics of jawless early vertebrate fishes
Many lacked paired fins - not precise swimmers
Narrow mouths - filter feeders (e.g. algae)
Evolution of the jaw in fish
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
What is likely the key driver of selection for jaws in fishes
Efficiency in respiration
Challenges of living in water?
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
How challenges of living in water were overcome?
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
2 main types of telosts (fish)
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
Gills Anatomy
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
Gill filaments
lined by skin (epidermis)
contains cells which aid osmoregulation
rigid core
Secondary lamellae in gills
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
Three functions of gills
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
Fish ventilation when mouth is open:
Opercular chamber is -
Opercular valve is -
Opercular chamber expands (pressure negative)
Opercular valve is closed
Fish ventilation when mouth is closed:
Buccal chamber is -
Opercular valve is -
Buccal chamber is contracting (pressure positive)
Opercular valve is open
Ram ventilation in fish
Sharks are an example
- Keeps mouth open while swimming forward
- Only found in fast swimming fishes
- some fishes can use both types of ventilation
2 subclasses of chondrichthyes
Elasmobranchii
- Sharks and rays
- Cartilaginous skeleton
- Ram ventilation
Holocephali
- Chimeras
- AKA ratfishes
- Little known about their biology
Elasmobranchs
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
Osteichthyes
Bony fish
- all have a bony endoskeleton
2 subclasses:
◦Actinopterygii: ray-finned fishes
◦Sarcopterygii: lobe-finned fishes
Characteristics of Osteichthyes
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)
Alien species
Exotic or feral - not native species
Human assisted dispersal of alien fish species
Australia is an island - in order for fresh water fish to get here we have to bring them
