The Biology of Fish II Flashcards
List some constraints of aquatic existence
- bones, scales and skin
- respiration (obtaining oxygen)
- buoyancy and depth regulation
- ion exchange (maintaining stable internal environment within body)
- heat exchange (regulating body temperature)
- reproduction
- feeding
- dense medium for movement
- navigation through complex, volumetric
environments
Describe the basics of the Chondrichthyes
- cartilaginous fishes
- Elasmobranchii (sharks and rays)
- Holocephalii (deep-sea chimaeras
Give an Elasmobranchii
Cetorhinus maximus
Give a Holocephalii
Hydrolagus colliei
Describe the basics of the Osteichthyes
- bony fishes
- Actinopterygii (ray fins, including teleosts)
- Sarcopterygii (lobe fins, including lungfish)
Give an Actinopterygii
Pristella maxillaris
Give a Sarcopterygii
Protopterus aethiopicus
Describe fish bones
- bony skeletal elements start off as cartilage then become calcified and vascularised
- ossification of dermal elements: scales become bony.
- become thinner and more mobile.
In Osteichthyes, skeleton + scales … of total weight
c. 20%
In Chondrichthyes, skeleton + scales … of total weight
c. 12%
Describe early Osteichthyes
- thick leathery skin
- thick interlocking ganoid scales
ganoin
≈ enamel
Describe teleost skin
- thin
- bony dermal scales are thin and flexible
Describe teleost scales
- primitive teleosts have cycloid scales which grow in annuli
- advanced teleosts (esp. fast swimmers) have ctenoid scales with drag-reducing trailing edges
- serrated edge opposite edge that attaches to the skin
annuli
annual growth rings
Describe teleost reflective skin
- many teleosts appear silvery due to reflective layers in the skin, under the scales
- reflectors are guanine/tissue sandwiches of at least 5 layers
- light reflected from the outer and inner faces of the guanine layers interferes constructively
- reflectances may exceed 90%
Give a silvery teleost
Gyropelecus: hatchet fish
Give some reflective teleosts
- Neon tetra
- Goldfish
- Endler guppies
Describe the Chondrichthyes
cartilaginous skeletal elements are not vascularised
Describe the skeleton of sharks
- uses varying degrees of calcification
- jaws may be heavily calcified and thus are rigid
Describe the skeleton of skate fin rays
- may be totally uncalcified
- remain flexible
Describe shark skin
- thick and leathery
- crossed helices of collagen fibres
- provides a tough support for the pavement of scales and, in the mouth, for the teeth
- placoid scales (e.g. Whale shark)
Describe placoid scales
- aka dermal denticles
- same structure as a tooth
- three layers: an outer layer of vitro-dentine, dentine, and a pulp cavity
- do not get larger as the fish grows
- the fish grows more scales.
vitro-dentine
an enamel
How does shark skin reduce drag?
- water flows in under the fronts of the scales and out along the ridges on the outside of the scales
- spaces under the scales and their surface sculpturing vary along the body and fins, reflecting differences in the flow conditions
-creates micro-turbulence over the skin surface - reduces overall drag by c. 10%
Describe Osteichthyes respiration
- teleost gills enclosed in opercular cavities
- water is pumped in through the mouth and out through the gills
- pumping action of mouth and opercular cavities creates positive pressure across gills
- respiratory current is only slightly interrupted during each pumping cycle
Describe the mechanics of Osteichthyes inspiration
- mouth open
- opercular valve closed
- opercular chamber expanding
- negative pressure
- water sucked into the pharynx by lowering the floor of the mouth
Describe the mechanics of Osteichthyes expiration
- mouth closed
- opercular valve open
- buccal chamber contracting
- positive pressure
- water forced through gills by raising the floor of the mouth
- back flow prevented by buccal flap valve
Describe counter-current exchange
- blood flows through lamellae
- H2O from mouth flows between lamellae
- maximises exchange gradient across flow
Describe the gill lamella
- blood flows in thin flat spaces
- walls of which are held together by pillar cells
- blood-water distance varies with the fish’s lifestyle
- 10μm in sluggish tench
- 0.6μm in tuna
Describe Scomber
- mackerel
- high activity
- 0.73 oxygen consumption
- 31 secondary gill lamellae
- 1160 gill area
- 14.8 oxygen capacity
oxygen consumption
ml O2//g.h
secondary gill lamellae
mm-1 of primary gill lamellae
gill area
mm2 / gm of body mass
oxygen capacity
14.8
Describe Stenotomus
- porgy
- intermediate activity
- 0.17 oxygen consumption
- 26 secondary gill lamellae
- 506 gill area
- 7.3 oxygen capacity
Describe Opsanus
- toadfish
- sluggish activity
- 0.11 oxygen consumption
- 11 secondary gill lamellae
- 197 gill area
- 6.2 oxygen capacity
Describe perpetual swimmers
- some fish have reduced or lost ability to pump water across gills
- create respiratory current by swimming with their mouths open
List some perpetual swimmers
certain sharks, tunas, swordfish
Describe fish in low oxygen conditions
- supplement oxygen from gills with oxygen from air
- air breathing evolved independently many times
- a number of derived teleosts have accessory structures to obtain O2 from air
- lungfish (Sarcoptergyii) have true lungs
Describe the accessory structures of the low oxygen actinoptergyii
- large lips extended just above surface
- internal structures into which air is gulped
Describe Bettas
- tropical Asia
- labyrinths
- air sucked into mouth and transferred to labyrinth where gas exchange occurs
labyrinths
vascularised chambers in rear of head called
Describe Betta bubble nests
- male Betta gulp air and construct bubbles with saliva (contains adhesive proteins)
- once female Betta lays eggs, male will pick them up in his mouth and put them in his bubble nest
- guards the eggs until they hatch
Describe fry in Bettas
- specialised attachment cells that run from their heads to their anterior trunks
- keeps them from falling out of the nest
Describe mudskippers
- Periophthalmus cantonensis
- cutaneous air breathing
- enlarged gill chambers where they retain a bubble of air
- digging burrows
Describe cutaneous air breathing
- breathing through skin, mouth mucosa and pharynx
- only possible when skin is wet
Describe Sarcopterygii in low oxygen conditions
- true lungs in obligate air breathers originate from gut during development
- e.g. Australian lungfish (Neoceratodus forsteri)
Describe Actinopterygians buoyancy
- teleost swim-bladder is a gas-filled diverticulum of the gut that regulates buoyancy
- fish can adjust gas volume to obtain neutral buoyancy or ascend and descend
Give an example of a teleost
Astyanax fasciatus
Describe Physostomes
- in more primitive condition, swim-bladder opens into the gut via a duct
- gas can swallowed or burped out
- e.g. in sturgeon or carp
Describe Physoclists
- in the more derived condition, swim bladder volume is regulated by uptake or secretion of O2 from a gas gland on the ventral wall of the bladder
rete mirabilis
= lactate exchanger
Describe the first stage to how Physoclists fill the swim bladder
- gas gland is fed by a “rete” in which blood vessels entering divide and form a meshwork close to the blood vessels leaving
- lactate is pumped from the outgoing vessels into the incoming vessels.
- pH at the gas gland is lowered to c. 6.3, liberating O2 from the blood
- only takes 0.05s for pH lowering to cause gas release
- recovery takes c.15s
- blood stays in the exchanger for c.2s, which allows O2 release on the way in
- too brief for re-uptake on the way out
- once in, gas is retained by the bladder wall
-100x less permeable than tissues
Describe teleosts and pH
- oxygen-carrying capacity of teleost blood is highly dependent on its pH and CO2 content
- if the pH is lowered from 7 to 6.3. the blood can only hold half as much O2
- The Root effect
Describe the second stage to how Physoclists fill the swim bladder
- oxygenated blood enters the swim-bladder
- amount of O2 liberated or taken up can be controlled by the fish
Describe bladder wall permeability in teleosts
- contains layers of large-area 0.02μm thick guanine plates
- flexible
- solid-phase
- gas-impermeable
Describe the Root effect
asymmetrical
Summarise the Root effect
- oxygen is high
- lactate is actively transported from areas of low to high anteriorly
- lactate flows in direction of blood flow
- pH lowers
- O2 capacity low
- O2 enters swim bladder
- lactate flows back
How can pressure be used to determine depth?
- varies linearly with depth
- fish use rate in change in swim-bladder volume to determine depth
Describe Chondrichthyes buoyancy
- no swim bladders
When wouldn’t you need a swim bladder?
if you’re a Benthic bottom-dweller
Give an example of a Benthic bottom-dweller
- skates
- Dipturus laevis
Give an example of a Chondrichthyes
D. laevis
Describe buoyancy in sharks
- vast liver
- dynamic lift
Describe the basking shark
- 2 tonne
- 7m long
- close to neutrally buoyant
Squalene
hydrocarbon derived from the food
Describe the use of the liver for buoyancy in sharks
- up to 25% of body weight
- rich in squalene
- sea water density is 1025 kg/m3
- shark body density is 1060 kg/m3
- squalene density is 860 kg/m3
- such a heavy buoyancy organ has considerable inertia, slowing turning
- large volume increases the frontal area and hence the hydrodynamic drag of the shark
Describe dynamic lift in sharks
- many fast-swimming pelagic sharks
- frontal area is smaller
- swimming is cheaper
- if they stop, they sink
Describe skates
- relatively small livers
- heavier than water
Describe osmotic and ionic regulation in teleosts
- most teleosts are hypotonic to seawater but hypertonic to freshwater
- skin is fairly impermeable
- gills are v. permeable
What do teleosts do in the sea?
- salts excreted by specialised glands the gills (to prevent diffusion in)
- water leaves osmotically
- drink
- pass little urine (conserve water)
- secrete excess NaCl at the gills
What do teleosts do in freshwater?
- salts absorbed by the gills (to counteract diffusion out)
- water enters osmotically
- does not drink
- get some salts from their food
- pass copious dilute urine from the kidneys
Describe freshwater teleosts
10% increase in salinity between body fluids and freshwater
Describe marine teleosts
20% decrease in salinity of body fluids relative to seawater
Describe osmotic and ionic regulation in the Chondrichthyes
- approximately isotonic with sea water
- blood contains urea and tri-methylamine oxide
- hydrogen bonds are broken by urea solutions
- proteins of Chondrichthyes specialised
- effect is reduced by TMAO
- NaCl diffuses in at the gills
- excreted by the rectal glands
Where do Chondrichthyes obtain urea from?
- proteinaceous diet
- all are carnivores
Describe fresh water sharks
- tend to have reduced blood ionic and urea concentrations
- e.g. in Lake Nicaragua
TMAO
tri-methylamine oxide
Describe fish heat exchange
- blood is cooled to ambient temperature in the gills
- muscles’ blood supply along the mid-line
- cold blood passing inwards exchanges heat with the outgoing blood from the centre of the myotomes
What do fishes warm muscles require?
- large bodies to minimise losses due to conduction
- heat exchanger system in the thickness of the body
Describe fish deep temp
29 to ambient 19
Describe heat exchange in tuna (and some sharks)
muscles are supplied by vessels
running just under the skin.
Describe teleost reproduction
- majority use external fertilisation
- congregate
- make fertilisation pits, nests
- elaborate courtship
Describe Lebistes reproduction
- guppies
- fertilise internally
- viviparity
Describe freshwater fish reproduction
- eggs tend to be 1 to 5mm diameter
- produced in hundreds or thousands
Describe marine fish reproduction
- 1 to 2mm diameter
- produced in large numbers:
- sea provides a rich alternative planktonic niche for fish larvae
- larval development lasting a few weeks is common.
Describe the sardine
- up to 18 cm long
- 10,000 to 50,000 eggs
- 7mm larva
Describe sunfish
- up to 3 m long
- 100 to 500 million eggs
- 25 mm larva
Describe shark reproduction
- all Chondrichthyes have internal fertilisation
- sperm is transferred to the female’s oviduct along one of the male’s pelvic claspers
- male wrapped around female with left clasper inserted into cloaca
- elaborate courtship
- e.g. dogfish
Describe the Piranha
- Actinopterygian
- subfamily Serrasalminae
- omnivore
Describe the swordfish
- Actinopterygian
- family Xiphiidae
- predator
Describe the cichlid Pseudotropheus crabro
- Actinopterygian
- feeds on parasites from a catfish
Describe the dwarf pygmy goby
- Actinopterygian
- 1cm
- Pandaka pygmaea
- feeds on plankton
Describe feeding in Chondrichthyes
- large body size
- mostly marine
- few species
- predatory life is common
- e.g. Great white shark, Carcharodon carcharias
Give a Chondrichthyan filter feeder
Whale shark, Rhincodon typus
Describe Great White Shark
- C. carcharias
- > 7 m
- eats prey in large chunks
Describe Cretaceous shark fossils
- teeth over 12cm
- sharks must have been over 15m
- Carcharodon appeared in the Cretaceous but was even bigger
