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