Actinopterygii

Question 1

Non-teleost examples

Answer 1

1. Sturgeon - has a cartilaginous skeleton

2. Paddlefish - 2 species with cartilaginous skeletons

Question 2

Sturgeon

Answer 2

• secondarily lost bone
• found to have a swim bladder
• protrusible jaw
• lost their scales - have scutes instead
• live in FW or M
• can reach 8m
• endangered (caviar industry)
• reproduce later on in life - invest lots (vulnerable to exploitation)

Question 3

Paddlefishes

Answer 3

• rostrum (extension of cranium), filled with ampullary organs
• 1 species in Chinese river - FW, likely to be extinct, very protrusible jaw and feeds on fish
• other spp in USA FW, feeds on inverts - filter feeder
• both detect prey with ampullary organs

Question 4

Teleost morphology

Answer 4

• jaw and bones of skull more flexible to exploit different prey
• pharyngeal jaws - gill arches modified for processing food
• small scales - exoskeleton
• tail is homocercal
• swim bladder (formed from out pocketing of gut in development)
• lateral line system
• gills for respiration
• some fish are obligate air breathers though - labyrinth organ in head where gaseous exchange can take place
• fast moving fish keep muscles at higher temp than surrounding water - regional heterothermy

Question 5

Feeding mechanisms of teleosts

Answer 5

•jaws allow suction feeding
•have premaxilla, maxilla and mandibles
1. As move out they open their mouths increasing the buccal cavity size
2. Draws water into mouth
•huge advantage as can get close to prey and suck them in, without water pushing them away

Question 6

Pharyngeal jaws

Answer 6

•accessory jaws have hard grinding surfaces for crushing, or spikes to rip apart prey
•help with processing food in mouth
•seen in cichlids - may account for diversity and speciation
•moray eel accessory jaws - come out, grab prey and pull it down the throat
-“raptorial” pharyngeal jaws

Question 7

Homocercal tail

Answer 7

•symmetrical - used like a rudder
•can provide powerful force
•keeps fish in 1 horizontal plane
•combination of this and swim bladder keeps it buoyant, so doesn’t need to rely on fins as much
-can be used for different purposes
-can take on different body forms, leafy sea dragon - have projections making them camouflaged

Question 8

Swim bladder

Answer 8

• ancestral feature of all bony fish - originally lung
• some kept as lung, some lost etc.
• bony fish develop dorsally from gut
• can have attachement between gut and bladder, but is often lost
• if fish swims deep - more pressure of bladder = compressed and decreases in size
• vice versa - up = larger
• needs to keep same size (need air going deeper etc.)
• can release gas through gut - burping at surface or gulping for air, if connected to gut
• not connected - oxygen taken up or released via blood

Question 9

Gills for respiration

Answer 9

•mouth has a pump drawing water in - going over the gills
•covering gills is operculum
-bony covering with slit for water to exit
•movement of mouth and operculum creates current
•countercurrent exchanger - blood and water flow in opposite directions = max O2 into blood
•ram ventilation - swim with mouth open, if do all the time, have to stop active
-some only do it if want to move quicker

Question 10

Regional heterothermy

Answer 10

•water comes from gills is cold
•blood from gills comes into contact with warm blood from muscles
•exchange of heat between vessels - keeps areas warmer than others
-muscles
-gut
-brain
•found in cartilaginous fishes like sharks

Question 11

Eels

Answer 11

•reduced fins as live in vegetation/mud
•get Eu/N African spp and American eel
•incredible migrations when spawn, live adult life in FW and reproduce in M - catadromous
•both spp spawn in Sargasso Sea
•once bred, egg develops into larvae and into an elver
•elvers make way back into FW (1yr for USA and 3 yrs for other)
-have become adults by this time to travel into FW
•breed at certain times of year = mass congregations