Fish Diversity
- Created by: rosieevie
- Created on: 06-11-17 20:07
Basic Fish Lifestyle
Fish - no taxonomic validity (number of dif. lineages)
<50% living species of vertebrates (5 of 9 classes)
Dominant components of ecosystems - either numerically or as top predators
Fish design result of the physical properties of surroundings
What is a Fish?
Aquatic chordate with:
- Appendages = FINS
- Chief respiratory organs = LUNGS
- Bodies covered in SCALES
Not really taxonomic ranking, just conveninent description
Different lineages evolved fish = convergent evolution
Paraphyletic grouping - closely allied with sarcopterygian lineage includes us (we are obviously not fish)
Agnatha
Jawless living fish - ~84 species in 2 classes
Myxini (hagfish)
- Myxo = slime
- Entirely marine
- Nocturnal scavengers and predators
- Feed on annelidss, molluscs, crustaceans and dead/dying fish
- Lack vertebral column - notochord
Cephalaspidomorphi (lamprey)
- Marine, freshwater and euryhaline
- Anadromous (migrate up rivers to spawn)
- More derived morphological characteristics - closer to gnathostomes
Temperate and cold water - usually deep water
- Both lack jaws, internal ossification (cartilaginous), scales and paired fins
- Posses pore-like gill openings, anguiliform body and keratinised teeth on tongue
Myxini
2 toothed, keratinised plates on tongue - fold together and 'rasp' food from its prey. While feeding, respire through skin (cutaneous respiration)
Generate slime from mucus glands - mucus and thread cells, functioning to:
- Suffocate dying prey
- Protect against digestive enzymes
- Easily remove from carcasses
- Repel potential predators by clogging gills
- Support hagfish burrows
Backflushes gills and nostrils to remove slime
Knot-tying
- Moves knot headward to gain leverage - rotates mouth to slice and rasp
- Lack of vertebral column = flexibility while knot-tying
- Avoid suffocation to move slime headward and off body
Immature fish = both male and female tissue, single sex prodominates and fertilisation external
Cephalaspidomorphi
Heavily armoured fossils from Cambrian (544-505mya) - varied body types
One main characteristic - single, median nasal opening leading to olfactory sac and hypophyseal sac = nasohypophysis
Petromyzontiformes only extant order = lampreys and lampetra
- Caudal fin and 1-2 dorsal fins - not paired
- 7 gill openings on side of body
- Eyes and lateral line well-developed
- Prominant oral disc with numerous tooth-like keratin plates
- Ammocoete larvae are filter feeders - body form, appearance similar to lancelets (blind and toothless) - live to 7 years before transformation and move out to sea
- Adults parasitoids - oral disc attaches by suction and rasping erodes host tissue, ingested with body fluids
- Water pumped in and out of gill openings for respiration
- Spawn in freshwater then migrate to marine waters - undergo gut atrophy, osmoregulation changes, eyes and liver degenerate, body shrinks, genital papillae form, fins thicken
Gnathostomata - Chondrichthyes
Cartilaginous fishes - sharks, rays, skates, ratfish
- Primarily marine group
- Highly derived - specialised species with well-developed sensory and musculature systems
- Most shallow, temperate or tropical species - <85% <200m underwater, 50% <2000m
- Primarily nocturnal foragers, some apex predators
- More ray species (57%) than shark species (43%)
- Skeletons - partially calcifed cartilage
- Placoid scales (denticles)
- Similar to teeth
- Dentine crown coated in enamel-like material, vasculatised pulp cavity and bony base
- Early Chondrichthyes - tooth whirls
- True teeth - shed and replaced regularly
- Males have pelvic clasper, used in courtship and mating (hold onto female)
- Pelvic meta-pterygium (basal cartilage of pelvic fin)
Upper jaw (paltoquadrate) and lower jaw (Meckel's cartilage) evolved from gill arches
Gnathostomata - Osteichthyes - Actinopterygii
Primiative features - heterocercal caudal fins, non-overlapping ganoid scales, bony scutes
- Polypterus has a long and obligate air-breather
- Amia - facilitated air-breather using modified swimbladder
- Paired fins supported by fin rays
- Protrusible jaws
- Homocercal tail - outwardly symmetrical but with backbone passing into upper lobe
- Well-definied ossified skeleton with vertebral complex jaw system and bony spines supporting fins
- Vertebral column - highly flexible
- Well-defined guy associated with organ systems
- Closed circulatory system (often single circuit) at modest pressures
Dominant living fish in marine and freshwater - varied body plans at all trophic levels
- Most species dioecious with external fertilisation and development of the eggs w/out parental care
- r-strategy - produce large number of eggs w/ low survival expectation
Scale Types
Placoid scales - reduce effect of turbulent drag (chondricthyes)
Ganoid scales - plate structures with thick dentine layer
Leptoid scales - keratin-like material and able to see growth rings
- Cycloid scales - teleost fishes
- Ctenoid scales - teleost fishes
Sarcopterygii
Coelacanthimorhpa - tropical/sub tropical shallow fish
- Nocturnal
- Fat-filled gas bladder - passive buoyancy mechanisms
- Lecithotrophic young that develop in oviduct then ovoviviparity (k-selection)
- Single-line heart form - no left and right chamber division and mainly used in contraction
Origins of paired tetrapod pentadactyl limb - pectoral fins developed skeletal structures that robust enough to become adapted into walking limbs
Dipnoi - lungfish
- Air-breathing fish with alveolar lungs (oblidate air breathers except in Australia & young)
- South America, Central Africa and Australia
- Dioecious with internal or external nest
- Aestivation - prolonged torpor in mud burrows to avoid dessication
- Lungs are sub-divided with rich blood supply - homologous to tetrapods plus beginnings of seperate pulmonary ciculation from main body circulation
- Lobe-finned with muscles to move fins
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