Fish Diversity

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  • 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

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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)

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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
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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

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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
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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

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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
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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
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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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