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Ichthyology > Colour, camouflage & bioluminescence in fish > Flashcards

Colour, camouflage & bioluminescence in fish Flashcards

1
Q

2 kinds of colour

A

Biochromes - from pigments

Schematochromes (structural colours) - from reflection

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2
Q

name for cells responsible for colours

A

chromatphores

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3
Q

Chromatophores

A

mainly found in skin
occasionally subdermally

irregular shapes w/ branched processes

chromatosome: many chromatophores intertwined or overlaid

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4
Q

2 types of colour change

A
  1. physiological colour change
  2. morphological colour change
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5
Q
  1. Physiological colour change
A

s-t by movement of pigment within chromatophore

response to background colour

response to social, behaviour or chemical stimuli

nervous or hormonal control

e.g. flatfish

some fish can control chromatophores nervously - change colour as part of attack process - not organs, they are cells (chromatophores) so no muscle attached
how does this happen so fast? - hormones

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6
Q
  1. Morphological colour change
A

L-T due to change in number or type of chromatophores

life-history stages

migration

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7
Q

Functions of colouration

A
  • protection of CNS from UV in larvae
  • aid to thermoregulation
  • optical filter
  • main function: intra- + inter- specific signalling
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8
Q
  1. intra-specific signalling (within spp)
A

advertising + need to be seen

social signals:
- recognition of individuals in schools, or juvenile/adult recognition
- threat or warning
- sexual signalling

e.g. cichlid could be orange when brooding, young of this spp show preference for orange

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9
Q

Sexual signals

A
  • identification of opposite sex in dimorphic spp.
  • attraction of one for another

e.g. dragonette

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10
Q
  1. Inter-specific signalling (between spp)
A

concealment + disguise
1. background matching
2. countershading
3. obliterative colouration
4. disruptive colouration

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11
Q

Inter-specific signalling
1. background matching

A

general colouration of fish resembles that of the environment
usually morphological

fish on substrate = brown (plaise or flatfish)
fish in weeds/rocks = mottled green/brown (freshwater pike, Esox lucius)
pelagic fish = silvered (herring, Clupea harengus)

demersal fish
vegetal colouration

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12
Q

Demersal fish

A
  • vary in colour by physiological colour change to match background more fully
  • demersal colouration = ability for fish to blend into seabed, e.g. flatfish
  • may be aided by skin flaps or irregular outline to break up recognisable shape
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13
Q

Vegetal colouration

A

imitates vegetation, often associated w/ shape

Leafy sea dragon
a pipe fish
Juvenile bat fish mimicking dead leaf

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14
Q

Transparency

A

usually all organs concentrated near head

planktonic larval fish = transparent

most fish = silvered instead of transparent

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15
Q

Inter-specific signalling
2. countershading

A

distribution of light in sea = above
light from above -> lighten dorsal surface of fish & gradually lessens as you go down sides of fish, casting the lower surface into shadow

provides 3D information to eyes

countershading darkens dorsal surface + becomes progressively lighter as the intensity of the shadow increases

this is coupled w/ colouration to match background, e.g. demersal fish are brown

fish away from seabed = greyish (Hake Merluccius merluccius)
fish near surface = blueish (Dolphin fish, dorado, Coryphaena sp.)

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16
Q

Shape of fish + countershading

A
  • some visibility from bottom sides
  • dark dorsal surface blends w/ seabed
  • countershading reduces visibility on side and top sides
  • silhouette at the bottom

round pelagic fish will be seen from below + is likely to be a large solitary predator

small, pelagic, shoaling species (herring) tend to be laterally compressed - reduces arc of visibility (silhouette viewed from narrower area, many fish combine this with silvering)

17
Q

Inter-specific signalling
3. obliterative colouration

A

silvering - arises from 2 layers

18
Q

Inter-specific signalling
4. disruptive colouration

A

not to avoid being seen, but to avoid being identified as potential prey

bold patterns, stripes + bars to break up outline of fish

often associated w/ non-fishlike body shape

camouflage important body parts or draw attention away from important body parts - e.g. false eyes away from the head - butterfly fish (hides eye w/ stripe + eye spot on other side - confuses predators)

enough confusion/distraction to allow escape

19
Q

Advertising + Mimicry

A

often involves interspecific signalling, such as using bright colours + bold patterns to accompany unpalatability or venom

Lionfish have toxic spines

Scorpion fish = venomous + camouflage

20
Q

Mimicry - Mullerian and Batesian

A

Mullerian mimicry = toxic/unpalatable animals that use similar colour + patterns to help teach potential predators to avoid them

Batesian mimicry = non-toxic animals use similar colour + pattern to imitate toxic animals to gain some protection from predators

important that Batesian mimics = less abundant than their models otherwise warning becomes obsolete

21
Q

Bioluminescence

A

not same as “fluorescence” or “phosphorescence”

fluorescence = energy from source of light is absorbed + re-emitted as different wavelength

bioluminescence = excitation energy = supplied by a chemical reaction rather than light source

22
Q

Forms of bioluminescence

A
  1. Luminous bacteria
    - symbiotic relationship
    - bacteria get free home, oxygen + nutrients
    - fish get free light
    - glow continuously
  2. self -luminescence
    i. intracellular - light generated within fish tissues
    ii. extracellular - precursors discharged separately, combine + shine outside body
23
Q

Indirect control of bioluminescence

A

some self-luminous fish + all using bacteria have only indirect control of light

i.e. can’t switch it off

so fish have to screen it in some way:
- irises
- chromatophores
- rotation of photophore into pocket

24
Q

Direct control of bioluminescence

A

most self-luminous fish have direct neural or hormonal control over chemical process of light production

bioluminescent light usually of same wavelength as that in surrounding water:

light generating organ: photophore

blue-green 475nm

25
Q

Evolution of bioluminescence

A
  1. camouflage
  2. communication
  3. predation
26
Q

Evolution of bioluminescence
1. camouflage

A

simplest explanation: cryptic colouration

breaks up animal’s shape

countershading

photophores on body - hides silhouette

e.g. lanternfish (Lampanyctodes hectoris)

27
Q

Energetic consequences of camouflage using bioluminescence

A

during day:
only work at depth (e.g. 200-400m)
near surface = too costly

at night:
- ok near surface

recent survey of >350,000 observations of marine animals (down to 3,900 m) found 54.3% of all fish observed were bioluminescent or likely bioluminescent

28
Q

Evolution of bioluminescence
2. communication

A

intraspecific
- mutual recognition in shoal
- courtship - display/attract mate
- aggression to defend territory
- to shine through predator’s stomach wall as a warning to other fish

interspecific
- distract attention of attackers
- conspicuous warning signal
- lures

29
Q

Evolution of bioluminescence
3. Predation

A

suborbital/cheek organs as headlights

30
Q

Some deep sea stomiatoids have photophores that emit red light - why?

A
  • red light (600nm) = extinguished in upper layers
  • many deep sea crustaceans are therefore red, because in the absence of red light, they appear black
  • Stomiatoid fish produce red light + can see red light
  • so stomiatoids can illuminate red invertebrates w/ light that the invertebrates + other predators can’t see
31
Q

Attracting prey

A

bioluminescence = used as lure to attract prey

deep sea angler fish have light organ (esca) on their modified dorsal fin ray (illicium)

Ichthyology (10 decks)

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