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BIO224 - ichthyology > colour, camouflage & bioluminescence > Flashcards

colour, camouflage & bioluminescence Flashcards

1
Q

2 kinds of colour in fish

A
  • Biochromes – from pigments
  • Schematochromes (structural colours) – from reflection
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1
Q

what are Chromatophores

A

cells responsible for colour
- Characterised by irregular shapes with branched processes
- Found mainly in skin - Occasionally subdermally

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2
Q

what is Chromatosome

A

many chromatophores intertwined or overlaid

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3
Q

2 types of colour change

A

Physiological colour change
Morphological colour change

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4
Q

what is Physiological colour change

A
  • Short-term by movement of pigment within chromatophore
  • Response to background colour
  • Response to social, behavioural or chemical stimuli
  • Nervous or hormonal control (hormonal control = very slow, nervous = fast)
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5
Q

what is Pigment aggregated out through cell body

A

visible pigment

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6
Q

what is Pigment aggregated in centre of cell

A

underlying colour visible only, not pigment

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7
Q

what is Morphological colour change

A
  • Long-term due to change in number or type of chromatophores
  • Life-history stages e.g. juvinilles to adults, female to male
  • Migration e.g. salmon are silver when living in sea, have bars (verticle stripes) when in fresh shallow water with more background – more camouflage
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8
Q

4 Functions of colouration

A

Protection of CNS from UV in larvae
Aid to thermoregulation
Optical filter
Main function: intra- and inter-specific signalling

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9
Q

Intra-specific signalling

A

(within species)
1. Advertising and a need to be seen
2. Social signals:
-Recognition of individuals in schools, or juvenile/adult recognition
-Threat or warning
-Sexual signalling
e.g. this cichlid is orange when brooding, young of this species show a preference for orange

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10
Q

what are sexual signals in Intra-specific signalling

A
  • Identification of opposite sex in dimorphic spp.
  • Attraction of one for another
  • Good sexual signal for health – pigment = energetically costly – means you have enough energy to do so
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11
Q

what is Inter-specific signalling

A

(between species)
Concealment and disguise e.g:
- background matching
- countershading
- obliterative colouration
- disruptive colouration

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12
Q

what is background matching

A
  • General colouration of fish resembles that of the environment
  • Usually morphological
    e.g. fish on substratum = brown, fish in weed/rocks = green/brown, pelagic fish = silver
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13
Q

explain background matching in Demersal fish

A
  • Some fish can vary 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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14
Q

what is Vegetal colouration and some examples

A

Imitates vegetation in the water, often associated with shape
- hairy frogfish - same lifestyle as anglerfish, showing extensions and projections and colouration to blend in with seabed and surrounding soft corals
- Pygmy seahorse – good at physiological colour change to blend in
- Transparency = good method (but difficult) - common in planktonic larval fishes – organs tend to be near head

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15
Q

what is Countershading

A
  • Distibution of light in sea = primarily from above
  • Light from above will lighten dorsal surface of fish & gradually lessen as you go down sides of fish, casting the lower surface into shadow
  • This provides 3D information to eyes
  • Countershading darkens the dorsal surface and becomes progressively lighter as the intensity of the shadow increases
  • This is coupled with colouration to match background, e.g. demersal fish are brown
  • Fish away from the seabed = greyish e.g. hake
  • Fish near the surface = blueish e.g. dolphin fish
  • Silhouette can still be seen by anything directly beneath you, despite countershading
  • So a round fish that is pelagic will be seen from below and is likely to be a large solitary predator e.g. sharks
  • Small, pelagic, shoaling species (herring) tend to be laterally compressed – reduces their arc of visibility
16
Q

what is obliterative colouration

A
  • Refers to silvering in colour
  • Many fish in open ocean will combine lateral compression with this
  • Eyes assume light travels in a straight line and there is nothing there, even if it has reflected off something else first – works well in open oceans, not in more complex environments where there are more objects e.g. seaweed
17
Q

what 2 layers has silvering araised from

A
  • Stratum Argenteum : thick layer of guanine crystals subdermally along flanks, parallel to body surface (if random would be white)
  • Iridophores in skin : non-motile guanine crystals act as iridescent plates - iridophores are oriented vertically and act like thousands of tiny mirrors
18
Q

what is disruptive colouration

A
  • Not so much to avoid being seen as to avoid being identified as potential prey
  • Bold patterns, stripes and bars to break up outline of fish
  • Often associated with non-fishlike body shape
  • often also used to camouflage / draw attention away from important body parts e.g. eyespots placed on other end of body to draw animals towards the mouth
  • Sometimes the patterns just used for total confusion…Is it a fish? Which bit do I attack?
  • Advertising + mimicry often use bright colours and bold patterns to accompany unpalatability or venom e.g. lion fish
19
Q

2 main types of mimicry

A

Müllerian mimicry
Batesian mimicry

20
Q

what is Müllerian mimicry

A

Toxic/unpalatable animals that use similar colour and patterns to help teach potential predators to avoid them

21
Q

what is Batesian mimicry

A
  • Non-toxic animals use similar colour and pattern to imitate toxic animals to gain some protection from predators
  • Important that these mimics are less abundant than their models otherwise warning becomes obsolete
22
Q

3 sub-types of mimicry

A

facultative (or dynamic) mimicry
aggressive mimicry
protective mimicry

23
Q

explain facultative (or dynamic) mimicry and example

A

ability to switch on mimic colouration at will, or change appearance to mimic a variety of species
e.g. blue striped fangblenny = The only animal other than the mimic octopus known to show this

24
Q

explain aggressive mimicry and example

A
  • Mimic juvenile cleaner fish (Labroides dimidiatus) - Instead of cleaning fish it attacks them, removing scales and dermal tissue
25
Q

explain protective mimicry

A

In non-mimic form P. rhinorhynchos is often found associated with shoals of differently coloured fishes and appear to closely match the colour of their companions

26
Q

what is bioluminescence

A

Raphaël Dubois 1887
- Greek - bios = “living”, Latin – lumen = “light”
- Isolated light producing chemicals from the common piddock (Pholas dactylus)
- When ground up in cold water, the tissues glowed
- Extracted ‘light chemicals’ from these tissues
- Chemical reaction within the organism (requires O2):
Luciferin + luciferase + O2 = light + oxyluciferin
- Fluorescence = energy from a source of light is absorbed and re-emitted as a different wavelength (NOT the same as bioluminescence)
- Bioluminescence: excitation energy is supplied by a chemical reaction rather than light source

27
Q

2 Forms of bioluminescence

A

Luminous bacteria
Self-luminescence

28
Q

what is Luminous bacteria bioluminescence

A
  • Symbiotic relationship
  • Bacteria get free home, oxygen and nutrients
  • Fish get free light
  • But they glow continuously
29
Q

what is Self-luminescence

A

i. Intracellular
Light generated within fish tissues
ii. Extracellular
Precursors discharged separately
Combine and shine outside body

30
Q

what is Indirect control of bioluminescence

A
  • Some self-luminous fish and all those using bacteria have only indirect control of light - can’t switch it off
  • So fish have to screen it in some way:
    Irises
    Chromatophores
    Rotation of photophore into pocket
31
Q

what is Direct control of bioluminescence

A
  • Most self-luminous fish have direct neuronal or hormonal control over the chemical process of light production
  • Bioluminescent light usually of same wavelength as that in surrounding water:
    -Light generating organ: photophore
    -Blue-green 475nm
32
Q

3 uses for bioluminescence

A
  1. camouflage
  2. communication
  3. predation
33
Q

explain the use of bioluminescence for camouflage

A
  • Simplest explanation: cryptic colouration
  • Breaks up animal’s shape
  • Countershading – generate same wavelength + intenstiy light as the light around you
34
Q

Energetic consequences of bioluminescence for camouflage

A

During the day
- It will only work at depth (e.g. 200 – 400m)
- Near the surface it is too costly
At night
- OK near the surface (DVL – fish that migrate to surface at night show lots of ventral biolum.. to hide solhouette)

35
Q

explain the use of bioluminescence for intra and interspecific 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

36
Q

explain the use of bioluminescence for predation

A
  • Suborbital/cheek organs as headlights
  • Some deep sea stomiatoids have photophores that emit red light
  • Bioluminescence is also used as a lure to attract prey - Some deep sea angler fish have a light organ (esca) on their modified dorsal fin ray (illicium)
37
Q

why do Some deep sea stomiatoids have photophores that emit red light

A

Red light (600nm) is 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 and can see red light
So stomiatoids can illuminate red invertebrates with light that the invertebrates and other predators can’t see

38
Q

what is a photophore

A

light-generating organ (used in bioluminescence)

BIO224 - ichthyology (13 decks)

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