NEKTON Flashcards
What are nekton?
Those animals that are capable of overcoming the strength of water currents.
Epipelagic nekton is primarily composed of…
vertebrates & some cephalopod molluscs
EMBAH
Epipelagic Mesopelagic Bathypelagic Abyssalpelagic Hadalpelagic
What are the conditions of the epipelagic realm like?
- no firm support (requiring buoyancy)
- 3D, which is a challenge for locomotion and for predation risk
- no solid substrate so v few hiding places
- abundant light which impacts sensory options
How is neutral buoyancy achieved in the epipelagic realm?
- Add lighter than water material like air or lipids, or by using a swim bladder (bad for fast moving fish)
- use ancillary air sacs
- non compressible gas storage
- cartilaginous fish use lipid storage
- marine mammals store lipids as blubber - Replace heavier ions
- hydrodynamics
- heterecercal tails to generate lift and thrust (large top lobe)
A physostomus fish
Has a pneumatic duct to gulp atmospheric air
A physoclistous fish
Has gas glands to remove gas from blood via a rete mirable
2 main objectives for fish locomotion
- Generate thrust and lift/ propulsion
2. Decrease resistance
Different forms of fish locomotion
- elongate swimmers move using all of body (eel)
- fast swimmers use lateral waves that get longer towards base of tail (tuna)
- slow swimmers use only tail (porcupine fish)
- less active fish use only fins (parrot fish)
Why is turbulent flow advantageous?
less flow separation, producing a smaller wake and less resistance
How do pelagic cephalopods get around?
- swimming using paired fins on either side of mantle
2. via jet propulsion
How are ventral keels used in predator avoidance?
Teardrop shape formed and are therefore invisible from below
How is cryptic colouration used for predatory avoidance?
countershading on top, silvery reflective sides
- dark top, light bottom
Describe the epipelagic sensory system
- Large eyes with colour vision sometimes
- Lateral line system, a fluid canal lined with receptor cells and pores to detect changes in pressure
- no external ear openings, but many can echolocate
- great olfactory (smell)
- electroreception
How are mesopelagic fish adapted for low light, rare prey and rare mates?
- Large eyes/ large pupils
- only rods, no cones
- light absorbing section of rods larger
- tubular eyes common that point upwards
