Feeding Ecology of Fishes Flashcards
Teeth
tongue, maxilla, pre-maxilla, buccal surfaces, pharynx (gill arches)
well-developed + cardiform
may be specialised, e.g. plaice teeth are chisel-shaped for slicing bivalve siphons
Piscivores’ teeth may be small, or backward pointing, e.g. Lophius + hake have hinged teeth
Pharyngeal teeth = for grinding (e.g. cellulose from FW plants + animals that feed on bivalves)
Oesophagus & stomach
Oesophagus
- distendable, acts as storage
- lining only produces mucus, no enzymes in mouth pharynx or oesophagus
Stomach:
- well-developed in predators, large, always distendible w/ muscular walls
- U, J, or Y shaped w/ well defined pyloric sphincter + releases hydrochloric acid to prevent decay
- stomachs in herbivorous fish tend to be small or non-extistent
- detritivores such as mullet, have just a thickened region of intestine
Oesophagus -> proximal stomach -> distal stomach -> pyloric sphincter -> (pyloric caecae) -> intestine -> rectum
Intestine
- length of intestine closely related to diet
- predators have short (<body length) intestines
- Piscivores (eat fish) = 0.6x body length
- herbivores + detritivores (microphagous) = up to 20x body length
Pyloric caecae
- at pyloric end of intestine
- from 1 to >1000
- increase absorptive sa
What do elasmobranchs have instead of pyloric caecae?
spiral value - same function
- one -ve = reduces ability of large items to pass through, so stay in stomach + regurgitated
Digestion
food passes from stomach (chyme) -> intestine of predators in discreet gobbets rather than continuous dribble
digestion can be protracted, esp in piscivores, w/ outer layers being excreted while the remainder = still in stomach
Types of feeding
- predators
- grazers + browsers
- filter feeders
- suckers
- parasites
- symbiosis
not mutually exclusive (e.g. mackerel - grazers + filter feeders)
- predator
majority
all elasmobranchs (except 13 spp of filter feeders)
large, terminal mouths, well-developed biting or grasping teeth
- ambushers - float in water column or rest on sea bed
- searchers - Thresher shark
- Pursuers/stalkers - Archer Fish -> shoots jet of water at prey
Predators - Ambushers
rely on prey coming to them
often attract w/ lures
camouflaged
encounter rates unpredictable
generalists w/ wide diet
e.g. pike, anglerfish, Bearded ghoul
Predators - Searchers
actively seek prey
spend little time pursuing or handling
opportunistic
generalists w/ wide diet but often preferred foods
e.g. bass, Atlantic sailfish, Thresher shark
Thresher shark - hunt with tail
A protusible mouth only works if…
…you are stationary or moving very slowly
Predators - Pursuers/stalkers
actively seek out ‘difficult’ prey
have to become specialised to overcome prey defences
so specialist feeders
narrow diet
e.g. White shark, Archer fish
Location of prey by predators
involved mix of visual + non-visual (olfaction, lateral line, electric fields, touch) senses
many fish have specialised food locating adaptations: Barbels, fin rays, Ampullae of Lorenzini, etc.
Murky water fish + nocturnal fish rely more on chemoreceptors
- Grazers and Browsers
Herbivorous
- e.g. damselfish, cichlids, blennies, carps (pharyngeal teeth break down cellulose)
may defend feeding territory
carnivorous
- e.g. some catfish + cichlids browse on scales + mucous of other fish
omnivorous
- e.g. parrotfish browse coral polyps
many grazers + browsers have specialised morphology (mouth adaptations) may have narrow diet width or may be more generalist
e.g. parrotfish - teeth joined to form sort of beak
- Strainers/Filter Feeders
often large, toothless mouths
long gill rakers
food selection by particle size
phytoplankton or zooplankton
e.g. Basking shark
- Suckers
mostly bottom feeding fish sucking food/detritus into mouth + ejecting non-digestible items
grey mullets scrape mud in estuaries
sturgeons hoover river/seabed
carps suck anything
