Fish Predation + Feeding

optimal foraging theory

predation evolutionarily

very important: stresses animals, reduces prey fitness (nonconsumptive effects of predation, threat of predation everyday

tuna w/ schooling fish

cut off a section, herd into a ball, eat until some point where the bait of the ball is too small to be worth the effort

this increases catch efficiency b/c tuna can eat multiple @ the same time if the fish are small enough

gobies - density

density independent before maturing

density dependent after maturity: gobies become vulnerable to predators during territorial combats + sexual displays

gobies - predation + growth

growth lower around predators —> lower fitness = foraging less and more stressed

recruitment enhanced by presence of conspecifics and decrease with presence of predators

kelp bass

recruitment highest when predators absent

atavistic

inherent, ancient

fright response

broad head, wide downturned mouth, ringed broadly elliptical eyes

prey responses to avoid predation

eye spots (ocelli)

spines

camouflage

eye spots (ocelli) - why?

predators only eat things they can fit in their mouth

eye spots (ocelli) - stripe?

stripe through real eye to disguise it (tropical goby)

eye spots (ocelli) - tail?

to confuse predators to which side is the end

eye spots (ocelli) - skates

predator: hammerheads

they need to pin it down with their head so it can’t be too big

camo - halibut

shift into sand (as predator and prey)

camo - flatfish

chromatophores

confusion pattern

to hide eyes

camo - stripes

disrupt the silhouette in murky water

spines

just for dissuading predators, don’t help feed or attract mates

ex: lionfish, scorpionfish, pufferfish, stingray, etc

red queen hypothesis

predators + prey continually evolve in response to each other

anglerfish

large mouths, large teeth, bioluminescent lures

dragonfish

long teeth —> trap prey, sometimes prey only partially in mouth but can start digesting them

photophores along body, eye spots (head lamps, under real eye), lure, bioluminescent teeth

dragonfishes + light fishes light

emit light that others can’t see to see better (only helps themselves

hatchetfish

really shiny + reflective scales that are oriented perp to downwelling light, acting like a mirror

scopelarchus

have a yellow lens - photophores appear bright with yellow lens (can see laternfish (myctophids))

fish feeding

herbivores, omnivores, detritus feeders, carnivores

detritus feeder

consumes dead and decaying organic matter

herbivores

very few fish are true herbivores, most are opportunistic

harder to digest plants (takes more energy)

mouth position + fxn

terminal: body terminates at mouth that opens forward

superior (supraterminal): opens upwards

inferior (subterminal): opens downwards

protrusible: can extend

suction feeding

as mouth extends, prey sucked into mouth by vacuum —> close operculum, expand buccal cavity to create pressure + suction

mouth position examples

superior: hatchetfish, halfbeaks (at the top)

terminal: bluefish, surfperch (in the middle)

inferior: suckers, hillstream loaches (at the bottom)

inertial suction

rapid expansion of the buccal cavity

up to a 40-fold increase in the buccal cavity, water then passed over the gill rakers and into the opercular cavity

jaw protrusion

upper jaw protrudes in many teleost fish, forming a pipette mouth

gill rakers

bony extensions of the gill arch used for filter feeding

how food gets from rakers to gut

dead end sieving, cross flow filtration, cross flow w/ tangential shearing

dead end sieving

cross flow filtration

cross flow w/ tangential shearing

pharyngeal jaws

second set of jaws, evolved from modified gill arches, dentition and fxn depend on diet

winnowing (black perch) - food

bite turf, swish around, spit out algae, swallow inverts

moray eel - food

primarily eat large fish, capture w outer jaws + eat fish w inner jaws

bat rays - pharyngeal jaws

pharygeal plate

horn shark - pharyngeal jaws

placoid (sharper) teeth outside mouth, crushing plates inside mouth

(doesn’t lose teeth like other sharks

opaleye - food

scraping premax + dentary, strip algae off surfaces

completely flatten out mouth to the get @ the surfaces

gain vs food particle size

far left: sea bass eating copepod (unless can concentrate and eat a large amount at once)

far right: kelp bass eating surfperch

most basic predator rule

if they can fit it in their mouth whole, they’re gonna eat it