Planktivory

PlanktivorySuspension feeders:Animals that process large quantities of water through a feeding apparatus (gill rakers, baleen).

Gill rakers trap particles such as zooplankton, phytoplankton and detritus.

Includes: manta rays, basking shark, whale shark, megamouth, paddlefish, gizzard shad, menhaden, and bighead carp.  

Feeding strategies:

 A)   Obligate and faculative planktivores:

Most fish are planktivorous at some point in their life, either as holoplankton or meroplankton.

• Facultative planktivores: (ex. sunfishes) are opportunistic feeders. Prey selection depends on food availability

• Obligate planktivores: (ex. blueblack herring, Atlantic Menhaden) feed exclusively on plankton  

B) Ram feeding and suction feeding

Ram feeding: creates a forward motion in which water is delivered into the mouth; opens mouth wide as possible and rams prey

• continuous ram feeders

• intermittent ram feeders

Suction feeding: predator remains relatively stationary, comes close to prey and then sucks prey in.

• continuous suction feeders

• intermittent suction feeders

Suction feeder Nonsuction feeder

Jaw Protrusion

Sling-jaw wrasse

Ram Feeders• Continuous• Intermittent

Continuous ram feeders (tow-net)- water passes continuously through mouth, over gills and exits through gill slits or operculum.

~20 species fish

In fish: extensive elaboration of the branchial (gill) apparatus

Manta Ray:• They have no teeth. • Cephalic flaps channel water containing plankton into

mouth• To prevent gills from clogging, a screen of small tiny

protuberances located in the throat, hold the food until it can be swallowed.

Megamouth, Basking Shark and Whale Shark- Generally these planktivorous sharks have tiny numerous teeth and elongated gill rakers. The gill rakers help to strain plankton.

Basking shark- (10 meters long)

• Swims about 2 knots with mouth open and bristle-like gill rakers erect while filtering particulate matter

• It then closes its’ mouth forcing water over the gills; it is an indiscriminate planktivore

• Has five pairs of gill slits and can filters ~540 liters zooplankton/day and over 1500 gallons of water/ hour (1850 m3 water/hour)

• Basking sharks caught between Oct. And Dec., no visible gill rakers were found, but had immature or functionless, incompletely developed rakers (possibly has a resting, non feeding stage). Re-grows gill rakers by February.

Paddlefish- Order Acipenseriformes• freshwater, rarely brackish; found in China and the US• gill rakers are long and in the hundreds- used for

plankton feeding, minute teeth are presentPolyodon spathula (US- Mississippi drainage)- plankton-

feeding; non protrusible mouthPsephurus gladius (China- Yangtze River)- piscivorous

with a protrusible mouth

Continuous ram feeding

Intermittent ram feeders• takes one gulp of water at a time, extracts

particles and repeats the process• In using this method, the predator needs to be

able to grab prey before it moves out of the way.• Seen in whales, not sure about in fish????

Suction Feeders• Continuous• Intermittent

Continuous suction feeders (pump filter feeders)- creates and osculatory pump and draws water in over sieving device. Animal remains still while suctioning.

Ammocetes (lamprey larvae)-spends 3-7 years filter feeding and burrows into sand; Feeding:• a current of water is drawn in by muscular action• water enters buccal cavity and washes over gills• uses gills to filter particles for food• in ammocetes, filtering linked to breathing.

Intermittent suction feeders (intermediate feeding):

• relatively unspecialized• intermediate condition between ram and

suction feeding on individual prey• they don’t alter their swimming speed or

direction to focus attention on individual plankton.  

Diurnal and Nocturnal Planktivores

Typically feed by forming aggregations in the water columnprey- swimming crustacea, larvaceans and fish eggs• largely transparent except for some pigments on eyes or

gut and usually small size (< 3mm in size)

Planktivore:• find modifications to jaw, head and dentition:

usually small mouth, reduced or absent teeth• jaw protrusion mainly functions to produce suction• In Chromis viridis- uses ram-jaw, low suction to capture

evasive prey, but decrease jaw protrusion and increase suction when prey are less evasive

Diurnal Planktivores

adaptations - streamlining and deeply forked caudal fins; aggregation

ecology-feed along the reef edge mainly on transient zooplankton from open water; the fish depend on water currents to supply them with food; may feed in stationary aggregations

Diurnal Planktivory

Crepuscular changeover- diurnal fish leave typically in order of: small fish first….mid sized …. then largeVery active time.

In nocturnal species- fish enter waters above the reef at night fall by size order (small to larger)

Difficulty in visually locating prey in dim light• adaptation- large eyes ex. squirrel fish• Feed on larger zooplankton: Hobson & Chess found that

even the smallest nocturnal reef planktivores are limited to zooplankters larger than 1 mm; whereas diurnal planktivores with similar feeding structures have been found to feed primarily on organisms smaller than 1 mm.

Possibly due to:1.)   inability to see smaller ones2.)   more efficient3.)   prey more vulnerable

Nocturnal Planktivores

Adaptations to nocturnal threats from predators:• streamlined bodies and deeply forked tails are less

developed- possibly due to less threat to attack after dark

• less aggregation occurs at night• countershading using luminescent organsNocturnal planktivores more widespread throughout reef

than diurnal counterparts

ctenophore