How fish secure food
The first stage of securing food involves the search stage.There are two types of search active and passive.
ACTIVE SEARCH
means the fish is swimming and scanning the enviroment for prey with Polypterids this involves their limited eyesight but depends more on olfactrization and electrolocalization.Man Polypterids search by speculation.Like chickens scratching the ground they grub thru the substrate looking for various food stuff insect larvae etc.
PASSIVE SEARCH
saves the energy used in active search by laying in wait on the bottom or in some form of cover on soft bottoms Polypterids often slightly bury themselves (head burying) or completely with only their eyes above the subatrate.When prey is detected and in range they lunge forth and capture the prey(more on this later).Many young Polypterids often float motionless just below the surface waiting for prey that may fall into the water colum or fails to recognize them.
PURSUIT
The next stage of securing food is often pursuit this places the Polpterid in range to attack its prey target.Polypterids use a method called fast start performance this allows a fast burt of speed but it costs high speed endurance and manuverability.using ths method they hover motionless in the water colum or along lurk thru the weeds until a prey fish gets into range to attack and capture it.
ATTACK AND CAPTURE
depends on the prey if the prey target is active(swimming)the Polypterids using its fast start performance has to overtake its prey,draw into it's mouth and grasp it in its teeth.The actual strike using a fast start performance involves the body bending into an C shape along the lenght of its body then rapidly straightening this allows for maximum speed the prey is then impaled on the sharp jaw teeth designed for holding.If the prey object is passive(not swimming)or small ie.insect larvae,small crustaecions suction feeding may be used.This method of feeding this is acomplished by the rapid opening of the jaws and expansion of mouth cavity through cranial elevation this creates a negative pressure(vacuum) within the mouth that causes the water and presumably the prey in front of the head to be pulled into the mouth.The jaws then close and the gill slits (operculars) are opened to allow the engulfed water to flow out past the gills.
HANDLING
Handling refer to the activities post capture it inlcudes manipulating the prey to make it edible and digestable.One of the major chores in the handling phase is manipulating the prey into a headfifrst position for sswallowing if swallowed tail first the finnage of the prey even soft rayed fish can lodge in the mouth or throat of the Polypterid,however if consumed headfirst the finnage is depressed and prey escape is less likely since few fish can swim backwards effectively.
LIMITING FACTORS
Gape limitation actually depends on mouth opening to an extent, as well as pharyngeal gape (which is where another type of teeth used for processing prey come into play), but also dependent on the width between the cleithral bones, which are located near the pectoral girdle.
all of these factors influence what size prey a fish can take down; that's why bichirs are limited by the size of their mouths, as are gars, given they swallow their food. other fish, such as piranhas, are not as gape limited because they tear pieces of food off by biting (something the majority of North American piscivorous fishes did not evolve).
DOES SIZE MATTER?
Yes, predators select prey size carefully. There's something called optimal foraging strategy that means animals will get food in the most profitable way, i.e., the most energy gained from prey compared to the most energy used up getting that prey. This applies equally to herbivores as well as carnivores.
Work done several decades ago on sunfish demonstrated that they will swim a small distance to catch small daphnia but a longer distance to catch bigger daphnia. Small daphnia at a far distance will be ignored if small daphnia closer by are present. Since small daphnia provide little energy, the sunfish will only expend a small amount of energy catching them. Bigger daphnia return more energy, so it's worthwhile swimming more to catch them. If less food is about, the sunfish becomes less picky, swimming further to take smaller prey. When food is abundant, the sunfish is more picky, and will swim shorter distances for smaller prey.
This is a classic piece of work and should be mentioned in most animal behaviour test books. Optimal foraging has been demonstrated again and again, so even though still a theory, it does appear that animals largely work in an optimal way.
I'd caution against using optimal foraging theory as an excuse to mix small fish with big predators though. While I've seen it done with, for example, piranhas in big tanks with guppies, it isn't 100% reliable. In an aquarium fish will adopt learned behaviours, connecting the presence of humans with the appearance of food. That's probably going to override their optimal foraging programming.
During suction feeding (jaw opening > buccal cavity expansion > jaw closing).
These phases comprise the main sequences of rapid jaw and head movements that are essential to prey capture. Briefly, the expansive phase constitutes a rapid opening of the jaws and expansion of buccal cavity through cranial elevation, hyoid bar depression, and lateral expansion of the suspensorium. These movements together generate a steep negative pressure gradient within the mouth that causes the water and presumably the prey in front of the head to be sucked into the mouth. The compressive phase begins with jaw closure and progresses posteriorly with hyoid protraction and suspensorium adduction, while the gill slits (opercular cavities) are opened to allow the engulfed water to flow out past the gills.
CONSUMPITION,DIGESTION AND ELIMINATION
So the prey is now secure and manipulated into head first position and consumption can begin.If the food stuff is to large
to swallow bichirs have gular paltes they can use to slightly compress foods(gular plate the median or paired, dermal, flat bone(s) between the lower jaws of primitive Teleostomes)it is moved back into the pharynx the portion of the intestine between the mouth and the oesophagus and into the pharyngeal arch and pharyngeal jaw that contains the pharyngeal mill molar teeth in the pharyngeal region used for crushing food.Then into the stomach for digestion and chemical processing,then into
the intestines and thru the spiral valve spiral valve or helical fold in the midgut of some primitive Teleostomi. Functions to increase the surface area for processing food without lengthening the intestine.Then finally out the alimentary canal thus
completeing the process.
citations
Prey Capture in Actinopterygian Fishes: A Review of Suction Feeding Motor Patterns with New Evidence from an Elopomorph Fish, Megalops atlanticus1
Justin R. Grubich2,1
1 Department of Evolution and Ecology, University of California at Davis, Davis, California 95616
The Diversity of Fishes Helfman,Collette and Facey
The first stage of securing food involves the search stage.There are two types of search active and passive.
ACTIVE SEARCH
means the fish is swimming and scanning the enviroment for prey with Polypterids this involves their limited eyesight but depends more on olfactrization and electrolocalization.Man Polypterids search by speculation.Like chickens scratching the ground they grub thru the substrate looking for various food stuff insect larvae etc.
PASSIVE SEARCH
saves the energy used in active search by laying in wait on the bottom or in some form of cover on soft bottoms Polypterids often slightly bury themselves (head burying) or completely with only their eyes above the subatrate.When prey is detected and in range they lunge forth and capture the prey(more on this later).Many young Polypterids often float motionless just below the surface waiting for prey that may fall into the water colum or fails to recognize them.
PURSUIT
The next stage of securing food is often pursuit this places the Polpterid in range to attack its prey target.Polypterids use a method called fast start performance this allows a fast burt of speed but it costs high speed endurance and manuverability.using ths method they hover motionless in the water colum or along lurk thru the weeds until a prey fish gets into range to attack and capture it.
ATTACK AND CAPTURE
depends on the prey if the prey target is active(swimming)the Polypterids using its fast start performance has to overtake its prey,draw into it's mouth and grasp it in its teeth.The actual strike using a fast start performance involves the body bending into an C shape along the lenght of its body then rapidly straightening this allows for maximum speed the prey is then impaled on the sharp jaw teeth designed for holding.If the prey object is passive(not swimming)or small ie.insect larvae,small crustaecions suction feeding may be used.This method of feeding this is acomplished by the rapid opening of the jaws and expansion of mouth cavity through cranial elevation this creates a negative pressure(vacuum) within the mouth that causes the water and presumably the prey in front of the head to be pulled into the mouth.The jaws then close and the gill slits (operculars) are opened to allow the engulfed water to flow out past the gills.
HANDLING
Handling refer to the activities post capture it inlcudes manipulating the prey to make it edible and digestable.One of the major chores in the handling phase is manipulating the prey into a headfifrst position for sswallowing if swallowed tail first the finnage of the prey even soft rayed fish can lodge in the mouth or throat of the Polypterid,however if consumed headfirst the finnage is depressed and prey escape is less likely since few fish can swim backwards effectively.
LIMITING FACTORS
Gape limitation actually depends on mouth opening to an extent, as well as pharyngeal gape (which is where another type of teeth used for processing prey come into play), but also dependent on the width between the cleithral bones, which are located near the pectoral girdle.
all of these factors influence what size prey a fish can take down; that's why bichirs are limited by the size of their mouths, as are gars, given they swallow their food. other fish, such as piranhas, are not as gape limited because they tear pieces of food off by biting (something the majority of North American piscivorous fishes did not evolve).
DOES SIZE MATTER?
Yes, predators select prey size carefully. There's something called optimal foraging strategy that means animals will get food in the most profitable way, i.e., the most energy gained from prey compared to the most energy used up getting that prey. This applies equally to herbivores as well as carnivores.
Work done several decades ago on sunfish demonstrated that they will swim a small distance to catch small daphnia but a longer distance to catch bigger daphnia. Small daphnia at a far distance will be ignored if small daphnia closer by are present. Since small daphnia provide little energy, the sunfish will only expend a small amount of energy catching them. Bigger daphnia return more energy, so it's worthwhile swimming more to catch them. If less food is about, the sunfish becomes less picky, swimming further to take smaller prey. When food is abundant, the sunfish is more picky, and will swim shorter distances for smaller prey.
This is a classic piece of work and should be mentioned in most animal behaviour test books. Optimal foraging has been demonstrated again and again, so even though still a theory, it does appear that animals largely work in an optimal way.
I'd caution against using optimal foraging theory as an excuse to mix small fish with big predators though. While I've seen it done with, for example, piranhas in big tanks with guppies, it isn't 100% reliable. In an aquarium fish will adopt learned behaviours, connecting the presence of humans with the appearance of food. That's probably going to override their optimal foraging programming.
During suction feeding (jaw opening > buccal cavity expansion > jaw closing).
These phases comprise the main sequences of rapid jaw and head movements that are essential to prey capture. Briefly, the expansive phase constitutes a rapid opening of the jaws and expansion of buccal cavity through cranial elevation, hyoid bar depression, and lateral expansion of the suspensorium. These movements together generate a steep negative pressure gradient within the mouth that causes the water and presumably the prey in front of the head to be sucked into the mouth. The compressive phase begins with jaw closure and progresses posteriorly with hyoid protraction and suspensorium adduction, while the gill slits (opercular cavities) are opened to allow the engulfed water to flow out past the gills.
CONSUMPITION,DIGESTION AND ELIMINATION
So the prey is now secure and manipulated into head first position and consumption can begin.If the food stuff is to large
to swallow bichirs have gular paltes they can use to slightly compress foods(gular plate the median or paired, dermal, flat bone(s) between the lower jaws of primitive Teleostomes)it is moved back into the pharynx the portion of the intestine between the mouth and the oesophagus and into the pharyngeal arch and pharyngeal jaw that contains the pharyngeal mill molar teeth in the pharyngeal region used for crushing food.Then into the stomach for digestion and chemical processing,then into
the intestines and thru the spiral valve spiral valve or helical fold in the midgut of some primitive Teleostomi. Functions to increase the surface area for processing food without lengthening the intestine.Then finally out the alimentary canal thus
completeing the process.
citations
Prey Capture in Actinopterygian Fishes: A Review of Suction Feeding Motor Patterns with New Evidence from an Elopomorph Fish, Megalops atlanticus1
Justin R. Grubich2,1
1 Department of Evolution and Ecology, University of California at Davis, Davis, California 95616
The Diversity of Fishes Helfman,Collette and Facey
