Feeding Food Processing 1 Structure review 2 Function

Feeding & Food Processing 1. Structure (review) 2. Function (behavior, physiology) 3. Nutritional needs 4. Digestive efficiency

Food capture w Mouth and pharyngeal cavity w Jaws w Teeth - jaw, mouth, pharyngeal w Gill rakers

Fish Feeding - function w Herbivores w < 5% of all bony fishes, no cartilaginous fishes w browsers - selective eat only the plant w grazers - less selective - include sediments w Detritivores w 5 - 10% of all species w feed on decomposing organic matter

Fish Feeding – function w Carnivores w zooplanktivores w suction feeding w ram feeding w benthic invertebrate feeders w graspers w pickers w sorters w crushers

Fish Feeding – function w More Carnivores w fish feeders w active pursuit w stalking w ambushing w luring

Fish feeding behavior w Fish feeding behavior integrates morphology with perception to obtain food: w Search --> Detection --> Pursuit --> Capture --> Ingestion

Feeding behavior w Fish show versatility in prey choice and ingestion w Behavior tightly linked to morphology (co-evolution)

Fish feeding behavior w Behavior tends to be optimizing when choices are available w Optimal = maximize benefit: cost ratio w More for less! w Select the prey that yields the greatest energetic or nutrient “return” on the energy invested in search, pursuit, capture, and ingestion

Fish digestive physiology w After ingestion of food, gut is responsible for: w Digestion - breaking down food into small, simple molecules w involves use of acids, enzymes w Absorption - taking molecules into blood w diffusion into mucosal cells w phagocytosis/pinocytosis by mucosal cells w active transport via carrier molecules

Digestive Apparati trout carnivore catfish omnivore carp omnivore milkfish planktivore

Fish Digestion w Two major groups: w/stomach, w/out w w/out stomach: cyprinids (carps) w w/stomach: cold-water salmonids, warm-water catfish, tilapia, eels, grouper w note: all “pure” predators have a stomach and teeth w relative gut length (RGL): gut: body length w high RGL = species consuming detritus, algae (high proportion of indigestible matter)

Relative Gut Length

Fish Digestive Morphology: Major Divisions w w w w Mouth Esophagus Pharynx Stomach Intestine Rectum Secretory glands (liver and pancreas) often difficult to distinguish

Gastrointestinal Tract w Esophagus w Stomach w large in carnivores, small in herbivores/omniv ores w Pyloric caeca w Intestine w short in carnivores, long in herbivoresomnivores w Anus - separate from urogenital pore

GI Tract- Secretory Glands w Liver w w w produces bile (lipolysis) stores glycogen stores lipids w Pancreas w digestive enzymes w proteases - protein breakdown w amylases - starch breakdown w chitinases - chitin breakdown w lipases - lipid breakdown

Digestive Anatomy: Mouth/Esophagus w Channel catfish: large mouth/esophagus, capture prey, slightly predaceous, mouth has no teeth, no gizzard/cardiac sphincter w Common carp: small mouth for bottom feeding, pharyngeal teeth, grinds food w Tilapia: combination of bottom feeder, predator, efficient plankton feeder, uses gill rakers, pharyngeal mucous

Digestive Anatomy: Stomach w Channel catfish: have true stomach that secretes HCl and pepsinogen (enzyme) w Common carp: no stomach; however, “bulb” at anterior end of digestive tract, bile and pancreatic secretions empty into intestine posterior to cardiac sphincter, no secretion of gastrin (low p. H) w Tilapia: modified stomach, secretes HCl, welldefined pocket, p. H varies w/digestal flow, has pyloric sphincter

Digestive Anatomy: Intestine w Channel catfish: length less than whole body, no large/small version, slightly basic p. H, digestive secretions, nutrient absorption, many folds for absorption w Common carp: digestive tract is 3 x whole body length, similar in activity to that of channel catfish w Tilapia: tract is 6 -8 x that of body length, activities similar to that of other species

Digestive Anatomy: Liver and Pancreas w Both organs produce digestive secretions w Liver produces bile but is also the primary organ for synthesis, detoxification and storage of many nutrients w Pancreas is primary source of digestive enzymes in most animals w It also produces zymogens (precursors to enzymes)

Fish Digestive Physiology w Digestion is accomplished in w Stomach w low p. H - HCl, other acids (2. 0 for some tilapia!) w proteolytic enzymes (mostly pepsin)

Digestive Processes: Stomach w Catfish as an example - its digestive processes are similar to that of most monogastric animals w Food enters stomach, neural and hormonal processes stimulate digestive secretions w As stomach distends, parietal cells in lining secrete gastrin, assisting in digestion w Gastrin converts the zymogen pepsinogen to pepsin (a major proteolytic enzyme) w Some fish have cirulein instead of gastrin

Digestive Processes: Stomach w Flow of digesta out of stomach is controlled by the pyloric sphincter w Pepsin has p. H optimum and lyses protein into small peptides for easier absorption w Minerals are solubilized; however, no lipid or COH is modified w Mixture of gastric juices, digesta, mucous is known as chyme

Fish Digestive Physiology w Digestion is accomplished in w Stomach w Intestine w alkaline p. H (7. 0 - 9. 0) w proteolytic enzymes - from pancreas & intestine w amylases (carbohydrate digestion) - from pancreas & intestine w lipases (lipid digestion) - from pancreas & liver (gall bladder, bile duct)

Digestive Processes: Intestine w Chyme entering the small intestine stimulates secretions from the pancreas and gall bladder (bile) w Bile contains salts, cholesterol, phospholipids, pigments, etc. w Pancreatic secretions include bicarbonates which buffer acidity of the chyme w Zymogens for proteins, COH, lipids, chitin and nucleotides are secreted w e. g. , enterokinase (trypsinogen --> trypsin) w Others: chymotrypsin, carboxypeptidase, aminopeptidase, chitinase

Digestive Processes: Intestine w Digestion of carbohydrates is via amylase, which hydrolyzes starch w Others: nuclease, lipase w Cellulase: interesting in that it is not secreted by pancreas, but rather produced by gut bacteria w Note: intestinal mucosa also secretes digestive enzymes

Fish digestive physiology w Absorption is accomplished in w Intestine w diffusion into mucosal cells w phagocytosis/pinocytosis by mucosal cells w active transport via carrier molecules

Digestive processes: Absorption w Most nutrient absorption occurs in the intestine w Cross-section of the intestinal luma shows that it is highly convoluted, increasing surface area w Absorption through membrane is either by passive diffusion (concentration gradient) w Or by active transport (requires ATP) w Or via pinocytosis (particle engulfed) w Nutrients absorbed by passive diffusion include: electrolytes, monosaccharides, some vitamins, smaller amino acids

Digestive processes: absorption w Proteins are absorbed primarily as amino acids, dipeptides or tripeptides w triglycerides are absorbed as micelles w COH’s absorbed as monosaccharides (e. g. , glucose, except for crustaceans) w calcium and phosphorus are usually complexed together for absorption w all nutrients, excluding some lipids, are absorbed from the intestine via the hepatic portal vein to the liver

Summary of Digestive Enzymes

Fish Nutritional Needs w High protein diet: w Carnivores - 40 - 55% protein needed w Omnivores - 28 - 35% protein needed w w Birds & mammals - 12 - 25% protein needed 10 essential amino acids (PVT. TIM HALL)

Fish Nutritional Needs w High protein diet w Why so high? w Proteins needed for growth of new tissue w Proteins moderately energy-dense (don’t need dense source - ectotherms, low gravity) w Few side-effects - ease of NH 4+ excretion

Nutritional efficiency in fishes w Fish more efficient than other vertebrates: w Conversion factor = kg feed required to produce 1 kg growth in fish flesh w Fishes: 1. 7 - 5. 0 w Birds & mammals: 5. 0 - 15. 0

Nutritional efficiency in fishes w Fish more efficient than other vertebrates w Why? w Ectothermy vs. endothermy w Energy/matter required to counterbalance gravity w Bias of a high-protein diet

Nutritional efficiency w Maintenance ration (MR) = the amount of food needed to remain alive, with no growth or reproduction (% body wt. /day) w MR is temperature-dependent w MR increases as temperature increases w MR is size-dependent w MR decreases as size increases