Nutrition and Feeding of Fishes Flashcards
Aquatic environments present what research problems?
Limited observation of fish
difficulty in collecting metabolites
nutrition vs pollution
Ruminant
multicompartmental gastrointestinal tract with resident host of microoganisms resulting in differences in CHO, protein and lipid metabolism
Nonruminant
Simple stomach GI tract generally cannot digest fibrous feedstuffs. Fish and shellfish are included in this category
Intestinal length vs diet
more plant material in diet=longer intestines
Mouth
limited mechanical reduction
Exceptions/additions:
Tilapia-chew food
grass carp-pharyngeal teeth
filter feeders- gill rakers
Esophagus
Straight muscular tube; cardiac sphincter separates esophagus and stomach
Stomach
Gastric secretions in some fishes; gastrin is secreted by stomach under nervous control and stimulates gastric gland
Parietal cells secrete HCL
Chief cells secrete pepsinogen
HCl activates pepsinogen to pepsin
Intestine
Usually undifferentiated; site of furhter digestion and absorption. Chyme (stomach contents) stimulates secretion of prosecretin; becomes secretin in intestine and releases NaHCO3 to neutralize HCl; chyme also stimulates secretion of pancreozymin which stimulates pancreas to secrete digestive enzymes
Pyloric cecae
extensions from the anterior of the intestine in some fish to increase absorptive surface area
Pancreas
Discretely located into one organ or diffuse. Consists of two types of tissues:
1) Exocrine- produces digestive enzymes and bicarbonate that enter ducts connected to intestinal or cecal lumen
2) Endocrine-glandular cells called Brockmann bodies or islets of Langerhan; secrete hormones that regulate digestion and metabolism directly into the vasculature
Gallbladder
Hollow spherical organ located adjacent to liver. Stores bile and excretes it into the intestinal lument via the bile duct
Liver
Supplied with nutrients and other metabolites by the hepatic portal vein coming from the alimentary canal. Nutrients absorbed from the digestive tract are further processed at the liver and sent to other tissues.
Hepatopancreas
Each half opens into GI tract and influeces:
synthesis and secretion of digestive enzymes
absoprtion of nutrients
maintenance of mineral and organic reserves
distribution of stored reserves during intermolt
catabolism of organic compounds
metabolism of CHO and lipid
Gastric Glands
Three types:
Mucous cells- neck of gland
Chief Cells- body of gland; secrete pepsinogen
Oxyntic cells
in most fish there is only one cell type (oxynticopeptic cells) that produce both acid and enzymes
Control of Gastric Glands
chief and parietal cells are under extensive hormonal control
gastrin production inhibited by secretin and somatostatin
Secretin
basic polypeptide secreted from anterior intestine endocrine cells when acid is present.
stimulates flow of pancreatic juices with low enzyme concentration-neutralizes HCl with NaHCO3
Bile-1
continually formed in the liver by polygonal cells and concentrated in gall bladder. Flows into intestine via the bile duct-stimulated by neural and hormonal means. serves to emulsify fat and aids in its hydrolysis and absorption. reabsorbed in the lower GI tract and goes back to liver.
Bile-2
Compounds in Bile include bile salts and biliverdine/bilirubin:
Bile salts are break down products of cholesterol and steroids produced in the liver. These include taurocholate, cholic acid and allocholic acid.
Biliverdine (green) and bilirubin (red) are break down products of heme catabolism that function to emulsify lipids.
Neural Stimulation- Vagus Nerve
neural stimulation increases enzymatic portion of pancreatic secretions
Pancreatic Secretions- Zymogens-inactive enzymes
trypsinogen
3 chymotrypsinogens
proelastase
procarboxypeptidases A&B
Pancreatic Secretions-active enzymes
Lipase
alpha amylase
DNAase; RNAase
Intestinal secretions
From cells in glands along lumen of intestine
1) enteropeptidase-enterokinase
- —–proteolytic enzyme that converts trypsinogen to trypsin then trypsin converts all other inactive zymogens
