Nutrition and Feeding of Fishes

Question 1

Aquatic environments present what research problems?

Answer 1

Limited observation of fish
difficulty in collecting metabolites
nutrition vs pollution

Question 2

Ruminant

Answer 2

multicompartmental gastrointestinal tract with resident host of microoganisms resulting in differences in CHO, protein and lipid metabolism

Question 3

Nonruminant

Answer 3

Simple stomach GI tract generally cannot digest fibrous feedstuffs. Fish and shellfish are included in this category

Question 4

Intestinal length vs diet

Answer 4

more plant material in diet=longer intestines

Question 5

Mouth

Answer 5

limited mechanical reduction

Exceptions/additions:
Tilapia-chew food
grass carp-pharyngeal teeth
filter feeders- gill rakers

Question 6

Esophagus

Answer 6

Straight muscular tube; cardiac sphincter separates esophagus and stomach

Question 7

Stomach

Answer 7

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

Question 8

Intestine

Answer 8

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

Question 9

Pyloric cecae

Answer 9

extensions from the anterior of the intestine in some fish to increase absorptive surface area

Question 10

Pancreas

Answer 10

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

Question 11

Gallbladder

Answer 11

Hollow spherical organ located adjacent to liver. Stores bile and excretes it into the intestinal lument via the bile duct

Question 12

Liver

Answer 12

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.

Question 13

Hepatopancreas

Answer 13

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

Question 14

Gastric Glands

Answer 14

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

Question 15

Control of Gastric Glands

Answer 15

chief and parietal cells are under extensive hormonal control

gastrin production inhibited by secretin and somatostatin

Question 16

Secretin

Answer 16

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

Question 17

Bile-1

Answer 17

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.

Question 18

Bile-2

Answer 18

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.

Question 19

Neural Stimulation- Vagus Nerve

Answer 19

neural stimulation increases enzymatic portion of pancreatic secretions

Question 20

Pancreatic Secretions- Zymogens-inactive enzymes

Answer 20

trypsinogen
3 chymotrypsinogens
proelastase
procarboxypeptidases A&B

Question 21

Pancreatic Secretions-active enzymes

Answer 21

Lipase
alpha amylase
DNAase; RNAase

Question 22

Intestinal secretions

Answer 22

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