E-Liberary Pakistan: 6. ESSENTIAL NUTRIENTS

Introduction and classification

With the exception of the organically bound elements hydrogen, carbon, nitrogen and oxygen, there are about 20 or so inorganic mineral elements which are considered to be essential to animal life, including fish and shrimp. The essential mineral elements are usually classified into two main groups according to their concentration in the animal body; the macroelements and the microelements (Table 11)

Table 11. The essential mineral elements
Macroelements		Trace or microelements
Principal cations	Principal anions	Trace or microelements
Calcium (Ca)	Phosphorus (P)	Iron (Fe)	Fluorine (F)
Magnesium (Mg)	Chlorine (Cl)	Zinc (Zn)	Vanadium (V)
Sodium (Na)	Sulphur (S)	Manganese (Mn)	Chromium (Cr)
Potassium (K)		Copper (Cu)	Molybdenum (Mo)
		Iodine (I)	Selenium (Se)
		Cobalt (Co)	Tin (Sn)
		Nickel (Ni)	Silicon (Si)

¹ Underwood (1971); Reinhold (1975)

General function

The general function of minerals and trace elements can be summarised as follows:

Minerals are essential constitutents of skeletal structures such as bones and teeth.
Minerals play a key role in the maintenance of osmotic pressure, and thus regulate the exchange of water and solutes within the animal body.
Minerals serve as structural constituents of soft tissues.
Minerals are essential for the transmission of nerve impulses and muscle contraction.
Minerals play a vital role in the acid-base equilibrium of the body, and thus regulate the pH of the blood and other body fluids.
Minerals serve as essential components of many enzymes, vitamins, hormones, and respiratory pigments, or as cofactors in metabolism, catalysts and enzyme activators.

Macroelements

Calcium

Biological function: The principal biological functions of calcium may be summarised as follows;

Calcium is an essential component of bone, cartilage and the crustacean exoskeleton.
Calcium is essential for the normal clotting of blood, by stimulating the release of thromboplastin from the blood platelets.
Calcium is an activator for several key enzymes, including pancreatic lipase, acid phosphatase, cholinesterase, ATPases, and succinic dehydrogenase.
Through its role in enzyme activation, calcium stimulates muscle contraction (ie. promotes muscle tone and normal heart beat) and regulates the transmission of nerve impulses from one cell to another through its control over acetylcholine production.
Calcium, in conjunction with phospholipids, plays a key role in the regulation of the permeability of cell membranes and consequently over the uptake of nutrients by the cell.
Calcium is believed to be essential for the absorption of vitamin B12 from the gastro-intestinal tract.

Dietary sources and absorption: Rich dietary sources of calcium include limestone, oystershell grit, bone meal, rock phosphate (40–30%); crab meal, shrimp meal, meat and bone meal (20–10%); white fish meal, poultry manure, meat meal (10–5%); and brown fish meal, delactose whey powder, dried skim milk, poultry by-product meal, kelp meal, alfalfa meal (5–1%).
Calcium is readily absorbed through the gastro-intestinal tract (through vitamin D₃ action), gills, skin and fins of fish and crustacea. In general, dietary calcium absorption is facilitated by dietary lactose (by forming a soluble sugar-calcium complex) and by high gastric acidities (by aiding solubilization of the calcium salt).

Phosphorus

Biological function: The principal biological functions of phosphorus may be summarized as follows;

Phosphorus is an essential component of bone, cartilage and the crustacean exoskeleton.
Phosphorus is an essential component of phospholipids, nucleic acids, phosphoproteins (casein), high energy phosphate esters (ATP), hexose phosphates, creatine phosphate, and several key enzymes.
As a component of these important biological substances, phosphorus plays a central role in energy and cell metabolism.
Inorganic phosphates serve as important buffers to regulate the normal acidbase balance (ie. pH) of animal body fluids.

Dietary sources and absorption: Rich dietary sources of phosphorus include rock phosphate, dicalcium phosphate, bone meal (20–10% P); meat and bone meal, meat meal, white fish meal, shrimp meal, poultry by-product meal, dried poultry manure (5–2%); and rice bran, rice polishings, wheat bran, wheat mill run, dried brewers yeast, sunflower seed meal, cottonseed meal, rapeseed meal, sesame seed meal, dried delactose whey (2–1%).
Although soluble phosphorus salts can be absorbed through the skin, fins and gills of fish and shrimp, the concentration of phosphorus in fresh and sea water is low, and consequently body phosphorus requirements are usually met from dietary sources. Within plant foods, including cereals and oilseeds, 50–80% of the phosphorus occurs in the form of the calcium or magnesium salt of phytic acid; phytic acid being the hexaphosphate ester of inositol. This organic form of phosphorus must first be hydrolyzed within the gastro-intestinal tract by the enzyme phytase to inositol and phosphoric acid before it can be utilized and absorbed by the animal. As with calcium, the absorption of inorganic phosphorus salts is facilitated by high gastric acidity; the more soluble the salt the higher the availability and absorption of phosphorus.

Magnesium

Biological function: The principal biological functions of magnesium may be summarised as follows;

Magnesium is an essential component of bone, cartilage and the crustacean exoskeleton.
Magnesium is an activator of several key enzyme systems, including kinases, (ie. enzymes that catalyse the transfer of the terminal phosphate of ATP to sugar or other acceptors), mutases (transphosphorylation reactions), muscle ATPases, and the enzymes cholinesterase, alkaline phosphatase, enolase, isocitric dehydrogenase, arginase (magnesium is a component of the arginase molecule), deoxyribonuclease, and glutaminase.
Through its role in enzyme activation, magnesium (like calcium) stimulates muscle and nerve irritability (contraction), is involved in the regulation of intracellular acid-base balance, and plays an important role in carbohydrate, protein and lipid metabolism.

Dietary sources and absorption: Rich dietary sources of magnesium include; meat and bone meal, rice bran, kelp meal, sunflower seed meal (1.0–0.75% Mg); and wheat bran, wheat mill run, rice polishings, rapeseed meal, shrimp meal, cottonseed meal, linseed meal, poultry manure and crab meal (0.75–0.5%).
Magnesium is readily absorbed through the gastro-intestinal tract, gills, skin and fins of fish and crustacea. As with calcium and phosphorus, a proportion of the magnesium contained in plant foodstuffs may be present in the form of phytin (Ca or Mg salt of phytic acid).

Sodium, Potassium and Chlorine Biological function: Sodium, potassium, and chlorine occur almost entirely in the fluids and soft tissues of the body, sodium and chlorine being found mainly in the body fluids, and potassium occuring mainly in the cells. They serve a vital function in controlling osmotic pressures and acid-base equilibrium. They also play important roles in water metabolism.
Sodium is the main monovalent ion of extracellular fluids; sodium ions constituting 93% of the ions (bases) found in the blood stream. Although the principal role of sodium in the animal is connected with the regulation of osmotic pressure and the maintenance of acid-base balance, sodium also has an effect on muscle irritability, and plays a specific role in the absorption of carbohydrate.
Potassium is the major cation of intracellular fluid, and regulates intracellular osmotic pressue and acid-base balance. Like sodium, potassium has a stimulating effect on muscle irritability. Potassium is also required for glycogen and protein sysnthesis, and the metabolic breakdown of glucose.

Chlorine is the main monovalent anion of extracellular fluids; chlorine ions constituting about 65% of the total anions of blood plasma and other extracellular fluids within the body (ie. gastric juice). Chlorine is therefore essential for the regulation of osmotic pressue and acid-base balance. Chlorine also plays a specific role in the transport of oxygen and carbon dioxide in the blood, and the maintenance of digestive juice pH.
Dietary sources and absorption: Rich dietary sources of sodium, potassium and chlorine include: kelp meal, condensed fish solubles, dried delactose whey, shrimp meal, white fish meal, meat meal, meat and bone meal (4–1% Na in decreasing order); dehydrated cane molasses, condensed fish solubles, delactose whey powder, alfalfa meal, dried torula yeast, soybean meal, rice bran (4-2% K in decreasing order); dried brewers yeast, dried distillers solubles, wheat bran, cottonseed meal, meat and bone meal, wheat mill run, copra meal, rapeseed meal, peanut meal, and sunflower seed meal (2–1% K in decreasing order); salt (sodium chloride, 60% Cl) and potassium chloride (48% Cl).
Potassium, sodium and chloride are readily absorbed from the gastrointestinal tract, skin, fins and gills of fish and crustacea.

Sulphur

Biological function: The principal biological functions of sulphur may be summarised as follows;

Sulphur is an essential component of several key amino acids (methionine and cystine), vitamins (thiamine and biotin), the hormone insulin, and the crustacean exoskeleton.
As the sulphate, sulphur is an essential component of heparin, chondroitin, fibrinogen and taurine.
Several key enzyme systems such as coenzyme A and glutathione depend for their activity on free sulphydryl (SH) groups.
Sulphur is believed to be involved in the detoxification of aromatic compounds within the animal body.

Dietary sources and absorption: Rich dietary sources of the sulphur containing amino acids include fish meal, chicken eggs, and hydrolysed feather meal (the latter containing primarily cystine, Table 5). Sulphur containing amino acids and to a lesser extent inorganic sulphates are readily absorbed from the gastrointestinal tract of fish and shrimp.

Microelements

Iron

Biological function: The principal biological functions of iron may be summarised as follows;

Iron is an essential component of the respiratory pigments haemoglobin and myoglobin.
Iron is an essential component of various enzyme systems including the cytochromes, catalases, peroxidases, and the enzymes xanthine and aldehyde oxidase, and succinic dehydrogenase.
As a component of the respiratory pigments and enzymes concerned in tissue oxidation, iron is essential for oxygen and electron transport within the body.

Dietary sources and absorption: Rich dietary sources of iron include; blood meal (0.3–0.2% Fe); kelp meal, coconut meal, meat and bone meal, sunflower seed meal, dried distillers solubles (1000–500 mg/kg); alfalfa meal, crab meal, condensed fish solubles, fish meal, meat meal, poultry by-product meal, linseed meal, dried brewers yeast, dehydrated cane molasses, rice bran, delactose whey powder, and dried poultry manure (500–200 mg/kg).
Iron is readily absorbed through the gastro-intestinal tract, gills, fins and skin of fish and crustacea. Dietary iron availability and absorption is usually depressed by high dietary intakes of phosphate, calcium, phytates, copper and zinc. In general, inorganic sources of iron are more readily absorbed than organic sources; the ferrous iron (Fe++) being more available for absorption than ferric iron (Fe+++). Reducing substances such as vitamin C enhance the absorption of non-haem iron.

Manganese

Biological function: The principal biological functions of managanese may be summarised as follows,

Manganese functions in the body as an enzyme activator for those enzymes that mediate phosphate group transfer (ie. phosphate transferases and phosphate dehydrogenases), particularly those concerned with the citric acid cycle including arginase, alkaline phosphatase and hexokinase.
Manganese is an essential component of the enzyme pyruvate carboxylase
As a cofactor or component of several key enzyme systems, manganese is essential for bone formation (re. mucopolysaccharide synthesis), the regeneration of red blood cells, carbohydrate metabolism, and the reproductive cycle.

Dietary sources and absorption: Rich dietary sources of manganese include kelp meal (0.10% Mn), rice bran, dehydrated poultry manure, palm kernel meal, crab meal, wheat bran, wheat germ meal, wheat mill run, wheat middlings (300–100 mg/kg); dehydrated cattle manure, corn distillers dried solubles, rye grain, dehydrated cane molasses, dehydrated fish solubles, copra meal (100–50 mg/kg); wheat, rapeseed meal, sesame seed meal, linseed meal, brewers dried grains, safflower seed meal, shrimp meal and oats (50–30 mg/kg).
Manganese is readily absorbed from the gastro-intestinal tract, gills, fins and skin of fish and crustacea. Dietary manganese availability and absorption is reduced in the presence of phytates, and high dietary intakes of calcium.

Copper

Biological function: The principal biological functions of copper may be summarised as follows;

Copper is an essential component of numerous oxidation-reduction enzyme systems. For example, copper is a component of the enzymes cytochrome oxidase, uricase, tyrosinase, superoxide dismutase, amine oxidase, lysyl oxidase, and caeruloplasmin.
As a component of the enzyme caeruloplasmin (ferroxidase), copper is intimately involved with iron metabolism, and therefore haemoglobin synthesis and red blood cell production and maintenance.
Copper is also believed to be necessary for the formation of the pigment melanin and consequently skin pigmentation, for the formation of bone and connective tissue, and for maintaining the integrity of the myelin sheath of nerve fibres.

Dietary sources and absorption: Rich dietary sources of copper include condensed fish solubles, corn distillers dried solubles, dehydrated sugar cane molasses (100-75 mg/kg Cu); corn distillers grains with solubles, dehydrated poultry manure (75–50 mg/kg); dried brewers yeast, crab meal, corn gluten meal, linseed meal, soybean meal, dried brewers grains, wheat mill run, millet, cottonseed meal, wheat middlings, and copra meal (50–20 mg/kg).
Copper is readily absorbed from the gastro-intestinal tract, gills, fins and skin of fish and crustacea. Dietary copper availability and absorption is reduced in the presence of phytates, and high dietary intakes of zinc, iron, molybdenum, cadmium, inorganic sulphates and calcium carbonate.

Cobalt

Biological function: The principal biological functions of cobalt may be summarised as follows;

Cobalt is an integral component of cyanocobalamin (vitamin B12), and as such is essential for red blood cell formation and the maintenance of nerve tissue.
Although not confirmed, cobalt may also function as an activating agent for various enzyme systems.

Dietary sources and absorption: Rich dietary sources of cobalt include copra meal (2 mg/kg Co), linseed meal, dried brewers yeast, fish meal, meat meal, cottonseed meal, and soybean meal (0.5–0.1 mg/kg).
Cobalt is readily absorbed from the gastro-intestinal tract and the surrounding water by fish and crustacea. Dietary cobalt availability and absorption is reduced in the presence of high dietary intakes of iodine.

Iodine

Biological function: Iodine is an integral component of the thyroid hormones, thyroxine and tri-iodo-thyronine, and as such is essential for regulating the metabolic rate of all body processes.
Dietary sources and absorption: Rich dietary sources of iodine include all food stuffs of marine origin, and in particular seaweed meals (which may contain up to 0.6% I) and marine fish and crustacean meals. Iodine is readily absorbed from the gastro-intestinal tract and the surrounding water by fish and crustacea. Dietary availability and absorption is reduced in the presence of high dietary intakes of cobalt.

6. ESSENTIAL NUTRIENTS - MINERALS