Ms M. AMERIO
INTRODUCTION
In intensive pisciculture, feding, although dating back centuries in the economic achievement of fish rearing for commercial purpose, is more or less a recent science when speaking in terms of: definition and covering of nutritional requirements, distinction of the fed particularities, preparation and distribution techniques of feed. The cost of feeding now represents, as far as rearing prize species is concerned (sea-bass, trout) 60 % of the total cost of management, KLENTZ G.W. (Verone, 1982) (1) shows clearly an example of the high cost attributed directly to feeding: the weight growth of a group of fish having a consumption index ( gain in body weight/dry feed injested) of 1,9 kg of feed for 1 kg of fish, is more expensive ( in terms of feed costs) than a same group of a fish having a consumption index equal to 1,5.
There are numerous reasons for these high costs: high mortality rates during the different rearing phases, the high technology applied for the prepartion of the feed, the use of raw materials of animal origin, having a high unitary cost (special fish meal and oils).
Fresh and marine water fish, intensively reared, can but take a partial benefit from the natural feed of the environment, consequently they mostly depend on artificial feed.
Besides, fish are a “fantastic biological machine”as they have the great capacity of converting feed into flesh: they are capable of converting 1,5 to 2 kg of food into 1 kg of flesh, whilst for the same production, chickens require 2,3 to 2,4 kg and bovines 5 to 7 kg (2).
This great conversion capacity, well explained by the fact that as fish are heterothermic, they do not use up energy to keep a constant body temperature, and also because of their specific weight, not much effort is demanded of them for movement. There is also a smaller demand of energy for the energetic metabolism of excretion for fish, when compared to other species; the product from the nitrogene excretion is ammoniac instead of urea.
For the formulation of low costing compound feed, the feed requirements of the animals (concerning proteins amino-acids, lipids, etc…) must be known, along with the characteristics and nutritive content of the feed, and the price of each ingredient.
It is still unknown exactly, what use each species makes of each of the different feed components, and so quite often, the feed is calculated on the presumption that the food value of a substance is the same for fish as that for monogastric animals, or that an ingredient can be replaced by another when only taking into account the nutritive content.
It is therefore the quality of the feed which essentially plays the determinant part. Feed must be taken in a larger sense; as carrier of nutritive principles and substances which have an oligodynamic action, but the possibility of feed having eventual toxic actions or more precisely, which have an antinutrional action must be taken into consideration also. From this point of view the feed not only becomes a carrier of indispensable substances for body growth and maintenance but also a modulator of the organic defences and a way of immunity.
PROTEINS
The feed naturally ingested by fish (fish, crustacae, mussels, etc…) contains high concentrations of proteins substances (from 50% to 70% of the dry matter) The artifical feed scheduled for carnivorous fish is also manufactured in such a way that it contains at least 40% of raw protides (N × 6,25). Therefore fish have a great proteinic requirements when compared with other monogastric animals (chickens, pigs).
The great proteinic requirement can be justified very synthetically, by the three following factors:
- slow proteinic speed at muscle level (which make up 60% of the whole body ) when compared with other animal species. 3 g of proteins /g of R.N.A (ribonucleic acid) are synthetized per day. There is a much greater proteinic synthesis speed(10 to 20 times more) at liver and gill level.
- the high rate of amino-acids which are directly utilized by the oxidation processes for the energy supply and which can consequently become the limiting factors at proteinic synthesis level.
- the limited capacity of the use of carbohydrates at digestion level.
LUQUET (1975) (3) draws attention to the fact that the great doses of proteins, when feeding trout, can be a great waste. It must be considered that out of 100 g of proteins distributed to trout, 10 to 15 g are eliminated through excrements, 30 to 40 g through the gills and the urine, under the form of ammoniac. This evident bad use of proteins could be caused by a bad proteinic balance, but also by the fact that a great part of the proteins are used for energetic reasons. Lipides and carbohydrates also, can have an economic effect on proteins, but it must be taken into account the fact that lipides are expensive and that over a long period their use could create problems in the agglomeration preparation, not forgetting the damage of hepatic character.
At least 50% of proteins in fish feed is of animal origin generally (fish meal, blood meal, meat meal, lacto-serum) having a good biological value. The biological values of a proteins (Thomas, 1909, (4) is represented by the percentage relation between the nitrogene contained in the organisms and that really absorbed).
The formulation of fish also comprehends proteins of vegetables origin (soya meal, cereal by products, cotton meal). It is widely known that carnivorous fish make better use of proteins of animal rather than of vegetables origin, and as this has been remarked as far as trout are concerned, who are unable to one non proteinic nitrogen, urea, ammonium citrate, this last product can even be toxic.
The digestibility of proteins fish feed in influenced by numerous factors (directly concerning the fish or the feed- species, age, water temperature, ingestion, the treatment the feed received), any case it is greater for proteins of animal origin that for those of vegetable origin (biological value feed table).
The nutritive value of proteins, especially those of vegetable origin, can be improved by thermo-mechanical treatments, such as compressings, flakings, extrusion, etc…
The compressing treatment consists in forming cubes which can receive a more or less thermic treatment (dry or steam from 1 to 10 minutes); The flaking thermic treatment consists in steaming under high pressure (1.5 to 7 atmospheric pressure) over a very short time (a few minutes) which is then followed by a compressing treatment. The extrusion treatment is the preparation of the feed (grinding and adding water) followed by the cooking phase and setting of the product, (a homogeneous paste is then obtained and pressed through die holes. All the physical chemical phenomena which are verified during the different phase of treatment -gelatinization or dextrinization of the starches, denaturation of proteins, inactivation of the anti-nutritional factors are closely linked to each of the variable factors. concerned: moisture, temperature, pressure, duration of treatment.
The thermic treatments cause the denaturation of proteins, so facilitating the hydrolytic action of pepsine and tripsine (proteolytic enzymes) and quickening the digestion of the protein. To obtain the correct estimation of a protein, the amino acid compositions must be known along with their availability when the feed reaches the mouth of the animal, after the necessary manipulations have been carried out (drying, grinding, cubing, extrusion, etc…) For this, it seems necessary to carry out a correct analysis of the proteinic amino acid composition (a) Tryptophan is destroyed by the hydrolyse acid of proteins, this is why a specific hydrolyse is carried out in an alkalin environment. Methioine itself is affected by the hydrolyse acid treatment, as it oxidizes and changes into sulphonated methionine. Great quantities of sulphonated methionine can be found in the protein, if this latter has undergone, during food manufacture transformation, an oxidising or thermic treatment; so a measurement of methionine as sulphonated methionine should be made. COWEY C.B. (1978) (5) precises that the oxidised form of methionine could be utilized by fish, but this is not certain.
The thermic treatments, if carried out in certain humid concentrations and on raw materials which have a good sugar content, bring about the formation of the MAILLARD products (between E amino group of lysine and a radical glycoxydic). Following this chemical reaction, the lysine present in the feed is not completely available biologically. An extract estimate of the qualitative and quantitative composition of the food protein permits the verification whether or not the protein can satisfy the amino-acid needs of the species.
The necessary amino-acids for salmonidae and for sea-bass are as following, arginine, histidine, lysine, isoleucine, leucine, methionine, cystine, phenylamine, tyrosine, tryptophan, valine.
For fish, the isoleucine/leucine relation is important, as it must be always inferior to 1: 3. The knowledge of the amino acid composition permits the application of certain calculation methods: the chemical rate, the index of essential amino acids by OSER; the index of the proteinic balance by ARNOLD, which give the global estimate of the protein, without carrying out biological research, which is very difficult and costly when concerning fish.
It must be remarked that the different methods of calculation are restricted to taking into consideration the limiting amino acids, evaluating the proteins by respecting a minimum, or evaluating the proteins by comparing between their essential amino-acid patrimony and that of whole egg protein (taken as the protein of comparison)
Therefore this is not only a problem of covering the need in the different amino-acids but a problem of the amino-acid balance, between the essential and unessential amino-acid rates. The synthesis of a protein is a action carried out continually at the different organ levels and the speed of which depends on the concentration of the monopeptides which react well and are proportional to the product concentrations.
From one organ to another, varies the speed of the synthesis and that of a turn over change, according to the specific characteristics of the organ, for instance it is greater at liver level than at muscle level, ARNOULD (1971) (6) following a series of experimental controls, proposes an evaluation system of proteins, based on the calculation of the identified needs. ARNOLD'S amino-acid balance index is obtained in fact by the product of the relations between the different essential amino-acids of a given protein (egg protein) and the amino acid protein examined. In the calculation, the unessential amino-acids are taken globally into consideration. The more ARNOLD's index approaches I, the greater, from a biochemical point of view, the speed of the global synthesis of proteins and the less the waste caused by imbalances. The amino-acids causing the great imbalance, are shown clearly by their relation (the further they are from 1, the greater the imbalance). Normally, the fact that the whole rate of amino acids contained in feed is only employed partially is not taken into account; the concept of amino acid availability is identified with the concept of digestibility, in the sense that this is normally an integrant part of the proteinic structure, it becomes available at absorption level only when the proteins have been digested.
However there is no perfect superposition between the concept of digestibility and that of availability for the interferences in the digestive system, but with fish, on the contrary to what happens with pigs, there is little interference in the intestinal microflora on the amino acid rates and the transit time of food is rather quick.
Finally it must not be forgotton that the qualitative control of food, rich in proteins of animal origin must schedule the measurement of the amines-biogenes (histamine, putrescine, cadaverine, etc…) in other words, the composition which can form after the processes of decarboxylation of the amino-acids.
This parameter which also furnishes a measure of the quality of food conservation, is important. The amino-by products can create a toxic or pharmacological effect on the animals.
ANTINUTRITIONAL EFFECTS
INTRINSIC ANTINUTRITIONAL FACTORS
These are factors linked with the specific characteristics of a vegetable, varying in the same species from “cultivator to cultivate” and under genetic control. Some of these are thermolable and the appropriate treatments could reduce them remarkably.
EXTRINSIC ANTINUTRITIONAL EFFECTS
These are molecules of natural origin and have a synthesis which can contaminate food more or less accidentally. This accidental contamination is partly due to the technological evolution; what is meant by this, is the residue and metabolic waste from pesticides, and partly the metabolic waste from micro-organisms which can develop in foodstuff. The ingestion of substances which have an antinutritional effects, cause, apart from lower performance, a phenomenon linked with acute toxicity: hemorragies and death, or a phenomen of chronic toxicity: alternation in tissues, abnormalities of the vital organs, such as the liver and kidneys.
a) EXTRINSIC ANTINUTRITIONAL EFFECTS:
- Heavey metals
- pesticide residue
- Mycotoxins
Heavy metals
The risk of contamination of raw materials and of ready made foodstuff, caused by heavy metals must not be neglected above all, if the high contamination of the area is taken into accounts, which for some, lead especially, can cause great damage. It is widely known that the average levels of lead has greatly increased, and unfortunatly, it can be confirmed that in industrial contries, plants or areas having a “natural” level of lead are inexistant. Amongst the heavy metals which can be of risk to fish, let us state. apart from lead, arsenic, cadmium and copper.
Selenium, when in high concentrations can also have a toxic effect. It is difficult to say precisely the specific effect of each metal. They have without doubt, specific consequences on the immunity system and on the liver and kidney tissues.
As for arsenic, found in trout, doses of 7,5 mg/100g of dry matter over a period of 12 months, cause hepatomes. (7) Followings ingestion or contact with certain doses of arsenic, alternation in the gills and kidneys may be noticed.
The ingestion of hexavalent chrome has a direct consequence on the intestine.
The consequences of copper excess are: congestion of the gills, hyper excitability, an acute reaction to the infectious effect of Gram + bacteria; a 1 mg/g dose of the dry matter in the food diet causes a delay in the normal pigmentation of the trout.
Pesticides
A lot has been written on this subject, which should be taken into account. It seems advisable to recall that with pesticides, as with other toxic substances a remarkable noxious effect on young animals is noticed. The abnormalities remarked, lead from the simple loss of appetite to nervous disorders and sterility, etc…
Mycotoxin
Mycotoxins are metabolites, produced by lung uses. The toxic substances of mycelion origin, differing from those of bacterial or vegetables origin, do not give rise to the production of antibodies and consequently immunity. They have various effects on the organisms of animals (neurotoxic, nephrotoxic, hepatotoxic, hemotoxic, dermotoxic, enterotoxic, oseteotoxic, and immuno-suppression). There are more than one hundred mycotoxins, and syndromes of unknown etiology can be attributed to them.
Those studied concerning fish are aflatoxins. By this term is meant a group of metabolites, produced byAspergillus flavus and Aspergillus parasiticus stocks, during their growth on the foodstuff. Followings research work carried out in the states, foodstuffs containing more often aflatoxins are: corn cotton grains, flour extracted from cotton, peanut flour, rice, soya beans, etc…
The tonic effect that aflatoxin B1 has on trout was given special attention. JACKSON (1963) (8) showed the hepatocancrogenic effect of aflatoxin B1, given out in doses of 0,1 to 0,5 pp over a time laps of 4 to 6 months. Acute effects: hemorragies and hepatic necrosis are remarked within 3 to 10 days, when 0,5 mg/kg of body weight is given. Aspergillus flavus develops quite easily in pea nut and cotton grain flour (especially when these foodstuffs are stored in depots of holds of ships).
b) INTRISTIC ANTINUTRITIONAL FACTORS
Following their chemical make-up, the antinutritional factors of intrinsic origin can reduce the digestibility of proteins and of polysaccharides specifically or not inhibit the digestive enzymes, necessary for the decomposition of the macromolecules and or inferior to the absorption processes level of nutritive substances.
Tannins
There are aromatic substances of phenolic type. They are found concentrated in the external layers of certain cereal caryopsises (sorghum, barley). Consumption of food rich in tannin causes the reduction of the body growth and the use of proteinic nitrogen. The effect is caused by the capacity that tannin has, of linking itself in a non-specific way to proteins, by forming resistant complexes to the protease actions of the digestive system. They can have a cancrogenic effect: HALVER (9) Shows that doses of 7,5 mg/100 g of dry matter in the food diet causes hepatic histological alternations which bring about an hepatic tumer.
Phytic acid
or inositol hexaphosphoric acid and its salts
Phytates are widespread in cereals and can make up 35 to 97% of the phosphoric content, which in this form, can not be assimilated either by animal or man. Phytates play an antinutritional part, as they can interfere with the absorption of certain mettalic ions such as calcium, iron, magnesium, zinc, in forming insoluble complexes which are evacuated in the excrements. They can also link themselves with proteins as shown by SPINELLI J (1983) (10).Without trout fry, fed diets which have a 0,5% phytic acid level, a reduction of 66% in the digestion of proteins was remarked, together with decreases of around 10% in growth and the inconsumption ratio of the feed.
Lectins
Also known as hemoagglutins or phytoagglutins: These are macromolecules, which, depending on the type, agglutinate different types of isolated cells. Studies carried out on leguminous lectins have proven the capacity that these substances have of interfering in the absorption of nutritive substances, followings the interaction with the epithelial cells of the intestinal mucous membrane.
Resorchinols
By this term is meant, the different alchilic by-products of resorcinol, containing uneven numbers of 15 to 23 carbon atoms in the alchilic chains. These components, partially thermolable are found present in variable quantities in rye, wheat and tritical. It was found present in variable resorchinols play a possible antinutritional role, and have been stated as responsible for the loss in appetite and the decrease in growth, remarked in numerous animal species when given diets which have a high rye content.
Gossipole
The cotton grain meal contains a variable 0,03 to 0,2% of gossipole: phenolic type pigment, responsible for the toxic phenomenon remarked in monogastric animals. This pigment apart from being directly toxic, can link itself to lysine and consequently decreases the possibility of using proteins. It has been remarked that trout show a toxicity phenomenon caused by gossipole: anorexia and ciroide fluid in the liver.
Amylasic inhibitors
In wheat, barley and rye, are found great quantities of proteinic molecules, capable of inhibiting the amylasis (enzymes responsible for the destruction of the polysaccharides of the food diet). In wheat caryopsis, the amylastic inhibitors make up about 2/3 of the albumin content and around 1% of the proteinic content of wheat meal.
They are found in the endosperm of the caryopsis. From a nutritional point of view, the characteristics resistance of these inhibitors to thermic treatment and to the trypsine effects is interesting; these properties probably depends on the remarkable capacity of the proteinic molecule stabilized by the numerous dissulphuric bridges.
Research carried out on chickens, fed diets enriched in antiamylasic factors of wheat proved in the decrease of growth and the hypertrophy of the pancreas.
The amylasis activity of trout and the reports with the antiamylastic factors of cereals, is being investigated at present at my research institute within the frame of the finalized programmes of the C.N.R. (Centre National de Recherches).
Proteasic inhibitors
The most commonly known, are those of soya. It can be said that they are found in all leguminous, even if in variable amounts. Raw soya meal contains 1,4% of the KUNITZ trypsic inhibitor and 0,6% of the BOWMAN-BIRK chymotrypic inhibitor: the former is thermolable, the second (great inhibitor of chymotrysin) is relatively thermostable. They cause the hypertrophy of the pancreas and a decrease in the growth rate, probably as there is a second deficiency in essential amino-acids (sulphurated amino-acids especially) caused by the hypersecretion of the pancreatic enzymes.
Saponins
These are complex glycoxydes of triterperiod alcohols, found in soya at a rate of 0,5% about of the dry matter. By their polarity, they are insoluable in dissolvents. Such as hexane and consequently they remain present in soya extract. Saponins cause the bitter taste found in soya and have a hemolitic activity. In normal conditions they are not absorbed at intestinal level, while they are hydrolised by the bacterial enzymes in the sacrum and colon.
Glucosinolates
They are chemically made up of glycoxydes which have sulphur atoms in their molecules. They are generally found in the parenchymal tissue of crucifer grains. They have a concentration of around 4 to 10% in whole grains. From the hydrolysis of glucosinolates, made up by the enzymes known as mirosinasis, present in the grains, toxic compounds can be liberated. The mirosinasis enzymes is also synthetized by part of the bacteria which can live in the symbiosis of the subjects intestine. Industrial treatment adopted in the preparation of the colza meal can destroy this enzyme.
Cruda Fibre
Naturally found in foodstuff, it can mean in the case of fish and especially carnivorous fish a factor of antinutritional action, as it is hardly destroyed at all, due to the reduced dimensions of the digestive tube and feeble action of the cellulosolitic microflora there present, it reacts as an inert material, raises the transit speed of the food and reduces the possibility of using the other components found in the food. Otherwise it can have direct physical effect on the absorption of the digestive enzymes.
LIPIDES
By the term lipides (commonly known as fats) is meant the numerous substances, of different chemical nature characterized by common properties, among which is found their insolubility in water, their solubility in organic solvents and their presence in the molecules of radical fatty acids.
Lipides have different important functions:
The structural components of the membrane
The reserve and depositing substance
The components of the cellular surface which play a part in the determination of the immunity of the tissues.
and last but not least, some of them have essential biological activities.
From a biological point of view, lipides can be subdivided into two groups: depositing lipides and cellular lipieds. The depositing lipides are found in the differenciated cells, also known as fatty cells (adipocytes); they are a reserve material (they decrease during fasting) or they have a protective function. The cellular lipides extract themselves with more difficulty from cells (as they are often linked to proteins) and they do not diminish greatly during fasting.
Lipides comprise of the following: triglycerides, phospholipides, sfingomyelins, sterols and waxes.
Fats are the most important source of energy. The energetic reserve, furnished by lipides permit the fish in their natural environment, to answer the needs during certain physiological moments -fasting-reproduction and migration.
Before speaking of fats from a nutritional points of view, one of the most important roles that they play for fish must be remarked: phospholipides of cellular membranes, are responsible for the cellular exchanges and of the flexibility of the membranes, depending on the temperature and the pressure of the water.
To estimate the food value of lipides in the diet, certain factors must be taken into consideration :
digestibility
The presence of substances
Oxidizing level
Essential fatty acid content
Maximum level tolerated by the animal in question
The digestibility of fats by fish is greatly connected to the fusion point of the fat itself and consequently to the degree of saturation. The insaturable fatty acids are more easily digested than saturated ones (NOSE, 1966) (1)
Experiments carried out with salmonidae, fed diet containing saturated fats showed clearly, how these are the cause of what is known as the ciroid degeneration of the liver, which was pointed out by GHITTINO (32). The formation of the ciroide in the liver is a complex phenomenon and has multiple effects.
Fish species are capable of digesting high quantities in the diets (20 to30 % of the food) as long as there are adequate quantities of choline, methionine and vitamin E. Recent research work carried out showed that the digestibility of fats is not dependent on the temperature, at least where trout is concerned. (13) Ingested lipides are hydrolyzed in the digestive system by lipases and phospholipases; the fatty acids are thus liberated and afterwards they are metabolized in the liver. At this point, different metabolic processes occur: direct oxidation in the aim of producing energy, conversion into other fatty acid (elongation phenomena or dehydrogenation of the carbon chains).
The liver of fish plays an important part for the deposit of fats, which is quite different from with what takes place with other animals. Lipide depositing in the viscera and tissues of fish are characterized by great quantities of carbon long chain fatty acids (20–22) and containing up to 6 double vonds in the chain. The greater part belongs to the linolenic group (ω3). Some differences are remarked, depending on the fish species and the environmental factors. Fresh water fish lipides contain more ω6 fatty acids when compared to marine species (ω6/ω3 is equal respectfully to 0, 37 and 0, 16 for fresh and sea water species.
Fish phospholipides are particularly rich in long chain polyunsaturated fatty acids (PUFA). These are necessary in the food diet, where they increase the food utilization. Concerning the food for trout, at juvenile stage, it should contain 1 % of (ω3) linolenic acid.
It must be remembered that marine species have a greater requirement of 3 serie. Fish have the capacity of elongating the carbon chain of fatty acids, this depending solely on the precursors presence for the ω6 and ω3 fatty acids in the food. This metabolic system seems to be modulated by the concentration of some unessential fatty acids in the diet (oleic acid for example as given by HALVER, 1975) (9).
A high percentage of polyunsaturated fatty acids in the food cause difficulties for the stbility maintenance of fats, in storage conditions; the reason for which, so as to avoid it becoming rancid, or certain vitamins being degraded and the appearence of toxic phenomena in fish, it is necessary to employ anti-oxidizing substances.
The natural antioxidant, and perhaps the most efficient, is alphatocopherol-acetate (vitamin E) which by oxidising easily, protects the lipids rate from such a risk. The integration moment of the vitamins in the food must be taken into account.
The oxidization of fats can be the cause of serious problems when feeding fish: it is a reaction which can be verified quite easily-contact with oxygen -favoured by the presence of certain substances or metal which catalyse this reaction. Along with developing toxic substances, the fact that the fats becomes rancid can reduce the use of the other components in the feed (liposoluble vitamins, proteins). The consequence of injesting oxidized food is all the more serious for trout fry as for sea-bass fry.
Recent experiments carried out by GHITTINO, CORBARI and AMERIO (14) demonstrate clearly that after a relatively short period (20 to 30 days) of feeding a rancid fats diet, sea-bass fry have ciroid fluid in the liver, showing anemia symptoms and high death rates.
It must be remarked that certain natural oils (ex, cotton oil) toxic substances can be found present, such as cycloprenoid fatty acids (sterculic, malvalic acid).
VITAMINS
The research work carried out so to define the requirements, activity mechanisms and consequence due to dificiency or excess of vitamins in the diet, dealt especially with salmonidae (15).
VITAMIN A: indispensable vitamin. A vitamin A deficiency diet brings about the delay in growth and in bone development; disorders at epithelial cell level are remarked also. Excess of vitamin A cause hypervitaminose disorders: Let us recall that the liver of fish is an organ that metabolizes and accumulates fatsoluble vitamins. Vitamin A has a positive action on growth, due to the fact perhaps that is has a protective action on the epithelial cells of the gut, and it allows a good absorption of the nutritive substances and prevents the entrance of pathogenic micro-organisms in the organism. Concerning the stalibility of vitamin A, in the ration it must be remarked that its esters (acetate-palmitate) are more stable when compared to the free from. Vitamin A is sensitive to the presence of peroxides.
VITAMIN E: belonging to the tocopherol family, the most important being α tocopherol. Tocopherols are quite stable towards heat and acids, while they oxidize very quickly in the presence of a nascent oxygen, peroxides or other oxidized products. This is the reason why they play a protective role for fats. This action is found on both the inside and outside of the cell. The vitamin E esters or more stable when compared with free forms. Vitamin E along with selenium and vitamin C, have positive effects on the reproduction of fish specie.
VITAMIN B1 (Thiamine): It was the first vitamin to be considered essential for trout. Vitamin B1 deficiency syndrome includes anorexia, neurites, poor growth, increased sensivity to infectious agents. In practice, this deficiency can be found when fish are fed fish: In the fish viscera, there is an antivitamin-thiaminase which destroys the greater part of vitamin B1 present in diet.
COLINE, INOSITOL: they are essential for the normal metabolism of the fats.
VITAMIN C (L-ascorbic acid): Ascorbic acids is readily oxidized in to dehydroascorbic acid. It acts as a biological reducing element in hydrogen transport Vitamin C is involved in different reducing mechanisms: hydroxylation of tryptophan, of tyrosine and of proline. It is necessary for the formation of hydroxy proline which is one of the main constituants of collagen; it plays a synergistic role with vitamin E as an antioxidant; it is necessary in the synthesis of folic acid and increases immunity.
Concerning trout, a requirement of 200 mg/kg of food is noticed.
When formulating a food diet, so to cover the vitamin requirements correctly, without taking into account the specific needs, the real avaibility of the vitamin factors in foodstuff, the presence of anti-vitamin factors must be taken into consideration.
It is also very important to know the vitamin stability present in the food. This is a current and very important problem not only for the particularities of scientific character but also practical. Most vitamins have very feeble molecules which are easily changed in their structure with a consequent loss of certain physical, chemical and biological properties. The main factors effecting the stability of vitamins are as following :
Humidity -A great loss in vitamins was noticed in a sample having a value of moisture than 8–10 %. Concerning certain vitamins such as vitamin K3, C and B1, humidity can destroy them while increasing the catalytic activity of certain oligo-elements (Fe, Cu, I). In other cases, such as vitamin A, humidity can damage the protective layer and consequently increase their vulnerability to noxious agents.
Temperature: Activity losses of vitamins are found proportional to the temperature (increasing with temperatures of 18 to 40 ° C).
Other factors: Incompatibility existing between the different vitamins, E.G. vitamin C and B1, between choline and some components of B group vitamins; type of support ( losses are greater with a mineral support or a vegetable by-product support, such as grape skin).
Following recent research carried carried out by Prof. MARCHETTI (1980) (16) in Italy, from a total of 400 samples, it was found that the greater losses concerned vitamin K3 (70 % of that declared), vitamin B1 and vitamin C (50 %).
BIBLIOGRAPHY
1) KLONTZ G.W. - Esperienze e nuove acquisizioni nell'allevamento ittico intensivo - Acquacoltura 82 - Verona, 16 ottobre 1982
2) BARBUJANI F. - Convegno sui problemi dell'Acquicoltura in Italia - Chioggia Sottomarina, 9–11 maggio 1983
3) LUQUET P. (1975) - La Pisciculture française - 442 (11a) II trimestre
4) THOMAS - Citato da BORGIOLI E. in nutrizione a Alimentation degli animali domestici - Edagricole 1972
5) COWEY C.B. (1978) in Finfish Nutrition and Fishfeed Technology - Ed. da Halwer/Tiew vol.1, pag. 3–14
6) ARNOULD R. - in Proteins et acides amines en nutrition humaine et animale Ed. De Vyst A. 1972)
7) ASHLEY L.M. in Fish Nutrition - Ed. Halver - Academic Press.(1972)
8) JACKSON (1963) citato da Ashley L.M. in Fish Nutrition - Ed.Halver-Academic Press. (1972)
9) HALVER J.E. - Proc. 8th Int. Cong Nutr. Prague - CZECHOSLAVAKIA 1969
10) SPINELLI J. (1983) - Aquaculture 30, 71–83
11) NOSE T. (1966) EIFAC Fourth Sess. , Belgrade, DOC 66/sc II–7
12) GHITTINO P. (1970) - Ittiopatologia, Vol. II - Edagricole
13) AUSTRENG E. (1980) - Aquaculture 19, 93–95
14) GHITTINO L. (1984) - Riv. Ita. Piscic. Ittiop. 19 (3), 95–114
15) PHILLIPS A.M. Jr e BROCKWAY D.R. (1957) - Prog. Fish Cult. , 19 (3), 119–123
16) MARCHETTI M. (1980) - Techn. Molit., 31 (3)
