Most of the research and development concerned with feeds and fish nutrition in Greece is being carried out at the NCMR in Athens in collaboration with government hatcheries and fishfarms.
The Centre has been involved in fish nutrition activities since 1975 with the initial aim of producing practical diets for rainbow trout. Some six or seven people are at present involved, and work is now being extended into investigations on the nutritional requirements of other (marine) species of fish. Nutrition research at the NCMR is thus now concentrated largely on rainbow trout, sea bream, sea bass and grey mullet. The research can be divided into the following areas:
Investigation into the use of indigenous plant protein sources in fish feeds. Under present study is carob seed germ meal; SCP (single cell protein) produced from a carob extract substrate; sunflower meal; cotton seed meal and poultry by-products.
Investigations into the effects of different sources and amounts of essential fatty acids (EFA) in the diets on the growth and performance of fish. For trout both sources and dietary levels have been examined but for marine species the investigations have been concentrated on the effects of dietary levels and on the effects of fat oxidation.
The application of methods of food analysis to fish feed ingredients, for example, crude constituent analysis and evaluation of anti-growth factors.
The application of biochemical and histological techniques to the assessment of fish growth performance under differing nutritional regimes.
Investigations into food attractants and of the selectivity of food by fish. Studies are being made into the physiology of food satiation and of food deprivation. Acclimation of feeding patterns.
No industrial (private company) research and development investigations into fish feeds could be identified as taking place in Greece. However, the animal feed factory ELVIZ (Plati Imathias) has a good quality control laboratory that could, if routine commitments allowed, be involved in fish feed research and development.
University research into fish feed technology and nutrition is restricted to individual interests and is not of an applied nature.
There are several forms of fish feed: moist pellets, steam treated or extruded dry pellets and natural materials either of plant or animal origin. Animal material, for example, ground liver or raw fish, is sometimes fed directly as “wet” feed to fish. Plant material, for example, rice bran or macerated plant leaves, is often provided as a “supplementary” feed in extensive or semi-intensive fish farming.
In Greece, at present, rainbow trout, carp and eel are farmed as freshwater species; while sea bream, sea bass and mullet are farmed as marine species.
The type of feed best suited for rainbow trout farmed intensively is, without doubt, a pelleted feed. This is commercially produced in Greece and is also imported. Nutritional requirements for this fish are well known and feed standards and formulations are established in order to provide diets with suitable amounts of protein, fats, vitamins and minerals. Numerous research reports, feed manufacturers' data and a recent FAO report give details of trout pellet formulations (New, 1987) 1. Various diets can be formulated to meet specific production requirements but such feeds are not being produced in Greece at present.
1 New, M.B. 1987 Feed and feeding of fish and shrimp. Rome, FAO, ADCP/REP/87/26, 275 p.
The feeding of eels is described by project consultant, Dr Shigeru Arai in his report on eel farming in Greece 1. Eels will grow satisfactorily on either moist food presented as a “dough” or as pelleted feed. The protein feed for eel culture in Greece is at present imported from Italy. Feed cost is currently Dr 135/kg. There appear to be no reliable figures for the food conversion of cultured eels in Greece. In 1986, 776 t of eels were produced.
Very few carp are farmed in Greece, circa 100 t/year. A further 300–400 t/year are captured from extensive water sources.
For intensive and semi-intensive carp farming, dry pelleted feed is well accepted. A diet containing a slightly lower level of protein to that contained in rainbow trout diets is generally given to carp. Literature on a number of practical diets for carp has been published, and animal feed manufacturers in northern Europe produce diets specially formulated as carp feeds2. The pellets forming carp diets can be of a very simple composition. Pellets can be made solely from fish meal, sorghum meal and wheat meal or from fish meal, wheat, soybean meal and oil. Such diets give satisfactory growth.
A carp pellet is being produced in Greece at the present time (ELVIZ). The yield from the extensive or semi-intensive carp rearing waters can often be improved by fertilization or the feeding of a supplementary feed such as rich bran or other vegetable waste.
A pelleted feed imported from France or Italy is at present being fed to sea bream cultured in Greece. The most satisfactory diet contains approximately 55% protein and 12% lipid. The commercial diet approximates to these requirements. However, fresh fish is also being fed to cultured sea bream. As explained later this practice is not to be encouraged for intensive culture of fish.
At present the two largest marine fish farms in Greece use either a moist pellet made from an equal mixture of dry commercial pellets and “trash” fish (often sea bream with deformed vertebral columns) or fresh fish and squid. It is claimed that the feeding of dry food to broodstock fish prior to their breeding results in poor egg quality. A dry pellet with high protein and lipid levels should be developed as a suitable food for marine broodstock fish.
1 Arai, S. 1987 Eel culture in Greece. Rome, FAO, FI:DP/GRE/85/002/1, 10 p.
2 See, for example: Muir, J.F. and R.J. Roberts. 1982 Recent advances in aquaculture London, Groom Helm, Vol. 1, 453 p.
The same comments apply as for sea bream.
This fish (or rather a number of genera and species belonging to the family Mugilidae) is reared extensively in polyculture in lagoons without supplementary feeding. Mullet can, however, be cultivated intensively and cage culture of mullet is practised in at least one farm in Greece. It is difficult to say what is the “best type” of feed suited for farmed mullet. This depends on the method of farming.
The protein requirement of young grey mullet (Mugil capito) has been shown to be about 24% protein for maximum growth at 23°C. This relatively low figure should make this species attractive for culture.
There is general agreement that for the species of mullet intensively farmed in Greece the “best suited” and one that is appropriate for growth is a pelleted feed. The constraints for this method of feeding lie in feed technology and production techniques and not necessarily in the fact that mullet is not such a high priced fish as sea bream.
There is only one animal feed mill in Greece that is currently producing food for fish. This company, ELVIZ, S.A. (Hellenic Feedstuff Industries, Plati Imathias) produces some 2 500 t/year of fish feed compared to 7 000–10 000 t/year imported from Italy and France (Trouvit; Aqualim). The Project Document (GRE/85/002) reports an intensive farmed fish production of approximately 3 250 t/year. Information from the project marketing consultant, John Arrundale, gives an intensive farmed fish output of approximately 3 000 t/year. This would give a food conversion ratio (FCR) of approximately 3:1 which is high for trout but may be more in line with that attained with some marine fish.
The ELVIZ plant can produce 160 000 t/year animal feed while another company plant at Ioannina should be capable of producing 50 000 t/year by the end of 1987. The plant at Plati consists of two steam pelleting mills and two new extrusion pelleters (the extruders are only just coming on line). The plant appears to have good technical management and has a new quality process control laboratory which is very well equipped.
According to the technical management, 500 t of pelleted fish food can be produced in 24 hours and there is capacity to produce at least 10 000–12 000 t/year of fish feed.
The technical staff of ELVIZ and the nutrition group at NCMR are collaborating in order to improve formulation and processing of fish diets.
It was reported to the feed consultant and to the national counterpart that a committee of the Ministry of Agriculture had recently produced a report on fish feed production. The committee had suggested that 30 000 t/year fish food output should be viable as a production unit and that a 2 500 t/year pilot plant (possibly using an existing plant) should be used, for fish feed production. It is regrettable that the technical manager of the only company in Greece producing fish feed, and the only one involved in improving the technology of fish pellet production, should not have been a member of, or co-opted onto this committee.
As has happened throughout Europe, when fish feed production reaches a certain capacity its manufacture is hived off from the parent animal feed mill which originally produced the feed and an independent plant established. Greece is not yet ready for this move although it is hoped that this will happen in the future. For the present there should be concentration on improving the technology of the already existing infrastructure. For example, extrusion pellets have not yet been produced at ELVIZ (the plant being very new). This should be done using a standard trout feed formulation. Trials should also be made with post-pelleting fat spraying and with improved grinding and milling of raw ingredients. The use of binders should be investigated, preferably of local origin. All these issues, however, are technological and it should be possible to solve them within the next year or so.
A visit was made to a new feed mill at Ioannina, where the technical management were equally as cooperative as ELVIZ at Plati. The management at both mills appear to be willing to use their extruders or steam pelleters for pilot runs. The minimum pilot batch run for ELVIZ, Plati, is 2 t, while ELVIZ, Ioannina, state that they would be prepared to consider trial batch production of fish feeds of 600 kg. However, at present, no post pelleting fat sprayer is available. One should be purchased so that production could begin. This approach along with laboratory scale feed investigations (NCMR and the National Hatchery of Louros) should be followed in order that dry pellets of constant quality might be produced. It is suggested that a fish feed technologist might be appointed in order to liaise between ELVIZ and NCMR.
Dry pelleted foods are being made by the two largest trout farmers in Greece. Discussions were held with both farmers and a visit was made to Ammos Voidomati, Konitsa. This farm and its feed mill were of high standard. Good pellets were being produced (although expensive) with an output of 3 t/h. The other farmer has a pelleting capacity greater than his requirements. Both farms indicate the technological efficiency in trout feed production of which Greece is now capable.
Greece, as previously mentioned, has few indigenous plants which have a high and available protein content to make them suitable as fish meal replacers in fish diets. Perhaps such products as tomato seed meal or carob germ seed meal might be considered, provided that the toxins contained could be removed. Also animal by-products as protein sources are not abundant. However, Greece does have a source of fish meal substitution in the form of waste or “trash” fish. Greece is surrounded by water in which myriads of small fish grow. It is estimated that more than half of the catch in Greek waters is composed of small and “trash” fish.
The fish that are caught in larger quantities and have a low commercial value are sardines. In a study made in 1983 by Tsimenides the production potential of sardines for 1984 was estimated at 5 000 t/year. It was, however, recognized that this is a low estimate on the amounts of fish reaching various parts of Greece and did not include fish thrown back into the sea. It is a common practice that Greek fishermen discard fish which will not bring a high price on the market.
The following table contains data provided by ETANAL (Organization for the Development of Fisheries) which refer to the quantities of “sardines” (more than one species) sold in auction halls of Greece during 1985 and 1986 together with amounts not sold.
QUANTITIES OF SARDINES PASSING THROUGH THE AUCTION HALLS OF KAVALLA, THESSALONIKI AND PATRAS DATA FOR 1985 AND 1986 COMBINED
|Total (t)||1 116||1 456||728|
At this point, the possibility of feeding raw fish direct to the cultured fish should be examined. This is done in Greece at the moment and small amounts of fresh fish are fed both to trout and to marine farmed species. However, if fish culture is to develop in Greece it is strongly recommended that the practice of feeding raw fish be generally discontinued. Although there is no reason why raw fish should not be fed when farm conditions are hygienic, such conditions are not always easily obtained on fish farms and the risk of infection and the introduction of putrefaction toxins becomes great. Therefore, in the hope of developing a healthy fish-farming industry in Greece, raw fish feeding should be discouraged. Also the presence of the enzyme thiaminase in fish that are fed raw to other animals can result in vitamin B deficiency and thiaminase activity has been reported in a wide range of fish species, both marine and freshwater.
Methods of silage production, either by acid preservation or by fermentation have been known since the 1920s. For some 10 years or more, in Denmark and Norway the acid preservation method of producing silage for use as an animal feedstuff has been carried out. Trash fish or fish waste is macerated and the pH reduced through the addition of acid to enhance the activity of the naturally present enzymes in the material to accelerate digestion and liquefaction. Further, the lowered pH inhibits bacterial degradation controlling putrefaction and the associated odours of decomposition. Silage may also be achieved by controlled bacterial fermentation. Fish silage produced by the addition of external acids has received most attention with regard to its use in fish diets. Various acids, both inorganic and organic, have been used. Rainbow trout have been successfully fed on silage produced using hydrochloric acid, and the technology for producing such feeds for salmonids is well developed. However, further development of such feeds may be required for marine farmed fish where palatability can play an important role in feed acceptability. There may be tryptophan loss and susceptibility to lipid oxidation in silage products but these undesirable changes may be met by addition of tryptophan-rich protein or antioxidants to the silage before use.
Silage produced by lactic acid bacterial fermentation is a method of protein hydrolyis which may be particularly suited for use in Greece. The substrate needed for good lactic acid bacteria growth, molasses, is available in Greece and the temperature for efficient fermentation is likely to be achieved. Preliminary feeding trials indicate that fermented silages are nutritionally equivalent to fish meal.
Therefore, it is suggested that, as part of the Greek National Plan for Aquaculture, a study be made of the use of silage as a fish feed particularly in the more isolated marine fish farms.
The problems experienced with finfish farming are the same in Greece as those experienced throughout the world. The situation was summed up by the advisers of the Agricultural Bank of Greece (which has a considerable influence on the development of aquaculture in Greece), who said, “it's all a question of small fish (fry) and expensive foods”.
The problems in the feeding of “grow-on” post-larval fish appear technologically soluble (this does not mean that no research is required on, for example, palatability of feeds and improved formulation). However, the feeding and rearing of young marine fish is still beset with difficulties after many years of investigation in many countries. Marine hatcheries will be reported on by other consultants to this project (Berg/Cittolin), but the major problem faced is a nutritional one, namely the acceptance and utilization of preferred food.
While not wanting to expand on this matter in detail, it would seem important to encourage the development of a “broad brush stroke” approach which is being adopted by the Leros Aquaculture Group. Here the larval feeding of a number of commercially exploitable marine fish is being examined. In addition to the commercial rearing of sea bream (Sparus auratus) and sea bass (Dicentrarchus labrax), other species such as: Dentex dentex (synagrida), Puntazzo puntazzo (hioma) Spondyliosoma cantharus (scathari) and Diplodus sargus (sargo) are being examined. (It would be useful to see well controlled data on the comparative growth rates of the post-larval stage of these species of fish when fed compounded diets.) The responses of the larvae of these fish (behavioural, mortality, etc.) are being examined in relation to the presentation of various natural and processed food. This work is being carried out by a commercial enterprise but should be encouraged.
There is a need to develop a collaborative research programme on larval nutrition and feeding. This should include an input from not only “live food” experts but also nutritionists and behaviourists skilled in the presentation of artificial food to live organisms. Also, any national development plan for aquaculture must contain provisions for the instruction of fishfarming staff in marine hatchery techniques.
The new experimental hatchery which is being built for the Institute of Marine Science in the University of Crete (EKEK) should play a major part in the development of hatchery techniques for Greece.
As mentioned previously, the amount of feed required for growing fish in Greece is at present approximately 10 000–12 000 t/year. Most of this is pelleted feed of which 70% is imported and 30% produced locally.
Fresh animal by-products have been used in the past (together with pelleted feed) for the rearing of fish. This practice has been forbidden by law due to the health hazards it presents. However, fresh fish is still used to some extent in the feeding of the broodstock of marine fish.
Unlike terrestrial animals, fish require diets with a high content of protein for good growth (more than 35%). This creates certain limitations concerning the number of raw materials that can be used as protein supplying fish feed ingredients. Table 2 lists raw materials suited to fish feed production available in Greece, either produced locally or imported.
|Plant Materials||Quantities available (t)||Price (Dr/kg)|
|Wheat middlings||300 000||17|
|Cotton seed meal||180 000||20|
|Soybean meal||145 000||36|
|Sunflower seed meal||30 000||16.5|
|Seed oil cake meal||3 000||18|
|Carob seed germ meal||2 000||18|
|Corn glyten feed||1 200|
|Fish meal 1||50 000||86|
|Meat and bone meal||-||45|
|Skim milk||5 000||60|
|Dried brewers' grain||7 500||12|
1 Totally Imported
Exchange: US$ 1.00 = Dr 132 (August 1987)
Table 2 does not attempt to give a complete list of all the raw materials used in animal feeds; nor does it give information on carbohydrate sources or fats and oils. Rather it is intended to show protein sources suitable for fish feed production, and their availability and cost.
Fish meal is used in compounded fish diets at levels ranging from 20 to 50% whereas other materials are generally included up to levels of about 25% depending on the type of diet. As the present total fish feed requirement is about 10 000 t/year, it would appear that there are enough protein sources in Greece, with the exception of fish meal, to supply the raw material for present needs. Fish meal availability is, therefore, the main constraint on the production of a totally home-produced fish feed.
There are, however, certain problems concerning the quality of protein sources for feed that are produced in Greece. Poultry by-product meal, for instance, differs widely in composition. For example, one manufacturer produces a meal with a lipid content of 20% and a crude protein content of 40% while another produces a meal with a 15% lipid content and a protein content of 60%.
Quantities of some produced protein sources for fish feeds vary in their availability. Feather meal produced in Greece is mostly used directly by the poultry producers and it can only be incorporated into fish feeds when there is a surplus. Imports must be made to meet this situation. Commercial production of fish feeds demands a constant supply of raw feed materials both in quantity and quality.
Recent research in Greece has shown that carob seed germ meal may be incorporated into trout diets at levels up to 40%. Satisfactory growth was obtained in larger fish.
Carob seed germ meal can contain up to 40% crude protein (4–5% oil).
Another plant protein available in Greece is tomato seed oil cake meal. This contains about 30% crude protein and 1–2% oil.
Problems encountered with the introduction of new plant protein material into fish feeds are those of amino-acid composition and the likelihood of the presence of toxic materials in the plant. There may also be a problem of palatability. Nevertheless, if price and availability are favourable then such sources should be exploited. It is possible to remove toxic constituents by simple leaching or steam extraction techniques.
Although Greece has few sources of protein suitable for fish feeds, it has a more than adequate supply of linseed oil. This can be used to increase the oil content of trout diets to about 14%, as a high fat content is beneficial for trout growth. Linseed oil has a high content of linolenic acid, which is an indispensable fatty acid for rainbow trout. Fish oil (another source of EFA) is not available in Greece. Thus, this local product will find an important place in Greek fish feed production.
Feed cost as well as quality, which is measured by feed conversion ratios (kg of fish fed/kg of fish produced) has a large contribution to the operational cost of an aquaculture unit and/or selling price of fish, the magnitude of which depends on the species of fish reared.
The costs of imported pelleted complete fish feeds for intensive aquaculture vary considerably. For example, feed for the on-growing of sea bream and sea bass ranges from Dr 106 to 183/kg while that for trout from Dr 95 to 148/kg. Eel food is bought at about Dr 135/kg and carp pellets Dr 85/kg. Food for young fry is much more expensive, ranging from Dr 221 to 420/kg.
The cost of Greek produced dry pellets is much cheaper: trout Dr 60/kg; carp Dr 55 (?)/kg.
Food conversion ratios also vary considerably. For example, a private company gives their best food conversion for sea bream as 2:3 while another “state” company gives ratios of between 2 and 4. However, for trout the food conversion ratios are more stable, the value generally being given as 1:8. For carp feed conversion, ratios of about 1.4–1.6 have been reported by a unit rearing them intensively, while there are no reliable data for eel or for the limited intensive rearing of mullets.
The contribution of feed to the operational cost of a unit producing either rainbow trout or marine fish (sea bass/sea bream) is given as an example, as follows:
|Operational Cost of a Unit Producing Rainbow Trout|
|Dr/kg of fish produced||% of Total Cost|
|Other costs (fry, salaries management, etc.)||38.6||14|
|Operational Cost of a Unit Producing Marine Fish|
|Value of fry||276||23|
|Repayment charges and loans||216||18|
|Total Cost||1 118|
Rainbow trout is produced mainly in small units operated by members of a family. The production of such units amounts to 35/year. Rainbow trout is sold, at best, for Dr 320/kg. Under such conditions the annual income of a trout producer (and his family) is about Dr 1.5 million, an amount which is quite low and prevents him from making new investments and a better marketing of his product. The contribution of feed to the total operational cost is about 64% and to the selling price about 54%.
A reduction of feed cost by about 20% by the production of cheaper feed based on locally available materials would almost double the farmer's income allowing expansion of trout production.
The feed cost for rearing marine fish is, in absolute values, higher than that of rainbow trout (both feed conversion and feed value are higher). The percentage contribution to the total operational cost is, however, much lower (one third of the final value) since the value of the fry in this case is high amounting to about one quarter of the total cost.
Sea bream is sold by the farmer at Dr 1 600–2 000/kg while sea bass is sold at Dr 1 300/kg. This makes an average profit of about Dr 200/kg, which, for a unit producing an equal amount of fish to that of rainbow trout units, would allow a calculation of an annual profit of 10 times as much. Feed costs are not, therefore, in the case of these marine fish, of paramount importance as they are for rainbow trout farming. Feed quality is perhaps more important for marine fish in order to guarantee fast-growing fish free from diseases.
Nutritional requirements of marine fish are not adequately known and diets used for them are based mainly on formulas developed for salmonids. The growth potential of these fish might, therefore, be even higher than that exhibited by the use of diets commonly available on the market if diets meeting possible specific requirements of these fish were in use. This is a matter for further research and development, to be carried out by countries interested in the cultivation of these species.
There is at present limited carp production (one farm for intensive and one for semi-intensive rearing). Carp is sold by the farmer at Dr 250–300/kg. Feed costs are only slightly lower than those for trout, and growth time lengthened due to a considerable reduction of growth during winter months. The economics for intensive production of carp in cages are, therefore, expected to be worse than those of rainbow trout. The contribution of feed cost to the semi-intensive rearing of carp is not known. Carp is imported from other countries at lower prices than that produced locally. Production of low valued pellets for carp would help in the expansion of its production to meet current requirements at competitive prices.
Eel is mostly exported and is sold at about Dr 600/kg. There is only one farm for intensive eel rearing, which produces very little so that production is needed for the expansion of its farming, as suggested also by the specialist in eel farming.
Mullets are reared mainly extensively. Their value ranges from Dr 400 to 900/kg depending on their size. Supplementary feeding can however be considered as a possible means for increasing their production in the near future.
Assuming a 7 000 t import of pelleted food and a 2 500 t Greek output and a costing of Dr 125/kg, then the total food bill for intensively farmed fish in Greece is approximately Dr 1 200 million. This amount would increase as amounts of fish produced intensively or semi-intensively increase. A pellet mill working as a sub-unit of a larger factory could cover current requirements, a larger independent unit being constructed when larger amounts of feed are required.