For any contemplated increase of market-size trout in Greece, it is essential that fingerling production be considerably increased. The two governmental hatcheries, at Louros and Edessa, should plan a brood-stock programme. In addition they should initiate feeding experiments as the small-scale trout farmers are incapable of conducting control experiments and determining the results obtained. Such studies should evaluate the feeds available in the country, since prepared imported feeds are costly (for example, fresh dromitsa and sardines can be obtained at 4.50 Gr.Dr./kg, while Dutch feed costs 37 Gr.Dr./kg1. Technical assistance in this discipline should be requested from the University of Ioannina for the Louros hatchery, and from the University of Thessaloniki, for the Edessa hatchery. If both Universities cannot be involved it is recommended that suitable candidates receive further training or specialization in other countries.
The hatchery, with a water temperature of 13.3°C provides small trout once a year to private fish farms in the area. The brood stock is Salmo irideus, which is a well domesticated trout. This strain, however, has a very high percentage of “glassy and soft eggs”. Although such eggs are normally discarded at the hatchery, their occurrence greatly increases the work load, reduces the percentage of eyed eggs, increases fungal growth, wastes space and feed, and makes planned production goals impossible.
The only possible recommendation at present is to change the strain of trout as soon as another strain can be selected and successfully brought to maturity. In the meantime the best available green eggs should be set aside for brood stock replacement. The poorly shaped small fish and those maturing at one year of age should be discarded. The best of the two- and three-year old brood stock should become the source of egg production. Each year, the very best eggs available from the largest and most perfectly shaped brood stock should be set apart for brood replacement. None of the brood stock should be kept after three years.
Although the hatchery is provided with many raceways the water supply is inadequate, as most of the water from the nearby springs is utilized by a grain mill and other facilities. A larger supply of water should become available.
The brood stock appears to have a better quality of eggs, although the water temperature is by one degree higher (14.4°C) than at the Louros hatchery. There are over 80 fingerling raceways at the station, with an abundant water supply throughout the year. Although younger brook stock is being kept at this station, no records are available on females spawned, number of eggs per female, number of non-viable eggs, egg loss, percentage of green to eyed egg, to suggest replacement at the Louros hatchery by these brood stocks.
As characteristics in trout strains change through the years, every effort should be made to have the strain improved. To achieve this goal, selection of the most desirable specimens and preservation of their progeny during rearing until they become ready as the new generation of brood stock is required. Every effort should be made to eliminate those fingerlings which mature at one year, as they downgrade the quality and market value.
For an upgrading brood stock programme the water temperature is an important parameter. Every attempt should be made to correlate the water temperature where the new strain will be held with the temperature the brood stock had originated. The commonly accepted water temperature range for brood stock is 5.5°C to 14°C. In selecting a strain of brood fish for the Louros hatchery careful attention should be paid to the temperature the new strain has been accustomed to. The Voidomatis Spring, when checked in late November 1973 had a temperature of 9°C, and is reported to be about 11°C in the summer. These temperatures are preferred over those of Louros and Edessa for brood fish holding and egg development. The Naousa Spring, with a water temperature of 12°C is only partially used. It is considered as the best site for production, which could also include a brood stock programme in the Edessa area.
There is a limit or carrying capacity to every rearing, holding pond or raceway. The water quality, temperature and volume of the water, water rate exchange, the water surface area in relation to the volume, cleanliness of the rearing pond bottom, size, age, number of trout and species, plus the type of feed and feeding frequency all influence the biological ceiling. One of the best single checks to establish the raceways' holding capacity is the dissolved oxygen content at the lower end and near the bottom. When after feeding or during the warmest part of the day the dissolved oxygen content is down to 5 ppm, the trout holding capacity of the raceway has been reached.
The existing rainbow trout diseases (protozoan, bacterial, fungal and viral) in northwestern Greece have been recently reported by Carlson (FAO/UN, 1973). As viral diseases do not respond to chemical or drug treatment suspected fish should be destroyed by burying in quicklime or burning, and the raceways thoroughly sterilized prior to receiving new supplies of fish. In such cases it is suggested the Governmental hatcheries replace the stock destroyed.
During the present survey trout suspected of being infected by a viral disease were observed at two new fish farms near Kerassovon. Although the disease is not endemic to the area the possibility of its reoccurrence cannot be excluded. To avoid future epizootics it is recommended the Government establishes a policy with regard to the control of live egg and fish from one private farm to another and their importation to Greece. Governmental approval for transport of live egg and live fish would be based on information given by producers, as given in Appendix 1. The information provided will assist the Government or the authorities concerned in future planning with regard to the requirements of the trout industry, and also to follow more closely those fish farms which have frequently disease problems. The isolation and elimination of diseased fish in such farms would thus be facilitated.
Knowledge of the nutrient requirements of trout has steadily improved during the past few years and it is now possible to formulate high quality feeds which will meet the physiological requirements and at the same time enable the achievement of maximum returns. The moist or dry fish feeds developed in industry, contain the essential nutrients (protein, carbohydrate, fat, minerals and ballast matter) in optimal combination. Although a plentiful supply of protein increases the rate of growth, excess protein does not necessarily lead to better results. A low grade feed might contain 28–35 percent protein, and a high grade feed 45–50 percent. In practice, great variations are to be found in the protein content of trout feeds. In areas where there is a cheap and abundant supply of fish or meat, trout diets may contain as much as 60 percent protein. The tendency, however, is to decrease the protein levels as low as 20 percent.
The Greek artificial trout feed is not very good, while the diet consisting of freshwater fish and sardines with poultry wastes and dry feed may cause nutritional problems. The commonest cause of dietary trouble in rainbow trout is the utilization of cheap food lacking essential amino acids.
Imported trout feeds are available in the country, but in relation to the Greek feeds they are expensive. As already indicated, assistance should be provided by the Universities of Ioannina and Thessaloniki for programmed feeding experiments aimed to select the most economical feed ingredients available in the country, and which also demonstrate good growth rates.
A variety of devices has been developed for the artificial incubation of salmonid eggs; these range from troughs with longitudinal flow to the “California” battery system. Hatchery troughs have three principal uses: to hold eggs for shipping and hatching; to hold the prefeeding dry (yolk-sac stage) until the swim-up stage, and to feed the swim-up fry until stripped or ponded outside. These three life phases are contrasting, but not necessarily conflicting and can be carried out in the same trough with proper design and planning. Few private fish farms have this capacity and the two Government stations have obsolete hatchery troughs.
For any alterations or re-arranging the hatchery installations a number of biological factors should be considered. Direct sunlight kills fish eggs. Numerous compartments with upwelling water are necessary to hold developing fish eggs. Pre-feeding fry have a negative phototropic response. The best time to syphon crippled or abnormal larval fish is just before they reach the swim-up stage. To accomplish this a fairly long trough and water flow sufficient to separate the weak from the strong fry is essential. Natural lighting at the outlet or lower end of the trough will assist separation as it encourages fry to work up to the head of the trough. The trough should be of convenient weight for feeding and other necessary day-to-day activities. The California standard hatchery trough has been widely copied (see Leitritz, 1959, p.66).
The Louros and Edessa hatcheries could be improved to handle a higher number of eggs and fry with one row of the California type trough instead of the two rows of tank troughs presently used. The capacity of the hatchery pipes on one side of the building should be also increased to supply each trough with 54 litres of water per minute, and the windows on this side should be darkened. The floor drains need to be enlarged with a larger gutter, and a supply of baffle plate screens and baskets are also required.
A recommended task is the routine grading of fish from the hatchery troughs before being transferred to outdoor tanks or raceways, as the fish in any raceway should be as near as possible to uniform size. The common size to transfer fish to outside raceways is about one gramme.
The outdoor fingerling or under-yearling raceways at both Governmental hatcheries are functionally good. The Edessa raceways, however, have many crosswalks, which are not only expensive to construct but also hamper the cleaning process. The walks also interfere with the feeding procedure. If the concrete raceway walks are constructed without reinforced steel the top supports (crosswalks) are necessary; they should be, however, as narrow as possible.
A crowding screen or rocks to confine fish to a restricted area for grading or spawning is widely used in the United States of America. They are slightly longer than the width of a raceway and are wedged between the walls when put into use.
No brood fish raceways were seen. Broodstock was being held in fingerling raceways. Large fish hold better in wider raceways with a higher water rate flow.
The production of marketable trout for the Epirus area is at present too large for prime demand, and the crop is too seasonal. It should not be overlooked that trout production in the country does not benefit from proper diets, regular grading and frequent feeding schedules. Improved diets and improved trout cultural routines will increase growth rates in less time. Two crops in one year will reduce the size of the trout and prolong the marketing period. When three spawning periods have been achieved at the fish farms, continous marketing of trout might be feasible.
Both Governmental stations appeared to be understaffed resulting in some inefficiency in carrying out normal operations. With a sufficient number of technically trained men considerably more can be accomplished than merely trout production. The accumulation of data on the acceptability of different types of locally available feed ingredients would assist in an accelerated trout production programme.
