PROJET REGIONAL MEDITERRANEEN DE DEVELOPPEMENT DE L'AQUACULTURE MEDITERRANEAN REGIONAL AQUACULTURE PROJECT TECHNICS USED FOR INTENSIVE REARING AND ALIMENTATION OF FISH AND SHELLFISH Villanova di Motta di Livenza - ITALIA - Vol. II COASTAL FISHCULTURE IN THE UPPER ADRIATIC Mr G. RAVAGNAN I. INTRODUCTION Coastal fishculture in the Upper Adriatic means especially "Venitian Valliculture" and before treating specifically this form of fishculture, I think it advisable to expose some fundamental considerations at first, which enhance this form among other aquaculture systems or indicate the reasons of its present technical orientations. I. 1. Rearing methods In general, the practice of fishculture is grouped into three fundamental methods: extensive, intensive and semi-intensive. These methods differ from one another by the different energetic derivation of their feed diet and, on this presumption, a rearing is counted as extensive when the ambiant environment provides the total feed requirements; intensive when, on the contrary, the feed requirements come entirely from outside; semi-intensive when, the environment along with feed from outside is employed to cover the feed requirements (RAVAGNAN, 1978). I.2. Classification of extensive rearings Extensive rearings cover the most varied technical aspects which are more or less perfected, depending on the socio-economical context where they are found. They can be briefly classified as following: – "Primordial" extensive rearings which differ from the simple water level fishing by the presence of facilities which are not very numerous, primitive and often precarious. – "Structured" extensive rearings fitted with the static and rational. facilities. – "Equipped" extensive rearings which are not only "structured" but are also furnished with the facilities and equipment which give them a good functional feature. I.3. Form of energy Every aquaculture system is always designed to transform a certain quantity of energy into a useful product for man and concerning the different production methods directly connected with aquaculture, three forms of energy employed can be remarked: – "Primary" energy is incident solar radiation; – "Subsidiary" energy is that part of the eco-system (as in rearing) obtained from the adjacent eco-system (tides, winds, temperatures, nutritive salts, etc... ); – "Auxiliary" energy is derived from circuits which are activated by man. 2. VALLICULTURE Vailiculture is a typical example of brackish water extensive fishculture, and therefore carried out in coastal, lagoonal or estuary zones. In the VENICE region, since the beginning of the 16th century, it has not been a primordial or approximative production activity but a well advanced and highly organized one. It originated from lagoonal fishing along with the capacity of observation by the operators of long ago. It derives its name from the latin word "vallim". which means defense, protection, enclosure, and which in our case means the man-made enclosures of water beds which are used for fishculture and they are marked as "valli" in the Venitian documents of the beginning of the 14th century (See BULLO, 1940). 3. THE "VALLE" 3.1. Structures and characteristics The "valle" is a portion of the aquatic eco-system, located on the coast and isolated by man for the practice of fishculture. Long ago "valli" were surrounded by reed, rush or net fencings. These were precarious installations incapable, in any case, of ensuring the independant management of the waters or a satisfactory biological control of the enclosures. Later on, the fencing structures employed were dykes or embankments, water tight structures ensuring complete isolation, to which devices, allowing communication with the outside, were attached. Man proceeded with his work, guided by nature at the beginning, in limiting himself to capturing the natural seed without altering the characteristics of the places, later on, by hindering the movement of the fish and finally, by inventing a satellite eco-system, capable of optimizing its own ecological efficiency, as well as obtaining energy supplies from the basic eco-system. Apart from the enclosure structure and controlled communication devices, a "valle" is equipped with a sea water and fresh water supply (the latter when possible) filter dams, crawls, (colaùri) fishing and selection tanks (lavorieri), Wintering tanks (peschiere), fertilizing systems, and different pumping devices. The surface area of a "valle" can range from tens to thousands of hectares. In the VENICE region, the average size reaches around 300 to 400 hectares, the minimum surface area is 10 to 20 Ha and maximum 1 600 Ha. In this region there is an overall surface area of 18 000 hectares divided up into 47 "valli", nearly all of them are of the "equipped" type, very few of "structured" type and none of "primordial " type. 3.1.1. Ambient conditions The type of soil generally found in the "valli" is of sandy or clayey nature. The depth of the rearing ponds is around 80 cm while for fishing or wintering ponds much greater depths can be found. The typical "valle" environment is that found on coasts or in estuaries; environments having sudden and great variations in salinity and temperature. The coastline where the Venitian "valli" lies has seven important rivers flowing into it, one of which, is the river PO; Nearly all of the "valli" have an indirect communication with the sea, via, more or less important lagoonal water beds which have a very inferior thermic capacity than that of the sea. Consequently, throughout the seasons or in coincidence with particular events, such as the swelling of rivers or sea storms, the salinity conditions are subject to variations of between 5 and 32 ‰ and the temperature is also influenced by the seasons, varying from a minimum 1 - 2° C in Winter, reaching a maximum of 30 - 32° C in Summer. With such conditions, it is very comprehensible that valliculture can only permit the rearing of euryaline and eurytherme species. Fish species generally reared in the "valli" and duration of the rearing season In the Venitian "valli" the following species are most commonly found: Dicentrarchus labrax European sea-bass Sparus aurata Gilthead sea-bream Liza aurata Golden grey mullet Crenimugil labrosus Thicklip grey mullet Mugil cephalus Flathead grey mullet Liza saliens Leaping grey mullet Liza ramada Thinlip grey mullet Anguilla anguilla Eel Atherina boyeri Atherine Along with these species mentioned here above other species can be reared in valliculture such as those given here following: Gobius ophiocephalus Snakehead goby Solea solea Sole Pleronectes flesus European flounder Only the Atherina boyeri and Gobius ophiocephalus reproduce in "valli" ponds while the other species mentioned here reproduce at sea. We have some rearing examples of fresh water species in "valli"; in particular salmo gairdneri and Acipenserides. P. labrax, S. auratus, Mugilides, A. boyeri, Gobius ophiocephalus , A. anguilla show good resistance even in the high temperatures (28 - 30° C) usually reached in the "valli" water in Summer. The minimum lethal temperatures for these species, range between 3 an 5° C (with the exception of A. anguilla which resists even at 0° C). In Winter, the temperatures in the "valli" ponds nearly always drop to 2 - 3° C and sometimes even lower. This explains the necessity of equipping for the wintering of the fish. The rearing operational temperatures range from 10 - 12° C to 28 - 30° C, optimal temperatures are 20 - 26° C. The rearing season starts in the middle of March and continues until the end of October: this covers a duration of about 7 months, with an optimal performance period of four months. Management The management of the "valle" even though entailing various operations, has three fundamental phases which are: seeding, fattening, harvesting or in other words the placing of the products into the rearing, their stay in the ponds, and their capture when they reach commercial size. Seeding Seeding can be carried out following the different methods, which are employed individually or all together. These methods consist in: a) to encourage the "rise" or in other words the migration (anadromous movement) of the young fish from the sea towards the trophic environments,such as those found in the "valli" and to hinder their "return" which is their migration backways (catadromous movement); b) to capture the fry at sea and place them into the rearing ponds; c) to activate the artificial reproduction process, employing more or less complex technics. The "rise" was the only seeding method employed in valliculture long ago; however, soon afterwards, the capture of fry in coastal zones was introduced and when means of transport and advanced techniques were available, they were caught in far off places. At the present time, many artificial reproduction facilities are employed, and it is considered that their popularization and the perfectioning of technologies are essential, not only for the development of sea fish capture but also for the survival of valliculture itself. Artificial or better controlled reproduction has been carried out for all Mugilidae for D. labrax, S. auratus, S. solea and others up to present. The only species where massive reproduction was carried out, was with D. labrax and S. auratus in commercial hatcheries. These species are the most valued, while being at the same time the most difficult to find. The quantity of fry placed into the "valle" every year varies according to surface area available, the trophic characteristics of each "valle" and the distribution of seed depending on the different species. The average amount per hectare/year can be estimated at around four to five thousand fry, 85 % of which is represented by five species of mugilidae and 15 % by S. auratus and D. labrax. The seed requirements for the Venitian valliculture can be roughly estimated at 80 million fry/year. The rate of seed distributed can vary, depending on the year or the species. This is explained by the fact that the marine resources can vary from year to year, something that the valliculture can neither schedule nor control.