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 requirement; 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 (RAVAGNAM, 1978).

I.2. Classification of extensive rearing

Extensive rearings cover the most varied technical aspects which are more or loss 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 rearing 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

Valliculture 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 cur case means the manmade enclosures of water beds which are used for fishculture and they are marked as “valli” in the Vanitian 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 road, rush or net fencings. These were precarious installations incapable, in any case, of ensuring the independent 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 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:

Along with these species mentioned here above other species can be reared in valliculture such as those given here following:

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:

1. 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);

2. to capture the fry at sea and place them into the rearing ponds;

3. to activate the artificial reproduction process, employing more or complex technics.

The “rise” was the only seeding method employed in valliculture long age; 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.

The survival rate of fry; when examined at commercial size, is around a minimum of 10 – 20% and a maximum of 30 – 50%, depending on the species reared and the rearing technics employed. “Valli” having great amounts of D. labrax present, see the production return drop.

The seeding of eel was only started in the Venitian “Valli” (apart from some exceptions), in the late fifties. The amount of elvers coming from the sea generally sufficed for the standard production of each modal of “valle” employed (sandy or clay), judged in an optimal manner of the “quantity-size” relation and varying on average from 30 to 60 Kg/Ha/year.

From 1957 onwards, the Argulus giordanii, crustacean ectoparasites of the Branchiuri group, infested at first, the VENICE lagoon “valli” and afterwards all the “valli” in the region. These destroyed a great amount of the production and so upset all equilibrium which would have permitted a constant and rich production return. From this on, is spite of the persistant presence of Argulus, extra seed of elvers were added, especially “ragani” which are young eel having a body weight of between 15 and 30 gr. The results are not up to expectation and the productions dropped to a third or half of what they were. There are no major difficulties in finding eel seed, especially concerning elvers.

Seeding of the “valli” is normally carried out during the months of March, April and May and sometimes in the Autumn months (October – November) for A. anguilla and M. cephalus.

The fry known as “novellame” are placed at first first into small ponds (a few hectares of surface area) and afterwards they are set free into big ponds known as the “laghi di valle”.

Fattening

The weight increase of the population in the “valle” depends solely on the feed resources found in the rearing ponds, which is the biogenic capacity of the environment. By biogenic capacity is meant, the capacity of the environment to transform into a product of commercial interest a more or less important part of its own natural productivity.

In general, the breeder does not intervene directly to increase the natural productivity, but restricts himself to ensuring that there is a good exchange of water. There is no need for a continuous water renewal, in the “valle” but an adequate quantity and punctual intervention is required. In other words, a flow of a sufficient quantity of water, at the appropriate time, in a given phase and circumstance.

The hydrous management of the “valle” concerns the defence and enrichment interventions (the conservation and improvement of the ecological effectiveness of the ponds) and the coordination of the rearing operations (seeding, fattening, harvesting, etc…) In can be calculated that three complete water renewals of the “valle” are required for one year; one at the beginning of Spring, one during the fattening season, and one at the end of Autumn or the beginning of Winter which corresponds to the harvesting phase.

Harvesting

If the seeding of the “valli” is obtained by the “rise” which is the tendancy that certain fish have of coming into the lagoons or “valli” from the sea, in the search of feed, the harvesting of fish is obtained when these populations return to the sea. urged by the instinct to reproduce or by the thermic conditions. With the exception of A. anguilla the whole population, although sexually and commercially immature, tend to swim back into the sea every year, as they flee above all the low winter temperature of the ponds.

A. anguilla on the contrary can resist to cold, and only heads towards the sea when its sexual maturity puts and end to its trophic period.

Therefore, this fish stays in the “pasture” areas from when it enters into the “valle” at elver stage to the age of eight or twelve years, depending on whether it's male or female.

The harvesting is performed by the double action of draining (which is a great decrease of the water level inside the “valle”) and of “refilling” which is the introduction into the “valle” of a hotter and nearly always more saltly flow of water. Therefore by exploiting the rheotactism of the fish as well as the difference of temperature and salinity, the movement of the fish towards the harvesting ponds is obtained. a well designed “valle” will have the possibility of directing all fish towards one harvesting pond. A “valle” can have many ponds spread out or having a very particular structure.

The harvesting pond is located directly behind the control structure for communication with the outside and it must be deep enough to enable a depth of 150 m of water when the ponds must be linked up with the fattening zones by a system of sub lagoonals canals, which have a slightly sloped bottom. So that at the harvesting period the fish are either pushed by the draining action and guided by the refelling action.

On the inside and edges of the harvesting ponds are found many important structures. The principal ones, being the structure for the introduction and that for the capture. The former is located at the intersection point between the “pasture” ponds and the harvesting ponds, this is a dam, having many openings equipped with sluice gates and devices which enable the directing of the fish into the pond; the latter is a dam enabling the capture of the fish within the the pond itself and capable of stopping both their escape towards the sea or their return into the harvesting ponds, and also of separating eel and other fish species or selecting different size eel themselves.

At a certain distance (on the inside) from the main capture structure (which is that placed on the sea-rearing “border”) a second one is nearly always found for the capture of the product inside the harvesting pond when the current flows towards the sea and not towards the rearing ponds.

On the edges of the ponds there are structures permitting the selection of the immature fish (from a commercial point of view) directing them towards the wintering ponds, and mature fish ready for market.

Wintering the fish

In Venitian valliculture language “wintering” means, all the operations which are required to preserve the good health of the fish, by protecting it against frost and bad weather. It is not a typical phase of production but rather the defensive organization of the rearing during the Winter stasis. However, the importance that such a period has on Venitian valliculture (due to cold winters), impels us to give great consideration to this.

Wintering begins in November by the advancement or transfer of the fish into special ponds known under the name of “peschiere” and finishes at the end of March with the “opening” of the “peschiere” and the introduction of the fish into the “pasture” areas.

The difficulty of Wintering varies from species to species. The A. anguillas is the most resistant and for which n9o wintering pond is scheduled, as during Winter, it resists by plunging down deep into the bottom of the pasture ponds. The other species having in order less resistance are as following:

D labrax, M. saliens, M. cephalus, Liza ramada, Crenimugil labrosua, Liza aurata, S. auratus. This latter is put to Winter separately, into special ponds where it stays at low densities and where the temperature must be maintened at least at 6° C.

During the Winter, the fish lose more or less a lot of weight, depending on the climatic conditions of the season. In the most unfavourable conditions there can be a loss of 10% or more. The optimal temperature for wintering is that which corresponds to the metabolic equilibrium of the fish, based on the minimum requirement of energy. It varies according to the species in relation to the thermic level of the feeding stimulus.

The wintering “peschiere”, characteristic of valliculture, are composed of a series of canals of 3 to 6 meters in width and of variable lengths (from 30 to 100 meters), all connecting with one another (even if they are separable by means of sluice gates or grills) and positioned in such a way so as to give shelter to the fish from winds blowing from any direction. Between one canal and another, a more or less wide patch of elevated land is found (about 1 m above the water level) where the cultivation of evergreen plants is carried out and which serve as windbreak hedges. The sandy bottom “peschiere” having a fresh and salt water supply are the more reliable.

The canals of a “peschiere” are all the more efficient when they are deep. A depth of 4 – 5 m or more, having a width of not more than about 6 m, ensures the protection against winds, an important thermic capacity and an abundant reserve of oxygen in frost.

If the “peschiere” are located near rivers or sand hills which exert a pressure on them, there will be a slow filtration through the sand layers capable of maintaining a certain renewal and of fournishing heat to the environment. This filtration is a very efficient natural heating system.

To winter a quantity of ten tons of fish peschiera ponds of 40 000 m² in surface area must be available. A “valle” of 400 ha must ha must have at least 300 000 m² of “peschiere”.

Some years ago, the valliculturer realized that, what limited production, was the wintering capacity rather than the biogenic capacity of the “valle” environment, and devoted his technological research to making the traditional ponds more efficient and experimenting on less costly systems, which were more reliable, when put into use.

Many “peschiere” had stand-by heating installations put in, the most valued products were wintered in cement tanks which had a heating system and were sheltered and finally good results were obtained with heated sub-marine tanks.

Productive potentiality of the “valli”

The productive capacities of the Venitian “valli” reach 150 Kg/ha/year, 50 % of which are Mugilidae; 25 % of D. labrax and S. auratus and 25 % of eel.

Taking into account the climatic conditions in which the work is carried out, this level of production could be considered as quite satisfactory but it is certain that a much higher production could be obtained with Venitian valliculture.

Rearing cycles

Each species reared has its own individual growth index, in relation to which, the commercial size of the product will be defined.

For example:

S. auratus has a rearing cycle f about 18 months, it reaches commercial size from the 7 – 8 month and the optimal weight is 400 g at the end of the cycle; D. labrax requires a rearing cycle of 37 months to reach a weight of 400 – 500 g; M. cephalus and C labrosus reach their optimal weight of 800 – 1 000 g in about 53 months; L. aurata, saliens and ramada which have an inferior growth index, reach optimal weight of 300 g over a period of 21, 36 months; A. anguilla has a much longer rearing cycle, and it is only captured when it is silvery, in other words when it reaches sexual maturity. At this stage, it can vary in size, depending on it's sex and the climatic conditions found in the “valle”. In general the Venitian “valli” produce eels of weights from 200 to 600 g.

The present evolution of valliculture

For more than ten years, Venitian valliculture, so as to increase its capacity of production, has for aim to overstep the limit imposed by the natural biogenic capacity (to which the productivity of extensive rearing is linked precisely) and directed research towards techniques which would be capable of obtaining good productions in small surface areas as well as increasing the environmental productivity. Many problems were encountered and can be regrouped as following: on one hand, those concerning the adoption of artificial reproduction, intensive and semi-intensiverearing techniques of certain fish species reared, and on the other hand those concerning the adoption of feed chains, on which extensive rearing is based together with operational interventions capable of potentiating them.

From the experiments carried out on these two subjects originates the “integrate - valliculture” system, based on the penetration, from an energetic and functional point of view, between the intensive and the extensive. The structured “valli”, when this system is employed, has some intensive rearing sectors and others extensive. The former produce independantly and serve as well as first stage for the extensive. From this relation originates a production method of semi-intensive type, where estensive ponds make good use of their natural biogenic capacity and benefit from the energetic supply from the intensive sectors which are as following, semi-reared fishculture material, water current, and rearing catabolites.

2) Plan of the energy flow in an integrated valliculture system. It can be noticed that the intensive sectors are supplied with auxiliary energy and artificial feed. On the contrary, the extensive ponds have a supply of primary energy and natural feed. The subsidiary energy could help especially the extensive and building ponds by having fry caught at sea placed into them. By integrating the system a lot of energy passes from the intensive to the extensive in the form of; Hydric flow, fish and organic matter. At the bottom can be seen the productive outlets, some directly coming from the intensives others from the extensives.

Intensive rearing

All fish species reared in integrated valliculture (with the exception of Atherina boyeri and sometimes part of Anguilla anguilla), start their cycle in the intensive rearing sectors. Some stay there until they reach commercial size (D. labrax and A. anguilla) on the contrary to others (S. auratus, Mugilidae and part of A. anguilla, that stay for more or less long periods, as to complete their cycle, pass into the extensive sectors.

The structure of the intensive sectors vary from species to species, as does the rearing density which ranges from a maximum of 25 – 30 Kg/m. 2 for D. labrax to a minimum of 0,5 – 1 Kg/mé for Mugilidae.

Extensive rearing

The extensive ponds, receiving their fish from the intensive, along with the organic waste matter supply, must have many culture operations carried out principally concerning the good management of the water (by means of pumps) and the draging of the soil bottoms (carried out with the appropriate devices).

In this way, valliculture greatly reduces the duration of the rearing cycles and increases, by 300 Kg and more/Ha/year, its production potential of the extensive ponds.

Production potential of integrated valliculture

An integrated valliculture unit has the aim of obtaining the highest possible productions with a minimum input of energy coming from outside, therefore it aims at developing to a maximum the natural productivity.

The dimensions of the intensive rearing sectors are calculated, not only in relation to the commercial criterions but principally with respect to the energetic - productive benefit that the extensive sectors can take from their integration with the intensive sectors. The production potentiality of integrated valliculture, on an equilibrium basis, therefore combines that of the intensive sectors, reaching in this way remarkably high levels. Experimental facilities located in VENEZIA have shown that it is possible to obtain productions of around 1 000 Kg/Ha/year, 60 – 70 % of which coming from the intensive sectors and 30 – 40 % from the extensives.

Experience ha shown the benefit of multiplying the production lines, by operating in the extensive ponds rational polyculture, so that the available trophic structure may be used to the full.

Consequently, great importance must be given to the choice of species to be reared, to the size relation between the different fish populations, to the period and method concerning their introduction into the environment, to the succession of types of culture and operational interventions linked with increasing the production speeds.

It is rightly affirmed that the lower the trophic level to which an organism is introduced the higher the energetic return of the production process will be However it must be remarked that certain fish or shellfish species, even when placed at a quite higher trophic level (3° or 4°) feed of small benthonic or planktonic organisms which are not directly of interest in the humain diet if not introduced into a certain level of the feed chain. In other words, energy is spared, avoiding, this way, a decrease in the production speed.

3.) Concerning this plan, the fundamental trophic circuits and the principal productive “outlets” of integrated valliculture system can be remarked

Here also can be noticed how the intensive rearing sectors give a supply of energy into the natural circuits, in the form of organic matter.

4.) The waste matter circuits in an integrated valliculture system are underlined here. The plan represents a complete system from artificial reproduction stage to the finished product.

The waste matter is an integral part of the productive system. A well managed complex should and could give out through the outlet less nutrients than it receives from the outer ecosystem flow.

The practice possibilities of the Venitian “valliculture” model.

There where traditional valliculture is found or can be carried out (in other words extensive fishculture), integrated valliculture can also take place. This is perhaps, applicable for all the Mediterranean region, and can be applied for the lagoons, estuaries, ponds, marshes or coastal zones which are liable to inundation and gives satisfactory results when the climatic conditions are suitable.

Principal problems linked with development programmes

To conclude, let us point out the principal difficulties linked with valliculture development and therefore sea and brackish water fishculture.

Although not being pessimistic, we believe that a serious programme must be based on a realistic view of the real possibilities together with the difficulties which are none the less important.

Let us not take into consideration those problems arising with the training of personnel, the commercialization of the products, the financing of the different initiatives, etc…, not because we consider them of less importance but we think that the first to be considered must be the following:

1. fry collection,

2. ecological defence

3. allotment of regions

a) Fry collection

To seed with marine fish species, fishing at sea is still employed (apart from some species to some degree) which favours the rearing in zones which have an abundant production of fry (Meridional Mediterranean zones) and encourages the breeders working in less favourable zones (Northern Mediterranean zones) to fish new material further away and to transport them to their facilities. As salt and brackish water fishculture only employs marine reproduction species, the continuation and development of this activity are linked inevitably to the corresponding availability of fry.

This is the reason why it is necessary to apply suited capture, transport and rearing technologies, to ensure the best possible use of the actual resources (which already offers the possibility of tripling on average the survival rates and therefore the productivity potential) and to supply, at industrial level, artificial reproduction techniques.

One wonders whether the capture of fry at sea has not the effect of weakening the general productive resources. Normally, the reply can be but reasuring if the poor survival rates in marine environments are taken into consideration. In practice, the more fry transported from the sea into rearing the more satisfactory the results, from a production point of view. The questions arising, when this method is employed are, in our opinion, as following:

1. How many fry can the sea furnish?

2. What can be done to maintain (and if possible increase) this valuable potential?

It is difficult to give an answer to the first, without carrying out minute investigations and covering a very vast geographical zone. For the present, we can not have recourse to the very approximative estimations which can however deduce that the present commercial production of Mediterranean rearing facilities come from a few hundred million of fry and that the quantity of available fry could be doubled by developing for this purpose the lagoonal and estuary zones which are neither used for fishing nor rearing.

In answer to the second question, it must be remarked that the capture of nearly all the fry born at sea would perhaps bring about eventually a decrease in the number of “free” breed stock (a greater decrease as the rearings become more sophisticated) and eventually a scarcity of fry. It appears that this aspect should be carefully examined, in taking into consideration that it could prove perhaps helpful, not to stop altogether the capture of fry, but to give back a certain number of mature breeders into the sea.

However, the fact that only artificial reproduction can ensure the development of coastal fishculture must be kept in mind; This alone indeed permits the control of the reproduction cycle without which fishculture could never be an independant and complete bioculture.

b) Ecological defence and allotment of regions

The ecological defence of the region (in this case the coasts, the sea, water beds, lagoons, estuaries, rivers, etc…) is essential not only for the promotion of new fishculture enterprises but also to ensure they very survival of the enterprises already existing.

There are still numerous and vast zones, in good ecological condition, available, but it cannot be denied that many others are no longer in god condition and that others are more or less in danger.

Normally, fishculture is not incompatible with other activities; on the contrary, there are some of industrial type, with which it can fully harmonize; it can also benefit from their presence sometimes when it uses warm affluents.

However, it would be absured to believe that there would be neither damage nor conflict if it is not decided that in certain zones to make fishculture the more privileged activity in relation to all others.