Fish Farm

  • Introduction
  • How a fish farm works
  • Fish farm structures
  • Fish farm activities
  • Fish farm ecosystem value

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    The Italian name valli da pesca (fish farms) derives from Latin vallum, which means barrier or protection. A fish farm is a lagoon area, separated from the open lagoon by a fixed fence nowadays made up of barriers and stakes in which lagoon fish breeding, a kind of extensive fish farming is practised.
    This system needs big sheets of water, so that the production is sufficient to cover the running expenses, even if the yield for land measure is low.
    The documents from 11th century on witness that the fish farms belonged to few noble families and to the Benedictine monasteries who usually granted annual contracts of hire which could be renewed to the same lessee for many years. In the fish farm contracts of hire that the Venetian government used to draw up some articles were included in which the duty to care about the building of barriers and ditches as protection of the fish farms and in general of defensive works of the lagoon environment was assigned to the lessee. The costs that the fish farmers had to bear for the works and the improvements had to be refunded by the Doge's administration. Within the fish farms the breeding of animals and hunting were practised and both these activities represented a large supply of food that allowed food self-sufficiency in case of need.
    In the Venetian lagoon their total development covers an area of about 92 square km which represents 1/6 of the lagoon area: there are smaller fish farms which cover an area of just few dozen hectares, and others which are up to 1500 hectares large (from Cavazzoni S., "La laguna: origine ed evoluzione" and Zanetti M., "La valle da pesca lagunare: caratteri strutturali e funzionali" in "La laguna di Venezia").
    They are situated in the most inland part of the Northern and Southern lagoons, in the lagoon edge area (see the map salt marshes and fish farms) in the website of the Environmental Database, in the section images).
    The fact of being separated from the lagoon by fixed fences saves them from the ebb and flow of the tide: the setting of fixed floodgates in the fish farms was due to the need to save the fish farm environment from the variability of the lagoon environment, above all as far as the pollution caused from the industrial areas and from the chemical fertilisers employed in the countryside is concerned.
    The fish farm is a partially artificial area, created with productive purposes, but that keeps elevated levels of natural features, contributing to the protection of the lagoon environment. Moreover, it represents an important place for the nest-building of a lot of birds. (from Torricelli P., Bon M., Mizzan L., Aspetti naturalistici della laguna e laguna come risorsa, Parte Prima: Aspetti naturalistici della laguna).

    How a fish farm works

    The fishes in the Upper Adriatic reproduce in the sea, in the area of the tegnue, where a great deal of gorges protects them from the streams and from any possible predator (See the rock outcrop card).
    During their youth stage, on the other hand, they move to the inland part of the lagoon, because there they can find food and there are no predators. It's just the custom of the fishes to move to the inland part that is exploited by the fish farmers who catch the fishes during the phase called montata “swimming up” and prevent them from going out of the fish farm barring the entrance. The only fish that is bred in the fish farm and that doesn't reproduce in the Adriatic Sea is the eel, whose area of reproduction is situated in the Mexican Gulf.
    While the fishes go down to the sea every year during wintertime, (the "smontada", that is to say “the swimming down to the sea”), once the eels have entered the lagoon, they remain there, deep in the mud of the bottom of the lagoon for a few years until they reach their sexual maturity: then, they migrate towards the sea to reproduce. According to some scholars, the fish farms probably existed in the lagoon even before the foundation of the city of Venice. This practice has been led for sure since the Middle Ages, when the embankments were mobile and made up of reed hurdles (grisole): this technique allowed to catch the fingerlings, while currently, due to the fixed embankments set after the fall of the Serenissima (the Republic had always prevented the building of fixed embankments because one of its principles was to eliminate any obstacle to the free expansion of the tidal wave) and to the variability in the quantity of fish that runs up naturally, the introduction of the fingerlings must be artificially made (from Cavazzoni S., "La laguna: origine ed evoluzione", in "La laguna di Venezia").
    Laws concerning the fish farms have been issued right since 1314, and in 1719, in order to delimit the area subject to these ordinances and to other laws issued by the Magistrato alle Acque, 100 boundary stones were put to fix the lagoon boundary. The fish farms belonged to rich families who didn't care nor were interested at all in the breeding of fish but who mainly cared about the hunting resources that could be found there. At the beginning the fish farms were of two kinds:
    · Seragia fish farms: the level of water within the fish farm depends on the level of the external water, because the fish farm is surrounded by a continuous structure made up of stakes, grisole and poles tied up together by some wicker;

    ·Embankment fish farms: the level of the internal water is made independent from the external one by fixed ground embankments, openings (chiaviche), floodgates governed by the fish farmer.

    The banking process of the fish farms started between the19th and 20th century following some researches and observations performed by scholars as Giustiniano Bullo, who created a surrounding canal and applied it to his own fish farm called Pierimpié. Afterwards, in the middle of the 20th century, the Italian government provided incentives for the embankment of the fish farms.
    The catching of the fingerlings from the open lagoon environment is carried out by "pescenovellanti" (fingerlings fishermen); at the end of the 19th century this profession was one of the most important fishing activities for Burano’s, Caorle’s, Cortellazzo’s, Pellestrina’s and Chioggia’s fishermen; it took place from the second half of March until the first half of June and was very profitable (from A. Granzotto, P. Franzoi., A. Longo, F. Pranovi, P. Torricelli, La pesca nella laguna di Venezia: un percorso di sostenibilità nel recupero delle tradizioni. Lo stato dell’arte). Since ancient times the fishermen in Comacchio fish farm have started a process of fixed banking with steady embankments of all their lagoon area and specialized in the eel breeding.

    Fish farm structures

    The main structures in the fish farm are:

    Openings (chiaviche)Structures that allow the communication between the lagoon environment and the lagoon on one hand, and between the fish farm and the rivers on the other: openings (chiaviche), made up of mobile floodgates supported by hand governed masonry frames, form them. Their use allows to measure out the optimum degree of salinity for the bred fish species and to perform the change of water.
    There are a few structures of this kind spread along the whole fish farm, and they are mainly used to link the different internal sheets of water, while the main one, which connects the fish farm to the lagoon, is situated near the "cason di pesca" (a house where the fish farmers still nowadays live).

    2.     Structures employed to carry water, made up of straight artificial canals, and from winding natural canals.


    3.     Structures employed to catch the fish: they are called "lavorieri"; they belong to very large sheets of water, which are connected directly to the main opening "chiavica". In the lavorieri the fishes in the fish farm get trapped during a particular phase of their breeding cycle. The lavorieri are closed by the "cogolere", made up of two vertical reed hurdle structures that form an acute angle.

    4.    Structures for the fish farming: they are called "pescherie di sverno", sheets of water where the fishes introduced at the beginning of the spring that haven’t reached the right size to be put on the market are kept during the winter.

    It usually takes two or three years for most of the fishes in the fish farm to reach the right size to be put on the market, while the necessary length of time for the growth of the eels is about eight years.
    To protect these sheets of water from the cold wind during wintertime tamarix hedges (Tamarix gallica) used to be planted along their boundary. They represented an excellent habitat for the purple herons (Ardea purpurea) too. Currently, synthetic nets are employed.
    The pescherie di sverno are deep, so that the water on the bottom can keep warm and the fishes can take shelter there in wintertime.
    In the fish farms where there is fresh water too, a layer of fresh water flows on the surface of the pescherie di sverno that, afterwards, during wintertime, freezes and isolates the other underlying layers from the cold.

    5.     Structures for accommodation: the "cason di pesca" is the operation and managing centre of the fish farm; it usually shows a 19th century style and it is employed as accommodation for the staff who lives there for some time during the year. The tool storehouses, the refrigerators, and the main cavana, where the boats are kept, are located beside the cason .
    The buildings are located on rising grounds ("motta") never flooded by the tide and built by men hoarding inert material.

    Fish farm activities

    The annual activity of the fish farms starts at the beginning of spring.
    Initially, the fingerlings are put into the sheets of water of the fish farms. Most of the fingerlings are produced within the structure, some other is caught in the sea ("pesca del pesse novelo"), while just little of it reaches the fish farm running up naturally.
    At first the fingerlings are put into the seragio del pesse novelo, a section separated from the rest of the fish farm, where the fish is kept at least for two months so that it can acclimatize to the conditions of the fish farm. In the seragi it is very important that a level of salinity and of oxygenation suitable to the surviving and to the growing up of the fingerlings are kept. Once the fishes have reached a sufficient size, they are put into the proper fish farm through some openings (chiaviche).
    From this moment until the beginning of the autumn the fishes stay within the chiaviche operated by the staff of the fish farm.
    Then, at the end of the autumn, the fishes are led towards the lavorieri, situated near the sea: they are put into the fish farm through the cold water openings (chiaviche), which makes the fishes head towards the sea, where the temperature of the water is higher and when, in wintertime, the reproduction takes place.
    The fishes caught in the lavorieri are selected and those that have reached a sufficient size are sent to the fish markets, while those of smaller dimensions are led or put into the pescherie di sverno, (winter fish pond) within which they will spend winter.
    In these structures the temperature, the dissolved oxygen and the salinity must be constantly checked not to compromise the vital conditions of the fishes.

    Sometimes in the fish farms hunting activities take place too, and in the fish farms where this activity is practised it is possible to find some typical structures: the botti da caccia. (from: Zanetti M., “La valle da pesca lagunare: caratteri strutturali e funzionali” in “La laguna di Venezia”).

    Fish farm ecosystem value

    The importance of the fish farms in the lagoon ecosystem was already clear to the Serenissima, which in 1624 in order to save the fish farms from public use and to preserve their functionalities, declared that they belonged to those who performed the fishing activities.
    In the fish farms the embankments show the typical vegetation of the salt marshes halophilic environments, and the biodiversity is high, even if it is quantitively modified compared to the original, thanks to the richness of the trophic chains largely corresponding to the lagoon original ones, which represent the basis for the bred fish species.

    In these areas not only do the Anatidae and other waterfowls that come to the lagoon to spend winter from Northern Europe find the optimum environment for the nest-building, wintering and their food supplying, but also other birds that permanently live in the lagoon, small mammals, and reptiles.Gilthead seabreams (Sparus aurata)
    In the fish farms the eels (Anguilla anguilla), the grey mullets (Mugil cephalus), the European seabasses (Dicentrarchus labrax), the gilthead seabreams (Sparus aurata) are bred. All these species can tolerate big variations in the salinity (euryhaline).
    The fish farm offers ideal conditions to the nest-building of a lot of birds, most of all in the beds of reed of the soft water environments.
    Nest-building species as the mallard (Anas platyrhynchos), the marsh harrier (Circus aeruginosa), the common moorhen (Gallinula chloropus), the common coot (Fulica atra), the snowy plover (Charadrius alexandrinus), the common tern (Sterna hirundo), the penduline tit (Remiz pendulinus), the purple heron (Ardea purpurea), the common redshank (Tringa totanus), the black crowded night heron (Nycticorax nictycorax) can be found.
    Great crested grebe (Podiceps cristatus)

    Other species only pass during wintertime as the great crested grebe and the eared grebe (Podiceps cristatus and P. nigricollis), the great white (Egretta alba), and several species of Anatidae.
    Besides the fishes and the birds, small mammals as the harvest mouse (Micromys minutus), the water shrew (Neomys fodiens), the polecat (Mustela putorius), the stone marten (Martes foina) the European water vole (Arvicola terrestris), the weasel (Mustela nivalis), the hedge hog (Erinaceus europaeus) can be found in the fish farms.
    The dark green snake (Coluber viridiflavus), the grass green snake, the tessellated grass snake (Natrix natrix and N. tessellata) make their appearance too.


    The fish farm vegetation rising out of the water is typical of the salt marshes (the Sea lavender, the Glasswort and the Puccinellia), even if with different dominances and associations. While in the salt marshes the evolution of the vegetation stops because of some limiting conditions as the salinity, in the fish farms the ground is more suitable to a progress of the sequence towards the beds of reed.
    The associations that can be more usually found in the salt marshes within the fish farms are: Sea lavander- Puccinellietum palustris, characterized by Puccinellia festuciformis, Limonium serotinum and Juncus maritimus (in the less halophilic environments); and the Puccinellio –festuciformis –Arthrocnemum fruticosi, which includes the Sarcocornia fruticosa, on very salted and dry grounds during summertime.Sarcocornia fruticosa

    The under water vegetation is mainly made up of two vegetation associations of phanerogamae that form a precious food source for the anatidae: the Zostera noltii association, which develops in the brackish areas with a good water change, and the Ruppia maritima association which is present in the areas of less salinity and of more stability.
    In the soft water areas there are beds of reed represented by the Phragmites australis graminaceous plant, which can bear the presence of salt, even if in low concentration. Where there is only soft water it is possible to find the Typha, most of all the Typha latifolia. (From Sburlino G., “La vegetazione delle valli da pesca della provincia di Venezia”, in AA. VV., “Le valli da pesca del comprensorio veneziano dal Tagliamento al Brenta”).
    The importance of the fish farms lies in the fact that such environment has substituted, in its function of ecological niche, the strip of the marshes and of the swamps that once could be found in the lagoon edge area. The total closure of the fish farm embankments has deprived the lagoon of the advantages deriving from this substitution.
    Among the fish farms that are still active in the Northern lagoon the Val Dogà which, with its 1685 hectares, is the largest, Grassabò, Dragojesolo, Cavallino, Lio Maggiore, Liona, Perini can be mentioned.
    In the Southern lagoon the fish farms Serraglia, Averto (partially employed as a WWF oasis), Contarina, Zappa, Figheri, Pierimpié, Morosina, Millecampi. (from Rallo G., “Guida alla natura nella laguna di Venezia- Itinerari, storia, e informazioni naturalistiche”).

    A discussion is currently on about the opportunity to reopen the fish farms to the expansion of the tide.