Fish Farm
Introduction
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:
- 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).
- Structures employed to carry water, made up of straight artificial canals,
and from winding natural canals.
- 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.
- 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.
- 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 ecosystemic 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.
Fauna
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.
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. 
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.
Flora
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.
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.
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