Abstract in English:
In intensive fish farming use of electric engines is indispensabile to allow
oxigenation, feeding, water circulation and ponds cleaning.
These practices are necessary for a good growth of fishes.
Many of these operations are practiced into the water while the fishes are present.
As fishes are susceptible to sound that can be interpreted as alarm signals and
generate panic and stress.
As the engine, when used into the water or in contact with it, hourly make a sound in
a wide frequency range.
As the fishes, by acoustic sensors on the side of the body, detect pressure variations
caused by engine sounds, in this relation are given the first result of a sampling
carried on a fish farm in Italy.
By using a specific instrumentation contituted by an high sensitivity transducer for
absolute siund measurements over the frequency range 0,1 to 180 kHz (model B&K
8103), and a 6 channels data logger (model B&K 3032A pulse system), sound levels
have been measured under different farming conditions.
The transducer have been positioned in the pond at 0,6 m from water surface.
The sound levels have been measured in presence of three oxigenation devices and
without them.
The values have been processed by frequency analisys in the range 1 to 16 kHz.
Variations have been underlined in higher frequency in the first type of oxigenation
device and matching up to 1 kHz in the second type.
The results are also examined in order to evaluate the lower sound levels in the
estimated range of fishes hearing.
Therefore this system allows to know the best adaptability of the equipments to fish
farming. |