It is widely recognised that fish welfare and stress are inextricably linked. When welfare is compromised and fish are under stressful conditions there are a wide range of negative effects that have been reported. These include a reduction in feed intake, growth, food conversion efficiency and flesh quality; an increase in disease susceptibility and aggression; disruption of the reproductive axis and ultimately, in extreme cases mortality.

1. July | August 2012
Noise a source of stress for farmed fish
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The International magazine for the aquaculture feed industry

2. FEATURE
Noise
a source of stress for farmed fish
By Rogelio Sierra Flores1 2, Andrew Davie1, Tim Atack2 and Herve Migaud1, Institute of
Aquaculture, University of Stirling, UK and Ardtoe Marine Laboratory, UK
I
t is widely recognised that fish welfare involves a series of complex terms but essen- or tissues and specialised cells distributed
and stress are inextricably linked. When tially sound is energy traveling as a mechanical throughout the animal body, giving the fish the
welfare is compromised and fish are wave caused by changes in the medium pres- ability to sense and discriminate sounds based
under stressful conditions there are a sure. Detection of those variations is known on their direction, distance and source.
wide range of negative effects that have been as the audible sound and its loudness depends Fish auditory thresholds are believed to
reported. These include a reduction in feed on the specific sensitivity to the frequencies. be primarily in the range of 20 to 3,000 Hz.
intake, growth, food conversion efficiency The colloquial term ‘sound volume’ often con- However sensitivity does clearly vary with
and flesh quality; an increase in disease sus- founds the definitions of sound pressure and species (Figure 1) and stage of development.
ceptibility and aggression; disruption of the sound intensity: sound intensity is the rate of Reports have indicated that some fish species
reproductive axis and ultimately, in extreme flow of energy through an area (W/m²), while could even detect very low frequencies in the
cases mortality. sound pressure is the ‘strength’ of the sound infrasound range (<20 Hz) as well as possibly
wave (Pa). Sound pressure levels (SPL) are in the ultrasound range (>20 kHz) although
Research has focused on numerous differ- the logarithmic expression in the relative scale this may depend on sound levels fish are
ent potential stressors including environmental decibel (dB) of the root mean square (RMS) exposed to. Whether fish perception of these
factors such as light, temperature and water compared to a reference value. Thus, to sound frequencies is functional hearing or an
quality as well as physical stressors like crowd- quantify anthropogenic sounds in the culture artefact of past auditory requirements needs
ing, handling and transportation. However, the environment, we use the SPL of a given noise further clarification.
potential for sound to act as a stressor has over the background reference.
been largely overlooked in aquaculture. ‘Grunts’ and ‘clicks’
Sound perception Fish do not only passively perceive
The importance of sound Aquatic animals are provided with a wide sounds generated in their environment, they
Sound plays an important role in the life range of sensory organs and systems to can also be vocally active as shown in many
of terrestrial and aquatic animals as a means perceive and filter relevant environmental species. The swim bladder has an audi-
of communication as well as its role in echo- tory accessory function reflecting sound and
signals. The capability of fish to cast and
location, predator avoidance, or even just the recognise sound is well documented for amplifying their communications. Some fish
perception of changes in the environment. also use this ‘sound box’ to generate vocali-
some species, showing significant variability
As such it deserves greater attention than among them. sations for a variety of potential reasons
it has received so far as a parameter to be including maintenance of contact, warning
In general, sound perception in fish is
monitored/managed in culture settings. localised to three interconnected systems: of predators, aggression or mate choice.
It must be acknowledged that air and water Atlantic cod (Gadus morhua) is a particularly
the auditory, the equilibrium and the lateral
are two completely different acoustic environ- line. They involve a series of complex organs vocal species which produces sounds during
ments. With water being a aggression, chasing, escaping
thousand times denser than but mainly during courtship.
air, a greater energy input Cod vocalisations are
is required to initiate sound named ‘grunts’ and ‘clicks’
propagation which results based on the human percep-
in sound underwater hav- tion of the sound. The ‘grunts’
ing a greater velocity with are produced by repeatedly
less attenuation. In practical contracting the drum muscle
terms this means that great- sending vibrations to the swim
er energy is required to cast bladder. One grunt is a repeti-
a noise underwater although tion of single pulses of 60 to
water is less restrictive to a 200 ms in frequencies ranging
spreading sound wave, and Figure 1: Hearing thresholds comparison of humans, dogs, bats from 30 to 250 Hz (Figure 2).
thus aquatic fields can be and fish. Hearing thresholds for five selected fish species (Atlantic It is believed that during
very noisy environments. cod, Atlantic salmon, Common carp, Tunids, and goldfish) courtship females will assess
The concept of sound Adapted from Popper et al., 2008 the fitness of the males based
28 | InternAtIonAl AquAFeed | July-August 2012

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4. FEATURE
EXPERT T●PIC
on their grunting. As such, male grunting In captivity sound sources are more spe- tank walls all create obvious perceptible
project included four tilapia farms in China. These identify the key problems and causes related to in April, 2011. Over 40 farmers, processors, tech-
vigour has been related to the volume of the cific, being related to the general operation noise (Figure 3). Some basic activities
farms represented both small- and commercial- water management.
drum muscle mass as well as the individual’s of an aquaculture facility including equipment nicians and government showed attended sound
like hand feeding officers a low the
specific immune condition. During mating the and general project is an activities. Literature workshop. Participants found the workshop above
scale production facilities utilising two different The second husbandry assessment of the level increase of 8-11 dB re µPa very
production systems (pond and cages). Aside from regional environmental impacts of fish farm clusters, informative and helpful. This enhanced the produc-
female will settle on the ground, while males suggests that general activity and farm noise background noise.
identifying similarities and differences among criteria which will be jointly conducted by SFP and Hainan ers’ awareness of increasing demands for certified
‘perform’ a courtship characterised by both will generate low frequency vibrations i.e. However, the analysis showed that other
and requirements used by the three standards, Research Academy of Environmental Sciences, the sustainable seafood from reach worrying thus
vocalisations and a swimming pattern around <1kHz which is within the auditory sensi- daily activities can overseas markets, levels.
this project also identified outstanding issues in the leading environmental research institute in Hainan. further facilitating the engagement of Chinese
the female. tivity of fish. Thus,
farms, which most producers were able to address The study will examine the potential for regional stakeholders into a supply-chain dialogue around
In enclosed aquaculture systems it is very prior to quantifying
as a result of the trial audit. To date, all four farms scale improvement by looking at carrying capacity sustainability.
likely that mating performance/mate choice how sound could
are now certified under one or more of the com- and the potential for zoning in a specific area.
could be impaired if the males ‘singing and act as a stressor, SFP is currently working with local institutes of
mercial aquaculture standards. somehow restrained it was felt impor- data becomes available aquaculture and environmental sciences to identify
dancing’ performance is As more first-hand
by the physical conditions. While every effort (along with more pre-
SFP is widely acknowledged for its expertise tant to a more in-depth understanding of and evaluate both qualitatively and quantitatively
by has been directed to optimising broodstock existing policies and management measures), the the environmental impacts of tilapia farming in
stakeholders in Chinese tilapia, including key cisely catalogue the
US and European buyers and retailers, as well as AIP will establish a working group that convenes Hainan. This includes an ecological study as well as
holding tanks to ensure enough space and sound-scape in a
producers and processors in China, aquaculture the key buyers, suppliers and producers along the socio-political analysis to advise local governments
low turbulences to allow paired mating, little typical land-based
institutes, industry associations, and local Chinese Chinese tilapia supply-chain to share the scientific and industrial associations about how to efficiently
thought has been put into the acoustic condi- aquaculture facility.
governments. Given the high level of trust that SFP findings. The AIP will then form a multi-stakeholder address the environmental issues associated with
tions experienced by fish in culture. A sound map-
enjoys with the tilapia supply chain it was appropri- policy roundtable to further discuss the problems tilapia farming in Hainan. The preliminary results will
ping exercise
ate that a tilapia Aquaculture Improvement Project and solutions. The AIP participants will eventually be shared with key stakeholders at the Aquaculture
Negative effects of sound was performed
Figure 2. Waveform and spectrogram of four different
(AIP) was officially launched in 2011. anthropogenic agree on the actions and timetables necessary to Policy Roundtable this fall in China.
The negative effects of in the facilities of
cod grunts recorded in SFP facilities of Ardtoe Marine
the is also developing partnerships with
sound are well documented in the natural achieve the sustainability objectives defined by
SFP has now initiated two research projects Ardtoe Marine Laboratory, Scotland during Spring 2010.
to environment where a wide farming on the the group. SFP will play a leading role in engaging Chinese universities and large feed manufacturers
assess the impact of tilapia range of species Laboratory in
external environment. The first project, started stakeholders, providing scientific advice and facilitat- to improve feed sourcing for tilapia farming in
have been shown to alter their natural com- Scotland which
in April 2011, involves monitoring water qual- ing communication.
munication and behaviour with there even revealed a surprisingly quiet background China. This work is to be undertaken through
Accidental and/or intentional knocks against a
ity on selected farms in Hainan province, and in sound level in the rearing tanks as com- research projects on improving feeding efficien-
being evidence of panic and confusion tank wall, which can cause strong behavioural
was undertaken different Hainan Institute of Up-to-date progress
response to by the anthropogenic sound pared to what would be expected in cy reactions in the fish stocks, generates low
and developing alternative feeds with fewer
stimuli. In the natural marine environment shallow coastal waters. That said, sound impacts on wild fisheries.
Aquaculture. Dozens of water quality param- SFP has worked closely with local tilapia associa- frequency sounds with volumes ranging from
eters such as chemical oxygen demand (COD), tions to assess different tilapia standards that are
these sound sources are diverse and include disturbances were evident. Common hus- 21-39 dB depending on the vigour/cause of
nitrogen and phosphorus content, and heavy available in activities like workshop introducing More InforMatIon: Such SPL are clearly per-
offshore engineering, pile driving, seismic sur- bandry the market. A hand feeding, walk- the perturbation.
metals were analysed for five farms over two three international standards for tilapia farming, i.e. Sustainable Fisheries Partnership
veying, busy shipping areas as well as naval ing, hand netting, talking, water inflow, ceived by the fish and could possibly trigger a
croppings (10 months). The study helped 20/02/2012 bubbles, and knocks in Haikou Website: www.sustainablefish.org
_OffshoreMaric_Quarter_SplitAd_OMC_Quarter BAP, GlobalGAP, and ASC, was held against the stress reaction.
activity. aeration 07:53 Page 1
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July-August 2012 | InternAtIonAl AquAFeed | 29
July-August 2012 | InternAtIonAl AquAFeed | 27

5. FEATURE
Fish reaction ly correlated to peak cortisol concentrations. of elevated cortisol to the oocytes reducing
Stress reactions in fish in response to sound Tested sound levels were comparable to those their viability. Another possibility is that the
perturbations can be behavioural, acoustic encountered during the site sound mapping, courtship ritual could have been disrupted by
and/or physiological. Behavioural responses which suggests that a perturbation as simple as the randomised sound exposure masking the
are the apparent avoidance or freezing reac- knocking a tank wall can be strong enough to grunts and interrupting the mating behaviour
tion. Acoustic responses are more difficult to trigger a significant increase of cortisol. explaining the reduction in fertilisation rate.
Regardless of the causative mechanism, the
fact that fertilisation success and egg quality
were so clearly affected in sound stressed
broodstock should be taken as a clear indica-
tion the acoustic conditions in culture deserve
more attention.
Implications for other species
While evidence suggests that Atlantic cod
is one of the more acoustically sensitive fish
we firmly believe that there are implications
for this work in most other cultured species.
Future work should focus on the long-term
Figure 3: Noise disturbances monitored in an aquaculture on-growing tank. effects of noise as a stressor including tem-
Waveform and spectrogram representations: A) Background sound level; B) Hand porary auditory thresholds adaptation as cop-
feeding commercial dry pellets of 4.5 mm two times five pellets at the time; C)
ing strategies. Acclimatisation to noise might
Knocks against the tank wall. Three sets of three knocks caused with the bare
fingers. be possible, although negative physiological
responses could be present even without a
clear behavioural response.
characterise, however evidence suggests that Recovery from the sound perturbation In terms of the culture facilities we use,
fish may attempt to alter their vocalisation was also rapid indicating it to be an acute clearly more attention has to be paid in
form and structure (length, frequencies and stress response that fish should be able to reducing the noise caused around land-based
amplitude) to increase transmission probabil- cope and adapt to. This would in turn suggest aquaculture facilities and, by doing so, making
ity as has been reported in other vertebrates. a minor impact in the long-term performance aquaculture production more reliable and
Finally, the physiological responses are of the fish stocks although, in fish farm facili- predictable possibly helping to reduce the
varied as a stress activation of the sympathetic ties, those acute sudden noises are common commonly reported variability in fish perform-
nervous system (SNS) and the hypothalamic- and frequent. Thus, the second phase of the ances in most aquaculture facilities.
pituitary-interrenal (HPI) axis can impact on work considered how short ‘acute’ sound Instituting some routine simple and
many processes however evidence of sound stressors applied over a long time frame can cheap sound measurements on a farm
stimulating these processes is lacking to date. impact on fish performances. could mitigate many unnecessary distur-
Buscaino et al. (2009) demonstrated in sea bances that might be acting as stressors
bass and sea bream that sound perturbations Sound stressors over time: affecting the welfare and thus performance
above a threshold can result in an increase in a significant impact of the fish. The results of doing so may well
blood glucose levels and haematocrit which We discovered that cod broodstock be seen in the bottom line. ■
confirms the involvement of the HPI axis in exposed to six hours of daily randomised
this species. noise at a SPL of 34 dB re µPa (comparable Acknowledgments
to a loud knock on a tank wall) significantly
This project was co-funded by the Mexican
Acute stress response impacted on the their spawning perform- Council for Science and Technology (CONACYT)
Our studies have shown that noise does ance. Egg production in terms of volume of and EU FP7 project 232305 “PROSPAWN”.
elicit an acute stress response in Atlantic cod eggs and egg size was comparable between
(Gadus morhua) juveniles. Fish exposed to broodstocks that were both exposed, and
sound in the 100-1000Hz range for 10 min- not exposed, to sound though in the sound References
utes, using suspended underwater loudspeak- exposed population fertilisation rates were
Buscaino, G., F. Filiciotto, et al. (2010). "Impact of
ers, showed a significant increase of plasma reduced by almost half. an acoustic stimulus on the motility and blood
cortisol concentrations within 10 minutes of Work is currently underway to investigate parameters of European sea bass (Dicentrarchus
exposure. why sound perturbations result in such a sig- labrax L.) and gilthead sea bream (Sparus aurata
Furthermore, the response was dose nificant reduction in fertilisation success with L.)." Marine Environmental Research 69(3): 136-
dependent as sound pressure levels were direct- one possibility being the maternal transfer 142.
30 | InternAtIonAl AquAFeed | July-August 2012

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