May/June 2010 - Global Aquaculture Alliance

water Temperature (° C)
30
20
10
0
Guayaquil, Ecuador
Auburn, Alabama, USA
J F M A M J J A S O N D
Match
in a process caused by a 10° C temperature
is called the Q . To illustrate, if fish
10
grow 1.8 times faster at 30° than at 20° C,
Q is 1.8.
10
Water temperatures at most locations
vary between seasons, even in the tropics.
This phenomenon is illustrated in Figure
1 with data from Auburn, Alabama,
USA, at 32° 36’ N latitude and for Guayaquil,
Ecuador, at 2° 9’ S latitude.
A small difference in temperature can
appreciably affect shrimp growth rate.
Suppose shrimp grow at 1.20 g/week
during a period when water temperature
averages 27° C. Assuming Q = 2 for
10
shrimp growth, an increase in temperature
to 29° C should increase growth rate
to 1.44 g/week. Of course, plants and
animals have a range of temperature tolerance,
and Van Hoff’s law does not
apply outside the temperature range for
optimum growth. In the example above,
if 29° C is above the optimum temperature
for shrimp growth, there would be a
Figure 1. Water temperatures
at a temperate
and tropical location.
decrease in growth at the higher temperature.
A study in Poland revealed that a
difference in 1° C from the mean seasonal
temperature can alter common carp production
in intensive systems by 1,000 kg/
ha.
Animal Health, Reproduction
Water temperature has an indirect
role in the health of aquatic animals
because it influences the occurrence and
outcome of infectious disease. The
immune systems of aquatic animals generally
function most efficiently within the
temperature range for optimum growth.
At higher or lower temperatures, the
immune systems are less effective in preventing
disease.
Rapid temperature changes also
impair immune function. Each pathogen
has an optimal temperature range. For
example, the bacterium that causes
enteric septicemia in channel catfish is
most virulent at water temperatures of 22
to 28° C. This temperature range in the
major catfish-farming area of the United
States occurs in spring and autumn, so
these are the times that major outbreaks
of the disease occur.
Water temperature plays an important
role in determining the rate of ovulation
and milt production in fish under natural
and induced situations. Timing of this
physiological response is related to a
degree-hour response – water temperature
multiplied by the number of hours from
the onset of ovary maturation or dosing
when inducing ovulation until ovulation.
Ovulation in common carp, for example,
requires 240 to 290 degree-hours.
Water Quality
Water temperature greatly influences
water quality because the growth and
metabolism of phytoplankton, bacteria
and other microorganisms increase with
increasing temperature. Moreover, water
holds less oxygen at higher temperatures.
Dissolved-oxygen depletion is much
more likely to occur during hot weather
than during cooler periods.
Rates of chemical processes such as
ionization, mineral dissolution, adsorption
and ion exchange also increase in
response to greater water temperature.
The onset of potentially harmful water
quality events is faster in warmer weather.
Aquaculture managers should be especially
vigilant regarding water quality
during the warmest months and periods
of unusually high temperature.
production
Smoked seafood like this smoked trout continues to grow in popularity. The golden
color is due to the interaction of carbonyls with amino components on the flesh surface.
Smoked Fish
Old Product With New Appeal
Offers Enhanced Taste, Shelf Life
Summary:
Aquaculture has enabled many fish species to be produced
affordably, which makes more product available
for “specialty” processing like smoking. The objectives
of the smoking process are to uniformly impart
the desired sensory characteristics to the product,
extend shelf life and avoid the deposition of harmful
compounds. The flavor and aroma of smoked fish
are primarily due to the presence of phenols. Smoked
methods do not adversely affect the protein quality or
fatty acid profile of fish flesh.
Smoked fish, arguably one of the oldest of all processed fish
products, continues to increase in popularity. Traditional
smoked favorites include chub, whitefish, haddock, cod and kippers,
but new species, including many from aquaculture, are now
available in the marketplace.
Some of the new finfish species include eel, salmon, trout,
dogfish, sturgeon, mackerel and shark. Recently, oysters, clams,
mussels and scallops have also become available in smoked form.
New value-added products featuring smoked fish or shellfish
have been enthusiastically received by consumers. The list includes
George J. Flick, Jr., Ph.D.
Food Science
And Technology Department
Virginia Tech/Virginia Sea Grant (0418)
Blacksburg, Virginia 24061 USA
flickg@vt.edu
pâtés, dips, spreads, salads and snacks.
Smoked fish have also been marketed with
pepper coatings, herbed seasonings (especially
dill) and honey glazing, and infused
with various other flavorings.
Aquaculture has had a significant
impact on the availability of smoked
products. In prior years, smoked products
were considered a luxury or specialty ethnic food due to their
high cost. However, aquaculture has enabled many fish species
to be produced affordably, which makes more product available
for “specialty” processing and keeps consumer costs low. Recent
fishery statistics show that some of the newer value-added products
on the market are gaining rapidly on some of the more traditional
fresh and frozen market forms.
Aquaculture has enabled many fish
species to be produced affordably,
which makes more product available
for “specialty” processing.
Fish Preservation
The smoking process provides fish and other smoked products
some protection against spoilage when compared to fresh
products. Modern smoked products need to be stored at temperatures
between 0 and 3° C to reduce spoilage and prevent the
growth of toxin-producing microorganisms. When smoked
products are properly stored, they should have shelf lives that
range from one to four weeks. Products that have been heavily
smoked may not require refrigeration.
The preservation of fish and shellfish through smoking is achieved
through several steps that are considered as a single unit process:
• Drying. Surface drying provides a physical barrier to the
penetration of bacteria and does not create an acceptable
growth environment.
• Salting. Salting reduces water activity, which inhibits the
growth of many pathogenic microorganisms. However, for
salting to be completely effective, it may be necessary to
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