MATCHING WATER SOURCES TO AQUACULTURE PRODUCTS


| Groundwater | Surface Water | Rain | Municipal Water Sources | Natural or Re-hydrated Seawater |
| Re-circulation as a Source | LarvalBase |


Table 1
: Acceptable range of water quality parameters for aquaculture sites. 
Table 2,  part 1, Table2, part 2: Water Sources and Some Associated Water-Quality Parameters
Table 3: Recommendations for the safe reuse of wastewater in aquaculture 

 

What comes first, the water or the fish? Often, aquaculture projects come about from one of two situations. Either someone is knowledgeable about a species that they are hoping to culture and wants to find a site with a source of water to fit the species or has a site with an available source of water and is looking for a suitable species to rear. Water source and species selection are closely linked. If large quantities of water are involved, such as is the case with pond or flow-through culture, then it is very difficult and expensive to treat water beyond using simple screens and aeration. Pumping from deep wells, heating, or chilling large volumes of water is energy intensive, expensive, and unlikely to be economically or environmentally sustainable over the long haul. For all these reasons, water quality from the source should be well matched to the environmental optima of the species to be cultured if the project is to be a success.

Temperature is often one of the most important factors when matching a water source and a culture species. Except for small water volumes used for egg or broodstock holding or for re-circulation systems, attempting to significantly change the temperature of the culture water by heating or cooling is costly. Exceptions to this rule are geothermal or waste heat from a power plant to heat water, or possibly the use of deep, cold marine water for cooling warm water. The amount of water needed for a fish production system will depend on the intensity of culture. In extensive systems, water requirements may be based upon management concerns, such as the time to fill a pond, or the amount water needed to makeup for evaporation or leakage. It is recommended that enough water be available for aquaculture ponds to fill in two weeks. Amounts needed for evaporation or leakage will depend on the area where the ponds are located.

For intensive systems, water requirements will be dictated by the first limiting water-quality parameter. Typically, oxygen is first limiting, followed by carbon dioxide and ammonia. A mass-balance approach can be used to determine water requirements for a given species and level of production. Conversely, this approach can also be used to determine the potential production levels of a given species for a known water source. The mass balance approach is very powerful and can be used to examine and identify which water-quality parameter is limiting for a given set of circumstances, and which water treatments will have the greatest impact on production.

The mass balance approach accounts for all inputs/ outputs and production/consumption of a compound of interest in a defined system. Compounds can get into or out of the system either predissolved in the water flow or they can transfer into the water once it is already in the system (form air, feed, light, and so on). Flow (Q, in volume/time, m3/hr) in a system times concentration (C, in mass/volume, g/m3) equals the rate of mass flowing (g/hr) into or out of a system pre-dissolved in the water. Transfers (T), production (P), and consumption (R) are also rates in mass/time (g/hr). Transfers of mass into or out of the system come from or go outside of the system. For example, oxygen may be transferred into a system and carbon dioxide out of a system due to aeration. Compounds can also be taken up or released by the fish, bacteria, or some other internally generated activity of the system, to or from the water. Typically this relates to the biomass (B) of organisms contained in the system. For example, the consumption of oxygen by fish depends on the size and number of fish. Accounting for all the ins and outs and conversions that occur can be expressed mathematically. Mass is conserved, so the mass of a given compound into and out of a system is in balance, and this can be expressed in the equation below. The same approach can be used for energy, which is also conserved.

QinCin + T + (P - R)B = QoutCout

where Qin is the influent water flow (e.g., Lpm), Cin is the influent concentration of the compound in water (e.g., mg/L), T = transfer of the compound into (or out of, if negative) the tank (e.g., mg/hr), P = production of the compound in the tank (e.g., mg/hr/kg of organism), R = consumption of the compound in the tank (e.g., mg/hr/kg of organism), B = biomass of the organisms in the tank (e.g., Kg), Qout = effluent water flow (e.g., Lpm), and Cout = effluent concentration of the compound in water (e.g., mg/L).

For example, if we have a spring that produces 100 m3/hr of water at 15'C (59 °F), and it contains 10 mg/L of oxygen, and we want to know the biomass of rainbow trout (Oncorhynchus mykiss) that can be maintained with this water, we can use the above equation to figure it out. We need to know what the trout will do to the oxygen in the water and what the minimum level of oxygen should be to keep our trout healthy. For this example, we will assume that the trout removes oxygen at the rate of 200 mg O2/kg of fish/hr and requires a minimum of 5 mg/L to stay healthy. The concentration to keep the fish healthy will be equal to the outflow concentration since when it gets to that level, we want to get rid of it.

For our example the equation has the following values:

Flow (Qin and out) = 100 m3/hr or 100,000 L/hr

both in and out

Transfer of oxygen (T) = 0 mg 02/hr (we have no aeration in this example)

Production of oxygen (P) = 0 mg 02/kg of biomass/hr (if there were plants or algae in the system then this might be a nonzero number)

Consumption of oxygen (R) = 200 mg 02/kg of fish/hr

Concentration of oxygen in the inflow (Cin) = 10 mg/L (this is saturation at 15 °C)

Concentration of oxygen in the outflow (Cons) = 5 mg/L (set as the minimum acceptable level)

Plugging in the values:

QinCin + T + (P - R)B = QoutCout

(100, 000 L/hr • 10 mg/L) + 0 mg/L/hr

+ (200 mg/kg hr • B kg) = (100,000 Lfhr • 5 mg/L)

Solving for B, (kg of trout)

B = 2500 kg (5500 lbs)

The same exercise, repeated with each water-quality factor, can be used to determine the first limiting water quality parameter. This approach can also be used to determine which water treatments will be necessary to increase production. In the foregoing example, the effect of aeration can be addressed by adding in a value other than zero for the production term. The calculations become more difficult when re-circulation and multiple treatments are considered.

Surface water sources, especially those from established ecosystems, will contain pathogens and potential predators. Pollution may also be a concern for rain, surface, and groundwater sources that are in proximity to a pollution source. Various screens and sterilizers are available to reduce predators and pathogens, but treatments for pollution will depend on the nature of the pollution, and may not be treatable.

Regulations for the removal of water from either a groundwater or surface-water source exist at multiple levels in almost all countries. This is true for marine or freshwater sources. Additional regulations govern discharge of water from aquaculture facilities. Property owners should check with local authorities and government agencies regarding rights and permits for development of the water source.

Compiled after:
MICHAEL B. RUST, JOHN COLT
Northwest Fisheries Science Center Seattle, Washington
In:
Encyclopedia of Aquaculture, 2000. 

 

Table 1:   Acceptable range of water quality parameters for aquaculture sites. 

Parameter

Acceptable range

pH

6.0 - 8.0

Alkalinity (measured as CaCO3)

100 - 400 ppm

Total hardness

100 - 400

Carbon dioxide

0 - 15

Iron (Fe) - ferrous

Less than 0.1 ppm

Ammonia (NH3)

Less than 0.02 ppm

Nitrate (NO3)

0 - 3.0 ppm

Nitrite (NO2)

0.1 ppm

 

Table 2, Part 1: Water Sources and Some Associated Water-Quality Parameters
           
Source

Quantity

Pathogens
and
Predators

Salinity

Temperature

Suspended
Solids

Groundwater

Generally
stable, but
may vary
with
season or
year

Not usually
a problem

Fresh to full
strength
seawater

Stable over
the short
term, can
vary
seasonally

Low

Rivers,
streams,
and lakes

Streams and
rivers
variable,
lakes
generally
stable, but
can vary
with
seasons

Common
and
should be
expected

Fresh

Variable short
term and
seasonally,
varies more
than
ground-
water

Varies, can
be high
during
runoff
events

Oceans, seas,
and bays

Stable,
although
elevation
can vary
with tides

Common
and
should be
expected

Brackish to
seawater

Variable

Varies, can
be high
during
strong tides and
storms

Municipal
water
sources

Limited and
expensive

Reduced,
but not
eliminated
from
source

Fresh

Variable

Low

Rain

Highly
variable

Low pro-
bability

Fresh

Variable

Very low

Recirculation
systems

Can
intensify
use of
existing
source.

Requires
treatment,
difficult to
eliminate
pathogens
completely

Fresh to full
strength
seawater

Set by
operator,
stable

Depends on
treatment

Table 2, Part 2: Water Sources and Some Associated Water-Quality Parameters
Source

Dissolved

Oxygen

Other
Dissolved
Gasses

Total Gas
Pressure

Metals

Oxidizers

Buffer
(pH)

Groundwater

Low

Carbon
dioxide, and
argon can
be high
depending
on geology

Can be
above
saturation
variable

Iron and
manganese
may be a
problem in
water with
low DO.

None

Depends on
geology

Rivers,
streams,
and lakes

Low to high
variable

Generally low,
but carbon
dioxide can
be high and
variable if
there is a
lot of
respiration

Same as
above

Depends on
industrial
and
domestic
discharges
in proximity
to inflow
lines

None

Depends on
geology and
source of
water

Oceans, seas,
and bays

Low to high,
variable

Same as above

Generally
below
saturation
at depth

Same as above

None

Generally well
buffered,
ocasionally may
reflect
buffer
capacity of
rivers
flowing into
it.

Municipal
water
sources

Low to high

Low

Variable.
Can be
high in
summer

Should not be
a problem

Chlorine
and/or
ozone is
often
used

Depends on
source and
treatment

Rain

High

Low

Saturated

Depends on
industrial
air pollution
upwind of
catchment
area.

None

Poorly
buffered,
can be acidic

Recirculation
systems

Depends on
treatment

Carbon
dioxide can
be high

Generally
not a
problem,
unless
pump has
a suction
leak

May build up
from feed

Ozone is
often
used to
maintain
ORP and
kill
pathogens

Highly
buffered
and
controlled

Table 3: Recommendations for the safe reuse of wastewater in aquaculture: source, condensed from Pullin (1993).

The term ‘wastewater’ is used here in a generic sense to mean human excreta: whether fresh (‘nightsoil’); in the form of sewage or wastewaters in the narrow sense (excreta, with added water to facilitate waterborne transportation); or other partially treated forms such as septage.

 
  • More research on the public health aspects of existing wastewater-fed aquaculture systems is essential before they are further developed or promoted elsewhere.

  • In wastewater-fed fish culture systems, the presence of industrial effluents should be closely monitored and minimized.

  • Wastewater should never be used for aquaculture without pretreatment. This is important for pathogen removal.
     

  • A tentative critical density of 105.ml-1 total bacteria should not be exceeded in wastewater-fed fishponds, except locally for a few hours during loading of pretreated wastewater.
     

  • Loading of wastewater into fishponds should be suspended for two weeks prior to fish harvest to eliminate Cryptosporidium.  Post harvest, fish should be held for at least a few hours isolated, clean water to facilitate evacuation of their gut contents.
     

  • The threshold concentration of total bacteria in the muscle of fish harvested for human consumption from wastewater systems should not exceed 50.g-1.  Salmonella should be absent.

 

 

  • Viable eggs of human trematode parasites should be absent from wastewater-fed fishponds.  Nightsoil should be stored for two weeks to eliminate such eggs before reuse in fishponds.  For bilharzia (Schistosoma spp.) control, a carefully designed package of chemotherapy, health education, improved sanitation and snail control in fishponds and other waters is recommended.

  • Vegetation in wastewater-fed ponds should be kept to a minimum to reduce the breeding of insect and other disease vectors and intermediate hosts.
     

  • Good hygiene should be promoted at all stages of handling and processing fish (evisceration, washing, cooking) as these can be major sources of infection.
     

  • The culture of molluscs in wastewater-fed systems is not advisable because of their propensity to accumulate large quantities of contaminants (for example, metals and pesticides).
     

  • Culture of luxury aquatic produce, such as crustaceans and high value finfish, in wastewater-fed systems is not recommended.

 

Pullin RSV, Compiler.  1993.  Discussion and recommendations on aquaculture and the environment in developing countries.  In:  Pullin RSV, Rosenthal H, Maclean JL, editors.  Environment and aquaculture in developing countries.  ICLARM Conference Proceedings.  31.  p. 312-338.


| Groundwater | Surface Water | Rain | Municipal Water Sources | Natural or Re-hydrated Seawater |
| Re-circulation as a Source | LarvalBase |

Created by B. Ueberschär, 25.01.2003