It will be helpful for the students who are interested in Aquaculture.

1. ASRAFUL ALAM 1
Water Quality requirements & its Management in Aquaculture.
Mohammad Asraful Alam
Institute of Marine Sciences & Fisheries, University of Chittagong
asraful.imsfcu86@gmail.com
Why Should Study water quality requirements & its management:
Successful aquaculture depends on providing animals with a satisfactory environment in which to grow. Thus, it is
important that the aquaculturist have an understanding of water chemistry and possess the skills necessary to provide a
suitable environment for the venture to be successful. "Water quality determines to a great extent the success or failure
of a fish cultural operation" (Piper et al. 1982). Water is an essential requirements for fish or any other species as water
quality is determined by various physic-chemical & Biological factors that directly or indirectly effect for fish (survival,
growth, and reproduction). So, an experienced aquaculturist needs a clear concept about this topic. (Boyd 1995, Thomas
1994).
Hundreds of water quality variables may effect the well-being of fish or crustaceans, but, fortunately, only a few normally
play a decisive role(Boyd 1995). Physical parameters – Temperature, Turbidity, Salinity & water colour. Chemical
parameters- Dissolved oxygen (DO), Biological oxygen demand (BOD), Carbon-di-oxide (CO2), pH, Alkalinity, Conductivity,
Chloride, Hardness, Ammonia (NH3), Nitrite (NO2-) & Nitrate (NO3-). Biological parameters- Plankton, Primary
productivity.
Temperature
Temperature is defined as the degree of hotness or coldness in the body of a living organism either in water.
Effects:
Water temperature greatly influences physiological processes such as respiration rates, efficiency of feeding and
assimilation, growth, behavior, and reproduction (Meade 1989; Tucker and Robinson 1990).Temperature also affects
oxygen solubility and causes interactions of several other water quality parameters. Dissolved oxygen requirements are
more critical in warm water than cold water. Fish and invertebrates have a very low tolerance for sudden changes in
temperature, that is, often rapid changes of as little as 5°C (9°F) will stress or kill them. More than O.9°C (l°F) per minute
can cause thermal shock and death. (Thomas 1994). Temperature affects both the host and pathogen in a culture pond
(Boyd 1995).
Optimum Level:
The temperature for optimum growth of fish is called the SET, standard environmental temperature. The optimum
temperature range varies for different species. The SET for rainbow trout is 59°F (15°C), and 85°F (29.5°C) channel catfish
(Robert C Summerfelt et al). Fish can be grouped according to their temperature requirements as cold-water, cool-water
or warm-water species. Cold-water species are those preferring water temperatures of 15°C (59°F) or less; cool-water
species prefer 15-20°C (59-68°F); and warm-water species prefer waters above 20°C (68°F) (Romaire 1985).
In Pond production the optimum range of temperature is 26°C to 32°C.
What happens when consistently below recommended Value?
Below 15°C: Growth stops and death occurs at extremes.

2. ASRAFUL ALAM 2
Below 15 to 26°C: Reduced feed intake and growth rates. Higher FCRs. Fish more stressed at lower temperatures,
therefore, more susceptible to disease.
What happens when consistently above recommended value?
Lower solubility of oxygen, stress and death at extreme temperature.
Management:
By water exchange, planting shady trees or making artificial shades during summer’s thermal stratification can be
prevented. Mechanical aeration can prevent formation of ice build-up in large areas of the pond. Creating some Deep
areas. By circulating the Water.
Turbidity:
Turbidity refers to an optical property of water that causes light to be scattered or absorbed rather than transmitted
through the water in a straight line. Turbidity is caused by suspended material (such as soil particles, plankton, and organic
detritus) and soluble colored organic compounds (Boyd 1995).
Effects:
Turbidity restricts light penetration as a result little dissolved oxygen is produced by photosynthesis. Higher turbidity can
cause temperature and DO stratification in prawn ponds. It can cause clogging of gills or direct injury to tissues of prawns.
Clay turbidity that restricts visibility to 30 cm (12 in.) or less can inhibit the development of good phytoplankton blooms
(Romaire 1985).
Optimum Level
Boyd and Lichtkoppler (1979) suggested that the clay turbidity in water to 30cm or less may prevent development of
plankton biomass. 30cm to 60cm & as below 30cm is generally good for fish production. According to Alabaster and Lloyd
(1980) good to moderate fisheries can be maintained in waters with 25-80 mg/L suspended solids. Good fisheries cannot
be expected in waters with suspended solids concentrations above 80 mg/L.
Seechi disk transparency between 30cm & 40cm indicates optimum productivity of a pond for good fish culture (Santhosh
& Singh 2007).
So, optimum turbidity range 30cm-80cm is good for fish health.
15 to 40cm is good for intensive culture (Bhatnagar et al. 2004).
Management:
Addition of more water or lime (CaO), alum Al2(SO4)314H2O at a rate of 20 mg/L and gypsum on the entire pond water
at rate of 200 Kg/ 1000m3 of pond can reduce turbidity.
[N.B: It is reported that alum and ferric sulfate are more effective than hydrated lime and gypsum in removing clay
turbidity. Both alum and gypsum have acid reactions and can depress pH and total alkalinity, so the simultaneous
application of lime is recommended to maintain the suitable range of pH. Treatment rates depend on the type of soil.]
Salinity:
Salinity is a measure of the concentration of dissolved ions in water expressed in grams per liter (g/L) or ppt (Parts par
thousand). For better survival and growth optimum range of salinity should be maintained in the aquaculture ponds.
Salinity varies with different type of species.

3. ASRAFUL ALAM 3
Effects:
When salinity is changed by more than about 10% within a few minutes or hours, fish and invertebrates may not be able
to compensate (Boyd 1990). Although they can accumulate with gradual change.
If the salinity of water increases, the solubility of dissolved oxygen decreases and the percentage of total ammonia present
as toxic un-ionized ammonia decreases.
Optimum level:
Most freshwater fish of importance in aquaculture reproduce and grow well at salinities up to at least 4-5 ppt. Although
many freshwater fish can live in waters with salinities up to 7 ppt, they may not grow well at this salinity.
For example- the optimum range of salinity for black tiger shrimp is between 10 and 25 ppt, although the shrimp will
accept salinity between 5 and 38 ppt since its euryhaline character.
Management:
Sodium chloride (NaCl) in the form of common rock salt can be used to raise salinity in culture systems. The ability to
tolerate sudden decreases or increases in salinity can be improved in some animals if adequate environmental calcium is
present. Replenishment of water. Aeration to equalize the salinity all over the water column.
Water Colour:
Color is a result of the interaction of incident light and impurities in the water. The colour of an object is defined by the
wavelengths of visible light that the object reflects.
Effects:
Actually water colour has no direct affect on aquaculture pond. But knowing the pond water colour aquaculturist can
understand pond condition i.e. water colour indicates pond condition.
Optimum Level:
The addition of humic substances in water imparts a tea-colored or reddish hue. Iron associated with humic substances
can impart a yellow color. Unproductive waters generally have a bluish color and are very transparent. Impending oxygen
shortages in the water can often be detected by changes in color. Water colour is golden or yellow brown if diatoms are
more. This type of water is best for prawn culture. According to Bhatnagar et al. 2004 dark brown colour is lethal for
fish/shrimp culture. Light green colour- good for fish/shrimp culture, dark green colour is not ideal for fish/shrimp culture
and clear water is unproductive for fish/shrimp culture.
Green, bluish green/ brown greenish colour of water indicates good plankton population hence, well for fish production.
Management:
Application of organic and inorganic fertilizers in clear water ponds may increase productivity. In too greenish colour use
copper sulphate (CuSO4).
Dissolved Oxygen (DO):
Dissolved oxygen refers to the level of free, non-compound oxygen present in water. Non-compound oxygen, or free
oxygen is the oxygen that is not bond with any other element. Dissolved oxygen is the presence of these free oxygen
molecules within water. The principal source of dissolved oxygen in the water is atmospheric air & photosynthetic
planktons.

4. ASRAFUL ALAM 4
Effects:
It affects the growth, survival, distribution, behavior and physiology of shrimps and other aquatic organisms. (solis 1988).
Oxygen depletion in water leads to poor feeding of fish, starvation, reduced growth and more fish mortality, either directly
or indirectly (Bhatnagar and Garg, 2000). Fish should not be fed when the DO concentration decreases to 3-4 mg/L or less
(Tucker and Robinson 1990). Less than 5 ppm dissolved oxygen create diseases for fish.
Optimum Level:
Small fish consume more oxygen per unit weight than large fish of the same species. In generally, warm-water species
tolerate lower DO conditions than cold-water species. (Thomas 1994). According to Swingle (1969) Warm water fish in
ponds die after short-term exposure to less than 0.3 mg/L DO. To support life for several hours a minimum of 1.0 mg/L is
required and 1.5 mg/L is necessary to support fish for several days.
A minimum DO concentration of 5 mg/L is recommended for warm-water fish and 6 mg/L for cold-water species (Thomas
1994).
Crustaceans are also sensitive to low DO conditions. The lethal concentration for many Peneaid species ranges from 0.7
to 1.4 mg/L.
The optimum dissolved oxygen is 5-8 ppm.
What happens when consistently below recommended Value?
Below: 0 – 1.5 mg/l- can be lethal especially if exposed for long periods.
Below: 1.4 – 5 mg/l- fish survive, but reduced feed intake higher FCRs, slow growth, stress, and increased susceptibility to
disease results. Buildup of toxic wastes because they are not broken down (oxidized).
What happens when consistently above recommended value?
Gas bubble trauma when the water is supersaturated to levels of 300% and above.
Management:
If DO is high can be reduced by removal of some of the animals from the system, removal of organic materials in the water,
or by partial water replacement. Introduction of the hot water gradually with pipes to reduce. Avoid over application of
fertilizers and organic manure to manage DO level. Physical control aquatic plants and also management of phytoplankton
biomass. Recycling of water and use of aerators. Artificially or manually beating of water. Avoid over stocking of fishes.
Some factors that effects in DO in aquaculture pond:
Decreases as the temperature increases.
Decreases exponentially with increase in salinity.
Decreases with lower atmospheric pressure and higher humidity.
Increases with depth.
Biochemical Oxygen Demand (BOD):
BOD is the measurement of total dissolved oxygen consumed by microorganisms for biodegradation of organic matter
such as food particles or sewage etc.

5. ASRAFUL ALAM 5
Effects:
Reduce DO level in aquaculture pond.
Optimum Level:
BOD level between 3-6 ppm is optimum for normal activities of fishes.
Management:
Add lime, suspending use of fertilizers, removal of nonbiodegradable/ floating organic matter from the pond surface,
aeration, screening to reduce BOD level. Before stocking, pond water may be allowed to stabilize for few days (5-15days).
Carbon-di-oxide (CO2):
Carbon-di-oxide is common component in all water. Biological activity is greater in aquaculture ponds than in most natural
waters, and diffusion is relatively less important in controlling dissolved carbon dioxide concentrations in aquaculture
ponds. Dissolved carbon dioxide concentrations cycle daily and the amplitude of those daily fluctuations depends on the
relative rates of photosynthesis and respiration.
Effects:
Bohr-Root effect - The conditions decrease the affinity of hemoglobin for oxygen which reduces oxygen uptake by blood
at the gills, even if environmental dissolved oxygen concentrations are high. (Tucker and Robinson 1990).
[N.B-High environmental concentrations of dissolved carbon dioxide (hypercapnia) reduce carbon dioxide excretion at fish
gills, causing elevated levels of plasma carbon dioxide and uncompensated respiratory acidosis.]
Nephrocalcinosis- The condition which is prolonged exposure to elevated levels of dissolved carbon dioxide is implicated
as causing calcareous deposits within kidney tubules, collecting ducts, and ureters, results in high mortility (Smart et al.
1979; Schlotfeldt 1980).
High CO2 concentration decrease the pH level.
Optimum level:
CO2 concentration of 10-15 mg/L is recommended as a maximum for finfish (& concentrations in open pond waters
averaged less than 6 mg/L(Boyd 1990,1995).
The optimum level of C02 is 5 ppm.
Management:
Proper aeration can “blow” off the excess gas. Application KMnO4 at the rate 250g for 0.1 hectare. Free CO2 can be
removed from culture water by the addition of calcium hydroxide (Ca(OH)2), commonly referred to as slaked or hydrated
lime. The addition of 1.68 mg/L of hydrated lime will remove 1 mg/L of carbon dioxide (Boyd 1982).
pH:
pH is the measured mathematically by, the negative logarithm of hydrogen ions concentration.
Effects:
Seven major effects of low pH on fish gill structure or function. It also affects the metabolism and other physiological
processes of culture organisms. Affects the solubility and chemical forms of various compounds some of which can be
toxic.

6. ASRAFUL ALAM 6
Optimum Level:
The pH generally between 7 & 8.5 is more optimum to fish life. But the optimum range of Penaied shrimp is 5.5 to 8.5.
What happens when consistently below recommended Value?
Below 4 acid death point.
4 – 6.0 Survive but stressed, slow growth, reduced feed intake, higher FCR.
What happens when consistently above recommended value?
9 – 11 Stressful for catfish, slow growth rate.
Above 11 alkaline death point. All life, including bacteria in pond will die at this point.
Management:
Add gypsum (CaSO4) or organic matter (cow dung, poultry droppings etc.) and initial pre-treatment or curing of a new
concrete pond to reduce pH levels. Use of quicklime (CaO) to rectify low pH of aquatic body.
Alkalinity:
Alkalinity is a measurement of the acid neutralizing capacity of water. Alkalinity is determined in fish ponds by the quality
of the water source and the nature of the bottom muds.
Effects:
Total alkalinity does not have a direct effect on fish but, generally speaking, waters having a total alkalinity below 30 mg/L
are considered poorly buffered against rapid pH change. It has also effects on photosynthesis. If alkalinity is too low (less
than 20 mg/L), the water may not contain dissolved carbonates for photosynthesis to occur, thus restricting phytoplankton
growth. Also effects on Nitrification- the conversion ammonia to nitrate.
Optimum level:
A total alkalinity range of 20-400 mg/L is considered satisfactory for most aquaculture purposes (Meade 1989; Tucker and
Robinson 1990). Optimum level of total alkalinities is ≥20 ppm.
What happens when consistently below recommended Value?
Extreme fluctuations in pond pH levels during the day which is stressful to the fish. Fish are under physiological stress. Low
levels of primary production which results in lower natural sources of food.
What happens when consistently above recommended value?
Water will be well buffered and diurnal fluctuations in pH will be less extreme. Fish will be less stressed physiologically.
Young fish will have more natural food available. However, hard water in catfish hatcheries should be avoided.
Management:
Fertilize the ponds to check nutrient status of pond water. Alkalinity can be increased by calcium carbonate, concrete
blocks, oyster shells, limestone, or even egg shells depending upon soil pH and buffering capacity.
Conductivity:

7. ASRAFUL ALAM 7
Conductivity is an index of the total ionic content of water, and therefore indicates freshness or otherwise of the water
(Ogbeibu and Victor, 1995). Conductivity can be used as indicator of primary production (chemical richness) and thus fish
production. The greater the proportion of ions in water, the higher the conductivity.
Effects:
There is no direct effects. Due to the change of salinity it changes as it is a measure of the dissolved mineral content
(salinity) of water and changes in direct proportion to salinity (Boyd 1995).
Optimum Level:
As fish differ in their ability to maintain osmotic pressure, therefore the optimum conductivity for fish production differs
from one species to another. The acceptable range 30-5000 mSiemens/cm for pond fish culture. (stone and Thomforde
2004).
Management:
As salinity has a direct influence on it try to maintain salinity level.
Chloride:
Chloride is a common component of most waters and is useful to fish in maintaining their osmotic balance. Chlorine may
sometimes be present in municipal water that is used for holding fish or it may be applied to holding facilities or ponds to
effect disinfection.
Effects:
High amount of Chloride ion present in aquaculture pond causes toxicity of aquatic organisms. Changes in gill structure
reduce respiratory and osmoregulatory efficiency. Fish may react by "coughing" or by increasing ventilation rate. Death
probably results from hypoxia.
Optimum Level:
In a practical sense, water should not be considered safe for holding aquatic animals if any measurable concentration of
total residual chlorine is present (Boyd 1995).
Management:
Don’t adding chlorine gas to control disinfectant if needs have to evacuate the fishes from the pond first.
Hardness:
Numerous inorganic (mineral) substances are dissolved in water. Among these, the metals calcium and magnesium, along
with their counter ion carbonate (CO3-2) comprise the basis for the measurement of ‘hardness’. Calcium is required for
osmoregulation, but it is also important for bone formation in fish and exoskeleton formation in crustaceans.
Effects:
If the water less than 5 ppm, the growth rate is affected & causes eventual death of the fish. Hard waters have the
capability of buffering the effects of heavy metals such as copper or zinc which are in general toxic to fish.
Optimum Level:
Optimum hardness for aquaculture is in the range of 40 to 400 ppm of hardness. A hardness of 15 ppm or more is
satisfactory for the growth of fishes and prawns and don’t require additional lime.

8. ASRAFUL ALAM 8
Management:
If total hardness is too low it can be raised by liming. Adding lime to water increases the total alkalinity and total hardness
by the same amount.
[N.B: As a rule, the most productive waters for fish culture have a total hardness and total alkalinity concentration of about
the same magnitude (Romaire 1985)].
If it is desired to raise total hardness without affecting total alkalinity, agricultural gypsum (calcium sulfate, CaS04) can be
added. Calcium chloride is also used to increase hardness. Add Zeolite to reduce hardness & can be reduced by water
exchange. During heavy rainfall avoid runoff water into the pond.
Ammonia (NH3):
Ammonia by-product of protein breakdown. It occurs in both a toxic form (ammonia) and nontoxic form (ammonium)
depending on the pH of the water. The sum of the two (ammonia & ammonium) is called total ammonia or simply
ammonia. Total ammonia is often written as TAN. Total ammonia concentrations are generally highest in ponds receiving
large amounts of feed (Cole and Boyd 1986)
Effects:
Ammonia in the range ≥0.1 mg/L tends to cause gill damage, destroy mucous producing membranes. “Sub-lethal” effects
like reduced growth, poor feed conversation, osmoragulatory imbalance and kidney failure. Suffering from ammonia
poisoning generally appear sluggish.
Optimum Level:
The optimum level of NH3 is 0.3 to 1.3 ppm. & less than 0.1 ppm is unproductive.
Management:
Increase pond aeration. Regular water change out. Formaldehyde and Zeolite treatment. A dosage of 50ml per 100 gallons
to chemically bind up to 1 ppm of ammonia, can be useful. Addition of liming agents such as hydrated lime or quick lime
decrease ammonia & it’s effective in ponds with low alkalinity.
Nitrite (NO2-):
Nitrite is an intermediate in the process of nitrification, which is the two-step oxidation of ammonium to nitrate carried
out by highly aerobic, gram-negative, chemoautotrophic bacteria. Nitrite is, however, routinely found in intensive pond
aquaculture systems because large amounts of nitrogen are added in the form of manufactured feed, fertilizer, or manure.
Sometimes it’s called as invisible killer of fish.
Effects:
It Oxidizes hemoglobin to methemoglobin in the blood, turning the blood and gills brown and hindering respiration. It also
damages nervous system, Liver, spleen & kidneys of fish.
Optimum Level:
The ideal and normal measurement of nitrite is zero in any aquatic system. According to Stone & Thomforde (2004)
optimum level of nitrite is 2.5 mg/L.
Management:

9. ASRAFUL ALAM 9
Use of bio fertilizers to accelerate nitrification. Increase aeration. Reduction of stocking densities.
Nitrate (NO3-):
Nitrate (N03) is a common form of inorganic combined nitrogen in natural waters and aquaculture systems. Most of the
nitrate found in unpolluted natural waters is the end product of nitrification. Nitrate may be applied to pond bottom soils
to prevent reducing conditions that lead to sulfide production.
Effects:
Where ammonia & Nitrite were toxic to fish, Nitrate is harmless. Meck (1996) recommended that its concentrations from
0 to 200 ppm are acceptable in a fish pond and is generally low toxic for some species whereas especially the marine
species are sensitive to its presence.
Optimum Level:
Nitrate level are normally stabilized in the 50-100 ppm in range.
Management:
Increase plant density and by the use of denitrifying biological filtration nitrate concentration can be reduced. Dilution by
water change (ensure water used for change has a lower nitrate level).
Plankton:
Aquatic pelagic organisms, which are carried about by the movement of the water rather than their own ability to swim
are called planktons. The plant components are called as phytoplankton and animal components as zooplanktons and they
serve as fish food organisms. Plankton density Variation depend upon the fertilizers used & fish species culture N, P & K
are most important elements for plankton growth.
Effects:
Excess production of plankton forms algal bloom. It Causes shallow thermal stratification prevents the light penetration
for photosynthesis to depths below 1m so leading to the anoxic conditions resulting in fish kills.
Optimum level:
Bhatnagar and Singh (2010) suggested the optimum plankton population (approximately 3000-4500 Nos. L -1) in pond
fish culture.
Management:
When plankton scums appear, DO should be measured daily to ensure that oxygen is present in depths below 1.3 m. Light
penetration and distribution of DO in ponds can be facilitated with copper tetraoxosulphate (CuSO4) in one or two
applications, a week. The quantity of CuSO4 in waters with 25ppm hardness is 800 g/ha surface area. Using herbivores
that reduces the blue-green algae & total plankton biomass.
Primary productivity:
This is the rate at which photosynthesis takes place. The most commonly used index of productivity is the DO content of
the water. Primary productivity may be reported as net or gross. A fish pond can be considered good in productivity if it
is slight green in colour, with no scum on the surface and having a transparency of about one feet.
Effects:

10. ASRAFUL ALAM 10
Primary productivity plays a vital role in an aquatic culture system.
Optimum Level:
According to Bhatnagar et al. (2004) 1.60-9.14 mg C L-1 D-1 (GPP)—is optimum level for primary productivity.
Management:
Productivity can be improved by use of organic/inorganic fertilizers in ponds. In case of plankton bloom / swarm;
feed/manure application can be suspended for some time.
References
1. Fundamentals of Aquacultural Engineering, (1994), Thomas B. Lawson, Department of Biological Engineering,
Louisiana State University.
2. Pond Aquaculture Water Quality Management, (1995), Claude E. Boyd, Alabama Agricultural Experiment station,
Department of fisheries & Allied Aquacultures , Auburn University, Alabama.
3. Water Quality Considerations For Aquaculture, Robert C. Summerfelt, Department of Animal Ecology, Iowa State
University.
4. Central Water Commision, (CWC), (2000), Water and related statistics, New Delhi.
5. Water quality guidelines for the management of pond fish culture Anita Bhatnagar, Pooja Devi International
Journal of Environmental Sciences Volume 3 No.6, 2013.
6. American Public Health Association (APHA), (2002), Standard method for examination of water and wastewater.
7. Subramanian, (1994), Hydro geological studies of the coastal aquifers of Tiruchendur, Tamil Nadu, PhD thesis,
Manonmanian sundaranar University, Thiruneveli, p 75.
8. Shah. T., Molden. D., Sakthivadivel. R. and Seckler. D., (2000), The global ground water situation: Overview of
opportunity and challenges. International water management institute, Colombo.
9. Sadashivaiah C. Ramakrishnaiah. C.R., Ranganna. G., (2008), Hydrochemical Analysis and Evaluation of
Groundwater Quality in Tumkur Taluk, Karnataka State, India, Int. Jour.Environ. Res. Public Health, 5(3), pp 158-
164.
10. Thussu. J.L., (2006), Geology of Haryana and Delhi. Geol. Soc. Ind. Publ., p 116.
11. Wilcox, L. V., (1995) Classification and use of irrigation waters, US Department of Agriculture, Washington DC, p
19.
12. Wilcox. L. V., (1948), The quality water for irrigation use. US Dept. Agric. Bull., 40