Water quality is the most important factor affecting fish health and performance in aquaculture production systems.

1. R. K. Brahmchari
Assistant Professor
College of Fisheries, Dholi
(RPCAU)
Muzaffarpur, Bihar
Role of Chemical
Parameters of
soil & water on
Fish Health

2.  The single, most important factor affecting fish health &
influencing disease in fish ponds is water quality.
 Component of water
 Natural water consist of 8 ions: 4 negatively charged 
chlorides (Cl-), sulfates (SO4
--), carbonates (CO3
--) & bicarbonates
(HCO3
-); 4 positively charged  sodium (Na+), potassium (K+),
magnesium (Mg++), & calcium (Ca++)
 Key nutrient ions in traces: Phosphates, nitrate & silicate 
algae growth; minerals: copper, iron zinc, fluoride, cobalt and
molybdenum  these are important in minute amount, but
can be toxic to fish at higher levels
 Principal dissolved gases in water: O2, CO2 & N2
– The ratio of water solubility of CO2 to O2 to N2 is 70:2:1

3. What do fish want?
 Low ammonia & nitrite: NH3, N02, N2 etc
 Optimum water hardness, pH & temperature
‒ Hardness: a measure of the concentration of divalent
metal ions such as calcium, magnesium, iron, zinc etc.
‒ In most water, it consist mainly of calcium & magnesium
salts, with trace amounts of other metals.
 Low levels of organic pollution
 Stability not fluctuation: constant changes  stress
(eg. pH, temp.)

4.  pH describes how acidic or basic a substanceis.
 H refers to the amount of hydrogen ions and hydroxide ions
present in a liquid, such as fish tank water.
 The pH scale ranges from 0-14.
 If water contains an equal amount of hydrogen ions (H+) &
hydroxide ions (OH-), it is neutral (pH 7.0).
 An increase in the amount of H+ ion, will cause water to
become more acidic, having a low pH.
 Conversely, increasing the amount of OH- will cause water to
become more basic (alkaline), having a high pH.
1. pH

5.  The pH is determined by taking the negative logarithm of
the H+ concentration (-log(H+)).
 The logarithmic scale means that each number below 7 is
10 times more acidic than the previous number when
counting down.
 Likewise, when counting up above 7, each number is 10
times more basic than the previous number.

6. Aquatic pH levels. The optimum pH levels for fish are from 6.5 to 9.0.
Outside of optimum ranges, organisms can become stressed or die.

7. Effects of pH on aquatic life
 If the pH of water is too high or too low, the aquatic
organisms living within it will die.
 pH can also affect the solubility and toxicity of chemicals
and heavy metals in the water.
pH Effects on fish
4 Acid death point
4 to 5 No reproduction
4 to 6.5 Slow growth
6.5 to 9 Desirable ranges for fish growth & reproduction
9 to 10 Slow growth
≥11 Alkaline death point

8. Alklosis Alkaline pH Effect  Occur above pH 8 to pH 9
 Alkalinity is related to the amount of dissolved calcium,
magnesium, and other compounds in the water and as
such, alkalinity tends to be higher in "harder" water.
 When the pH of freshwater becomes highly alkaline (e.g.
9.6), the effects on fish may include: death, denaturing
cellular membranes like gills, eyes, and skin and an inability
to dispose of metabolic wastes.
 At high pH (>9) most ammonium in water is converted to
toxic ammonia (NH3) which can kill fish.
– These levels can also cause gill and kidney damage,
impaired growth, and decreased resistance to disease.

9. Causes of acute high pH:
 High level of alkalis leaching out of inadequately cured
concretetanks.
 Improper use of slaked or hydrate lime will rapidly rise the
pH.
 Chronic high pH in ponds is caused by the presence of
excessive phytoplankton and thus excessive
photosynthesis which consume CO2 during the day time.

10. Diagnosis:
1. Case history: improper lime treatment of the pond, cloudiness
of the skin and gills.
2. Clinical signs:
 High pH in ponds is dangerous because it increases the amount of
toxic unionized ammonia.
 Corneal damage.
 Long term conditions above 9.0 can cause kidney damage.
 Hypertrophy of the gill mucous cells and epithelial cells.
 Alkaline pH increases the mortality of incubating eggs (acid water is
somewhat bacteriostatic).
3. Measurement of the pH of the water by colorimetric test or
digital electronic pH meter.

11. Treatment
 Deficiencies in hardness can be corrected by adding Gypsum
(calcium sulfate).
– The amount of gypsum needed to roughly balance hardness and
alkalinity can be calculated by subtracting hardness from alkalinity
and multiplying that value by two.
– For example, if hardness is 30 mg/L as CaCO3 and alkalinity is 90
mg/L as CaCO3, then 120 mg/L of gypsum will be needed.
 An emergency treatment that quickly reduces high pH is the
application of alum (aluminum sulfate).
– It is safe, relatively inexpensive that reacts in water to form an acid.
– Alum may also help to reduce pH indirectly by removing
phosphorus—an important nutrient for plant growth.
– It does not have a permanent effect and it may need to be applied
more than once until plant or algal growth decreases.
– Initial dose of 10 mg/L alum (12 kg of alum per acre-foot of water)
followed by additional applications in 5- to 10-mg/L

12.  Most frequently recommended treatments for high pH—
sodium bicarbonate (also called bicarbonate of soda or
baking soda)—is the least effective.
– It is a weak acid  large amounts must be added to
significantly reduce pH, especially in waters with high total
alkalinities

13. Acidosis  Acidic pH Effect  Occur below pH 5.5
Low pH levels can encourage the solubility of
heavy metals.
– As the level of hydrogen ions increases, metal cations
such as aluminium, lead, copper and cadmium are
released into the water instead of being absorbed into
the sediment.
– As the concentrations of heavy metals increase, their
toxicity also increases.
– Aluminum can limit growth and reproduction while
increasing mortality rates at concentrations as low as
0.1-0.3 mg/L

14. Diagnosis:
1. Case history:
 In acute cases there are mortalities with tremors (twitching
movements of one or more body parts), hyperactivity and dyspnea
(difficulty in breathing).
 In chronic cases there is increased mucous production.
2. Clinical signs
 Acute acidosis  characterized by tremors and hyperactivity, gill
tissue is the primary target organ in which low pH stimulates
increased mucous production which interferes with gas and ion
exchange leading to respiratory and osmotic stress.
 Chronic acidosis  associated with poor growth, reproductive
failure and increased accumulation of heavy metals.
3. Measurement of the pH of the water by colorimetric test or pH
meter.

15. Treatment
 If alkalinity and hardness concentrations are below the
suggested level, both can be increased by adding
agricultural limestone [CaCO3].  It will not increase pH
beyond a maximum of 8.3.
 The use of hydrated lime (CaOH2) or quick lime (CaO) is
not recommended because either of these compounds
can cause the pH to rise very rapidly, to levels that are
harmful to aquatic life.

16.  Nitrogen is an essential nutrient 
required by all plants & animals 
for the formation of amino acids.
 In its molecular form, nitrogen
cannot be used by most aquatic
plants  it must be converted to
another form.
 One such form is ammonia (NH3) 
it may be taken up by plants or
oxidized by bacteria into nitrate
(NO3
-) or nitrite (NO2
-).
2. Ammonia
Fish
+
Feed
Ammonia
(NH3 & NH4
+)
NO2
-
(Nitrite)
NO3
-
(Nitrate)
Plants,
Phytoplankton,
atmosphere (in
ponds
Nitrosomonas,
Nitrospira
Nitrobacter,
Nitrospira
IOI

17.  Ammonia exists in an pond in two forms:
– free or unionized ammonia (NH3) &
– ionized ammonia, called ammonium (NH4)
– Together, these two forms of ammonia are
called TAN which means total ammonia nitrogen
 Free ammonia is highly toxic compared to ammonium (not
that this means you can relax if your ammonia is in the
form of ammonium).
 The proportion of toxic to less toxic ammonia depends on
several factors, the most important being pH and
temperature.

18. Effects of ammonia on aquatic life
 Ammonia is a toxic compound that can adversely affect fish
health  Ammonia Poisoning (New tank syndrome)
 Ammonia poisoning can happen  suddenly or over a
period of days.
 Lethal concentration for different fish species  ranges
from 0.2 to 0.5 mg/l.
 Plants are more tolerant of ammonia than animals, and
invertebrates are more tolerant than fish.

19.  The nature and degree of toxicity depends on many factors,
including the
– chemical form of ammonia  (NH3),
– the pH and temperature of the water,
– the length of exposure, and
– the life stage of the exposed fish.
 Clinical signs of ammonia poisoning
– Acute toxicity is associated with anorexia (stop feeding), lethargy,
swim erratically, behavioral abnormalities and neurological signs.
– Fish may gaspfor breath at the water surface
– Purple or red gills
– Loss of appetite
– Fish lays at the bottom of the tank
– Red streaking on the fins or body

20.  At higher levels (>0.1 mg/liter NH3) even relatively short
exposures can lead to skin, eye, and gills damage.
– Gill Hyperplasia - the gill filaments are swollen and clumped
together, reducing the fish's ability to 'breath'.
 Elevated levels can also lead to ammonia poisoning by
suppressing normal ammonia excrement from the gills.
– If fish are unable to excrete metabolic waste product there is a
rise in blood-ammonia levels resulting in damage to internal
organs.
The gill filaments are swollen and clumped
together, reducing the fish's abilityto 'breath'.

21.  Ammonia toxicity is thought to be one of the main causes of
unexplained losses in fish hatcheries.
Treatment
 Lower pH below 7.0  every 1 unit decrease in PH there is a
ten fold decrease in unionized ammonia  But this must be
done with great care because rapid drop in pH cause other
problems.
 25 - 50% water change  add freshwater
 Use chemical to neutralize ammonia – zeolite (Aluminium
Silicates)  15-20 Kg per ha
 Discontinue or reduce feeding

22.  Nitrite, an intermediate in the oxidation of ammonium to
nitrate.
 Nitrite poisoning follows closely on the heels of ammonia
as a major killer of fish.
 The LC50 of Nitrite toxicity for the majority of freshwater
fish ranges from 0.60 to 200 mg/1. Saltwater fish have a
much higher tolerance for nitrites.
 Symptoms
– Fish gasp for breath at the water surface
– Fish hang near water outlets
– Fish is listless
– Tan or brown gills
– Rapid gill movement
3. Nitrite

23.  Freshwater fish are hyperosmotic to their environment 
require an active uptake of ions across the gills (chloride
cells of gills)  to compensate for ions lost with urine &
via passive efflux across the gills.
 Problems with nitrite in freshwater fish stem from the fact
that NO2
– has an affinity for the branchial Cl– uptake
mechanism,  presumably Cl– /HCO3
– exchanger; thus,
whenever nitrite is present, a part of the Cl – uptake will be
shifted to NO2
– uptake
 Nitrite Toxicity, Methemoglobinemia or Brown Blood
Disease is a disease caused by high nitrite concentrations
in the water.

24.  The blood appears to be the primary target of nitrite
action.
 From the blood plasma  nitrite diffuses into red blood
cells  where it oxidises iron in haemoglobin (Hb) to the
+3 oxidation (ferric) state.
 Haemoglobin that is changed in this way  called
methaemoglobin or ferrihaemoglobin, which lacks the
capacity to bind oxygen  This leads to tissue hypoxia.
4 Hb(Fe2+)O2 + 4 NO2
– + 4 H+ = 4 Hb(Fe3+) +4 NO3
– + O2 + 2 H2O
 It gives whole blood a brownish colour condition known
as 'brown blood disease’
Ferrousstate Ferric state

25. Mechanism of detoxification
 The RBCs of fish contain methaemoglobin reductase 
reconverting methaemoglobin to haemoglobin.
 This occurs steadily and restores the normal proportion
of haemoglobin within 24–72 hours if a fish is
transferred to water that lacks nitrite.

26. Treatment
 Water exchange
 Add salt, preferably chlorine salt  sodium chloride 
addition of 1.0 ppt (1 gram per liter) salt will yield
approximately 500 ppm chloride (more than enough to
do the job).
 Addition of nitrifying bacteria (nitrobacter)
 Reduce feeding
 Increase aeration

27.  Although far less toxic than ammonia or nitrite, high
nitrate levels, can still kill fish if high enough  Nitrate
poisoning or nitrate shock
 Nitrate poisoning occurs when fish are exposed to
gradually rising nitrate levels over a period of time.
 As levels climb the existing fish become used to it at first,
levels can rise to 100ppm or even 150ppm before the fish
start to become ill and die
 Overfeeding and overstocking are also significant
contributors to rising nitrate levels.
4. Nitrate

28. Symptoms
 Loss of appetite
 Fish become listless
 Fish may show loss of equilibrium
 Fish may lay at bottom of the tank
 Rapid gill movement may be observed
 Fish may curl head to tail (advanced stages)
Nitrate poisoning in goldfish

29. A Nitrate level of around 15 -20 ppm is usually required in
ponds for phytoplankton production.
Treatment
 Water exchange  20-25%
 Increase aeration
 Reduce feeding

30.  Salinity is defined as the sum of all ions in water which
comprises mainly of sodium, chloride, calcium,
magnesium, potassium, bicarbonate and sulfate ions.
 Salinity is measured in grams of dissolved material per
litre.
Eg. Seawater has avg. salinity 35 gram/litre (35 ppt)
 Water bodies can be differentiated into three major
categories using salinity.
– Fresh water  relatively low salinity
– Sea water  has high salinity
– Brackish water  lies between the two extremes
5. Salinity

31. Effects of salinity on fish
 Salinity is a vital water quality parameter for fish growth 
retard fish growth at different saline conditions.
– Euryhaline
– Stenohaline
 Fish in marine or freshwater environments use energy to
hold ions in or off their bodies respectively
through osmoregulation.
 Shifting salinity ranges result in excessive osmotic pressure,
& a general stress response  lower their resistance to
disease.

32.  Dissolved oxygen gets into the water by
– diffusion from the atmosphere,
– aeration of the water as it tumbles over falls and rapids, and
– as a waste product of photosynthesis.
 Factors affect the DO level
– Reduced DO levels in stream/pond water may be because the
water is too warm.
– Decreased DO levels may also be indicative of too many
bacteria and an excess amount of BOD which use up DO.
– A third reason for decreased DO may be fertilizer runoff from
farm fields. [If the weather becomes cloudy for several days, respiring
plants will use much of the DO while failingto photosynthesize.]
6. Dissolved Oxygen

33.  Large daily fluctuations in dissolved oxygen are characteristic of
bodies of water with extensive plant growth.
 DO levels rise from morning through the afternoon as a result of
photosynthesis, reaching a peak in late afternoon.
 Photosynthesis stops at night, but plants and animals continue to
respire and consume oxygen.
 As a result, DO levels fall to a low point just before dawn.
Dissolved oxygen levels may dip below 4 mg/l in such waters.

34. How dissolvedoxygen affects aquatic life
 The recommendedminimum DO requirements:
– Cold water fish - 6 mg/l (70% saturation)
– Tropical freshwater fish- 5 mg/l (80% saturation)
 When the DO drops below 3 mg/l, even the hardy fish die.
 Keep in mind that even though there may be enough DO to
keep an adult alive, reproduction may be hampered by the
need for higher DO for eggs and immature stages.

36. Consequences of Unusual DO Levels
1. Hypoxia
 Hypoxia or oxygen depletion is a phenomenon that occurs in
aquatic environments as dissolved oxygen becomes reduced in
concentration to a point detrimental to aquatic organisms living.
 DO is typically expressed as a percentage of the oxygen that would
dissolve in the water at the prevailing temperature and salinity (both
affect the solubility of oxygen in water).
– An aquatic system lacking dissolved oxygen (0% saturation) is
termed anaerobic.
– Reducing or anoxic is a system with a low DO concentration in the
range between 1 and 30%. Most fish cannot live below 30% DO
saturation.
– A “healthy” aquatic environment should seldom experience DO of
less than 80%.

38. Clinical Sign
 Oxygen deficiency causes asphyxiation and fish will die, depending
on the oxygen requirements of the species.
 Collect near the water surface, gasp for air, gather at the inflow to
ponds where the oxygen levels are higher
 Reduce food intake
 Fish become sluggish, fail to react to irritation, lose their ability to
escape capture and ultimately die.
 The major pathological-anatomic changes include
– a very pale skin colour,
– congestion of the cyanotic (blue/purple) blood in the gills,
– adherence of the gill lamellae, and
– small haemorrhages in the front of the ocular cavity and in the skin of
the gill covers.

39. Treatment
 Water exchange  20-25%
 Increased aeration
 Add oxygen enhancer (work for short period)
 Reduce stocking density

40. 2. Hyperoxia
 Hyperoxia is the stateof water when it holds a very high
amount of oxygen.
 At this state, water is described as having a dissolved
oxygen saturation of greater than 100%. This percent can
be 140-300%.

41. How Can Water be More than 100% Saturated?
 100% air saturation is the equilibrium point for gases in water,
because gas molecules diffuse between the atmosphere and the
water’s surface.
 According to Henry’s Law, the DO content of water is proportional
to the percent of oxygen (partial pressure) in the air above it.
 In water it usually is expressed in milligrams per liter (mg/L), parts
per million (ppm), or percent of saturation.
 As oxygen in the atmosphere is about 20.3%, the partial pressure
of oxygen at sea level (1 atm) is 0.203 atm. Thus the amount of
dissolved oxygen at 100% saturation at sea level at 20° C is 9.03
mg/L
 This shows that water will remain at 100% air saturation at
equilibrium. However, there are several factors that can affect
this.

43. Dissolved oxygen often reaches over 100% air saturation due
to photosynthesis activity during the day.
 During photosynthesis, oxygen is produced as a waste
product. This adds to the DO concentration in the water,
potentially bringing it above 100% saturation.

44.  Supersaturated water can cause gas bubble disease in fish
and invertebrates.
 If fish are exposed to such water, their blood equilibrates
with the excess pressure in the water.
 Bubbles form in the blood and these can block the
capillaries; in sub-acute cases the dorsal and caudal fin can
be affected, and bubbles may be visible between the fin
rays.
 The epidermal tissue becomes necrotic and cases are
known where the dorsal fins of fish have become
completely eroded.
 In severe cases, death occurs rapidly as a result of blockage
of the major arteries.

45.  Significant death rates occur when dissolved oxygen remains
above 115%-120% air saturation for a period of time.
 The remedy is to remove the fish and transfer to normally
equilibrated water.