Water quality problems in fishNitrogen components and metal toxicity

By Abisha.S.JMFT160085

Nitrogen components

Ammonia

•Ammonia is a major metabolic waste product from fish. •It is excreted across the gill membranes and in the urine.•The primary source of ammonia in aquaculture systems is fish feed.

Ammonia exist in 2 forms

Ammonium ions

Free Ammonia

Water temperature ↑ Ammonia ↑ PH ↑ Ammonia ↑

But Salinity ↑ Ammonia ↓

Ammonia is more toxic at low DO

Major sourcesExcretory product of fishDecomposition of organic wastesIn aquaria ammonia toxicity is through inadequate biofiltration

Lowest lethal limit of toxicity for fish – 0.2-0.5 mg/l of free ammonia

Maximum level of ammonia that fish can tolerate is 0.01-0.02 mg/l

Toxicity of Ammonia depends on

Species of fishExposure to level of free AmmoniaPeriod of exposureAny previous acclimatization effects

Exposed Fish•Changes in blood chemistryEx- Raised pH Osmoregulatory problems Respiratory difficulties

Physiological effects

Disturbs Osmoregulatory system by increasing Fish permeabilityIn FW fish - increases Urine flowIn MW fish - increases Drinking rate

Respiration is affected Ammonia attack and destroy mucus of gills and cause them to swell upThis stimulate hyperplasia.

At high levels – Ammonia acutely lethal to fishDestroys epithelium of skin and gut causing hemorrhageAffects fish’s CNS causing

Excitability and abnormal swimming

Exposure to Chronic – sub lethal levelsResults in Growth suppression

Control measuresIn emergency situationsAmmonia quickly reduced by

Partial water exchange Addition of Zeolite Transfer of fish to ammonia free water

Long term measuresImproving biofiltrationReducing SDRemoving other sources of ammonia by reducing the level of organic wastes

Nitrite

Less toxic than ammoniaNitrite toxicity influenced by environment factors

Water hardness reduces nitrite toxicityIt occurs when there is inadequate biofiltration

Fish Exposed to Nitrite

Gills absorbs NO2

Enters the blood

Within blood oxidises the respiratory pigment (Hg) into methemoglobin

Methemoglobin is less efficient in carrying Oxygen to tissues

Lethal level -10-20mg /litLethal toxicity varies with speciesEg- Guppies can tolerate upto 100mg/Lit Discus -0.5mg/lit can cause disease

Nitrite poisoning causesListlessnessAnorexiaPigmentation of liver, spleen, kidney

Behavioural symptoms Increased Gill beat ratePiping at the water surface

It could cause Cardiac arrest

Chronic exposure to sub lethal nitrite levelsLinked with ↑ susceptibility to bacterial infections

Fish has brown blood and brown gills

Control measures

By partial water exchangeBy improving biofiltration(to allow greater colonisation of Nitrobacter)Addition of NaCl at 100 mg/l to water reduces nitrite toxicity in case of cyprinidsHard water reduces nitrite toxicity

NitrateEnd product of bacteria- mediated nitrification under aerobic condition.More toxic in salt water than fresh water.It has Lowest limit of lethal toxicity of 50-300mg/lit

General information about nitrogen component problems in aquaria

New tank syndrome- due to that the filter has not fully matured

High Ammonia and nitrite indicates that the filter is overloaded either the fish population is too large filter bed is too small

Overfeeding also cause this overloading effect

Another cause is excessive cleaning of filter medium

High Ammonia and nitrite indicates that the filter bacteria have been inhibited or destroyed by some type of toxins

Bacterial filter toxins takeup in the form of insecticides pesticide- methylene blue and some antibiotics also have same effect

Heavy metals Small quantity of such heavy metals are needed for fish.Eg- Zinc is the component of enzymes.

When present in high concentration these heavy metals are toxic to fish

4 common metals are studiedCopperCadmiumMercury Zinc

The most common metal pollution in freshwater comes from mining companies. They usually use an acid mine drainage system to release heavy metals from ores, because metals are very soluble in an acid solution.

Metals in water can exist as several chemical forms depends on the water hardness,pH value, temperature & dissolved substances in water

Eg- Cu is more soluble in soft water (exist as highly toxic as free Cu) while in hard water it forms calcium carbonate.This calcium carbonate precipitates out and less toxic to fish.

Diagnosing lethal doses of heavy metals is extremely difficult.Most metals damage the blood,internal organs & gill damage Copper and Zinc causes- Respiratory stress by damaging gill lamellae.Cadmium is linked with vertebral damage in common minnows

Water chemistry influences metal toxicity.Hardness reduces Heavy metal toxicity of copper.

Iron and lead should never be present in levels above 0.03mg/l

Cu levels should be half that 0.015mg/l

Pesticides

Water supply companies add insecticides to the water to kill any pests such as Water lice.

These insecticides may take the form of pyrethrin or permethrin.

These are usually added to water supply in spring and autumn levels of 5-10 mg/l over a 7day period.

Susceptibility to pyrethrin and permethrin depends upon sp. Killifishes- die within 48hrs at level of 74µg/litTrout – die within 48hrs at level within low as 2.5-6µg/lit

Harmful directly or indirectly.Most are non specific poisons

Eg-organophosphate inhibits cholinesterase activity in vertebrates

In affected animals normal nerve functions are grossly disturbedResults in death due to asphyxiation

These chemicals are biologically active for only a few days. So the effects are acute poisonings or fish kills

Simillarly pesticides at low concentration can severely affect the aquatic ecosystem by killing the invertebrates

Thank you