Water Quality Management For Recirculating Aquaculture
AquacultureWater Quality Management for Recirculating AquacultureWater quality is a term that reflectsthe overall ability of culture water toprovide optimal growth conditions forthe species of interest. Water sourceis the most critical considerationwhen determining a facility locationand the production capacity of thesystem. Inadequate water quality andquantity will cause major issues interms of production yields, fish health,and profit. While water quality canbe remediated with filters and othertreatment techniques, these optionsincrease production costs. The following considerations should guide thedecision to establish an aquacultureoperation at a given location.BiofilterWATER SOURCEWell Water – Well water is generallythe best option for an aquacultureoperation but should be tested forbasic water quality parameters suchas ammonia, iron, alkalinity, and asuite of contaminants like pesticides,heavy metals, and other toxinsbefore a facility is built. Well wateris typically free of any form of lifeor chemical contamination, but it’simportant to note that the aquiferis subject to the watershed use andchemistry of the underlying bedrock.Limestone bedrock produces waterwith high hardness and alkalinity,whereas granite bedrock will producelow alkalinity and hardness. Well water will generally be devoid of oxygenand may have other dissolved gasseslike carbon dioxide, nitrogen gas, andhydrogen sulfide gas. The water mustbe aerated or degassed to atmosphericsaturation levels before the water enters the culture unit. Other dissolvedcomponents such as iron and magnesium can also cause issues for fish.Aeration can help these componentsprecipitate out of solution and returnto non-toxic levels for fish, dependingon age and species.Municipal Water – Municipal wateris typically treated with a chlorine and/or chloramine compound to kill anypathogens that may be present. Thesecompounds are extremely toxic toboth fish and the beneficial bacteriafound in the biofilter of recirculating aquaculture systems. Chlorineand chloramine compounds must beremoved from the municipal waterbefore they come in contact with theculture water.Surface Water – Ponds, lakes, andrivers contain insects, fish, amphibians, parasites, pathogens, pesticides,and organic or heavy metal contamiFA 0003A December 2014
Aquaculturenants. The contents of surface waterscreate biosecurity concerns and shouldbe avoided if at all possible. If thereis no alternative water source, watershould be filtered through a 20-µmscreen or sand filter and then treatedwith a powerful oxidizer like hydrogen peroxide or ozone. This treatmentshould be followed by ultraviolet sterilization and activated carbon filtrationbefore any surface water enters thefacility. Contaminants in surface waterare often cyclic in nature and mustbe continuously surveyed during theculture season when possible.It may be prudent to use a distillation process or reverse osmosis (RO)filtration to ensure that only cleanwater enters the facility, especially ifthere are heavy metals or pesticidespresent. This style of filtration canbe cost prohibitive, especially if largevolumes of water are required. Keepin mind that certain salts (i.e., electrolytes), are required for fish to maintainoptimal osmotic balance for reducedstress. Commercially available oceansalt mixes can be dissolved in purifiedwater to create the proper salinity.Typical salinities for freshwater fishrange from 0.5- to 8-parts per thousand (g/L).contained within the aquaculture system. No other physical factor affects thedevelopment and growth rates of fishas much as water temperature. Eachspecies of fish has a temperature rangeit can tolerate. Within that range, thereis an optimum temperature for growthand reproduction which may changeas the fish grows. Many biologicalprocesses, such as spawning and egghatching, are geared to natural annualchanges in environmental temperature. Each 10 C temperature changehas a two-fold effect on the metabolicrate of cold-blooded animals. Forexample, increasing water temperature10 C will double the metabolic rateof an organism, which correlates tohigher food consumption and growthrate as well as an increased biologicaloxygen demand (BOD). However, thisrelationship only holds true within theacceptable temperature range for anygiven species. Outside this temperature range, proteins and enzymes thatperform essential metabolic processesof a given species begin to denatureand break down such that they are nolonger useful.Rain Water – Rain water is naturallydistilled and will lack the hardnessand various salts needed for osmotic equilibrium. Rain may be a goodsource of water, but it is also subject toatmospheric conditions. Pesticides andpathogens may be in the air, so rainwater should be treated in a similarfashion to surface water to ensure thatit is adequate to sustain life.PHYSICAL PARAMETERSTemperature – Water temperatureaffects metabolic and biochemical processes of the culture species and bacteriaSubmersible water heater2Like fish, pathogens have an optimumtemperature range for development,and outbreaks are more prevalentduring these conditions. Most chemical substances dissolve more readilyas temperatures increase. In contrast,gases such as oxygen, nitrogen, andcarbon dioxide become less soluble astemperature rises.Temperature shock, caused by rapidtemperature change, can stress fish andlead to death. This is most likely whenfish are transported for stocking. It isimportant to slowly acclimate fish tothe desired temperature in order toprevent shock. Prior to stocking, waterin the transport container should betempered with water from the tanksthey will be stocked into. For small,sensitive fry, a temperature rate of 3.6 F(2 C) per hour is suggested. Larger,more hardy, fish can withstand morethan a 9 F (5 C) per hour change intemperature. Tropical fish species cangenerally tolerate an increase in watertemperature better than a decrease.The opposite is true for temperate andcool-water species. Fish that initiallysurvive a temperature shock may besufficiently stressed to later succumbto infection, disease, or parasites.The physical and chemical propertiesof certain water components can bealtered by changing water temperature. For example, the maximumamount of dissolved oxygen (DO)water can naturally hold decreaseswith increasing temperature (seeDissolved Oxygen on page 3).Additionally, the percentage of totalammonia nitrogen (TAN) that is in thetoxic form increases with increasingwater temperature and pH (Table 1.)(see Ammonia Nitrogen on page 3).For these reasons, it may be useful tomaintain temperature and pH at thelowest end of the optimal range forany given species.
AquacultureTable 1. Relative percentage of total ammonia nitrogen (TAN) in the toxic,unionized form at a given temperature and pHTemperature ( C)pH8121620242832Table 2. Dissolved oxygen (DO)concentration at saturation at agiven water temperatureTemperatureDissolved OxygenConcentration(mg/L)7.00.20.20.30.40.60.81.0 C d Oxygen – Dissolvedoxygen (DO) is arguably the mostimportant water quality parameter forfish survival. Concentrations of oxygen are expressed as parts per million(ppm) by weight, or milligrams perliter (mg/L). The concentration of DOper unit volume of water intrinsicallybecomes less as water expands atwarmer temperatures. The equilibriumconcentration of gasses achieved whenwater is exposed to the atmosphere forany given water temperature is calledsaturation. For example, the DO saturation level for water at 50 F (10 C)is 11.3 mg/L, whereas DO saturationat 86 F (30 C) is 7.5 mg/L (Table 2.).Systems that use liquid oxygen cancause excess levels of oxygen, knownas supersaturation. Supersaturationof oxygen can be harmful becausedissolved oxygen taken into the gillscan return to a gaseous state, causingbubbles in the blood and leading tomortality. Aeration with air will onlybring the DO concentration to thesaturation level. Aeration is the onlycompletely safe way to regulate DOconcentration of 46.6Most warm water fish require aminimum of 4 ppm and cold waterfish require 5 ppm DO to achieveappropriate growth, reproduction,and health. Early life stages of fish aretypically more able to survive oxygendeprivation than adult fish because ofthe relatively high ratio of gill surfacearea to body weight. In other words,juvenile fish are able to take up moreoxygen per unit body weight thanadult fish. Chronically low DO levelscause stress, increasing the chance ofinfectious diseases.yet there is less oxygen available perunit of water at these higher temperatures. It therefore becomes moreimportant to provide aeration at highwater temperatures.The most common usage of oxygen inaquatic organisms is for respiration.Respiration breaks down organicmolecules like carbohydrates, liberating energy that is used to performbiological processes. The oxygenrequirement for aquatic life is directlyaffected by the temperature andthe biomass of all aquatic life in thesystem (fish, bacteria, etc.). Higherwater temperatures and biomass havea higher BOD. Problematically, optimalgrowth rates occur at the upper end ofa species temperature tolerance range,pH – Acidity, or pH, refers to thecapacity of water molecules to donatehydrogen ions (H ). Pure water has aneutral pH 7.0, with pH 1 to 6.9 being acidic and pH 7.1 to 14 being basicor alkaline. The ideal pH for aquaculture is 7.0; the acceptable range is 6.5to 9.0 for most aquaculture species.The pH has many implications forthe biological and chemical processesthat occur in an aquaculture system.Sudden changes in pH can stress theculture animals and kill beneficialbacteria in recirculating aquaculture3
Aquaculturesystem (RAS) biofilters. Increasing pHalso increases the percentage of toxicunionized ammonia nitrogen (Table1.). For this reason, it is important tomaintain temperature and pH at thelowest end of the optimal range forany given species.Fish have less tolerance of pH extremesat higher temperatures. Ammoniatoxicity becomes an importantconsideration at high pH (see Ammonia Nitrogen on page 5), and hydrogensulfide is more toxic at low pH. ThepH of culture water is influenced bythe amount of carbon dioxide present.Much of the CO2 present is the resultof animal respiration. Since CO2 inwater is an acidic substance, the pH ofwater will continually decrease overtime without proper aeration. Theamount of the pH fluctuation dependson the alkalinity or buffering capacityof the water. The addition of agricultural lime (CaCO3) or baking soda(NaHCO3) to the RAS increases thepH buffering capacity of the water.Salinity – Salinity is a measure of thesalt concentration of water and is typically expressed in parts per thousand(PPT) or grams per liter (g/L), but alsomay be measured in terms of specificgravity. Salts are inorganic moleculesthat easily dissolve into chargedparticles, or ions, when put into water.These ions formed from the dissociation of salts in water are criticallyimportant for many biologicalprocesses. The ions must exist inspecific concentrations and ratios foranimals to function properly. Somecommon salts are sodium chloride(NaCl), potassium chloride (KCl),calcium chloride (CaCl2), andmagnesium sulfate (MgSO4).Knowing the salinity is extremelyimportant for regulating salt balance(osmoregulation) to promote propercellular function. Salt concentrationtypically occurs through diffusion ofsalt and water across fish gills andskin as well as active filtering throughthe kidneys.Salts are used as a treatment for certain pathogens that are intolerant ofsalinity changes. Salts also cause fishto produce more mucus and sloughoff external parasites. Salt is used toreduce stress during hauling becauseit helps fish osmoregulate more easilysince the blood and water salinitiesare the same. Each fish species has anoptimal salinity level depending on itsnatural environment, and successfulaquaculture operations must provideoptimal salinity levels. Some species,such as salmon and barramundi, havea wide range of tolerable salinitiesbecause of their anadromous nature.Other species require water with asmaller salinity range.Solids – When fish are fed, approximately 25% of their feed immediatelybecomes waste. Solid organic matterin recirculating systems is problematicfor water quality and must be removedGranular sodium chloride salt4from the water as quickly as possible.Solids generally come in the form offecal matter, dead and decaying organisms, and uneaten feed. Solids removalis important for avoiding water qualityissues such as spikes in ammonia oroxygen deprivation. Solids come in allsizes. There are different managementstrategies for each size class.Total Suspended Solids – Suspended solids are particles that are largeenough to be filtered out of the waterby mechanical filtration (using a filterscreen, sand filter, swirl separator, etc.)and/or can be settled out of the watercolumn given sufficient “quiet” time.Suspended solids include colloidal(0.001 to 100 µm dia.) and settleablesolids ( 100 µm dia.).Settleable Solids – Settleable solidsare those with great enough mass tobe settled out of the water in a “quietwater” area with high retention timeand low water velocity. These particlesare the largest portion of the solidswithin the suspended solids category,having a diameter greater than100 micrometers.
AquacultureDissolved Solids – Dissolved solidsare microscopic in size and have characteristics that allow them to stay insolution regardless of settling or“quiet” time. These particles largelyconsist of proteins and amino acids,which are generally removed from thewater by floatation. The stickinessof proteins forms bubbles in water,when aerated which can be removedfrom the system via capillary rise in thenarrow gap between two surfaces using equipment like foam fractionators,also known as protein skimmers.CHEMICAL PARAMETERSHardness – In municipal water,hardness is the measure of the water’scapacity for precipitating soap. Soapis precipitated chiefly by calciumand magnesium ions, but also maybe precipitated by hydgrogen ions orions of metals such as aluminum, iron,manganese, strontium, and zinc. Foraquaculture, hardness is important forlarval fish development because thedissolved minerals in the water areused to create the skeleton and organsof the body and to aid in osmoregulation. For fresh water, hardnessmeasures are related to the underlyinggeology of the area. Limestone bedrock tends to produce water with highhardness and alkalinity because ofthe calcium carbonate (CaCO3) thatis dissolved in the water. Hardnessgenerally occurs in a 1:1 proportionto alkalinity, known as “carbonatehardness”, but can be greater or lowerthan alkalinity depending on chemicalcomposition of the water. Total hardness is usually not as important astotal alkalinity in pond fish culture.Alkalinity – Alkalinity is a measure ofthe dissolved carbonates in the water,or the ability of water to accept andneutralize acidity (hydrogen ions).This alkalinity measurement includesthree forms of negatively chargedcarbon ions: carbonate (CO32-), bicarbonate (HCO3-), and hydroxide (OH-).Alkalinity and hardness are usuallyreferred to in conjunction becausethe original measure of alkalinityis expressed in terms of equivalentconcentrations of calcium carbonate(CaCO3) needed to neutralize acidity,but alkalinity and hardness representdifferent types of measurements. Mostwaters of high alkalinity also have highhardness, but this is not always true.Fish grow well within a wide rangeof alkalinity and hardness. Total alkalinity values in the range of 40 to 300mg/L are ideal for promoting a strongbiofilter and processing nitrogenouswastes. However, alkalinity greaterthan 300 ppm may begin to causeCO2 buildup in the system at low pH,leading to fish health issues.At low alkalinity, water loses much ofits ability to buffer against changes inacidity. In RAS operations, the bacterial decomposition in the biofilter is anacidification process that can result inhazardous pH levels when alkalinity islow. Fish also may be more sensitive tosome toxic substances such as copperat low alkalinity. The use of sodiumbicarbonate (baking soda) to increasealkalinity levels is a relatively easysolution to this issue.Nitrogen – Nitrogen is a majorcomponent of protein, and proteinis a large component of fish feeds.The constant influx of protein meansthat nitrogen processing is critical topromoting healthy fish. Digested fishfeed becomes waste that is excretedfrom the fish in the form of ammonia.Promoting nitrogen cycling throughbiofiltration rivals dissolved oxygenas the most important factor for fishsurvival and growth in recirculatingaquaculture.5Ammonia Nitrogen – Ammoniais excreted into the water by fish asa result of protein metabolism. Someof the ammonia reacts with water toproduce ammonium ions (NH4 ). Theremainder is present as un-ionizedammonia (NH3). Un-ionized ammoniais more toxic to fish than ammonium.Standard analytical methods do notdistinguish between the two forms;both are lumped as total ammonianitrogen (TAN). The fraction of totalammonia that is un-ionized ammonia(NH3) varies with salinity, dissolvedoxygen, and temperature, but is determined primarily by the pH of thesolution. For example, an increase ofone pH unit from 8.0 to 9.0 increasesthe amount of un-ionized ammoniaapproximately 10-fold. These proportions have been calculated for a rangeof temperatures and pH values and aregiven in table 1. Note that the amountof NH3 increases as temperatures andpH increase.To calculate the un-ionized ammonia,determine the percentage from Table 3by using the measured pH and temperature values. Un-ionized ammonia(ppm) (ppm total ammonia x percentage of un-ionized ammonia) / 100.The amount of un-ionized ammoniathat is harmful to fish varies with species. In trout, 0.0125 ppm un-ionizedammonia will damage gills, kidneys,and the liver and reduce growth rates.These same observations occur inchannel catfish exposed to un-ionizedammonia levels greater than 0.12 ppm.Although mortalities may not occuroutright because of ammonia stress,chronic exposure to low levels of unionized ammonia may increase thechance of infectious diseases. Criticallevels of un-ionized ammonia have notbeen determined for many aquaculturespecies, but it is best to maintain ammonia at the lowest possible level atall times.
AquacultureDealing with ammonia issues in wateris a constant struggle, and it is muchmore problematic when fish are heldat high densities with high feedingrates at high water temperatures. Themetabolic rate of fish and beneficialbacteria is higher at warmer temperatures, so the rate of ammonia production and processing increases whentemperatures rise within the species’optimal range. Beneficial bacteria useammonia as a nitrogen source andalkalinity as a carbon source to feedthemselves and grow. It is critical toprovide adequate amounts of alkalinityto process ammonia when the ammonia levels are rising. One fast way todo this is by adding sodium bicarbonate (NaHCO3), or baking soda, whichdissolves quickly in water. Calciumcarbonate (CaCO3), or agriculturallimestone, is also effective at raisingalkalinity, but dissolves much moreslowly and is best to add to the waterprophylactically so that it can dissolveconstantly. Maintaining alkalinity ataround 100 mg/L will help ensure thatnitrogen cycling occurs unhindered.One method of removing ammoniafrom water is to use a negativelycharged mineral called zeolite. Zeolitecan adsorb ammonium ions (NH4 )from the water. It is relatively ineffective at high pH when the ammonia isunionized (NH3). Because ammonianitrogen is mostly in the non-toxicionized form (NH4 ) at low pH already,zeolite may not be extremely effectiveat reducing toxic, unionized ammonia(NH3) issues. Additionally, high hardness and salinity can use up all bindingpower of zeolite, making it ineffectivefor removing ammonium ions.When the ammonia level spikes quickly, the most effective way of reducingit is to perform a water exchange. It isimportant that the water used for thisexchange has very similar temperature,Sodium bicarbonate (baking soda)salinity, and pH as the culture water,with no ammonia present. Keeping alarge head tank of water adequate toperform a 100% water exchange of thesystem will greatly decrease the risk ofcrop failure due to ammonia toxicity.Nitrite – Nitrite (NO2-) is the intermediate product of the oxidation ofammonia to nitrate, and it is also toxicto fish at high levels. The processingof ammonia to nitrate is generallyperformed by bacteria of nitrosomonasgenus in fresh water. Nitrite enters theblood of fish across gill membraneswhere it combines with the oxygen-carrying portion of red blood cells(hemoglobin) to form a compoundcalled methemoglobin, which cannotcarry oxygen. Methemoglobin hasa brown color that it imparts to theblood of fish suffering from nitrite poisoning. Nitrite poisoning thus has thename “brown blood disease.” Becausenitrite interferes with oxygen uptakeby the blood, the symptoms of nitritepoisoning are quite similar to thosecaused by oxygen depletion, exceptthe nitrite poisoning symptoms persisteven when the DO is at saturation.6The nitrite concentration that is toxicto fish depends on the fish species, theamount of chloride ions (Cl-) presentin the water, and the quantity of dissolved oxygen. Rainbow trout becomestressed at 0.15 ppm nitrite and die by0.55 mg/L. Channel catfish are moreresistant to nitrite, but 29 mg/L cankill them.Nitrite is usually not a problem if thereare three or more parts of chloridespresent in the water for every part ofnitrite. Chlorides do not affect theamount of nitrite in the water, butprevent the uptake of nitrite by theblood of the fish. Chloride is the sameelectronegativity and approximatelythe same size as nitrite, and it cancompete with nitrite for uptake in theblood. Any time there is 0.1 ppm ormore nitrite present, the water shouldbe checked for chlorides to see if saltneeds to be added. The addition of25 ppm salt (NaCl) for each ppmnitrite has proven to be an effectivetreatment. A freshwater flush also isrecommended to reduce nitrites.
AquacultureNitrate – Nitrate (NO3-) is the finalmetabolite of ammonia in the nitrification process. Processing of nitrite tonitrate is generally done by Nitrobacterspp. in fresh water. Nitrate is relativelynon-toxic to fish. An acceptable levelof nitrate for trout is below 250 ppm,whereas catfish can tolerate 400 ppmnitrate. Daily water exchanges at 10%of the total system volume are a standard practice in recirculating aquaculture to prevent the buildup of nitratein the system. Because nitrate is thefully oxidized form of nitrogen, highoxygen levels must be maintained inall areas of the recirculating system toprevent reduction of nitrate back tonitrite or ammonia.Nitrate is regulated in Iowa for environmental water quality and humanhealth concerns, so effluent waterleaving an aquaculture facility mustmeet certain criteria to be in compliance with the Clean Water Act (see“effluent considerations”).Nitrogen Gas – Denitrificationmay occur in the absence of oxygen,causing the formation of nitrogen gas(N2), which can be aerated out of thewater and ventilated out of the facility. Dissolved nitrogen gas does notnegatively affect fish at or below 100%saturation. However, supersaturationlevels as low as 102% can cause gasbubble disease in fish. Gas bubbledisease occurs when a dissolved gasemerges from solution and forms bubbles in the blood of a fish. Gas bubbledisease can be caused by any supersaturated gas, but is usually caused byexcess nitrogen. Any reduction in gaspressure or increase in temperaturecan bring nitrogen out of solution andform bubbles; the process is similarto the “bends” in scuba divers. Thesebubbles can lodge in blood vessels,restrict circulation, and result in deathby asphyxiation. Gas supersaturationcan occur when air is drawn in by ahigh pressure water pump or whenair is injected into water under highpressure that is subsequently depressurized. Water that is heated or drawnfrom deep wells is potentially supersaturated. Ensuring high levels ofaeration and ventilation will helpprevent the formation and supersaturation of nitrogen gas in the water.Carbon Dioxide – All waters, particularly ground water, contain somedissolved carbon dioxide. Almost allliving organisms continuously addCO2 to the water through respiration.CO2 forms an acid when it is addedto water, resulting in a pH decline.Conversely, pH increases when CO2is removed. Carbon dioxide can bea problem when associated withoxygen depletion, but usually is nota problem by itself unless it is presentat extremely high concentrations( 20 mg/L). When dissolved oxygenis limited, elevated CO2 levels mayinterfere with the ability of fish to takeup the remaining oxygen. Mechanicalaeration along with proper ventilationin RAS operations can reduce highlevels of CO2.The relationship among CO2, pH, temperature, and alkalinity can be used tocalculate CO2 concentrations. Table 3can be used to determine CO2 levelsfrom the pH, temperature, and total alkalinity (mg/L CO3) of the water. Findthe factor in the table that correspondsto the observed pH and temperature,and multiply this factor by the totalalkalinity to find the CO2 concentration. For example, at pH 7.4 and 68 F,alkalinity 200 mg/L CO3. The factor0.084 is taken from the table, so 0.084x 200 16.8 mg/L CO2. Generally, waters supporting good fish populationshave less than 5 mg/L CO2. Carbondioxide in excess of 20 mg/L may beharmful. If dissolved oxygen contentdrops to less than 5 mg/L, lower CO2concentrations may also be harmful.Chlorine and Chloramine – Chlorine gas (Cl2) is unstable and will aerateout of water within 24 hours whenTable 3. Multiplication factors to determine carbon dioxide from pH,temperature, and total alkalinity*. Multiply the factor in the table by thetotal alkalinity (mg/L) to obtain the carbon dioxide concentration (mg/L).Temperature41 F50 F59 F68 F77 F86 F95 F6.06.26.46.66.85 C2.9151.8391.1600.7320.46210 C2.5391.6021.0100.6370.40215 C2.3151.4600.9210.5820.36720 C2.1121.3330.8410.5310.33525 C1.9701.2440.7840.4930.31330 C1.8821.1870.7490.4730.29835 0.0730.0460.0300.0180.0110.007pH* For practical purposes, CO2 concentrations are negligible above pH 8.47
Aquacultureexposed to the atmosphere. Chloramine (NH2Cl), on the other hand, isvery stable in water and must eitherbe filtered out by activated carbon, orbroken up with a sulfur-containingcompound like sodium thiosulfateor sodium sulfite (food grade). Thechloramine molecule is a combinationof chlorine and ammonia, and onceit is broken up, both of those toxicchemicals are released into the water.Moreover, if sodium sulfite is thechosen de-chlorinator, dissolvedoxygen will also be eliminated fromthe water and pH can decrease inpoorly buffered water. To counterthese effects, municipal water withchloramines can either be filteredthrough carbon filters or held for 24hours in a holding tank with adequatesodium sulfite added (approximately1 g per 10 gallons of water) to breakup the chloramine and aeration tooff-gas the chlorine. The holding tankmay also contain biofiltration materialto process the ammonia before it isallowed to enter the fish culture unit.The addition of sodium bicarbonate(baking soda) at a rate of 0.5 gramsper gallon (0.14 g/L) is also recommended in poorly buffered water. Itis a good practice to chemically testwater for the levels of free and totalchlorine prior to releasing it into theculture water.WATER QUALITYMONITORINGGood water quality is the goal for anyaquaculture operation. Among theparameters most critical to monitor ona frequent or even constant basis aretemperature, dissolved oxygen, andpH. Each species of fish has differenttolerance ranges for each parameterused to quantify water quality. Tilapiaare amongst the most tolerant fishspecies, whereas trout are amongst theWater quality probemost sensitive. The more sensitive afish species is to poor water quality,the more important it is to monitorcontinuously.Manual Monitors – These optionsinclude chemical analysis andelectronic probe methods for datacollection. While chemical analysisis the least costly up-front for smallscale operations, it is quite timeconsuming and requires a competent,detail-oriented worker. Probe metersare a substantial initial investment( 2,000- 3,000), but they significantlydecrease the time required to obtainan accurate reading and are idealfor medium-to-large aquacultureoperations. Calibration is required forany probe, and they should be testedagainst known standards to evaluatethe accuracy of the readings. Waterquality probe technology is constantlyimproving, and calibrations andcompensations for some systems areautomated, which can decrease theskill, time, and maintenance requiredby workers.8Automated Monitors – Automatedsystems are ideal for large commercial-scale operations, especially thosethat need continuous monitoring.These systems utilize probes that arein-line in the plumbing with waterflowing through them, or ones thatare constantly submerged in wa
Aquaculture FA 0003A December 2014 Water Quality Management for Recirculating Aquaculture Water quality is a term that reflects the overall ability of culture water to provide optimal growth conditions for the species of
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