5:54 am, June 17, Thursday

Phase II results: 2008

Physical characteristics of water and its importance in fishery

For fish life, water has great importance, with all its features and characteristics: mechanical, physical, organoleptic, chemical, biological, bacteriological and radioactive. . Water movement, flow velocity, currents are physical-chemical factors influencing directly and indirectly fish life, causing in time morpho-functional adaptation.

Water flow rate is important depending on fish species that grow in water. Thus, for cyprinids there are appropriate waters flow rates of 5-30 cm/s; for barbel and chub 30-50 cm/s and for salmonides 50-100 cm/s. Fish minimum reaction speed seems to be 2-10 cm/s. The equilibrum organ is the lateral line. Effects of water flow velocity on fish are divided into direct and indirect. The direct ones are concerning: fish mouvement and transportation; eggs and larva transportation to great distance and the indirect ones, strongly felt by fish, relate to: changes of hydrological conditions, water temperature changing, dissolved oxygen changes, salinity changes, phyto and zooplankton production, bottom of ponds quality.

Vertical currents have a role in mixing water, oxygen, salinity and temperature uniformity.

Density and viscosity of water in lakes varies according to the temperature. Thus, the highest density recorded for water temperatures of above 4°C and decreases at temperatures higher or below than 4°C. In the surface layers, water density is lower, increasing to the bottom. Water viscosity decreases in relation with temperature increasing , the amount of organic and inorganic suspensions. Water density and viscosity have great influence on the phenomenon of free floating aquatic organisms. The water temperature is lower, the density and viscosity of water are higher, allowing a better floating to aquatic organisms. In water, the resistance is approximately 100 times greater than in air.

Water pressure is strongly felt by the fish, even at atmospheric pressure change.

Water transparency depends on the amount of suspension, on the nature its bottom and on its depth. For carp, the water is suitable when the transparency is of 25-40 cm and for trout of 60-65 cm. Turbid water has direct effects on fish (prevents breathing, blocking gills, cause fish death by asphyxia) and indirect effects through changes that occur on water: decreases brightness, reduces photosynthesis, increasing temperature by increasing caloric absorption, retention in water of a lower quantity of oxygen, reducing the productivity of ecosystems. Fish were adapted to turbid water, meaning that they have small eyes and their skin produces a mucous that rapidly precipitates suspension, clearing the water.

Water temperature – water heating is generally made from sunlight. Calorific radiation generated by the sun are absorbed by the upper layers of water, plus the heat from the atmosphere and borders. Water heating is in direct relation with the surface. In deep lakes there is a thermal stratification of the water. Water temperature is in relation to water depth, location of the farm area and season. Thus, in the summer, water temperatures in surface waters in the lowland region ranges from 20 to 25°C and in the mountains between 14 and 16°C. Temperature decreases with depth, reaching the bottom up to 4°C. Water temperature decreased vertically is achieved gradually and uniformly to a certain depth, where there is a sudden drop. This level is called a thermal jump blanket or metalimnion. Water layer above is called metalimnionului Epilimnionand the one under hipolimnion. Epilimnion is well lit, oxygenated, warm and richly populated with plant and animal organisms. This layer represents the  trophogen blanket, where organic matter is formed by macro and microscopic plants. Hypolimnionul is dark, cold, low oxygen, rich gas: CO2, SO2, CH4, gas resulting from the decomposition or fermentation of organic matter. With air cooling, the surface water cools, becomes heavier and falls below its place being taken by the water warmer and lighter, which ascends to the surface. Vertical current is increasing and remains until all the water temperature in the tank reaches 4°C. With thermal uniformity the solvit oxygen uniformity is made. In winter, the surface water cools further to 0 ° C when ice crystal formation is favored. Under ice bridge formed, the temperature rises to bottom, reaching 4 ° C, representing winter reverse thermal stratification. Spring air temperature increases, leading to melting ice. Surface layers of water begin to warm, become denser and descend to where the layers are the same heat water, destroying thermal stratification of water in winter. The process continues until the water becomes the same temperature of 4 ° C throughout its thickness. The phenomena of thermal stratification of water in summer and winter and uniformity of temperature in autumn and spring are of great importance for biocenosis. Water temperature affects its density, stratification, currents, water movement, dissolved oxygen, biochemical and biological processes, intensity of water, fish metabolism and vitality, breeding age, nutrition, feed consumption, fish pathology. Water temperature has an impact both on fish growth and on their health. Immune system in most species of fish in optimum operating temperature around 15 ° C. Under thermal comfort zone, physiological changes occur indicators of fish: reduced basal metabolism, oxygen consumption, respiratory rate, gill absorption and penetration of toxins, kinetics of extraction  reactions, gastrointestinal driveability, and above the comfort zone, all these indicators mentioned are increasing. Sudden temperature fluctuations are dangerous to fish, especially the sudden drop in temperature (higher variations of 7 ° C), which may cause thermal shock, characterized by bronchial and cardiac paralysis, stress, energy and immunological consequences. Sudden temperature changes often occur during transportation of fish, fish transfer from one category of pools to another, if the power system fault – and drain if water levels drop suddenly. Water temperatures too low can lead to fish necrosis and epidermal hyperplasia. Water temperature too high can lead to anorexia, suffocation in fish, reduced fertility gametes and some abnormal embryos or death. Indirectly, water temperature affects fish health by: modification of water quality parameters in fish living respectively in oxygen content SOLVIT, dissociated ammonia, toxins, stimulate the development of algae and bacteria involved in decomposing organic matter mineralization. Light has a direct influence in shaping communication and movement of fish and an indirect one, namely: excite basal metabolism, induces nictemeral biorhythm, Hypovitaminosis A causes dark influences sexual maturation factors, it influences physical and biological processes of water, affecting the development microbiocenozei (support food), organic substrate biodegradation and the development of aquatic plants that occur in photosynthesis and water oxygenation. At water depth of 8-9 m, 90% of the  light disaprears. Fish see clearly at 1-5 m, but do not distinguish colors. Light changes fish color, being distinguished pelagic color, underwater meadows color.

Sound and vibration – Fish hear and emit sounds and their sounds are means of intra-and interspecific communication. Specialized organs in this regard are the bladder, special muscles, lateral line and membranous labyrinth. Fish feel mechanical vibration, audible and ultrasonic (water currents, explosions in water).

Water radioactivity – radioactivity of water is given by α rays, β, γ and X . Fish take radioactivity directly from water and indirectly through biomass consumed. Cumulated radioactivity in food chains. As regards sensitivity to radiation, the most sensitive are eggs, followed by juveniles, adults being the most resistant. Radioactive elements in water concentrate in skeleton opercule, gills, viscera and muscle and affect at molecular, cellular, tissue level. Irradiated adult carp shows dystrophic gonads and ova necrosis. In crucian carp there are recorded low platelet count and prolongation of clotting.

Organoleptic characteristics of water and their importance in fishery

A) Water smell comes from the penetration of natural or artificial substances in it: phenols, petroleum products, detergents, sewage, purine, decomposing organic matter which releases ammonia, H2S, indole, mercaptan, methane, fatty acids volatile etc. Intense smell of water prints in fish too a specific smell, making it of unused or decreasing its general value. In ponds with thick mud, the fish has the characteristic odor of mud.

B) water taste is given by all dissolved salts and by the presence of adventitious compounds.

Chemical characteristics of water and their importance in fishery

Chemical characteristics (water chemistry) may act directly on the fish through pathological disorders in fish, but also indirectly through the influence they have on bioagressors or creating discomfort that is generated by stress. Of the chemical characteristics of water there are mentioned: water reaction (pH), salinity, iron, active chlorine, nitrates, nitrites, ammonia, dissolved oxygen.

water pH – water reaction is conditionning physico-chemical and biological processes of water, affecting the toxicity of some compounds – such as NH3 is very harmful to pH> 8. Acidic or alkaline water (pH) act in both situations by a direct effect of fish irritation, which causes a hypersecretion of mucus, bleeding, skin  and gill lesions and even death. Acid or alkaline pH of the water for long time frequently preduces gills and skin injuries, and stress. Thus, a low value of pH (acid) increases the toxicity of metals and nitrites in water, while an alkaline pH increases the toxicity of ammonia. PH values ranging from 7 to 8.3 are good for fish life. Between 6-7 and 8.3-9 it influences ammonia and nitrite toxicity. PH levels above 9.2 and below 4.8 can cause trout’s death and values above 10.8 and below 5.0 are fatal for carp. Trout are more vulnerable to high pH and more resistant to low pH. Diseases of fish reared in water with acid pH occur in waters with low alkalinity (below 25 mg CO2). Photosynthesis can cause daily variations of pH one unit, with notable pathological consequences, especially in salmon breeding. Extreme pH values preduce tissue irritation, particularly in the gills, on the gills and on the underside of the fish appear haemorrhage; post-mortem, on the skin and gills of fish there is a lot of mucus mixed with blood. Among pathological fish states caused by direct action of pH water, the most common is inflammation of the gills. Waters with pH between 7 and 8 are hygienic. Water sources with a low pH (<7) are rich in carbonic acid, humic acid, phenols, containing organic substances, and those with an alkaline pH have a high content of Ca, Mg, Na, Mn as sulfates, carbonates, nitrates, phosphates. Regarding water quality in terms of pH for fish requirements are:

  • Water is good for fish at a pH between 6.5 and 8.0;
  • Water is dangerous when the pH is 5.1 to 6 or 8.0 to 9.0;
  • Water is unfit for fish if the pH is 4 to 5.1 or 9.0 to 10.0.

At a low water pH and a low oxygen content, a higher concentration of iron in water can lead to fish intoxication with soluble iron compounds. Bivalent iron compounds pass into insoluble compounds of trivalent iron covering gill filaments and preventing breathing. At low water temperatures and a higher concentration in iron, bacteria which deposit iron multiply excessively on gills and contribute to the oxidation of divalent iron compounds, reducing the gill surface, damaging the respiratory epithelium and suffocating fish eggs or killing by lack of oxygen. Water temperature can influence the toxic action of chlorine content. Thus, at a water temperature of 3-7 ° C and a concentration of 3.5 mg / l active chlorine it has a sublethal action on fish, especially carp. If carp exposed to 3.5 mg / l active chlorine at a temperature of 15-20 ° C, it dies within 1-2 hours. A long-term exposure to a concentration of active chlorine from 0.04 to 0.2 mg / L can lead to: neural disorders, restlessness, jumping in the water, cramps, lying sideways, spasmodic movements of the mouth of the disordered movements fins, heavy breathing, suffocation and death. Skin and gills are covered with a thick layer of mucus, gills’ bleeding or congestion occur at this level. Body surface is pale, gill edges are fringed, fins are coated with a white-ashy layer.

Nitrogenous substances in the water – with detrimental impacts on fish are: ammonia, nitrites (NO2) and sometimes nitrates (NO3). These substances in water result from the decomposition of dead organic matter, the reduction of nitrates and nitrites from various pollution sources such as mineral or organic fertilizer use, or may be metabolic products (eg ammonia). Ammonia (NH3) in water or body fluids of fish is present as molecular inextricably linked (NH3) or dissociated form the ammonium ion (NH4+), together forming the total ammonia. Ammonium salts dissociate in water according to the reaction: NH4+ + OH ↔ NH3 + H20. Ratio of the two forms of ammonia depends on pH and water temperature. The temperature and pH are higher, the ammonium ion is converted into ammonia. Along with the increasing of pH value increases also the amount of free ammonia and the reverse, lower pH increases the amount of ammonia ions. Toxicity of ammonium ions in water depends on the presence of ammonia molecules and their dissociation is base don the pH. Thus, toxicity increases in relation with water pH increasing. Toxicity also depends on the quantity of CO2 free of water, and it may influence the pH. Increasing the amount of CO2  free in water leads to the decreasing of ammonia toxicity.


In order to assess fish welfare level during slaughter there have been followed the objective welfare indicators applied to the slaughter units in our country. As control parameters, there are notable the opercular movements and the persistence of the oculomotor reflex on fish body position canges (pointing the individuals remained conscious after stunning). But as stunning procedures show a high variability (from the mechanical and electrical stunning to the use of low temperatures or even cases in which it doesn’t exist) and thus the sensitivity of the slaughter fish being variable, there was preferred the welfare level assessment on other parameters. Thus, the incidence of medical conditions was monitored on necropsy (hepato-pancreatic lesions observed in those individuals showing chronic stress and poor welfare default) and residue levels (heavy metals, pesticides, etc.). To establish protection and welfare of fish in the operating units, was investigated mainly water quality (pH, heavy metals, etc.). It was also set up a form of ethologic assessment, which will be used in next stages. Water, the living environment of fish, has a particularly importance by its characteristics and attributes, influencing: fish lifetime in the world, ecological zonation of species, development of ecological niches for certain fish populations,  fish pathology development, production levels, fish sanitation and fish products, including food  biosafety for people.

Materials and methods

From several ponds of some farms located in Oltenita were taken water and fish samples. From the water samples were determined the physico-chemical parameters: pH, nitrates (N-NO3), nitrites (N-NO2), ammonium (N-NH4+), chlorides and dissolved oxygen. The methods for determining and interpreting the results were those provided by Law 161/2005. From fish samples (from both mentioned units and a slaughter unit) were determined the heavy metals (Pb, Cu, Hg); organochlorides and the content of radioactive elements. The level of heavy metals in fish samples was established by atomic absorption spectrometry technique. It was also performed a microbiological examination of fish samples, revealing: total number of germs (TNG), E. coli / g, Salmonella/25 g and Listeria monocitogenes/25 g.

Results and discussions

Assessment of the welfare of fish can not be done without considering their living environment, respectively water fish ponds. Water chemistry affect directly and indirectly fish by the induction to them pathological states, by influencing the bioagressors’ development or by creating discomfort which generates stress. Physico-chemical parameters of water in fish ponds – Oltenita area – are presented in Table 1. Analyzing data from the table the following issues are revealed:

Water pH in samples taken from Rasa farm ponds ranges within the values suitable to fish life (ie between 7 and 8), while the samples from Valea Argovei ponds exceed the admitted limits. Water pH values higher than 8 do not cause accidents by direct effects on fish, but affects the toxicity of ammonia and nitrite in water. Water reaction influences physical chemical and biological processes in water. Alkaline nature of water works by irritating the fish, resulting in a hypersecretion of mucus, bleeding, skin and gill lesions and stress. Increased pH may occur due to increased intake of nitrogen fertilizers in fish ponds or to the content of sulphates, carbonates, nitrates and phosphates from fisheries.

Nitrates in water have been detected in the samples from Valea Argovei ponds, in return in the water from Rasa farm, the concentrations exceeded admitted limits for the fifth class quality (category for the most polluted water) by about 4 times ( 3.1 to 3.9).

Regarding nitrogen, the overvalues from the fifth grade quality were by 4.5 times in the water samples taken from Valley Argova farm ponds, being undetected in samples from Rasa farm.

Table 1

Physical chemical parameters of water in fish ponds – Oltenita area

Water sampling point

Assessed elements

Physical indicators Nutrients General Ions Oxygen regime
pH Nitrates mg/dm3 Nitrites mg/dm3 Ammonium mg/dm3 Chlorides mg/dm3 Dissolved Oxygen mg/dm3
Valea Argovei Pond 1 8.62 0 1.37 0.16 137.77 4.2
Pond 2 8.64 0 1.35 0.17 138.86 3.8
Rasa Pond 1 7.72 59.68 0 0 172.11 3.6
Pond 2 7.54 47.94 0 0 181.11 1.68
Admitted Limitsaccording Law 161/2006 Class I 7-8 1 20 mg / L trout,80 mg / l carp 0.01 0.2 mg / l lev.toxic fish 0.2 Background 7 Salmon breeding from 4.5 to 10 mg / lCarp from 3 to 3.5 mg / l winter5 to 5.5 mg / l in the summer
Class II 3 0.06 0.3 100 6
Class III 6 0.12 0.6 250 5
Class IV 15 0.3 1.5 300 4
Class V > 15 > 0.3 > 1.5 > 300 <4

Ammonium concentrations were scored within admitted limits for water in the first quality class (low polluted waters). Nitrogenous substances in the water are pathogens for fish (nitrites, nitrates, ammonia) resulting from decomposition of dead organic matter, reducing nitrates and nitrites present in water from various sources of pollution (use of mineral or organic fertilizers) or products of metabolism. In water, ammonia may be present in molecular form, undissociated (NH3) or in dissociated form as ammonium ions (NH4+). The ration between these two forms of ammonia (dissociated and undissociated) depends on pH and water temperature. The conversion between NH4+ in NH3 is higher when both water temperature and pH are higher. Ammonium ions are non-toxic to fish, the toxicity of ammonium salts are given by ammonia molecules. Dissociation is dependent on water pH, toxicity increased proportionately with pH increasing due to the large amount of water molecules in non-dissociated solution. NH3 is a respiratory and nervous toxic, it enters the blood by the fish gill epithelium, and is settled in the brain, causing nervous symptoms. Nitrates are present togheter with nitrogenous substances: nitrates and ammonia – in surface waters. They  are present in a lower concentration, due to their pronounced instability, being easily oxidized or reduced by chemical or biochemical pathways. Nitrites came from degradation of organic matter in anaerobiosis conditions or may result from nitrites reducing. Nitrites enter the body by penetrating the fish gills, in the presence of chlorine molecules in water. Once in the blood, nitrites are bound to hemoglobin, thereby increasing the concentration of methemoglobin, reducing oxygen transport in fish body. Therefore may appear browning of gills and blood. When 70-80% of the total hemoglobin is blocked as methemoglobin, the fish become apathetic, do not react to stimuli, have accelerated breathing and die by suffocation. With  age, fish become more sensitive to high concentrations of nitrite in water. Gills crossing by nitrite ions is positively influenced by the presence of chloride in water. Maximum level of nitrates in the water to protect fish from their toxic effects mentioned above should be below 0.2 mg / l NO2. In our research, were observed excedings for 6.85 times of the maximum admitted limit (0,2 mg / l). Maximum level of nitrates in the water must be below 20 mg / l for trout culture and less than 80 mg / l for the carp.

Chlorines concentration in water recorded values over the admitted limit provided for the IInd water quality class by 1.4 times in water samples from Valea Argovei and by 1.8 times in Rasa farm. It is important to monitor the ratio nitrogen / chlorine in water in order to estimate the concentration of nitrite to ensure fish survival. This ratio must be, for trout ponds, around 17, and for other fish ponds around 8.

Dissolved oxygen in water is an important chemical factor that influence the fish life, facilitates mineralization of organic substances, affecting photosynthesis of aquatic flora and microflora, influence metabolism, assimilation and toxicity of water compounds. Analyzing of the dissolved oxygen values in Table. 1 shows that water framing within the IV and V quality class, and in terms of its utility is favorable for carp rearing. Oxygen concentration in water depends on temperature and water clarity. Factors that lead to decreased O2 in water are increased water temperature, high turbidity, the water smooth, the degree of eutrophication, low pressure, water pollution by oil, detergents, ice presence and water depth. Low concentration of oxygen in water increases the respiratory rate of fish, may resulting in loss of balance, crowding at surface of the water, asphyxia, low assimilation of food. Poor oxygenation of the water representing a stressor for fish, thes species showing anorexia, hypoxia, crowding in places where water current is stronger, water piping (surface-breathing), breathing rate acceleration and even death (before that fish having spasmodic movements which alternate with calm). Oxygen water requirements of fish varies with species, age, physiologic and health status, growth performance. Minimum limits for salmon species are 4.5 to 5.5 mg2/ l and maximum 9.3 to 10.0 mg / l, and for cyprinids at least 3.0 to 2.5 mg / l in winter and 5 -5.5 mg O2/ l summer.

Recommedation regarding water quality for fish exploitation:

– restoration of water through the buffer system management platform lime wet ponds – water recycling regularly – avoiding excess vegetation – to avoid the uncontrolled administration of mineral fertilizers, of the organic and the excessive furajării – maintain water pH neutral value by taking lime chloride (1 g active chlorine / m3 of water) 2-3 times during May to July and crushed lime (dose 150-200 kg / ha) 1-3 times per month or lime, spread evenly in tanks with fish – ensuring optimum levels of oxygen.

In Table. 2 are shown average values of heavy metals (Pb, Hg, Cd) and organochlorides in fish samples.

Table 2

Average values for heavy metals and organochlorides in fish samples

water sampling point Determined indicators
Pbmg / kg Cdmg / kg Hgmg / kg Organochlorinemg / kg
Valea Algovei Pond 1 undetected 0.020 0.040 undetected
Pond 2 undetected 0.018 0.032 undetected
Rasa Pond 1 undetected undetected undetected undetected
Pond 2 undetected undetected undetected undetected
Admitted limits accordin  Order NSVFSA 97/2005 0.010 0.005 0.001 0.002


Analyzing data from the table, it appears that lead was not detected in any of the fish samples taken. Cadmium detected in fish samples recorded values higher than the admitted limit (0.005 mg / kg) in samples taken in the two ponds of the farm in Valea Argovei. The exceeding was by 3.6 times in the first pond and by 4 times in the second pond. Lead and cadmium are associated with the sediment, are instable and show a availability to pass into fish orgaism. From the water it is absorbed by 3-10% and 40-50% by breathing. Lead enters the body and spread slowly in bones (40-50%) in liver (22%), kidney (11%). Lead ions with calcium ions attached to bones, producing formation and functional disorders of hematopoietic marrow, resulting in the appearance of red blood cells with basophilic corpusculi. Fish take cadmium directly from water or from food. Acquisition of water absorption of cadmium is achieved through the cell membrane and concentrates in fish organs of detoxification. Cadmium ion reached inhibit sulphide body, inhibit cholinesterase, affecting enzymes involved in carbohydrate metabolism and the whole process of glycolysis. Cadmium is carcinogenic action. Fish is high cadmium battery, sometimes reaching up to 0.15 to 3 ppm. Concentration of mercury in fish samples exceeded the permissible limit in samples taken from the basin no. A Aargau Valley 40 times, and the basin no. 2 of 32 times. No mercury was detected in fish samples from the fishery in the race no evidence, regardless of the basin from which the samples came from fish. Mercury usually get water elemental form or as inorganic salts. Absorbed on sediment particles and organic remains bound by them until they consume fish. Mercury intake is followed by its biotransformation in methyl-mercury (soluble molecule) readily cross cell membranes and accumulates in fish tissues. Direct deposit of methyl mercury in fish gills is favored by low pH. Microbiological examination of fish were determined: TNG, E. coli, Salmonella, Listeria monocitogenes. All the tests were negative, which shows good water status in relation to microbiological.


1. Water pH is neutral, favorable to fish life of in the water from Rasa farm and slightly alkaline in the water from Valea Argovei farm.

2. Regarding nitrates concentrations, the waters from Rasa farm ranged into the fifth water quality class.

3. Nitrites exceeded by 4.5 times the admitted limits for the fifth water quality class in Valea Argovei farm and by 6.85 times the limits for fish.

4. Ammonium concentrations are within the admitted limits for first water quality class.

5. Chlorides in water exceeded the admitted limit for the second water quality in Valea Argovei farm by 1.4 times and by 1.8 times in the water from Rasa farm ponds.

6. Dissolved oxygen has values within IVth an Vth water quality classes, therefore it is favorable to carp  exploitation.

7. Heavy metals determined in fish samples recorded overvalues in Valea Argovei Farm: cadmium by 3.6 to 4 times mercury by 32-40 times.

8. Microbiological examinations of fish samples turned all negative.