Sedna Technologies is highly engaged with the academic community and we are constantly collaborating on research projects as well as bringing on interns to further develop skills and growth. At Sedna, we have been working with Gregin Soju following his graduation from the Industrial Engineering Technology program at NSCC. On top of optimizing internal processes and documents, Gregin has also put together a comprehensive write up of how water quality influences the overall quality, growth and welfare of salmon in the aquaculture supply chain.

The Importance of Monitoring Water Quality in Aquaculture

For obtaining success in aquaculture the species should be provided with a satisfactory environment for growth. Water quality is determined by physic-chemical and biological factors that directly or indirectly affects the survival, growth and reproduction of the fish.

Hundreds of water quality variables may affect the well being of fish or crustaceans, but fortunately, only a few normally play a decisive role (Boyd.1995). They can be mainly divided into 3:

  • Physical Parameters : Temperature, Turbidity, Salinity and W
  • Chemical Parameters: Dissolved oxygen (DO), Biological Oxygen Demand (BOD), Carbon-di-oxide (CO2), Alkalinity, Conductivity, Chloride, Hardness, Ammonia (NH3), Nitrite (NO2), Nitrate (NO3)
  • Biological Parameters: Plankton, Primary Productivity


Water temperature greatly influences physiological processes such as respiration rate, efficiency of feeding and assimilation, reproduction, behaviour and growth. Temperature also affects oxygen solubility and causes interactions of several other water quality parameters.

Standard environmental temperature (SET) is required for the optimum growth of fish. The optimum temperature range varies from one species to another.

What happens when the temperature is below recommended value?

Below recommended values can cause reduced feed intakes leading to a reduction in growth and high death rates. Fish are more stressed at low temperatures, therefore more susceptible to disease.

What happens when the temperature is above recommended value?

There is a lower solubility of oxygen leading to stress and death at extreme temperatures.

Dissolved Oxygen:

Dissolved oxygen refers to the free, non-compound oxygen present in water. The leading source of dissolved oxygen in water is atmospheric air and photosynthetic planktons. It affects the survival, growth behaviour, distribution and physiology of the species. Depletion in the level of oxygen can cause reduced growth, poor feeding of fish and increased fish mortality either directly or indirectly.

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 optimum dissolved oxygen level is 5-8 ppm.

What happens when the dissolved oxygen is consistently below the recommended value?

Below 0 – 1.5 mg/l- Dangerous if exposed for long periods.

Below 1.4-5 mg/l – Fish survive, but reduced feed intake, slow growth, stress and increased susceptibility to diseases. It also results in building up of toxic wastes.

What happens when the dissolved oxygen is consistently above the recommended value?

Gas bubble trauma when the water is supersaturated to levels of 300% or above.

Carbon-di-oxide ( CO2):

In all water bodies CO2 is a common component. When compared to natural water, aquaculture ponds have a higher percentage of biological activity. Dissolved carbon dioxide concentrations cycle daily, and the amplitude of those daily fluctuations depend on the relative rates of photosynthesis and respiration.

CO2 concentration of 10- 15 mg/l is recommended as a maximum for finfish, concentrations in open and pond water averaged less than 6mg/L (Boyd 1990,1995).

The optimum level of CO2 is 5 ppm.


Low pH affects fish gill structure and function and affects the metabolism and physiological processes of culture organisms. It also affects the solubility and chemical forms of various compounds, some of which can be toxic.

An optimum pH value is between 7 and 8.5 for fish life.

What happens when consistently below recommended value?

Below 4: Acid death point.

4 to 6: 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 the pond will die at this point.

Ammonia (NH3):

Ammonia is a by-product of  a protein breakdown. Depending on the PH level of water it occurs in two forms; (ammonia) and nontoxic form (ammonium). The sum of the two is called total ammonium or simply ammonia. Ammonia in the range greater than or equal to 0.1 mg/L tends to cause gill damage, destroy mucous producing membranes. It also results in poor feed conversation, reduced growth and osmoregulatory imbalance.

The optimum level of NH3 is 0.3 to 1.33 ppm and less than 0.1 ppm are unproductive.

Nitrite (NO2):

Nitrite is an intermediate in the process of nitrification, which is the two-stepped oxidation of ammonium to nitrate carried out by highly aerobic, gram-negative, chemoautotrophic bacteria. It oxidizes hemoglobin to methemoglobin in the blood, turning the blood and gills brown and hindering respiration. It also damages the nervous system, liver, spleen and kidneys of fish.

The ideal and normal measurement of nitrite is zero in any aquatic system. The optimum level of nitrite is 2.5 mg/L.

Nitrate (NO3):

Nitrate (NO3) is a common form of inorganic combined nitrogen in natural waste and aquaculture systems. Most of the nitrate found in unpolluted natural waters is the product of nitrification. Nitrate may be applied to pond bottom soils to prevent reducing conditions that leads to sulfide production. Where ammonia and Nitrite are toxic to fish, Nitrate is harmless. Its concentrations from 0 to 200 ppm are acceptable in fishponds and is generally low toxic for some species whereas especially the marine species are sensitive to its presence.

The Nitrate level is normally stabilized in the 50 -100 pm in range.

Aquaculture Value chain

For better production and harvest, the water quality must be optimal throughout the supply chain. Transportation of fish is generally an  important  practice  in  aquaculture. In transporting fish, there are technicalities in which  one  needs  to  understand  for  successful transportation.

The slaughter period includes the effects of pre-slaughter treatments such as transportation, handling and stunning, in addition to the killing of fish. Most fish species are starved for a period before slaughter. During starvation the fish will lose biomass as they mobilise energy stores such as lipids, but after several days, the biomass reduction will slow down as the fish become hypometabolic and down regulate their metabolisms. Depending on the production system, the fish is then caught, stunned and killed or transported by some means to slaughter sight. This last period in the fish’s production cycle is probably the time when various welfare issues most strongly affect general muscle quality traits. So real time monitoring is necessary during the entire supply chain.

Stress is defined as a condition in which the dynamic equilibrium of  animal  organisms  called  homeostasis  is threatened  or  disturbed as  a result  of  actions of intrinsic or extrinsic stimuli, commonly defined as stressors. Stress during transportation includes water quality, handling, temperature and crowding.

This section provides annual statistics on the volume of aquaculture (In tonnes) production in Canada. The data is organized by species and province.

From the above figure, salmon is one of the species that is being produced in mass volume. The water quality must be maintained to optimize production.

Dissolved Oxygen and Salmon Growth:

USEPA (1986) performed a literature review and cites the effects of various dissolved oxygen concentrations on salmonid life stages other than embryonic and larval (Table 2). These effects range from no impairment at 8 mg/L to acute mortality at dissolved oxygen levels below 3 mg/L.


Salmonid mortality begins to occur when dissolved oxygen concentrations are below 3 mg/L for periods longer than 3.5 days (US EPA 1986). A summary of various field study results by WDOE (2002) reports that significant mortality occurs in natural waters when dissolved oxygen concentrations fluctuate the range of 2.5 – 3 mg/L. Long-term (20 – 30 days) constant exposure to mean dissolved oxygen concentrations below 3 – 3.3 mg/L is likely to result in 50% mortality of juvenile salmonids (WDOE, 2002). According to a short-term (1 – 4 hours) exposure study by Burdick et al. (1954, as cited by WDOE, 2002), in warm water (20 – 21°C) salmonids may require daily minimum oxygen levels to remain above 2.6 mg/L to avoid significant (50%) mortality. From these and other types of studies, WDOE (2002) concluded that juvenile salmonid mortality can be avoided if daily minimum dissolved oxygen concentration remain above 3.9 mg/L, and the monthly or weekly average of minimum concentrations remains above 4.6 mg/L

C02 and Salmon Growth:

Atlantic salmon post-smolts were exposed to six CO2 concentrations (5–40 mg/L) for 12 weeks in 12 ppt salinity RAS

Fish showed no mortality, cataracts, nephron calcinosis or signs of external injuries. Skin dermis layer was significantly thinner in fish exposed to 40 mg/L of CO2. Body weight and growth were significantly lower at CO2 concentrations ≥12 mg/L.

Temperature and Salmon Growth:

Efficient salmon growth was previously believed to be best promoted at water temperatures between 13 – 17 degrees Celsius (Wallace, 1993). However, recent studies show that growth is better achieved at colder temperatures. In controlled experiments in which salmon were fed at temperatures of 13, 15, 17, and 19 degrees Celsius over 45 days, the experiment showed that the most efficient growth was achieved at a water temperature of 13 degrees Celsius (Ernst M Hevroy et al., 2013). Furthermore, salmon that lived at temperatures of 15 and 17 degrees Celsius grew efficiently in the first two weeks but exhibited reduced feed intake and growth over the remainder of the study period. Additional research is necessary to determine whether the optimal temperature is lower than 13 degrees Celsius. This finding indicates that the best temperature interval, or the comfort zone for the salmon, should be somewhere around or below 13 degrees Celsius.

Nitrate and Salmon Growth

Nitrite has an affinity for the mechanism of absorption of chloride in the gill; that is to say, NO₂¯ can replace Cl¯ in gill transporters of chloride / bicarbonate (Cl¯ / HCO₃¯). Therefore, provided that NO₂¯ is present in the water, a part of the absorption of Cl¯ will shift towards the absorption of NO₂¯, which can also lead to the accumulation of NO₂¯ in plasma and have a negative effect on productive performance and animal welfare.

Experimental Study:

The study was conducted with 810 Atlantic salmon parr divided into 15 ponds, where they were exposed to five different nominal concentrations of NO₂¯ (0, 0.5, 2.5 and 10 NO₂¯ -N, mg / L) and with a constant nominal concentration of Cl¯ (200 mg / L), for 12 weeks.

Growth rate reduced

The study’s results showed that the specific growth rate (SGR) was significantly reduced compared to the control, during the first three weeks, in fish exposed to the highest concentration of nitrite (10 mg NO₂¯ -N / L) and a Cl¯: NO₂¯ -N ratio of 21:1. “The results suggest the activation of compensation and adaptation mechanisms in the last stages of the experiment,” wrote the study’s authors.

As explained by the main author, Xavier Gutiérrez, who is general manager of NIVA Chile, “in the study no significant effects of NO₂¯ were found on the gill tissue, associated mortality, food intake and conversion (FCR) and physiological markers (Cl¯, glucose and pH). However, it was found that nitrite entered the plasma of fish exposed to the two highest nominal concentrations of nitrite, 5 and 10 mg / L, and Cl¯ : NO₂¯ -N ratios of 43:1 and 21:1, respectively”.

Industry standard ‘not enough’

The authors concluded that “the ratio of Cl¯ : NO₂¯ -N previously recommended for fish culture in RAS of 20:1 (Timmons & Ebeling; 2007), which today uses the industry as a standard, is not enough to protect Atlantic salmon during the early stages of nitrite exposure. Consequently, it is recommended to maintain a ratio of Cl¯ : NO₂¯ -N above 104:1 to avoid the accumulation of nitrite in the plasma of the Atlantic salmon in parr stage and growth losses”.

Ammonia and Salmon Growth:

Ammonia is toxic to fish and aquatic organisms, even in very low concentrations. When levels reach 0.06 mg/L, fish can suffer gill damage. When levels reach 0.2 mg/L, sensitive fish like trout and salmon begin to die. As levels near 2.0 mg/L, even ammonia-tolerant fish like carp begin to die. Ammonia levels greater than approximately 0.1 mg/L usually indicate polluted waters. The danger ammonia poses for fish depends on the water’s temperature and pH, along with the dissolved oxygen and carbon dioxide levels. Remember, the higher the pH and the warmer the temperature, the more toxic the ammonia. Also, ammonia is much more toxic to fish and aquatic life when water contains very little dissolved oxygen and carbon dioxide.

Figure (a) represents relative growth and Figure(b) represents relative mortality due to IPN virus susceptibility as a function of the degree of intensive rearing in juvenile Atlantic Salmon. Each circle represents an experiment with different water quality treatments, and each point represents an average of the experiment groups estimated as a percentage of the control groups (dashed line). All treatments are within the normal range of salmon farming, and the treatments within each experiment range from optimal (left side) to sub-optimal (right side).

In extensive systems, the farmer has no possibility to control the water quality and few means to avoid suboptimal levels of, for example oxygen concentration. Intensive industrial framing on the other hand, includes high fish density produced with less water, high energy feed and fast growth, short generation time and season-independent production. In these systems, the fish farmer may easily monitor and change water quality traits, but these systems face the challenge of finding a balance between what is economically optional for the farmer and the limits of acceptable fish welfare.


Traceability has become an important tool to communicate ethical quality of fish products. Food and feed operators should be able to identify any person from whom they have been supplied with a food, a feed, a food-producing animal, or any substance to be, or expected to be, incorporated into a food or feed. There should be systems and procedures to identify other businesses to which their products have been supplied. This can be done using paper and pen having large batch sizes, but if technologies such as sensors or data carries are used, this would speed up the product registration and open possibilities for the use of the data in the management of food production chains. The data captured by traceability systems could then be used for other processes such as process rationalisation, process optimisation and marketing.

  • Helps to trace the movement of products from origin to point of sale.
  • Helps to find inefficiencies in the operation
  • Saves money and time.
  • Ensure quality throughout the supply chain and prevent losses.