Managing water quality and preventing disease from affecting your yields is a complicated process that can involve many different technologies and solutions.
To help companies protect against waterborne infection and disease, Evoqua recently hosted a webinar dedicated to understanding and improving water quality in land-based hatcheries that you can watch here.
In addition to sharing some expertise, we have compiled detailed answers to our 15 most frequently asked questions when it comes to aquaculture.
The post covers a range of topics, from UV and Ozone to filtration, so if you have unanswered questions about aquaculture and its application, read on to learn more.
- What is UV Transmittance (UVT)
- What impact does sea temperature have on choosing your RAS equipment?
- What type of UV systems are best for hatcheries – medium or low pressure?
- How do low pressure UV systems perform with a cold-water feed?
- How do you know what UV dose is required?
- What are the Norwegian Veterinary Institute (NVI) standards, and why are they important in aquaculture?
- What different diseases are fish susceptible to?
- What are the key challenges to the industry when applying advanced disinfection technologies to new or emerging fish diseases?
- What impact does water quality have on the aquaculture industry?
- How is filtration used to treat water in aquaculture?
- What are the origins of suspended solids?
- What factors affect the production of suspended solids?
- What are the key challenges with RAS systems?
- Are Ozone and UV are competing technologies?
- What is important to consider in choosing the right ozone equipment?
1. What is UV Transmittance (UVT)?
UV transmittance refers to the percentage of light that passes through a water sample at the wavelength of 254 nm. At this wavelength, UV light penetrates the cell wall of the micro-organism. The amount of UV delivered to the organism is called the intensity. The UV energy permanently alters the DNA structure of the micro-organism in a process called thymine dimerization which inactivates the micro-organism and renders it unable to reproduce or infect.
2. What impact does sea temperature have on choosing your RAS equipment?
Water temperature plays an important part in deciding the type of RAS plant equipment to be used. For example, water temperature over 10 degrees Celsius can cause corrosion issues on standard 316L or 304L stainless steel.
However, there are options we can provide to overcome corrosion caused by temperature, so high temperature is never an issue for us when providing equipment for RAS. One of the solutions we can offer is sacrificial anodes.
Sacrificial anodes do just what they state - sacrifice themselves to protect the stainless-steel equipment. Sacrificial anodes are consumable for the equipment and need to be replaced quarterly, although timing does depend on each plant. The other option available is super duplex steel — which is more expensive but is resistant to high levels of corrosion.
3. What type of UV systems are best for hatcheries – medium or low pressure?
NIVA (Norwegian Institute for Water Research) has conducted detailed research on the applicability of UV treatment for various fish diseases and has confirmed that UV is effective*.
It has also confirmed medium pressure UV (polychromatic output) is more effective than low-pressure UV (monochromatic output), on a like for like basis. Some organisms absorb at different wavelengths, so medium pressure can be more efficient when dealing with these specific pathogens.
4. How do low pressure UV systems perform with a cold-water feed?
The UV efficiency of low-pressure lamps depends on the lowest temperature spot on the lamp.
Optimum UV efficiency is achieved when this temperature is approximately 40ºC (100% maximum efficiency). With water temperature 5 degrees warmer, low pressure lamp output falls to only 20% of its maximum. If the water temperature falls more than 5 degrees, then the effect will be even more significant.
5. How do you know what UV dose is required?
UV Dose is the product of UV Light Intensity (quantity of UV light per unit area falling on a surface) and Residence Time (contact time in the reaction chamber). It is measured in mJ/cm2 (millijoules/ cm2). There are specific doses needed for specific fish diseases found in aquaculture systems. For more information on sizing UV systems and calculating the correct UV dose, click here.
6. What are the Norwegian Veterinary Institute (NVI) standards, and why are they important in aquaculture?
In 1984, Infectious Salmon Anaemia (ISA), a viral disease, was discovered in Norway in an Atlantic salmon hatchery. 80% of the fish in the outbreak died[1].
UV systems are critical in battling ISA, but their installation must be approved according to the Norwegian Water Disinfection Regulation for Aquaculture Applications. This approval comes from the NVI and the independent third party for field-testing is the Norwegian Institute for Water Research (NIVA).
The NVI is responsible for the contingency planning and competence development aimed at eliminating disease and preventing threats to the health of fish, as well as animals and human beings. Today the core activities comprise of diagnostics, research, innovation, monitoring, risk assessment, consulting, and communication which help to maintain high levels of fish health across the aquaculture industry.
7. What different diseases are fish susceptible to?
Infectious diseases caused by bacteria, viruses, and parasites are the primary concern in aquaculture. Effective control of these diseases is one of the most critical elements in successful aquaculture. Common diseases that can be prevented by disinfection and filtration water treatment solutions include:
- Infectious Salmon Anaemia
- Sea lice
- Ectoparasitic infestation including velvet or rust, Flukes, Nematodes, and Leeches
- Bacterial diseases like Fish Tuberculosis, Cotton mouth disease, Columnaris, Dropsy, and Furunculosis
- Fungal diseases like Dermatomycosis and Branchiomycosis
- Protozoan diseases like Costiasis, Whirling Disease, Ichthyophthiriusis
- Viral diseases like Viral Haemorrhagic Septicaemia (VHS), Infectious pancreatic necrosis (IPN), Spring Viremia of Carp, Channel Catfish Virus Disease and
- ‘Other’ like Piscicolosis Acidosis, Alkalosis Argulosis, Epizootic ulcerative syndrome (EUS) or red-spot.
For emerging diseases, we can reasonably estimate the performance of our treatment solutions against a new pathogen if we have existing data from a similar organism from the same species or genus. Of course, research is the best route and organisations such as NIVA are valuable sources of new research into new pathogens. Check with their site to see research either currently in progress or recently released.
8. What are the key challenges to the industry when applying advanced disinfection technologies to new or emerging fish diseases?
The major challenge for everyone in the aquaculture industry is emerging diseases, on which no testing has been carried out. Lack of testing means there no guaranteed disinfection levels for equipment.
To be able to give guarantees, validation testing must be carried out on the target organism by a reputable source. This is a long procedure that includes third-party laboratory testing with disinfection equipment.
9. What impact does water quality have on the aquaculture industry?
Water quality is important in fish farming as poor-quality water can affect the health and growth of the fish. Farmers must pay attention to the water's chemical and physical characteristics.
Fish farmers who wish to be successful need to understand the quality of their water. As fish use the water to live, feed, reproduce, grow and excrete waste into, the water quality can quickly decline in fishponds.
Farmers must match the needs of the fish with how they manage water quality factors including temperature, suspended solids, photosynthesis, dissolved gases, oxygen, carbon dioxide, nitrogen, ammonia, pH levels, alkalinity, water hardness, and more.
10. How is filtration used to treat water in aquaculture?
The metabolic activity involved in converting fish feed to fish flesh produces waste products. These consist of suspended solids and dissolved nutrients.
There are simple methods to remove suspended solids, and they apply to both flow-through and recirculation farms. Removal of suspended solids from flow-through fish farms has different requirements from other water treatment processes: concentrations of pollutants in fish farm effluent are relatively low and flow volumes are relatively high. These large water flow volumes require a careful choice of filtration systems to control costs.
11. What are the origins of suspended solids?
In any fish farm, suspended solids and dissolved nutrients can originate from:
- Uneaten feed
- Fish metabolism producing faeces
- Solids carried into the farm with the flow from the external water source
- Growth of micro-algae and bacteria.
In a RAS system, the mechanical filter is used to remove these suspended solids from the system water flow. These solids need to be removed to maintain a high level of water quality and prevent diseases from spreading in the RAS system.
An effective filtration system will allow the other technologies in the RAS system to enhance their performance and provide a suitable habitat for fish.
12. What factors affect the production of suspended solids?
Production of suspended solids within a fish farm is affected by a range of factors, including:
- Feed quality
- Rate of feeding
- Feeding method
- Water exchange rate - Tank hydrology
- Fish stocking density
- Dissolved oxygen level
- Efficiency of farm management and skills of personnel
The amount of uneaten feed can be reduced by a careful feeding regime that provides the correct amount of feed, at the time the fish require it, and by husbandry that provides water quality suitable for feed conversion. Substantial improvements in feed conversion ratios, and reductions in the faeces generated, have been achieved by improving fish diets; for example, by using ingredients with high digestibility and diets that are matched to the requirements of the fish species.
13. What are the key challenges with RAS systems?
While land-based aquaculture systems, such as RAS facilities, can offer a more sustainable alternative to traditional methods, they have their challenges. Potential issues include mortalities and diverse flavour profiles caused by biological conditions of land-based facilities that are hard to control.
A key factor in addressing these issues is understanding, maintaining, and improving optical water quality, especially in the UV range. This is what is often referred to as UV transmissivity (UVT).
The UVT of the water is an important parameter as it influences the efficiency of the UV system, often significantly – which in turn drives equipment sizing and therefore both CAPEX and OPEX.
Understanding the UVT is critical before implementing any solution – something that is cheap and easy to do with the right equipment. Sourcing raw water without high organic loadings that drive the UV down will also help to ensure that the treatment processes for water clarity are as efficient, optimized, and well-maintained as possible.
14. Are Ozone and UV are competing technologies?
Rather than competing, UV and Ozone are considered complementary technologies. Each system can have various process advantages depending on the disinfection need. The combination of both UV and ozone technology can provide plants with a double barrier approach.
15. What is important to consider in choosing the right ozone equipment?
For Ozone you need to consider the main elements of ozonation: oxygen; ozone generation; mass transfer; measurement and control, including de-ozonation. Integration of all these elements can improve operational performance and create a more nurturing environment for the fish stock.
If you would like to learn more about protecting and controlling your water conditions, Evoqua has a range of technologies, products, and services to keep water clean and fish free from disease.
Learn more here.
* UV treatment efficacy will depend on the feed water contaminant content, the specific product/system provided, and operating and maintenance conditions.
[1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0215478