Wednesday, November 4, 2009

Ozone & It s uses in Koi Keeping

Ozone and its uses in koi keeping.

Ozone systems provide the ultimate weapon in the koi keeper's armoury in the constant fight against disease and the struggle to maintain superb water quality. We have seen many advancements in koi system filtration in recent years – new filters, new media, Bio UVs, new probiotic filter products all designed to improve water quality and filtration and thereby ultimately koi health. None of these however comes close to delivering the benefits of Ozone systems, the advantages of which have long been recognised by the marine fraternity and like so many other great ideas, only now being introduced in to the koi world.

Without dispute, Ozone is the most effective natural bactericide and viricide of all disinfecting agents available to the koi keeper.

In our pond environment Ozone: -

  • Is highly effective in removing organics, and reducing ammonia and nitrites.
  • reverts back to oxygen quickly, leaving no detrimental residues when used correctly, and provides ultimate water clarity.
  • is economical and non-polluting when used correctly.
  • is used as a sterilising agent to kill viruses, bacteria and other pathogens.
  • improves biological and mechanical filtration by burning off proteins, ammonia and nitrite straight to nitrates and by enriching our pond water with Oxygen.
  • lowers biological oxygen demand (BOD) and raises the REDOX potential in the water (the ability of the water to oxidise pathogens).
  • Can remove toxic pollutants, such as hydrocarbons and other toxic substances from our pond water which cannot be achieved by any other form of mechanical or biological filtration.

For our koi ponds, in order to dose the pond water with the correct amount of Ozone we have to install an Ozone generator and a method of introducing the Ozone into the water in order to achieve the correct level of disinfection. We then have to remove the Ozone from the water before it returns to the pond in order to prevent it coming into contact directly with our koi – which could have lethal consequences.

This is achieved by passing air or Oxygen through an electronic ‘gizmo’ that generates Ozone by passing a high voltage electrical discharge through the air flow. The Ozone thus created is then drawn into a special protein skimmer or Ozone reactor especially designed for the purpose via a venturi or blown into the reactor via special air stones and into the water flow which passes through the protein skimmer. When the Ozone comes into contact with the water it quickly ‘burns’ off polluting organic material and breaks down back into Oxygen.

As well as disinfecting the water and killing bacteria, viruses and free swimming parasites, Ozone also kills algal cells. The disinfected water returned to the pond is also saturated with oxygen so that the biological filter is able to work at its full potential. Ozone is so powerful that it is like having a permanent and very strong dose of Chloramine T or Potassium Permanganate in the pond, without any of the chemical side effects. As Ozone also burns off proteins and organics water clarity is improved enormously and the water sparkles to the point where the colour of the koi is not impeded in any way by the depth of water, and koi that have pure white skin at the surface also have pure white skin 6 feet down.

In the example (below) the pond on the right does not use an Ozone system - note the air bubbles from the large air stone which look slightly brown or yellow in colour. The pond on the left uses an Ozone system. Note the blue - white stream of bubbles from the air stone. This helps demonstrate how Ozone removes the proteins from pond water which cause the water to look yellow/brown and murky.

The pond (below) utilises an Ozone system to give the superb water clarity you can see, even from this low resolution photograph. The two Tanchos in this picture are swimming six feet below the surface!

Whilst not a Utopia, since even with the use of Ozone koi can still need individual medication and treatment if required, the other major advantage of Ozone in our pond systems is that it virtually eliminates the risk of cross infection between koi. So even if a fish is introduced into the pond environment which itself is ill, e.g. carrying a bacterial disease, this is much less likely to be transmitted to other koi. Further, any treatment employed to an infected koi has a much improved chance of working effectively as the koi are living in a much cleaner environment, biologically speaking – i.e. in an environment containing fewer harmful pathogens.

This is especially noticeable when topically treating surface wounds, which once cleaned, heal much faster.

Similarly if parasites were present on certain koi, the water would still need to be medicated to eradicate the parasites on the body of the koi affected. Any medication used however, also works more effectively as the pond water is maintained at a much higher quality, with a higher Redox potential and with a lower biological Oxygen demand (BOD).

Frequently Asked Questions.

What is Ozone?

Ozone gas occurs naturally in the atmosphere. When a molecule of Oxygen, O², is bound to a third oxygen atom, it becomes Ozone, or 0³. Ozone is an unstable bluish water-soluble gas with a characteristic smell. At low levels it makes the air smell fresh and its colour makes the sky blue. Ozone is the 2nd strongest known oxidiser and the most powerful readily available water sanitiser. It kills bacteria and viruses over 3,000 times faster and is a 50% stronger oxidiser than chlorine. It is unsurpassed for control of many types of common bacteria such as E. Coli and faecal coliforms as well as the de-activation of virus, fungus, mould, mildew and cysts, and is not carcinogenic.

How does it Work?

Ozone is nature's way of purifying the air we breathe. As ozone circulates and comes into contact with airborne pathogens, one of the three oxygen atoms detaches itself from the Ozone molecule, attaches itself to the pollutant and oxidises it and turns it into a safer compound. Ozone is nature's way of cleaning our environment.

Ozone is such a strong germicide that only a few micrograms per litre are required to demonstrate germicidal action; it destroys all pathogenic and saprophytic microbes in water. Factors like humidity, temperature, pH, Ozone concentration levels, type of organism and contact time, will affect the kill rate for pathogens, but the action of Ozone gas in water is instantaneous and after oxidation, Ozone returns to its original form of Oxygen, with out leaving any toxic by-products or residues.

Ozone is a natural disinfectant and steriliser and unlike chlorine, it does not produce trihalomethanes or chloroforms in water and so leaves no harmful toxins or residues in the water.

Without dispute, scientifically speaking, Ozone is the most effective natural bactericide and viricide of all the disinfecting agents.

How do we measure the levels of Ozone in the pond water?

The Ozone dosing of water is measured in millivolt terms and is expressed as the REDOX or ORP level (Reduction /Oxidation potential) of the water. Normal pond water will have a REDOX level of around 200mv or less. Sterile water has a REDOX level of around 700mv. Some Ozone generators are designed to automatically regulate the ozone dosing to keep the REDOX level at a preset level, normally around 350mv - 380mv in a healthy aquatic environment, so that the water is not sterile or anything like, since it could not then support life.

What is a Redox reaction?

A chemical reaction in which electrons are removed from one atom (which is thereby oxidised) and added to another (which is thereby reduced). The movement of electrons is then measured on a millivolt scale.

What is Oxidisation?

Oxidisation is the process that causes steel and iron to rust, an apple to shrivel & go brown once cut open and is also responsible for the degeneration or ‘rusting’ of our bodies, causing cellular breakdown. Oxidisation or oxidative stress has been linked to many degenerative and chronic diseases including heart disease and cancer. It is also responsible for premature ageing. Oxidisation permanently disrupts and damages cell structure, thereby killing simple cellular organisms very quickly. Our beneficial nitrifying bacteria employ the process of oxidation to remove harmful ammonia and nitrite from our pond water by converting Ammonia to Nitrite and then Nitrite to Nitrate.

What causes Oxidisation?

Oxidisation is caused by oxygen molecules that are missing an electron, making them unstable. Oxygen cannot exist in this unstable form and has to be stabilised. The molecules collide with healthy, stable molecules be they in metal, or living cells and then ‘steal’ an electron in order to stabilise themselves. This damages and de-stabilises the molecule that they have collided with leaving it now missing an electron itself. The formally healthy molecule is now itself an unstable 'free radical' and will also try to stabilise itself by colliding with another healthy molecule and stealing one of its electrons. This creates a knock-on effect that damages and destroys living cellular structure, and in our pond environment this includes parasites, viruses, bacteria, algae or any other living organism with a simple cellular structure.

If Ozone kills bacteria, what about my Bio-Filter - won't that be affected?

Yes - but only beneficially! Pathogens are killed instantly as they pass through the Ozone stream in the Ozone reactor or protein skimmer, but obviously your nitrosammonas and nitrobacter do not, as they live on your filter media. True, they are free swimming as well, and any that pass through the Ozone system will be zapped. However, it is a recognised and fact that the beneficial filter bacteria have relatively short lives but multiply very quickly. Further it has been scientifically proven that nitrification bacteria will die faster without the presence of Ozone than with Ozone. This is almost certainly because the entire pond environment is cleaner and considerably more aerobic (oxygen rich) in an Ozone treated pond, and it is a well known fact that nitrifying bacteria reproduce and perform much better in oxygen rich systems. Many pathogens, on the other hand are anaerobic (live in a zero or reduced oxygen environment) and in a pond treated with Ozone there will be virtually no chance of anaerobic conditions existing. So the high Redox levels of the pond water is of considerable benefit to our friendly bacteria, but is definitely the enemy of pathogens.

If the Ozone kills only on direct contact in the Ozone reactor - what kills Algae and other organics that don't pass through the Ozone stream?

Ozone raises the Redox potential of the water substantially. This renders bacteria, algal spores and other organics much more susceptible to oxidisation - to having their cells destroyed or disrupted, even though they are not necessarily in direct contact with Ozone. Put another way, chemically the pond water is far more reactive as it is saturated with Oxygen, and single cell organisms or organisms with a simple cellular structure are easily oxidised and therefore tend to have a shorter life span. Direct contact with Ozone in the Ozone reactor means instant death, the higher Redox of the pond water means cells are easily oxidised (killed) and cannot reproduce effectively so their population decreases.

I've been told that Ozone makes the water sterile and can mean that the koi's immune system deteriorates as it doesn't have to work so hard any more?

This is simply not true! In a sterile pond environment, the Redox level is around 700mv - at this level all life would cease to exist in the pond. Koi ponds usually run at a Redox level of around 350 - 400mv. At this level the majority of pathogens are destroyed but your koi will be very happy and healthy. Also there is absolutely no scientific evidence that disinfection of pond water by oxidisation, whether this be by Ozonisation or chemical additives affects the immune systems of fish, including koi.

In their natural state, in rivers or lakes, each fish has a comparatively massive volume of water in which to live and the bacterial loading is much lower than in a man made koi pond. Using Ozone simply helps us reproduce nature. It is like attaching your pond to a freshwater stream, with new water flowing in on one side, and old flowing out of the other - effectively continually flushing out the system. Would a koi's immune system weaken in nature because it is not continually subjected to high bacteria counts? Of course not - quite the reverse!

In our experience of using Ozone systems over the last 5 years we have seen absolutely no evidence that koi removed from an Ozonised pond and moved into a 'conventionally' filtered pond are at any disadvantage, and we see no increase whatsoever in the incidence of disease because of moving koi between these environments.

This is simply more ill informed nonsense from the prophets of doom who simply can't - or won't accept new technology, even when it works brilliantly.

Can I use an Ozone system in place of a conventional filter?

No, you should consider an Ozone system to be a part of your overall filtration strategy, as it will not replace either the mechanical or biological elements of your conventional filter, but it will enhance the performance of your existing system thus rendering it far more efficient.

Can I still treat my pond with chemicals? and what happens when I do?

Yes of course, from time to time you made need to use a pond medication for parasites etc. When you do, simply switch off your Ozone generator. Ozone would destroy chemicals in the pond very quickly and would render your treatment useless. When your treatment is complete, switch on again and the Ozone will clear the chemical residue very quickly.

I have heard that Ozone is dangerous to human health - is this true?

Ozone is a powerful oxidising agent, and certainly if used carelessly or incorrectly it could be dangerous to health. However the same is true of almost all the chemicals we use in our hobby. Potassium Permanganate and Chloramine T are powerful oxidising agents and need to be handled and used correctly and definitely not ingested. Similarly Malachite Green, and Mercurochrome are dangerous substances which should not be handled with bare hands. Of course we know this and treat these substances with the respect they deserve. Indeed none of the substances we use in our day to day koi hobby should be ingested, inhaled or come in to contact with bare skin - again common sense.

Similarly we certainly don't want to breath in Ozone constantly as it can irritate the respiratory system, and therefore Ozone systems must be specified and installed correctly, with any residual Ozone produced gassing off to atmosphere - not inside your filter house! This is common sense, just as we should always install residual current circuit breaker devices in our electrical circuits anywhere near water - to prevent any chance of electricity and water mixing - which would almost certainly have fatal consequences.

Yet we frequently hear from people who seem to have an inbuilt fear of 'new' technology, or simply because they don't understand even the basics of how Ozone systems work, that they must be 'dangerous' and should be avoided.

Ozone has been in use as a safe and effective disinfectant for ventilation systems in offices, factories and even ocean going liners since the 2nd world war. It is most unlikely that such systems would have been developed or used if there had been an unacceptable health hazard. Ozone is used in many facets of industry, for many different industrial applications and to our knowledge no-one has ever died or been seriously injured as a result of Ozone poisoning!

Ozone has a very distinctive sharp, 'fresh' smell which many people identify with a disinfecting agent and it can be detected by the human nose at levels 10 - to 30 times lower than that which is recognised as being harmful to human health. In addition, Ozone is very unstable, and once created, immediately begins to decompose back to Oxygen again. This decomposition takes between a matter of several seconds and several minutes. It does not therefore even exist in a 'dangerous' state for a significant time.

We can therefore categorically state that a properly installed Ozone system would be a very safe part of your koi filtration system and one with which there would be no associated health risks whatsoever. The prophets of doom will have to look elsewhere!

Can I dispense with my UV system?

Theoretically , yes you can. However in practice we find it is best to leave the UV in place. This is because in most installations there is a much higher water flow through the UV than the Ozone reactor or protein skimmer. In summer the algae which causes green water can persist without a UV because Ozonisation improves water clarity dramatically and highly oxygenates the water. This provides the perfect environment for Algal growth and the use of a UV is of course beneficial. In addition, some Ozone generators have to be serviced from time to time and the UV can serve to keep the water clear whilst the Ozone system is switched off. We would recommend leaving your UV in place if you are using less than 1gm/hr Ozone per 1000 gallons.

Can I still use salt in my pond?

Yes, absolutely. The Ozone won't affect the salt and you will find your protein skimmer produces a lot more foam with salt in the water, so it actually works even more efficiently.

All sounds very complex - do I really need an Ozone system?

No, we can't claim an Ozone system is an essential part of a koi pond system, but that's what was said about bottom drains and vortexes a few years ago. Now very few 'proper' koi ponds are built without these essential items. For the serious koi keeper we would recommend an Ozone system be included as part of the overall filtration strategy. We believe that in the near future, Ozone systems will become just as much of a necessity as a bottom drain.

Koi are beautiful but expensive creatures and each year thousands of koi die needlessly from all kinds of illnesses most of which are simply caused by poor water quality - nothing more. In any koi pond one of the eternal and recurring problems that we have to overcome is bacterial disease and in a well stocked and mature koi pond the bacterial load on the system can become very high - especially in the summer months. Without doubt the single biggest benefit of installing an Ozone system is that the bacterial load on your system (and therefore on your koi) will be drastically reduced. Ergo less disease - more healthy koi. Unquestionably water quality will also be transformed using Ozone. Ask yourself why have marine/tropical aquarists been using Ozone to help manage water quality for the last 15 years or so? Why is the koi fraternity always the last to catch on?
The saying that we are not koi keepers - we are water keepers is absolutely true. If your pond water quality is superb, your koi are more likely to be healthy and live longer - it's as simple as that.

What comprises a complete Ozone system?

We need several items to build a complete Ozone system, rather like building your own Hi-Fi system. First we must have an Ozone Generator to create the Ozone initially and optionally a Redox controller which enables the system to operate automatically and switch on and off the Ozone supply as required. We then need some kind of Protein Skimmer or Ozone reactor to mix the Ozone produced with the water as efficiently as possible, allow it do 'disinfect' the water, and then remove any residual Ozone before the water is returned to the pond. We can also install an air dryer, especially on smaller systems, as Ozone generators produce more Ozone using dry air. Without doubt however, the most important element of any Ozone system is the Ozone reactor or protein skimmer.

But Like any good Hi-Fi system, it is pointless purchasing a very high quality amplifier if the speakers you will be using are poor quality. Similarly you can spend a fortune on a high quality CD player but if the amplifier is wrongly specified or poor quality you won't get the performance out of the system that you should. You get the idea, it's the same with Ozone systems - you need to match the Generator to the Reactor and other system elements to achieve the desired result.

At the smaller end of the scale, the Ozone reactors and skimmers tend to be very efficient, and this therefore means that the amount of Ozone we need can be reduced because the reactors are very good at mixing water/Ozone for optimum performance. Efficiency can be increased further by the addition of an air dryer.

At the other end of the scale, we need to produce more Ozone than we strictly need as the Ozone reactors are not as efficient when scaled up, and more Ozone gases to waste.

The technology sound complex, are these systems reliable?

Early Ozone generation equipment was not particularly reliable, as the generators produced a lot of heat, and early systems were water cooled. These were large and cumbersome and needed fairly regular maintenance. The latest systems (3rd generation) are all air cooled, are far more efficient and therefore produce less heat energy. The smaller systems , like the units from Sander and our own use tiny amount of electrical energy and are simple and very reliable devices which are guaranteed for two years. There are no moving parts in the generators and the only maintenance required is an annual clean of the generator electrodes.

The larger, more sophisticated Estrad units are air cooled but still use a comparatively small amount of electricity and there is therefore little wasted energy to convert to heat anyway. Again these units need minimum maintenance. The only moving parts are the cooling fans. These are also guaranteed for two years.

The protein skimmers have no moving parts (other than adjustable valves) and need no maintenance - not even cleaning.

The only item which needs more regular attention relates to systems utilising Redox controllers where the actual Redox sensor should be cleaned with a soft toothbrush about once per week to prevent it fouling.

Ok, I'm convinced, but how do I choose the right system?

Firstly, you obviously need to know your pond gallonage. From this you can first calculate the size of Ozone generator you will need by using the formulae of between 0.5gm/hour and 1gm/hour of Ozone for every 1000 gallons.

As a further guide, If you decide to use the Schuran or Sander Ozone reactors which we list, the amount of Ozone needed will be less than using other reactors. This is because in smaller systems, the Ozone reactors are generally much more efficient at using the Ozone produced. In larger scale applications, there is a compromise between the size of Ozone reactor needed to utilises the Ozone generated, and aesthetics. To get the same efficiency in a reactor required to handle 12 gm/hour of Ozone it would need to be much bigger and frankly, most of us wouldn't tolerate this kind of device in our garden. Therefore to allow the larger systems to be more compact and visually acceptable, the Ozone generators produce substantial volumes of Ozone to achieve the same result.

Furthermore, some Schuran protein skimmers are made to be used with a specialist Ozone reactor (the model 1) which make Ozone distribution even more efficient, allowing the use of a comparatively small generator for the chosen application.

We can obviously help by recommending a suitable system for your given application - please e-mail for further information at


Ozone Pollution Technology 1998


Ozone is enriched oxygen and is nature's powerful purifier. It is a short lived molecule that deodorises many organic and inorganic odours, both gaseous and particulate. It does this by a process of oxidation, permanently converting the odour into water vapour, carbon dioxide and other compounds. It kills germs by breaking down their protein structure.

Ozone is approximately 1.5 times more reactive as an oxidizer than chlorine. It also reacts up to 3000 times faster with organic materials such as bacteria. Unlike chlorine, ozone is highly effective against viruses as well. Importantly, ozone leaves no chemical residue as unused ozone decomposes back into oxygen. Since ozone is generated on-site, the safety problems associated with chemical storage, handling and transportation are eliminated.

Utilisation of ozone for increasing the storage life of food, particularly if held at low temperatures, is believed to have started in 1909 when, in the cold-storage plant of Cologne, the reduction in the germ count on the surface of meat stored there was observed after an ozone generator had been installed in the duct of fresh air used to ventilate the storage room.

The many possibilities for using ozone in the food industry and agriculture as well as in other fields are created by its bactericidal and germ-killing power. Not only does it act as a germicide but as a spore-killing agent as well. Foods exposed to its effect, undergo a pronounced change as a consequence of its action on the vital process of cells, the process of their metabolism particularly, through the inactivation of their metabolic products. At the same time it reacts with other materials present that can be oxidized and thereby it destroys odours.

Utilisation of these properties makes ozone eminently suitable for increasing the storage life of foods in unrefrigerated or refrigerated premises. Its use is economic as the investment and operational costs of the equipment are acceptable in relation to the size of rooms. Its application eliminates the risk of leaving the unpleasant odour or other traces of antiseptics used for preservation of foodstuffs.

Fish Industry Applications - Overview

Fishing boats which use ozone for water treatment and air sterilization in holds can stay out for longer periods than normal, and deliver fresher fish upon return to port. Use of ozone for air and water, during fish processing and refrigeration, greatly extends its freshness and delays its deterioration. Fresh fish in a retail cabinet with ozone will extend the shelf life by 1 to 3 days and eliminate the odours that customers find unpleasant. These are just some of the many ozone applications for the fish industry. Fish are ideally suited to ozone applications, throughout the entire industry food chain, from fishing boats through to retail shops.

Micro-organism Structure of Fish

The microbial structure of a fish depends on those present in the water it inhabits. The mucus protection on the skin of the fish can contain the following types of bacteria: pseudomonas, achromobacter, micrococcus, flavobacterium, corynebacterium, sarcina, serratia, vibrio and bacillus. Bacteria found on fish from cold waters are usually psychrophilic, whilst whose found on warm water fish are mesophilic. Fresh water fish carry bacteria peculiar to those waters, in addition to many of those found in salt water, and species of aeromonas, lactobacillus, brevibacterium, alcaligenes and steptococcus. In addition to those bacteria mentioned above, species of clostridium and escherishceria have been found in the intestines of all kinds of fish.

Fishing boats, crates and other containers, fisheries and operators, soon become contaminated by these bacteria, which are transmitted from the fish during cleaning and handling. The number of bacteria in the mucus and on the skin of a fish recently caught from the sea can vary from 100 per sq. cm to several million. Its intestinal fluid can contain anywhere from 1,000 to 100 million bacteria per ml. Scales can play host to between 1,000 and 1,000,000 per gram. Although rinsing reduces the surface bacterial count, it is obvious that this is not adequate. It appears that ungutted fish keep better than gutted ones, since this prevents contamination from the intestinal cavity. It is thought that bacteria spread into the tissue through the scales.

Oysters and other shellfish which move large volumes of water through their systems consequently absorb micro-organisms from the water and sea or river bed, including pathogens if these are present. Achromobacter and flavobacterium are the most common. The surface of prawns, crabs, lobsters and other crustaceans are covered in mucus, probably similar to that of fish, which can contain bacterial.

Because the surface flora of fish and other marine animals seem to consist mainly of bacteria from the water, refrigeration with ice will not result in further contamination.


Of all meats, fish is the most susceptible to autolysis, oxidation and hydrolysis of fats and microbial changes. Therefore, rapid preservation treatment is recommended and this should be more stringent that that used for red meat. When the fish is caught at some distance from the processing plant, on-board preservation measures should be taken.

Rigor mortis is an important factor in the preservation offish, since it delays post-mortem autolysis and subsequent bacterial decomposition. Any process which prolongs rigor mortis will therefore extend the preservation period. A major factor in this process is a reduction in storage temperature. Nevertheless this process is not sufficient in itself as most of the bacterial colonies mentioned can survive at low temperatures, and even at those approaching freezing point.

Reducing contamination in seafood is difficult to achieve using aseptic procedures. Nevertheless, some pre-processing contamination can be avoided, both on board fishing vessels and at plants by ensuring high standards of cleanliness and hygiene for decks, holds, buckets, crates and other containers used on board vessels and in plants. In addition, the ice should be of a high bacteriological standard.

Use of Ozone During Storage

The elimination of bacteria is a difficult process, but the fact that most germs causing contamination are found on the outside surface of the fish means that treatment with ozone is very effective, even in small doses.

Bacteria congregate on the surface of fish and shellfish. Ozonization actually prevents bacterial decomposition by destroying the bacteria, thus postponing post-mortem autolysis. As a result, rigor mortis is sustained for a longer period of time. This affects the preservation of fish and shellfish favourably. Rinsing fish and shellfish with water containing low concentrations of ozone helps to reduce the total bacterial presence on the surface of the fish considerably.

Experiments with Ozone Purifiers have been conducted to cover each stage through which the fish passes on its way to the consumer.

Ozone is used in Japan and Europe in the fishing industries to disinfect the water used for on board processing and ice making. Benefits include reduced mould and bacteria counts on the gutted fish. Treated fish are found to have counts of less than 1/1000th those of fish processed with untreated water and untreated ice (Bull, Japanese Soc. Fisheries 1979). Sensory and analytical studies indicate the use of ozone does not cause development of rancidity and the eating quality of fish processed in ozone treated water is better than the control.

A trial was conducted on shellfish in the hold of a fishing vessel, with the hatch opened 3 times a day only. An Ozone Purifier was placed in the hold and ozone was introduced at a concentration of 1.1 mg/hour per cubic metre of hold volume for an 18 day period. As a result, permitted preservatives were reduced to 10%. Odours in the hold were totally eliminated. The appearance of the shellfish after 15 days was striking. Discolouration of shellfish heads was actually eliminated (prawns, crayfish, etc.) The colour suggested that the shellfish had been caught the day before the vessel was put into port. The shellfish was at the rigor mortis stage. The rate at which the ice placed in the hold to freeze the shellfish melted, dropped by 70%. The floors of the hold were completely dry after the shellfish were unloaded. The experiment was repeated on board another vessel from the same fleet used for mackerel fishing, for a 3 day period, at the same rate of 1.1 mg/hour per cubic metre of hold volume. As a result, no preservatives were required. No odour was detected. The fish were at the rigor mortis stage. No rancidity was evident, either in the form of smell or taste.

A trial was conducted in a processing area using a concentration of 1.5 mg/hour per cubic metre of space. Several Ozone Purifier units were installed. The trial consisted of leaving the industrial waste from the day's processing in the area. The batch processed that day consisted of several tons of assorted fish. All windows and doors were kept closed until 7 a.m. the next day. Upon inspection at 7 a.m., deodorization of the area was 100%. For the first time ever, the computer installed in the processing area worked perfectly, which was unusual because of the high humidity concentrated in the area.

Specific studies on freshly caught Alaskan salmon found that the storage life could be extended by 33% to 50%, and that the development of rancidity was significantly slower when the salmon were washed and iced with ozonated water/ice.

Fresh fish in a self-service retail cabinet have been shown to extend their shelf life by 1 to 3 extra days when Ozone Purifiers were used. Odours were eliminated at the same time.


Autolysis starts once the fish dies. This is accompanied by loss of firmness and the development of abnormal odours; bacterial growth is uncontrollable under these conditions. As already mentioned, these changes are postponed by rigor mortis.

Fish preservation by means of refrigeration or cooling is temporary at best, due to the fact that muscular tissue of the fish autolises and its fats oxidize at temperatures slightly above freezing (rapidly during summer and more slowly as freezing point is approached). Small fish generally deteriorate more rapidly than larger ones and gutted fish autolise more slowly than whole ones.

Use of Ozone During Refrigeration

The addition of relatively low concentrations of ozone to cold rooms helps to destroy most of the bacteria on the surface of the fish, preventing spore propagation inside the room. This can be achieved with intermittent doses from an Ozone Purifier with concentrations of about 0.9 mg/hour per cubic metre of volume.

At these concentrations, ozone does not contribute in any way to an acceleration of rancidity as a result of an acceleration In the oxidisation of the fish, since the fish and other foodstuffs from the sea deteriorate through autolysis, which is a bacterial process. Ozone dosages act by paralysing the bacterial activity, and as a result, delays autolysis without ever reaching the oxidizational stage, since bacterial changes in fish do not commence until after rigor mortis, which is when the muscular tissue begins to release its fluids. Therefore the more this stage is delayed, the longer the fish can be preserved. Rigor mortis can be accelerated by the fish thrashing about in its death throes, by lack of oxygen and high temperatures. In contract, it is delayed by a low pH. The pH of fish is actually a major factor, not only because of the way in which it affects rigor mortis, but also because of its effect on bacterial development. The lower the muscular pH, the slower the bacterial decomposition. The effect of ozone on the pH is virtually nil, except when it is used to maintain it. A drop in the pH is the result of the conversion of glucogene into lactic acid.

Deterioration Process of Fish

In the case of fish, the transition from a fresh state to a state of change is a gradual process, which makes it difficult to determine when the first symptoms of deterioration appear. Researchers have long been seeking practical methods of establishing the quality of fish. Some favour using a method based on trimethylamine for saltwater fish. Others favour using various chemical tests, such as determining volatile acids and bases, the pH, or the hydrogen sulphide or ammonia content, etc. since bacteriological tests are too slow for such purposes.

There is a series of easily identifiable modifications that fish undergo as they change, until they finally rot. Their characteristic shiny appearance diminishes. It becomes discoloured and assumes a yellowish or dirty appearance. The viscous surface layer thickens, particularly around the fins and gills. The eyes gradually become sunken and wrinkled and the pupil becomes dull and the cornea opaque. The gills first acquire a pale pink tinge and finally become greyish yellow. The muscles lose their firmness and exude fluid upon pressure being applied. The dorsal fin can easily be pulled away from Its muscle, and In the extremities, particularly around the tall. A brownish-red colour appears as a result of haemoglobin oxidation.

Meanwhile, various odours begin to develop. First a fresh seawood smell which is normal, next a sickly smell, and then a smell of rotten fish, which is caused by trimethylamine. Then an ammoniacal smell occurs, and lastly a putrid smell due to hydrogen sulphide, indole and other unpleasant smelling substances.

The bacteria that most frequently play a role in the changes which take place in fish are those found in the mucus surface layer of the fish and those in the contents of its stomach. The most common kinds vary with the temperature at which the product is stored. Strains of pseudomonas are the most common at typical refrigeration temperatures, followed closely by various strains of achromobacter and flavobacterium.

There tends to be an increase in the number of pseudomonas in fish stored under refrigeration, whilst there is a decrease in the number of achromobacter. There Is an initial increase in flavobacterium, but this then drops. Bacteria first grow on the surface and then penetrate the muscular tissue. Fish have a high non-proteic nitrogen content, and autolytic changes caused by its own enzymes increase the reserve of nitrogenated nutrients even further, e.g., amino-acids and amines and also the glucose necessary for bacterial growth. The bacteria produced from such compounds such as trimethylamine, ammonia, amines (such as petrescine and dadaverine), lower fatty acids and aldehydes, mercaptanes and indole are compounds which indicate putrefaction. The muddy taste that fish sometimes acquire can be attributed to the growth of streptoacyes in the mud of the river or sea bed and the absorption by the fish of its characteristic odour.

Abnormal colouration can develop during changes. Pseudomonas fluorescens, yellow micrococcus and other species cause colours varying from yellow to yellowish green to appear. The presence of sarcine, mitrococcus and bacillus can produce a red or pink colouration, which is sometimes also due to mould or yeast. The development of certain non-sporulated yeasts cause the appearance of a chocolate-brown colour. Some pathogenic germs in the fish located in its muscle tissue give rise to lesions of colour modifications.

Shellfish are usually subject to the same types of changes as fish. Achromobacter, the species which develops most abundantly, causes changes in prawns kept under refrigeration, although a temporary increase in pseudomonas and a drop in flavobacterium, micrococcus and bacillus can take place. Changes in uncooked lobsters are attributable to the same types.

Oysters keep well at low temperatures while kept alive in their shells, but they decompose rapidly as soon as they die. The type of change in oysters extracted from their shells depends on their storage temperature. Oysters contain not only a high level of protein but also sugars produced by the decomposition of glucogene. The species of bacteria that produce changes at near-freezing

temperatures belong to the pseudomas or achromobacter families, and sometimes flavobacterium and micrococcus. This type of change is usually referred to as "souring" although it is actually due to a proteolytic process.

No comments:

Post a Comment