Koi Fish Breath

Breathe Easy

We know oxygen is a critical water quality parameter for our koi – a minimum of 5-6mg/l is usually recommended – but have you every wondered how they manage to extract it quickly die without access to air, but fish positively thrive underwater, and in this article we’ll look at how they do this.

Oxygen in water

You or I wouldn’t give a second thought to the oxygen content of air, however for fish it’s a different story. To begin with, water contains much less oxygen than air 6.3cm³ per litre at 20⁰C, as opposed to 210cm³. on top of this, water is denser and move viscous than air, which means it requires more energy to move it across the respiratory surfaces (gills in fish, lungs in mammals). 

In fact, around 10% of the oxygen absorbed by fish is used to move water across the gills. Just to complicate things a little more, the oxygen content of water, and the amount that fish require, depends on water temperature. Warmer water holds less oxygen, yet fish require more of it. For example, in one experiment it was found that at 20⁰C the resting oxygen consumption of carp is 48mg/kg/hr, rising to 104mg/kg/hr at 30⁰C. so spells of hot weather can place real challenges on the fish’s respiratory system to deliver the oxygen needed for health and condition. 

Gills

For most fish, including koi, the gills are the main site of gas exchange between the blood and surrounding water. Although the skin is a major site of gas exchange in larval fish, accounting for 85-90% of the total oxygen uptake, in adult fish this falls to 20% or less. Each gill consists of a branchial arch (or gill arch) that supports two comb-like gill filaments. The gill filaments consist of primary lamellae, upon which are numerous small secondary lamellae. It is at these secondary lamellae where oxygen is absorbed. These are eight branchial arches in total, arranged so that all of the gill filaments can potentially receive a steady flow of water.

The secondary lamellae provide a very thin (2-4um) barrier between water and fish’s blood supply. This allows oxygen to diffuse from the water into the blood, where it can then be carried to the rest of the body. The blood flows in the opposite direction to the flow of water, in a “counter-current’ system. This improves the diffusion of oxygen into the blood by maintaining a better concentration gradient (i.e. the level of oxygen in blood remains lower than in the water). Fish that are active often have increased numbers of gill lamellae, and a greater overall gill lamellae, and a greater overall gill are to help them obtain more oxygen from the water. For most fish, the gill area is around 150-350mm2/g bodyweight. In very active fish such as tuna this rises to 1500-3500mm2/g.

The gill area, coupled with the amount of water being passed over it (respiratory volume), determines how much oxygen the fish can extract from the water. As oxygen levels decrease, the respiratory volume increases to compensate, and the amount of blood being pumped through the gills rises. Unfortunately, as water flow over the gills increases it becomes harder for the fish to extract oxygen as efficiently. Under ideal conditions, 85-90% of the oxygen can be removed, falling to 10-20% at very high respiratory rates. If oxygen levels are low you will see the gill covers (opercula) beating more rapidly as the fish pumps more water.

Osmorespiratory compromise

Because of their high permeability and surface area, as well as being ideal for gas exchange, the gills also provide an area where ions (changed atoms) and water can move in and out of the fish. This presents a problem, as water will move into the fish, and important ions will move out. The fish has to compensate for this, by producing lots of dilute urine, and having mechanisms to take up ions into the body. For example, in a study involving trout, a period of exercise and increased oxygen use was followed by increased urine production. These are energy-consuming processes, and the balance between the need for gas exchange versus the need to minimise water/ion movement is called the ‘osmorespiratory compromise’.

Because of this dilemma, when oxygen concentrations are high, or if the fish is inactive, only a part of the gills may be used. This can achieved by reducing blood flow through the gills, or by adjusting the gill filaments to reduce water flow through them. This ensures the fish receives the oxygen it needs, whilst limiting the movement of water and ions. studies involving species closely related to koi have also revealed that the surface area of the gills can be reduces when oxygen demands are low.

 

Oxygen transport

Once in the blood, most of the absorbed oxygen is combined with haemoglobin in red blood cells and transported to various parts of the body. The ability of haemoglobin to carry oxygen depends on the concentration of hydrogen ions (H+); in other words the PH level. Because tissues in the body are constantly respiring, they are releasing carbon dioxide (CO²) into the blood. This decreases the PH. 

When the red blood cells arrive at the tissues, the lower pH causes haemoglobin to off load its oxygen. This can then diffuse into the tissues that need it. The blood pH remains low as it carries CO² back to the gills. Here it diffuses back out into the water, facilitated by an enzyme called carbonic anhydrase. The pH rises again and oxygen can once again be picked up, and the cycle starts again. 

The effect of the blood’s pH on its ability to carry oxygen is known as the Bohr effect, and it is essential for supplying oxygen and removing carbon dioxide.

A very low environmental pH, or lactic acid production caused through increased activity/stress, may depress blood pH and reduce its oxygen carrying capacity. Koi, like all fish, have mechanisms to prevent blood pH changing, and for quickly restoring it, however under extreme conditions these may be exhausted. Maintaining a correct pH is therefore important, as is providing plenty of oxygen if the fish are likely to be stressed. In addition, carbonate(KH) and general (GH) hardness should be kept at recommended levels. For a stable pH, healthy gill function, and help the fish maintain the pH of its blood.

Keeping koi healthy

From knowledge of how respiration works in koi, it’s clear that for top condition we need to keep oxygen levels high. This means less of the gills need to be used, and therefore the fish needs to use less energy for maintaining its water/ion balance. Water quality is also important, and mineral-poor, acidic conditions should be avoided if possible. By providing a good environment and minimal stress, your koi will be able to obtain the oxygen they need for top health and condition.

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Koi Fish Growth

Going for growth

This article gives advice on stocking levels and feeding. There are more koi foods on the market at the current day than ever before and finding the right food can be very difficult. 

The topic of stocking levels is also hugely controversial as most people tend to have a different idea as to how many koi they should actually have in their pond. I have been growing koi on a big scale for five years and have finally been able to begin to piece together a growing program anybody can follow.

Stocking levels

There is so much advice available on this topic it can tend to be very confusing, normally it can be very technical or unrealistic, for example, in order to get good growth rates you need to keep five koi in 4000 gallons. The majority of koi keepers don’t want to keep this few koi in their pond as it will look empty, so I have been able to find a balance that allows very good year-on-year growth rates and doesn’t make the pond appear empty.

One of my koi houses contains eight ponds that hold 4000 gallons which are set-up exactly the same. When I stock a pond for growing I always aim to keep the same size of koi together but this isn’t always possible in a hobbyist’s pond. I only over tend to grow tosai (one-year-old koi) and nissai (two-year-old koi) and from doing this I have devised a points system (fig 1) that can act as a guide for anybody stocking a mixed pond or a professional growing pond. 

The points systems will help you when stocking the pond with tosai, nissai or small sansei (three-year-old koi). If you use this system in a hobbyist pond I would add 15cm on to the length of the koi before calculating how many points it will take up. This will allow for the koi growing in the future and it is most likely that the koi will grow more than 15cm but by making this initial allowance it should set a stocking level that will more than compensate for this in the future. If you want to maintain smaller koi in the pond simply work out the points according to the current size of the koi when placed into the pond. I haven’t included koi over 55cm on the points scale because when dealing with growing larger nishikigoi there are more factors to take into consideration and I only over give advice of professionally growing larger koi case by case.

Figure 1: stocking rate points

Calculate the amount of points for your pond / 100 gallons = 1 point

Koi size class                      Amount of points

0 to 18cm                                             1.5 points

18cm to 30cm                                    2.5 points

31-40cm                                               3.5 points

41-55cm                                               5 points

Is it OK to mix smaller koi with larger ones?

This is one subject that has always stayed prominent with me from my time spent in Japan during the selection process where big koi would always be removed from the fry ponds and transferred into another pond with koi of the same size. The answer to the question is a mixed one. The teaching I received in japan was that small koi should never be grown with bigger ones for example: a yearling around 20-25cm should not be grown with a two-year-old koi of 35-40cm. The main reason being that the larger koi will always manage to get a larger share of the food and in the mud ponds will eat more of the natural food. 

However, there are some instances when it is OK to grow mixed size koi and when all of the koi are 55cm+ as at this size all of the koi will feed equally as well so there shouldn’t be any serious competition for food. Tosai growing-on ponds are becoming more popular in the UK – hobbyists are able to raise a batch of similar-sized tosai up to 35-40cm before placing them in the pond. This allows them to get better initial growth and be able to compete better in a normal pond environment. 

As a standard rule I would always advise trying to grow similar-sized koi together to get better results.

Type of food

What food is actually good for your koi?

Everybody has their own reasons for choosing a particular brand and other reasons for not liking another type of food. I tend to hear a lot of people saying: “I’ve tried this food for a couple of weeks and it created a lot more waste and bad water and the fish didn’t seem to like it as much as the other food.” This is where a lot of the negative criticisms of food come from. 

The initial problem to begin with when trying a new food is that people will just instantly change the koi from one diet to another and this can cause large amounts of excessive waste and poor water quality for weeks especially if the koi had been on their previous diet for some time. It is this that can also cause the koi to dislike their new food and not eat as well as previously.

My recommendations when trying new koi foods is to pre-mix it with the existing diet 50% new food 50% old food for two weeks. After this period begin to feed your new food only and this should prevent any digestive problem and help to maintain the water quality. Comparing one food against another is a difficult thing  to do as in order to make a fair comparison different foods should be tested in ponds that run exactly the same, with koi from the same batch – koi from the same oyagoi (parent koi) – and the water temperature and stocking levels also needs to be the same. I have done this over the years with many different foods and after testing most of the leading brands on the market today I have always had the best results with Saki Hikari and Tetra Koi Excellence. I rate the Saki Hikari as the number one of the market today and most effective in terms of the growth rates it can achieve but also the development of the koi, general health and water quality and clarity. The growth diet in particular is superb with a conversion ratio of 100% so for every kilo fed the total weight of the koi within the pond will increase by one kilo. The colour diet is also exceptional, for years I tried to find a colour food that would aid the development of the koi instead of making them look false or causing it to deteriorate by turning the white ground yellowish and finishing beni pigment to early.

Saki Hikari colour diet used in moderate levels does everything I expect of a colour food and I have even raised Shiro Utsuri on this food without discolouring the white ground. The end results were excellent with the white ground actually becoming much thicker and the general skin lustre including the sumi quality was excellent with skin taking on a glossy texture. The mix I like to use consists of 75% growth diet and 25% colour diet before moving solely onto Multi-season in the winter. Another added benefit with Saki is the added pre-biotic the ‘Hikari germ’ – I found that certain fish that picked up very small surface abrasions would heal without any topical treatment or antibiotic injection being given. Koi that were fed on this food for a full season also went through winter much better with no illness and all the fish tended to be much more active showing the sort of behaviour you get when the water is 20⁰C but in actual fact the water was only 8⁰C. in my opinion the Saki Hikari diet is the best and will be my choice until something comes along that can better it.

Amount of food and water temperature

Lack of food in relation to water temperature is possibly the largest cause for koi not gaining the amount of growth they could during each season. How many koi keepers actually know how much food they are putting into their pond each day? The answer is simple: not many. Certain levels of feeding can be given and these levels are calculate from different amounts of body mass percentages. 

The main three are 1%, 2% & 3% and what level to feed depends heavily on the water temperature. It is important to note that feeding 1% of the body mass during the summer season is only the maintenance level – it’s enough food to keep the koi ticking over and healthy. In japan most koi breeders will maintain the concrete ponds where they grow tosai at 25⁰C, which is the optimum growing temperature and this is when 3% of the body mass should be fed. However, when the temperature is below 20⁰C 2% of the body mass is more suitable – anything above this may cause the fish to become fatty and out of proportion. This could permanently change the body shape and structure of the koi. Once a feeding amount has been calculated it’s a good idea to make a food measure with amount of food marked on it so that the correct amount can be given easily everyday without having to weigh it.

Where a heater is installed, it is beneficial (in my experience) to heat the pond during summer so water can be held t 24-25⁰C from may through until October. When this temperature is maintained and the correct feeding level applied the growth rates will be excellent regardless of the age of koi, but of course, the water quality must be maintained a mentioned in part 1 of the series.

Turbo growth treat

Many different turbo growth treats or supplements are available today, some of which I think are unnecessary and can fowl up the system or cause the koi to become fatty. There is one however, which is heavily used by koi breeders in the mud ponds: silkworm pupae, which is around 55% in protein. Silkworm can fowl up the system if overfed and I always advise sieving it to get rid of the dust. The best way to feed silkworm is two to three times per week as a treat, but it could be fed daily for those who wish to get the most from their koi. Silkworm is said to make the whole structure of the koi much larger and a lot of volume can be gained due to it being a easily digestible, natural source of protein. If you wish to incorporate silkworm into the daily diet the water temperature must be 24⁰C or above and in cases where I have done this I made a mix of 50% Saki Growth 25% Saki Colour and 25% silkworm. This in my opinion is the most ultimate growth mix for nishikigoi but when feeding this sure to monitor the water quality very closely and good mechanical filtration as mentioned in part 1 is paramount.

Automatic feeders

Feeders are very useful piece of equipment and becoming cheaper. The benefits to be gained from having an auto feeder are that the feed can split up throughout the day. Fujio Oomo once told me that I should always use auto feeders because the koi will grow bigger. It is beneficial having smaller feeds going in throughout the day because the koi will be exercising on the surface looking for food rather than just giving the pond one big feed in the morning and another in the evening. The filtration system can also benefit from smaller feeds because the amount of waste after each feed will be much smaller so the system will be able to recuperate much quicker.

Getting feeding levels right

There may come a time throughout the growing season when the size of the koi has increased to such an extent that the feeding level will have to be raised so that the growth level can be maintained. Should you have to raise your feeding level just try to estimate the rough growth of each koi and recalculate it accordingly. As well as looking at increasing the food, take care not to overfeed – some typical signs to look out for are nitrite or ammonia spikes, especially if the system is well matured, but also study how long it takes for the koi to eat their food. Monitoring the time it takes to eat one feed will give you an indication whether they are being overfed. If the feeding time increases the lower the feed slightly until the normal feeding time is resumed. Likewise, you can also use this to judge if more food is required as the koi will eat their feed more quickly because they have grown and require more food.

Conclusion

Feeding and stocking levels are very important when growing koi. Getting it right can take a lot of commitment and observation to ensure you’re maintaining the right amount of food or not overdoing it. Finding the food that’s right for you can also be difficult, that’s why it is best to see some results from people (and their koi!) who have used the food before making a decision.

Notes

Out with the old

Something i always  see as important is the removal of koi that do not fulfil their potential. I know to a lot of people koi become their pets so this would be unthinkable but to anybody wishing to get the very best results, koi that loose their colour or don’t develop to the level of quality you expect should be moved on to another koi keeper who wouldn’t be quite so bothered as to what koi they have in their pond. Removing these fish makes way for something new that holds more potential than the previous koi.

Pellet size matters

To get maximum digestion from koi food the pellet size is crucial. Most koi food will state what size of koi the pellet is most suitable for but as a rule I like to feed a small pellet to any koi of 40cm or under. Small pellets are much easier to digest due to having a larger surface area. The maximum pellet size I would ever feed to koi over 80cm would me a large medium pellet so for koi over 40cm a medium pellet is the maximum. Improved digestion will certainly provide better growth but also better value for money from the food you are buying because the koi are getting more of the goodness.

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