Koi, like us, have their preferences but as Ian Watson knows there are a few simple rules to follow when feeding your Koi
There are many areas of koi keeping that generate a great deal of mystery, and koi food is no exception. Here, we shall concentrate on the basic and most important questions of why, what and when. Some knowledge of koi nutrition is very useful to the koi keeper, but really if you stick to a few, simple rules, your koi should stay healthy and that means you stay happy.
The question 'why do we feed koi?' may sound so obvious that it is not worth asking, but over the years, I have met many koi keepers who were not really sure of all the reasons for feeding their prized specimens. The constitution of koi food provides us with an insight into a koi's nutritional needs.
Frequently, people writing about koi food seem to be obsessed with protein, quoting precise figures for the optimum protein content of koi food. In fact, protein is important as the average koi consists of about 20% protein (most of the rest is water). This protein is the key structural element of fish tissue hence without adequate protein in their food, koi cannot grow properly.
The vast majority of koi foods contain between 30-40% protein, which is acceptable. However, this percentage is only a secondary consideration. The key factor is the koi's daily protein intake (measured in mg/kg of body weight). This is rather similar to the RDA (recommended daily allowance) that you see on the side of your cereal packet, which tells you how much of your daily nutritional requirement is supplied by a bowl of cornflakes. In exactly the same way, the higher the protein content of koi food, the less you need to give.
However, with so many different sized koi in your pond, all being fed at a wide range of temperatures, can you really be accurate when judging each specimen's daily protein intake per mg/kg of body weight? The fact is that it's impossible. Here, the first rule of koi feeding comes into play - there are no exact rules - everything is very much done on an ad hoc basis.
Besides protein, the other 60-70% of koi food mainly provides energy. Again, looking at the side of your cereal packet for reference should help to clarify this point. The nutritional breakdown will contain a value for total energy (in kJ or kcal), which may be broken down even further into energy from fat and energy from carbohydrate.
Fat and carbohydrate are both essential constituents of koi food and each performs different structural and metabolic functions. Fat comes in two forms - saturated and unsaturated (see the label of a butter substitute). Presumably, you have all been heeding the government health warnings and know that saturated fat is bad in excess.
Koi food naturally contains very little saturated fat, with the majority being health giving PUFAs (polyunsaturated fatty acids), which we are all encouraged to eat. Too much fat is a bad thing, as it leads to fat fish, which like fat humans, are unhealthy. However, those PUFAs are as vital for koi health as they are for humans.
Carbohydrate, the other energy component, is essential for manufacturing koi food and for making it float. Koi mainly use carbohydrates for energy as they only have a limited nutritional requirement for them. Naturally, too much carbohydrate is bad for koi as excess energy intake makes them fat (all you calorie counters know that too). As with protein, it is the daily energy intake that is important, so be careful not to overfeed your koi, or all the excess energy will tend to result in big fat deposits in the fish, no matter how nutritionally balanced the food is.
The next dilemma we face is what to feed our koi. I am perfectly happy to feed koi on nothing other than pellets from a reliable manufacturer, as these contain everything a koi needs to be healthy. However, different people may want different things from their feeds. I will admit that in all the trials I have carried out with koi food, the only thing I have studied is growth rates and the efficiency with which the koi turned the food into koi flesh. Others might consider colour to be the most important factor. Whatever you want for your koi, my advice is to use pelleted koi food as the basis for their diet.
The only advice I can give on choice of brand is to buy from a reliable source, never to buy repackaged food (you have no idea what it is, nor how old it is) and to keep it cool and dry once you get it home. Vitamins in particular have quite a short life once the package is opened, so I prefer to buy my koi food monthly. If I buy a bulk pack, I store what is not required immediately in an airtight bag in the freezer.
There are lots of treats that you can give your koi, but most do not contain essential nutrition. Shrimps, cockles and the like will be loved by your koi, but are not a dietary requirement. Some vegetable material can be useful, and koi will happily eat huge amounts of lettuce in hot weather.
Small koi can eat an amazing amount of duckweed, so if you have a excess of it, just stop feeding for a few days.
Go easy on starchy foods like peas and sweetcorn, once a week in the summer is enough, as too much of these can make the fish fat.
A little wholemeal bread can be useful in spring and autumn when the koi's appetites are low as it provides a bit of bulk and some energy to keep them ticking over. Normally the only food I give in winter is worms, but again these are fed only very occasionally. You could feed wheatgerm pellets in spring and autumn, but I think they are relatively expensive.
What you must never, ever feed to koi are other pet foods, especially dry cat and dog foods. No doubt the koi will love them, but they are totally unsuited to the koi's nutritional needs. The same applies to anglers' baits. Just because wild carp go crazy for banana and coconut flavoured fish meal boilies doesn't mean it's part of their recommended diet. Remember, the carp in angling lakes take natural food as well.
You will have noticed a decided lack of figures in this article - that's because I don't believe in them. There is no magical temperature when you must stop or start feeding your koi. Look at the koi. If they look hungry in cold weather, think about feeding them. But, take a look at the weather forecast first. If a spell of warm, settled weather is forecast, by all means feed a little wheatgerm pellets or a few worms. But, if a frost is forecast or a cold front coming in, put the food away. I hardly feed my koi in winter, and it does no harm. In warm weather, you must again take your cue from the koi themselves. In the hottest months, koi will quite happily eat all day. This is not really practical, but I like them to have at least three feeds a day. However, I am mean with my food, and it rarely takes my fish more than a couple of minutes to eat each feed.
If there are pellets left after five minutes, you have either got very slow eaters or you have fed too much. And please, keep an eye on the weather. Hot, thundery weather stresses koi as the oxygen level in the water tends to be low. Feeding increases oxygen demand, so in thundery weather, cut back on feeds and don't feed in the evening.
In all, when it comes to fulfilling koi's nutritional needs, interpreting your koi's behaviour correctly is far more important han being an expert on protein percentages.
If you combine this knowledge with the few simple recommendations mentioned here, then hopefully, your koi will be healthy, and you will be happy.