maria hayward
tough, adaptable fish, and more harm can be done by overfeeding them than underfeeding, and this can occur in two main ways. Firstly, overfeeding can directly harm the fish through problems such as fatty livers. But it also, of course, contributes to poor water quality, and this can lead indirectly to a multitude of health issues in koi.
what makes a koi food So what functions do the various
components of koi food have? The so- called ‘essential nutrients’ are proteins, lipids (or fats), carbohydrates, vitamins and minerals. (Good old water is often considered an essential nutrient in animal nutrition, but we can take it as read that it’s in abundance for our koi – let’s hope so, anyway!)
Carbohydrate Carbohydrates – organic molecules made from carbon, hydrogen and oxygen – are used in the animal kingdom for energy. They aren’t particularly effectively utilised by koi, so they tend not to make up a huge proportion of the diet. They are still present, however, although excessive carbohydrate can lead to a number of health issues, such as liver failure.
Protein
Proteins are macromolecules comprised of their component nitrogen-based amino acids. They are used as a source of energy for koi, as well as being essential for growth. When utilised for energy, the
protein undergoes a process known as transdeamination, in which the nitrogen is incorporated into ammonia and excreted across the gills. So although in simple terms higher protein means higher growth rates, it also results in increased levels of ammonia. However this depends on factors such as the quality of protein,
Shelf life
Whilst buying ‘bulk’ packages of koi feed can seem like a good idea from a financial point of view, bear in mind that the lipids contained in the feed can oxidise – or go rancid – within a short period of time, and it’s extremely difficult to tell if food has ‘gone off’. For this reason, only buy packaged food that can be used up within about two months of opening. Very old, severely oxidised food can have serious effects on the fish, courtesy of liver damage.
and how efficiently it can be utilised by the fish. Young, growing koi require a higher
protein content in the diet than older fish, and many manufacturers produce specific ‘growth diets’ to cater for such koi.
Lipids The correct technical term for fats is lipids. Like proteins, they are used as a source of energy, but they also form essential cell membranes. In addition, lipids carry various vitamins, including A, D, E and K (the so-called fat soluble vitamins). Koi diets should contain essential fatty
acids such as linolenic and linoleic acids, and the overall lipid content should be free of saturated fats (fats which remain solid at room temperature). Diets high in saturated fats can lead to significant health problems.
next month In the next issue we’ll be looking at the
role of vitamins and minerals in the diet of koi, and considering how diet can affect the coloration of our fish.
DAVE WOLFENDEN
Further information:
For more information about Tetra’s products and services go to
www.tetra.net.
Only buy packaged food that can be used up within about two months of opening
AUGUST 2010 35
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