Jacqueline Sanders wrote:

I have recently starting keeping fish in my pond , mostly koi and have
been told that I need to have plants in my pond which provide air for the
fish can you please advise on what plants to buy.

No, you don't _need_ plants. As someone who came to ponding from the other
direction though, I can't imagine why you would _want_ a pond without
plants :-)

Plants don't, as such, provide air (specifically Oxygen) for the fish. As
long as you have decent water movement and sufficient surface area for the
number of fish you're keeping, the Oxygen is dissolved in the water from
the air above the pond. Plants do add somewhat to the amount of Oxygen,
during the day, when they're photosynthesizing, but at night the process
runs backwards and they absorb Oxygen and excrete Carbon-dioxide. This can
occasionally result in _lowering_ the oxygen available for the fish, so
it's best not to count on plants giving them the oxygen they need.

That said, the plants you can or should have depends to a large extent on
your location. If you don't use plants to shade the pond and take up
nutrients, you'll get algae instead. If you have a pond the color of pea
soup, you won't see the fish. Algae is either controlled by restricting
the nutrients or sunlight it gets (using other plants - like lilies, water
hyacinth, duckweed or azolla to shade the water; practically any kind of
plant to take up nitrates, phosphates and potassium) or you can use a UV
light to kill it. I don't like the UV solution, because I feel it masks a
high-nutrient situation that you should be aware of, but many koi keepers
use it successfully.
--
derek