Water Gardens Gazette number 318

Well that holiday didn't seem long.

I went to the Kruger National Park and discovered a very interesting fact about a "marginal aquatic" plant that is creating a potentially devastating impact upon crocodile populations.

I don't think many of you have crocodiles in your pond but this is a fascinating story for anyone interested in ecology as all pond keepers are I am sure. The story concerns an invasive riverside plant called the Triffid Weed (Chromolaena odorata) which originates in South America.

The sex of unborn crocodiles is apparently determined by the egg temperature during the incubation period. The cooler the temperature then the greater the ratio of females to males and vice versa. It is possible therefore to get a complete clutch of either female or male crocodiles. A significant impact on this ratio can be made by as little as a change of between 1 and 2 degrees Fahrenheit (0.5 to 1 degrees C). The incubation temperature for almost all crocodiles wherever they live is close to 30 degrees Centigrade (86 F).

In the Lake St Lucia region of Eastern South Africa the accidental introduction of Triffid Weed is creating a situation where traditional crocodile nesting sites are now experiencing more shade and therefore lower incubation temperatures. The result is high ratios of female to male hatchlings which is threatening to wipe out crocodiles in that region. No it is not April 1st and the threat is being taken very seriously. Read more about this at

http://www.issg.org/features/chromolaena.html

On our trip it was fascinating to observe larger fish catching smaller fish in the shallows of rivers at night ... what a life these fish must lead. Of course the crocodiles fed on the larger fish as we also witnessed.

Back to pond keeping now.

2. Warm Water and Oxygen In Ponds

Western Europe has experienced record temperature levels and a number of people have reported gasping fish so I thought i would once again bang my oxygen drum. You will know by now my belief that any pond should contain 3 things .... water, oxygen and fish.

When water temperatures are high as they have been then a serious reduction of oxygen levels takes place in any water course for the simple unavoidable reason that water dissolves less oxygen as water temperatures increase. You can only do your best to compensate for this by ensuring your waterfall is working and that you also run a spray-type fountain. Of course if you have an air pump and air stones then keep the air pump running morning, noon and night.

Water at 25 degrees C can hold only 89% of the oxygen that water at 20 degrees can hold. At 30 degrees oxygen is depleted by about 20%. This is a great deal when seen from the perspective of the the fish and the bacteria in your biofilter. In fact because dissolved oxygen content is lower the biofilter works less well which creates more of a strain on the pond system.

At higher land elevations as in large parts of South Africa, and in places like the Rockies the problem is made even worse because oxygen concentrations are also influenced by air pressure. At about 5,000 feet above sea level water holds about 8% less oxygen than at sea level.

As I have said many times you cannot add too much oxygen to your pond. Waterfalls are essential I believe in any pond.

3. Thinking of Winter Yet?

I am always intrigued by the koi market participants and was prompted to write these few words following a request for information from a pond keeper who had a record "crop" of koi and was looking for possible buyers She could not seem to find anyone.