Allotment Articles 2.
There are many predators of fish, both big ones and small ones. Perhaps the biggest predators are the fish themselves, as big fish will always, given the chance, eat small fish. Big goldfish will eat small goldfish and big Koi have huge mouths enabling them to take fair sized fish. Usually small fish are faster than big ones, so when fish spawn you always get some surviving to maturity. However, when you think that the average goldfish will lay 1000 eggs, most of which will hatch, and you only find a dozen, or so in your pool, you can see the scale of the problem.
Most fish will nibble at dead fish, but will not bite
pieces out of a live fish, (apart from the odd fin nipper,) with the exception of catfish. If you see fish in your pool with gaping wounds it may be ulcers, or if a catfish is present, that is the likely culprit. Coldwater catfish are very aggressive unlike most tropical varieties and have stomachs that expand like snakes. They also have very large heads that are all mouth. Catfish are said to be able to swallow a fish their own size. They should not be confused with loaches that look more like eels, and have small mouths and however big, are quite harmless.
Most cats are skillful fishermen and have a great deal of patience waiting at the side of the pond for a fish to come within reach. Even the occasional ducking does not deter most cats when they have found that there is a tasty meal to be had from the fishpond. A pet dog may help to deter a cat, but the only foolproof method is to erect a 12inch high fence around the perimeter of the pond very close to the edge as this will stop them sitting on the side and fishing. This may also help to deter herons that can be a nuisance as they are said to walk into the water rather than land in it.
A predator that most people don't usually think of is the seagull. If you live near ploughed fields where flocks regularly gather it is only a matter of time before they spot the water in your pond and investigate. I have seen them dive bomb a large pool where there were small fish and from the frenzy that they were in I am sure they weren't just taking a drink! However like kingfishers they will only take small fish. Kingfishers will only be found near a large open, body of water and a net over the pond will soon stop them.
If you live near a canal, or river there is one predator that is almost impossible to stop and that is the mink. In recent years the actions of animal activists have caused it to become naturalized in many parts of the Country. It is a fierce predator with very strong jaws and razor sharp teeth that can cut through any net effortlessly and they are quite partial to the odd Koi carp. The only cure for this pest is a shotgun.
A somewhat smaller pest is the greater diving beetle that can fly like all beetles and will eventually find your pond. They grow to well over an inch in length and will quite happily kill and suck the juices out of small fish. The best thing to do with these little predators is to regularly check your pond and scoop any that you find out with a net before killing them.
Frogs won't eat fish, but they are often blamed for killing them. When it is time for the frogs to spawn the male will grab anything in the hopes that it is a female frog and can sometimes be found gripping a dead fish. However, in practice, a healthy fish is likely to be too fast for a frog to grab and it is probable that any fish that it does manage to grab is already very sick and likely to die anyway.
The most alarming cause of fish to disappear is that of burglars. You might think that nobody could catch fish in a pond in the middle of the night. It is hard enough when you are trying to clean your pond in daylight, but they do and this is a growing problem. Koi Carp are what they usually go for and they will overcome all obstacles to get them. One garden centre had an 8 foot high wall round their fish department, but that didn't stop the burglars getting away with thousands of pounds worth of big Koi. Alarms and movement sensors on floodlights may help, but where there is a will there is a way.
A new problem facing some fishing clubs with large lakes stocked with fish is that the actual fishermen themselves are emptying their pools of some of the more choice specimens. The stories go that the same is happening to some extent with our canals and rivers. It is customary for British anglers to put fish back where they catch them, but it seems that anglers elsewhere are in the habit of eating their catch! This type of loss is only going to happen where water courses, or pools are open to the public and the answer would seem to lie in educating newcomers to normal fishing practices.