History of pond or tank and fish (new arrivals etc) to help diagnosis #

The most common route of parasite infection into a group of fish is by the introduction of new fish without adequate quarantine (ideally a separate tank for at least 4 weeks) although contaminated equipment can also spread parasites.

Symptoms #

• Skin and gill flukes will cause flicking/flashing, restlessness, excess gill movements,
• If fish have problems with a parasite infection in their gills they will tend to congregate where oxygen is coming into the pond or tank.
• Alterations to the faeces such as stringy appearance indicate intestinal parasites.
• Weight loss usually occurs with intestinal parasites too, although other parasites such as eye flukes can cause problem with finding food.

Skin scrape for some larger fish such as koi #

This is a routine diagnostic procedure which can either be carried out by a fish health professional or by a knowledgeable fish owner. The fish is gently restrained and using a blunt scraper (not a glass microscopic slide) – even an old credit card will do – gently scrape at about 45° to the skin, towards the tail so you don’t damage the scales. Place the mucus sample on a glass microscopic slide, add a drop of pond water and put a cover slip on the top.

Start with a magnification of 100x and gradually work up to 300x or even 400x. Make sure you examine all of the sample.

If you can manage to gently restrain the fish without using any sedation this will increase the chance of finding parasites.

Examine at least 4 fish from a group to get a better idea of the level of infestation.

Mixed infections #

Your fish may have more than one type or species of parasite affecting them at the same time – for example, Flukes and Trichodina and or Costia.

How long do parasites live? #

One of the challenges in ridding your fish of some parasite infestations is in the case of egg-laying parasites. In the case of fish lice (Argulus) and ‘gill flukes’ (Dactylogyrus species) the eggs are extremely resistant to treatment, and can even overwinter.

Costia also can be a challenging parasite to treat. At temperatures between 10 and 25°C it reproduces rapidly, completing its life cycle in 10 to 12 hours. When temperatures drop below 8°C or if left in dry conditions the parasites forms into a resistant cyst, which can ‘wake up’ when conditions become favourable again. However it must find a fish host within 24 hours or it will die.

Trichodina have the ability to survive freely in pond water during their life cycle, although they also attach to fish – attracted by the bacteria and debris in fish mucus which occurs with poor pond hygiene associated with inappropriate filter management. They are very simple organisms without a nervous system, digestion etc which can limit the types of treatment. Since they feed on bacteria and organic material in the water, keeping the pond water clean and of good quality will certainly assist in controlling this parasite – hygiene is the key!

Tapeworms require an intermediate host outside of the fish to complete their life cycle, although they can still cause serious problems to the infected fish while they are present in its intestine.