It may come to a time when keeping fish that you will need to consider taking a skin scrape to diagnose a problem with your fish. Taking scrapes enables the fish owner to to see what is living on your fish that the naked eye cannot see and help diagnose any possible problem that can cause concern.
For scrapes you will inevitably need a microscope ideally with a magnification up to 400x, clean slides, and slip covers, a bowl or suitable container and scrapers. Scrapers are generally wooden "lollipop" sticks that can be obtained from your local GP, these come in sterile packs which helps give the sample less chance of contamination.
When taking a scrape it is always handy if you have an extra pair of hands, especially with larger fish and to have everything at hand ready to use before starting, this makes your job a lot easier and causes less stress to the fish.
To take the scrape place the fish into the container as you can see i use a large koi bowl ( picture here ), let the fish rest for a few minutes to get its breath back especially if you have had to chase the fish around the pond to catch him / her.
with wet hands hold the fish with one hand if possible ( larger fish may need another pair of hands).
Hold the scraper at a 45 degree angle to the body and from behind the gill gently draw the scraper backwards to lift off a sample of the mucus layer. Release the fish and let it settle back down again.
Take a clean microscope slide and smear the mucus sample onto it, add a drop of the pond / tank water ( NOT TAP WATER ), and add a cover slip.
You can now examine the sample under your microscope taking your time as some parasites are very small and some do not even move so observe the sample for a good 30 minutes checking under different magnifications and even different light levels you should be able to see any identifiable parasite if you take your time which then leads you to the correct diagnosis and then treatment.
Important factors to remember is that not every fish in your pond maybe infected it could just be that one fish and the way to check this is to scrape a sample of your pond fish just to be sure, this will save alot of money on treatment if only the one fish has a serious problem as it can be treated in quarantine.
Many people ask what is classed as a serious parasitic infection and generally with a scrape you will instantly know if there is a problem, 1 or 2 parasites may not be a serious reason for concern, however if the sample is literally alive then you will know straight away there is an issue that needs to be resolved.
Taking Scrapes sounds like a very daunting task especially for a beginner however if you have a local koi club then many offer a free scrape service and the knowledge and experience to advise you on what you should do, be looking for and what the best treatments are for your fish.
