My Fish Just Died!

By Bill "Pegasus NZ"

So your fish just died, or they are dropping like flies. What do we do?

If your fish has no visible signs of injury then usually we tend to just accept it as "one of those things that happen", but in many cases, and with little effort, a few things can be learned from the deceased fish. Unless your fish died from old age, which few fish do, then we need to establish if possible what caused its demise, but how do we approach this? Of course our first objective is to test our water, but if this shows no obvious causes then what do we do?

External examination of the fish can reveal many things, and apart from obvious wounds which might have been inflicted, there are other things we can look at.

Parasites are one of the main causes of fish deaths, and we get internal and external types that can sometimes lay dormant for months, then suddenly wreak havoc on our tanks. Bacteria buildups in our water can cause many problems, from inflamed gills to stress and breathing disorders. Fungi of various types will affect fish with open wounds, or fish in an unhealthy condition that have lost their immunity to resist the spores that linger in wait for the slightest chance to attack. Body slime, clouded eyes, fin and tail rot, shimmies, are all visible external signs, as are spots, blisters or cysts of any type or colour, which can include white spot and a yellow looking spot that could be Velvet disease, or an ugly parasite that has burrowed under the skin of the fish.

Then we have such things as Pop Eye caused by gas behind the eye, Dropsy , which shows protruding scales, and Swim Bladder problems, all which show visible external signs. Many of the above can be treated with various medications, but then we get the scenario where a fish refuses to eat, or lurks in a corner for days on end, or is just found dead in the tank one morning, or perhaps it was dashing madly around the tank before it died. Death by stress is hard to determine, as usually there are no visible signs.

Observing, not looking, at your fish each time you have a chance will tell you many things, and by doing this you begin to understand each fish and their general habits. It makes little difference if you keep goldfish or exotic species of marines that cost thousands, the same rules apply. They can't tell you they are ill, but they can show you in most cases, and anything that does not look normal should be treated with suspicion. Usually anything differing from these habits can be spotted soon and action taken. Flicking on objects in the tank is a sure sign of trouble, not feeding, trailing feces, cloudy eyes, patchy colours, slimy skin, cloudy skin, bloated body, erratic swimming, restless and lethargic behaviour are all signs you should be looking for, as all mean that trouble is just around the corner. Dinner time should be a mass of activity for all fish in most cases, and now is a good time to do a number count if that is possible

All external parasites can be identified such as Anchor Worm, White Spot, Flukes, Fungi, and so on. With a good quality scope we can also see various bacteria, but knowing the good ones from the bad is still beyond me. Just finding some simple answers can be so rewarding, even though you did lose a fish in the process.

These are the mysteries, the unknown causes that lead to the deaths of our fish, which can in many cases be looked into in a different manner in the hope of finding at least some answers to these mysteries.

Someone recently asked me about fish deaths, and I made the statement that "If a fish of mine dies, and it is not through any fault of my own, then I want to know the reason why."  In my early years, fish deaths caused me a great deal of concern, and more so when they became my means of earning a living. I learned in my early years how to dissect fish and examine the various parts with both a strong hand glass and a microscope. For quite some time it was still all just a mixed up mess of internal organs that I was not too sure if they were healthy or not, so I took some lessons and advice from a professor friend of mine at university and came away a little wiser, but still a little confused. It was not until I compared a previously healthy dead specimen to an infected one that I became aware of the various differences in the two dead fish. Guppies, Platies, Mollies and Swordtails were my test cases, and from these I learned a number of things.

The Microscope

This is such a handy piece of equipment if you want to delve into the inner workings of fish, for with it you can not only recognize some of the major parasites, but you can examine algae, your water, plant structure, along with just about everything that can attack your fish internally or externally. Algae alone holds a world of information, with unbelievable shapes and patterns that have to be seen to be believed, and your water, both drinking and in your tanks, hold more than you could possibly imagine.

To me the microscope became in a sense much like being a diver.

The non-diver can only look at the ocean from above, and sees a huge body of water holding untold mysteries, but seeing that same ocean from beneath the surface is a completely different world, one that never fails to fascinate me, and is different at every dive, even in the same area. My many years of diving are gone, but the memories remain, and hopefully always will.

The microscope is very much like this, for you are taken into a different world, one of which has been in existence since the beginning of time.

By just taking smears from infected parts of fish you can begin to recognize the microscopic life that infects our fish. With observation you can spot a healthy organ from an infected one, and examine all parts from the mouth to the anal region, which will tell you many things as to why your fish died. The intestines, the alimentary canal and the stomach will tell you exactly if the fish was eating, and what it ate for its last meal, and will also tell you if that meal was recent, or some time ago. The intestine is short in flesh eating fish, and long in vegetable matter eating fish Discoloured organs will give you clues also, and inspection of the swim bladder will in most cases enlighten you about swimming disorders. In Catfish the swim bladder differs from the normal fish. The world of wonders grows with each slide you make.

You don't have to be a scientist to look at these things, nor do you need a microscope costing mega bucks to observe some of the above, as a simple microscope from a children's toy store will reveal many things. I have had several over the years, and now I am looking at buying another as my last one mysteriously disappeared. One of my early ones was made entirely of brass, was very old indeed, and had a single lens, but the workmanship was outstanding and it gave me a lot of pleasure. Ones with built in lights are better than the reflector type, and three optics are always better than one. The quicker you can examine the fish after death, the better your chances are of seeing the parasite or infection in its active state. Once you isolate the culprit, take a slide and a slip and make up a sample that you can keep for future reference.

I am no expert in this field, but I don't like to accept something happening that I know nothing about, so to this end I tried to learn all I could about the life and deaths of my fish. Make it your goal to learn something new about your fish every day, should it be from reading a book, or surfing the net and forums, but do it. The knowledge you gain will never be wasted, not if you keep fish.

It is a well documented fact that a huge percentage of fish deaths are caused by their owners, either through neglect, or even over indulgence of kindness where we tend to overfeed, or add this and that to our water "just in case", or neglect to consider the "soup" that our fish are swimming in. Perhaps if you had done that water change instead of just topping up with water your fish might be still alive, or perhaps you changed too much water, or it was too cold and caused great stress to your fish. These are things that only experience and time will tell us where we went wrong, but watching others and learning all you can from any means possible is the best advice you can get. We have all lost fish, and made many mistakes, but with the technology of today and these excellent forums, perhaps our chances of success have just been increased by a huge amount.

Reaching that perfect balance where both your fish and yourself are without stress can sometimes be hard to achieve, but invariably if your fish are happy, so are you.

Take Care Always, Regards, ----------------------------- Happy Days, Bill (Pegasus NZ). From the beautiful little country at the bottom of the World. Come visit us at or


First published in the newsletter of The Vancouver Aquatic Hobbyist Club