Robyn's Fish Health Page Four
Last Updated: 7/2/10
Some Health Questions
Why Did My Fish Die?
Why Is My Fish Fat?
Why Did My Fish Die After a Water Change?
Where Did My Fish Go?
Why is My Fish Bent?
What's that Lump on My Fish?
Why Did My Fish Die After It Rained?
Why Did My Fish Die After the Toads Laid Eggs? - on
my toad page
If you have asked this question, you need to consider all of these many deadly possibilities.
- Water Quality - wrong pH, hardness, or salinity; high ammonia, nitrite, or chlorine
(from tap water); high solids (clog gills)
- Poisoning - "medication" overdose, pesticides, herbicides, fertilizer, copper, iron, plant
fertilizer overdose, nicotine (cigarette smoke), urine, bleach, soap, hydrogen sulfide (from rotting
food, dead animals and plants, stirred up bad gravel, etc.), other poison; leaching from rocks,
gravel, concrete, driftwood, etc.
- Gas Imbalance - too low oxygen, too high carbon dioxide, gas bubble disease (from well
water supersaturated with air)
- Temperature Problem - too cold, too hot, too fast a temperature change
- Medical Problem - internal parasites, external parasites, bacteria, fungus, virus (see this
page and table above)
- Physical Trauma - spawning injury, sucked into pump or filter, jumping out of tank or pond,
abuse from another aquatic animal
- Predation - cats, raccoons, opossums, snakes, bullfrogs, larger fish, herons, egrets,
kingfishers, people, etc. (see this page for all of these but
frogs which are on this page.)
- Stress - due to any of the above, overcrowding, fear (glass tapping, predators presence),
recent netting or move, or any abrupt change
- Electrical shock - broken heater or other electrical equipment, lightning strike
- Starvation - if the fish are being fed the right foods, this is highly unlikely. Starvation is
common with certain algae eaters that are not given supplemental foods when the algae is gone
with specialized fish that only eat certain things which they are not offered.
- Old age - extremely rare!
- There are more!
Many aquarists and pond keepers ask this question. There are a number of possibilities. Here
are some reasons a fish may be fat or have abdominal swelling, in no particular order. Even if an
aquarist sees a fat fish for him or herself, it is very hard to tell which of these things caused the
problem without an autopsy. Experienced aquarists though will be able to make a good educated
guess. Mostly this is done by knowing the species of fish in question, its history, and the shape
and size of the enlargement of the fish.
- Full of healthy roe or eggs - see my fish breeding page for
information; fish full of eggs are enlarged but not hugely so. Egg-laden fish may have an
enlarged vent (where eggs and waste come out). They should not have deformed scales or look
really abnormal in size.
- Egg-bound - this is where the female fish has eggs but does not lay them because conditions
are not perfect, or there is no male; the eggs may rot inside her causing an internal infection; treat
with broad-spectrum antibiotics like erythromycin.
- Internal bacterial infection - possibly dropsy or tuberculosis but also other bacteria, see the
bacteria section for more information; fish with this
tuberculosis often appear to have multiple little balls inside, some starting to protrude through the
fish's skin or may have a lump that is larger on one side of the body than the other; fish with
dropsy are enlarged and their scales stick out. Dropsy normally comes on quickly and makes a
fish look like a pinecone. Such fish are normally obviously ill, not eating, etc. Fish with
fish tuberculosis [who also may show lumps, kinked spines, weight loss (wasting) or weight
gain] often develop dropsy but dropsy often occurs without tuberculosis involvement. Recovery
is difficult in either case.
- Kidney disorder - a malfunctioning kidney may result in an accumulation of fluid inside a
fish; most common in goldfish; hard to treat but sometimes treatment with antibiotics and/or salt
helps; see here for photos of a goldfish with this
fish with this problem are grossly enlarged. The fish grows huge over a long period of time so
that the scales often do not stick out as with dropsy as they can grow as the fish grows.
- Tumors - tumors can be fatty (benign) or cancer (malignant); tumors are rarely treated but
cancerous tumors may be surgically removed from valuable fish; some tumors may be oddly
shaped and can grow large.
- Internal parasites - intense infestations of large internal parasites (mostly worms) can result
in abdominal swelling; if worms are detected protruding from the vent (anus) of the fish, then
treat with a medication that says it kills worms in fish; most common in larger wild-caught
- Normal - it is normal for some fish to appear fat; for example: fancy goldfish and balloon
- Ate too much - this is not very likely but a rare fish may be fat because it ate too much food;
reduce quantity of food given; some large predatory fish may appear enlarged after consuming
a large meal.
Reasons fish may die right after a water change:
1. The new water was too different in temperature resulting in shock.
2. The new water had chlorine from city water that was not treated with dechlorinator. Chlorine
will burn their gills and make them gasp and die.
3. The new water contained some sort of toxin.
4. The new water was too different in water chemistry. The pH or hardness levels were vastly
different. If you already had your regular water in the tank, this is not too likely.
5. The new water was from a well or sometimes city water that was supersaturated with carbon
dioxide. If too much is changed without heavy aeration, the bubbles can come out of solution
inside the fish, causing gas bubble disease, similar to the bends.
6. During the tank cleaning, debris and wastes were stirred up. If the tank was very dirty, this
could release hydrogen sulfide and/or methane which are toxic to fish.
7. Something used to clean the tank contained a toxin like leftover bleach or something.
Sometimes, fish vanish! Here are some possible reasons. I will assume the fish in question is
- Someone ate him! What other animals do you have in the tank? Consider them all including
fish, shrimp, crabs, snails, insect larvae, etc.. Are some prone to eating other fish? Do some
look a little bit too satiated now?
- He is in the filter or in another piece of equipment. Check everything.
- He is behind some tank decorations. Move everything around and look. Dead fish are
sometimes not as obvious if he has died.
- He died and was eaten after death by the other animals and the naturally occurring bacteria
and funguses in the tank.
- He jumped out. Search all around the tank. Fish can flop quite a distance. Once flopped
out, they may also be consumed by cats or dogs.
- Someone outside the tank ate him by going fishing. Is the tank covered? No? Do you have
a cat? Enough said.
- Someone ate him! Possibilities include: other fish, herons, cats, raccoons, turtles, snakes,
and many, many other animals. See my Pond Mammals, Birds, and
Page for a few dozen possible culprits.
- He jumped out! Check around the pond. After jumping out, he may have been eaten by any
- He is hiding among things in the pond. He may turn up later! I hope that is the case!
- He died in the pond and was eaten by the other animals (fish, snails, tadpoles, turtles, etc.),
bacteria, and/or funguses before you discovered him.
- He got sucked into the pump, skimmer, filter, or other pond equipment. Check around.
- A no-good excuse for a human being fish-napped him.
- Alien abduction! They know a good fish when they see one!
If you have any more things to add to this list, please contact me.
Here are some reasons a fish may develop a bent spine.
- If born that way, the fish may have a genetic abnormality.
- If born that way, the fish may have incurred a developmental problem while growing inside
the egg. This could be related to diseases, temperature, injury, etc.
- If the fish was shocked via a faulty heater, pump, etc. or via lighting (striking a pond or
surging through a house), this can result in a bent spine.
- A severe injury can bend the spine. Normally though if broken, the fish would die right
- Fish tuberculosis sometimes results in a gradual development of the curvature of the spine. I
have seen this often in zebra danios but also in a golden orfe and a few other species. A fish with
this condition (fish tuberculosis with a bent spine) is often also anorexic. See this section for more on fish tuberculosis.
- Certain vitamin deficiences can result in spine curvature.
- It seems that many fish nearing the ends of their lives get bent spines which usually match
one of the above problems but sometimes do not.
Sometimes fish develop various lumps, bumps, or growths. Here are some possibilities.
- Parasites- Various parasites can create lumps on fish. Tiny white bumps may be ick. Go
here to see an example of goldfish with ick. Tiny
may be black spot. Larger lumps may be the result of larger parasites. For example, after an
anchor worm or fish louse falls off, a fish may develop a red infected lump from the irritation.
Go here to see an example of a goldfish with a red
resulting from anchor worm.
- Bacteria - Infections can cause raised areas on fish. If the entire fish is enlarged, it may have
dropsy or a kidney malfunction. Fish tuberculosis sometimes manifests itself as acne-like boils
that can rupture the skin of the fish. Go here to see
of a zebra danio with a rupturing fish tuberculosis tumor. Bettas seem prone to developing
localized dropsy-like symptoms where they become enlarged. When those areas are then popped
with a pin, fluid comes out. The enlargement normally returns. This is different than cysts
below which are much more localized (small in one area and not over most of the fish). Go here to see an example of a betta with tumors that
bacterial in nature that were stuck with a pin, and fluid came out.
- Cysts - Sometimes fish get fluid-filled lumps. They may result from an injured area or for no
particular reason at all. They usually go away on their own and pose little threat to the fish.
- Viruses - Some viruses may cause lumpy areas. For example, carp pox can cause raised,
black or gray waxy splotches on fish. The virus lymphocystis is also called cauliflower disease
because it creates lumps that resemble cauliflower. Lymphocystis lumps are normally white or
the color of the fish and tend to spread over the fish with time. Go here to see an example of a goldfish with a strange
black lump that might be viral in nature.
- Tumors (non-bacterial) - Cancerous tumors are possible but rare. Fatty tumors are more
common. Tumors will not go away. They can be removed surgically. Depending on what they
are and how big they get, they may or may not be hazardous to the fish.
- Rain often alters the water chemistry. Rain water is almost distilled and has no buffering
capacity or hardness. Sometimes it is even acidic in pH. Adding a lot of rain to a pond will often
lower the pH, alkalinity, and hardness. When the alkalinity goes down, the pH changes faster. If
the change is drastic enough, the fish can suffer and even die. Test the pH, alkalinity, and
hardness of the pond water and compare it to your normal readings to verify if this is the cause.
If so, pond chemicals can be added to buffer the water (such as sodium bicarbonate which is
baking soda) and/or raise the pH if needed.
- Rain is also low in oxygen. If there is a lot of rain, the oxygen levels in the pond may
plummet. Fish can be seen gasping at the surface and hanging around near waterfalls. For this
reason, it is a good idea to provide aeration at all times in a pond but especially when it is hot out
as warm water holds even less oxygen. A single waterfall may not be enough. You can buy air
pumps with an air stone for more oxygen. Unfortunately, when a storm comes through, the
electricity often goes out. See this section for more on power
- Rain will flush things in to the pond from surrounding ground. That may include mulch
(bring in lignins and tannins and sometimes lowering the pH), dirt (clouding the water), and
chemicals. If there are pesticides, herbicides, or fungicides used in the area, those may end up in
the pond and kill fish. You can control what is used on your land but not necessarily the
neighbor's land. If a neighbor uphill from you uses chemicals, make sure to divert rain water
away from the pond. See this section for more on that.
If chemicals (natural ones or human made) end up in the pond, add a fresh mesh bag of activated
carbon to the filter or in moving water to remove them.
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