Parasite life cycle

The reasons behind the scarcity of black spot disease in aquariums can be found in the life cycle of the parasite that causes the disease.

The eggs fall into water in the droppings of birds that have eaten infected fish.  About a month later they hatch, and are called miricadia.  Think of them as little hairy egg-shapes that move the short hairs in unison to swim.

The miricadia swim until they encounter a snail, into which they burrow and develop.  About 6 weeks later, cercariae emerge.  These look like little tadpoles with forked tails, and their aim is to find a fish.

When they find a fish they burrow under the skin before losing their tails.  Now they are called metacercariae, and they protect themselves in the fish with a hard cyst that contains dark pigment.  These cysts appear as small black spots and give their name to the disease.

The next stage is for a bird to eat an infected fish, where it develops into a flatworm with a shape a bit like spoon with a broad handle.  Although the parasite feeds off snails and fish, it is on the bird that it places the greatest burden.

It is in the bird that they consume the resources necessary to reproduce and lay countless eggs which then fall into water in the bird’s faeces.

Barring highly exceptional and unlikely circumstances, the only way for parasitic black spot disease to get into an aquarium is when infected snails are introduced.

When it comes to ponds, however, the chances of infection are much higher.  Any visiting heron or kingfisher can cause and outbreak.

Effects on fish

Fish infected with parasitic black spot disease will usually display signs of iritation such as rubbing and flicking of the body.

The black spots themselves appear as small, dark, well defined, raised areas of skin about the size of a pin head.

Lasting damage is rare, although blindness can occur if the carcariae end up in the fish’s eye in large numbers.

Other than that, there is no cause for alarm when healthy adult fish are infected.  Young fish can be killed by the disproportionately high requirements of the parasite on their bodies, but the parasite will not complete a life cycle if it kills the fish.

It is worth noting at this point that on the rare occasion of aquarium fish becoming infected, the number of black spots on each fish will likely be huge.

This is because there is a high number of fish that are not eaten by birds.  So the flatworm needs to produce as many eggs as possible, in order to infect as many snails as possible, in order to get lots of fish, thus increasing the chance of an infected fish being eaten by a bird.

Miricadia on a snail that enters an aquarium will emerge to find they have no trouble finding a fish.  Not only that, they will all attack the same few fish.

Treatment

Other than removing snails, there is no other treatment necessary in an aquarium.  Providing the fish in the aquarium do not get eaten by a bird, and the same bird does not return to the aqarium a month later to deposit faeces in it, the parasite will die off.

In ponds on the other hand, it will probably be necessary to purchase treatment for the disease.  Copper sulphate can be used (only under licence in some parts of the world) to kill snails, and many commercial treatements are also available that target the parasite.

Although impossible to prevent, it is also wise to discourage herons and other fish-eating birds from visiting ponds.

Ammonia burn

Most examples of black spot disease in aquariums are the result of ammonia burn on the fish’s skin or fins.  When the affected areas start to heal, the small patches that recieved the harshest burn turn a dark brown or black colour.

The black spots themselves appear as discoloration of the skin, rather than something in or on the skin.  They can range in size from barely noticeable to a “rolled around in black paint” look, but are usually small smudges.

Blackened skin from ammonia burn is actually a good sign.  It means the ammonia has dropped back to a safe level, and the fish’s skin has started to heal.

However, it is a worrying sign that the ammonia level was raised in the first place.  Action needs to be taken to minimize the risk of raised ammonia.  A lot of fish that suffer ammonia burn don’t get the chance to get black patches on their skin.  They get killed instead.

Spot the signs

Fish in a tank or pond with high levels of ammonia will gasp for oxygen at the surface, float on their sides, sit at the bottom, lose their appetite, get red streaks in their fins, develop reddening around the gills, and/or make swimming look like hard work.

As soon as any of these behaviours are spotted, get the water tested to confirm ammonia poisoning and take action to remove it.

Removing ammonia

Changing the water is the best way to get rid of ammonia.  Do it every day until the ammonia levels are down to an acceptable level i.e. less than 4 parts per million.  An ideal level is less than 2 parts per million.

The other option is to use chemical treatment, but water changes are obviously better as they do not involve adding further chemicals to the water.

Prevention

Test the water regularly, and change it regularly.  High ammonia levels are a sign of a badly managed aquarium.

Do not overstock.  Too many fish produce too much waste, which contains ammonia.  If the filter can’t cope, ammonia poisoning is inevitable.

Do not overfeed.  Uneaten food decays, producing ammonia.

Use a treatment tank if the water needs to be medicated.  Medications for unrelated fish diseases can kill the bacteria in the filter that remove ammonia from the water.

Keep a very close eye on new tanks.  Ammonia poisoning occurs most often in new tanks.  Ammonia will peak at the end of the first week.  It is advisable to start with only one fish so waste is kept to a minimum.

Related articles

Choosing and Aquarium Filter

Goldfish Aquarium Water Testing

Changing the Aquarium Water

Preparation

Affected goldfish need to be removed from the tank and put into a treatment tank.  (Some people refer to a treatment tank as a hospital tank, isolation tank or quarantine tank.  These names are interchangeable.)

Any small tank fitted with a box filter and containing no ornaments or plants is suitable as a treatment tank.

The reasons for isolating the affected fish are:

• to help prevent the spread of secondary infections to other fish in the aquarium
• because one of the treatments is an antibiotic that will either wipe out or decimate the good bacteria population on biological filters
• it’s easier to keep treatment tank water in tip-top condition
• there is reduced (zero if it’s only one fish) chance of fighting or bullying causing further problems

The only other thing to do before commencing treatment is to raise the water temperature a couple of degrees in the treatment tank.  The bacteria that cause tail and fin rot prefer cooler water.

Treatment

There are two separate parts to successfully treating tail and fin rot: one is to treat the main tank, the other is to treat the affected goldfish in the treatment tank.

To treat the main tank, change the water, test the water quality and make any improvements that are necessary, and make sure the goldfish are receiving a healthy, balanced, nutritious diet.  Also make sure there is no rotting plant or food material in the gravel at the bottom of the aquarium.

To treat the affected goldfish, put a teaspoon of aquarium salt in for every gallon of water in the treatment tank.  Salt is a natural antiseptic and has wound-healing properties.

The other treatment, as already mentioned is antibiotic.  The most common ones used to treat the bacteria behind tail and fin rot are tetracycline, chloramphenicol and oxytetracycline.  Dosing instructions will be provided with the antiboitics, most of which come as commercial brands with user-friendly labels.

Obviously most treatment tanks are small, and some of the dosing instructions may be for larger quantities of water.  A handy tip is to pour 10 spoonfuls of water into a container, then add the antibiotic as stated on the label.  To dose the smaller quantity of water in the treatment tank, just use the same spoon to dole out 10ths of the large dose of antibiotic, until the correct amount is in the treatment tank.

One other handy tip is to completely ignore the length of treatment stated on the label.  Continue the treatment until tail and fin re-growth is noticeable.  Stopping treatment before this may mean the bacteria have been knocked down, but not finished off.

One proviso is that if the treatment has gone on for 3 times the length stated on the label, it is probably not working.  When this happens, change to a different treatment.

At all times, make sure the water quality in the treatment tank is what is should be.

Prevention

No secrets here.  Keep the water quality good, feed a healthy balanced diet, don’t overfeed, don’t have too many fish in the tank, keep the temperature steady, quarantine new goldfish, and make sure all the goldfish in the aquarium lead a stress-free life.

It is a serious fish disease that can eat into the body of the fish after destroying all of a fin, leading to death.  Even before it gets to that stage, it can lead to severe complications.  Very often, a fungal infection takes hold in the affected fin, making treatment even more problematic.

Symptoms

The first signs of tail and fin rot are red streaks in the fins.  The edge of the fin will then lighten, before it starts to rot away and gain a ragged appearance.  Small bleeds may also be present.

Biological symptoms include variations in the levels of calcium and haemoglobin in the fish’s blood.

If a fungal infection occurs, the edge of the fin may be smoother i.e. get eaten away in a more uniform manner – and have a white edge.

Causes

Tail and fin rot is caused by bacteria.  The specific bacteria that cause the disease are common and found in most bodies of water, including ponds and aquariums.  The problem arises when the fish are subjected to an external event or environment that make them susceptible to infection.

By far the most common factors are poor water quality (especially raised levels of ammonia and nitrite), and direct trauma to the tail and/or fins.  Direct trauma can be a result of nipping by other fish, bad handling by humans, or sharp edges on plants and ornaments in the water.  The stress of any of these events leaves the fish open to infection.

There are three different bacteria that can cause tail and fin rot:

1. Aeromonas – a rod shaped bacterium that can also infect humans, often resulting in the need for amputation.
2. Pseudomonas – another rod shaped bacterium that has “superbug” strains found in hospitals that cause necrotizing inflammation in humans.
3. Flexibacter – a bacteria that normally only affects fish, and is best known for strains that are bright yellow to the naked eye when colonies grow large enough.

To be precise, tail and fin rot is not a disease itself.  It is actually just a symptom of infection with one of these bacteria.

What the bacteria do is congregate in the intestine of the fish.  They then produce a mucous that contains molecules that are toxic to fish.  These toxic substances are absorbed through the wall of the intestine in much the same manner as essential nutrients, thereby entering the bloodstream.

The red streaks that are the first sign of tail and fin rot are caused by small blood vessels in the fins breaking apart under the action of the poison, and releasing blood.

Without a blood supply, the fins quickly lose their colour, break down and rot away.

While all this is happening on the outside of the fish, similar processes are destroying the blood vessels of the stomach, liver and kidney.

Preparation

Once ick has been discovered in a tank, the first task is to prepare the tank for treatment. If any filters contain activated carbon for chemical filtration, remove it. The activated carbon will remove the medication from the water. UV sterilisers and protein skimmers should also be switched off in order for the treatment to work effectively.

The water in most goldfish tanks is at room temperature (roughly 18 Celsius/65 Fahrenheit), so there is no general requirement for a thermostat. However, using one to gradually increase the water temperature by half a degree celsius every day will reduce the length of treatment. This is because the ick is only treatable during the theront (free swimming) phase of the life cycle. Due to the fact that an increase in temperature speeds up the life cycle, the theront phase will arrive quicker at higher temperatures.

If possible, bring the water temperature up to 26 Celsius (80 Fahrenheit) and the treatment will be over in 10 days. Keeping the temperature low will mean the treatment will need to continue for 6 weeks. One word of caution though – when the ick life cycle takes a week, a new dose of parasitic infection comes round every week. If anything is wrong with the treatment program it could result in heavy infestation, and goldfish dying off quickly.

Finally remove any snails, and check if any aquarium plants present are sensitive to the recommended treatement – malachite green.

Treatment

Malachite green is a widely available chemical treatment for ick. Other chemicals that can be used are formalin, copper, quinine hydrochloride, methylene blue and sodium chloride. However, non of these are any better than malachite green, which has the advantage of been successfully used to treat ick for many years.

Follow the dosing instructions on the label to the letter, taking care to avoid eye and skin contact. Malachite green leaves a stain on almost everything it touches.

At the ideal temperature, continue the treatment for 10 days. This will ensure that the theront phase of the ick life cycle will have been exposed to the malachite green. During the trophozoite and tomont phases, the chemical will have no effect on the parasites. In both cases they are enclosed in protective cysts that are impervious to any known treatment.

Although the life cycle only takes a week at this temperature, the treatment should go on for 10 days in order to make sure that all traces of ick have been removed.

It is worth noting that the treatment for ick treats the water. When treating the vast majority of goldfish diseases it is the goldfish itself that is treated. However ick can only be killed when it is vulnerable, and that is when it is out in the water.

Prevention

As is the case with every goldfish illness, prevention is better than cure. Make sure the water is tested regularly, feed the fish a balanced diet, change the water regularly and don’t put too many goldfish in the tank. These measures should be par for the course in every single goldfish tank and pond.

Also, never buy aquarium plants that are in a tank with fish in the pet shop. Tomonts stick to plants, and a single one provides an easy passage for up to 1000 individual parasites.

When bringing a new fish home for the tank, put it in a quarantine tank for whatever length of time the ick life cycle takes at the water temperature of the quarantine tank.

Ick is common and deadly, but following the advice above will save goldfish from the disease, and bring them back to rude health as quickly as possible.

Trophozoite

This is the phase of the ick life cycle when the parasite is living in the skin of the goldfish. It is a spherical shape with a cup shaped mouth at one end. The mouth contains very fine hair-like structures called cilia, that beat rhythmically and continuously inwards. These cilia scrape tissue from the body of the goldfish and pass it into the mouth.

Goldfish produce a natural reaction to the trophozoite – they surround it with a hard casing that forms a cyst. It is these cysts that are the most noticeable symptom of ick – the appearance of being sprinkled with salt.

Depending on the temperature of the water, the trophozoite grows to between 0.1mm and 1mm wide, and after about a week it falls off the goldfish. It swims in downward spirals to the bottom of the aquarium, or sticks to a plant or ornament.

Tomont

Once the released trophozoite has settled, it absorbs its own mouth and secretes a gel around itself, becoming known as a tomont (or trophont). It then starts to replicate inside the gel casing. The cells produced by the first few divisions form an internal wall on the gel casing, but the rest of them develop into parasites.

The number of cells produced in the tomont can reach 1000, and will usually be at least 600. This phase of the ick life cycle will be complete in anything between 8 hours and several weeks, depending on water temperature.

When complete, the tomont bursts and releases the individual cells called theronts. These look for goldfish to burrow into.

Theront

Theronts (also known as tomites) are microscopically small and oval in shape. They are good swimmers and move about the aquarium until they find a goldfish to latch on to and burrow into.

They swim with cilia and are thought to burrow into goldfish skin using these cilia, and possibly a combination of mechanical and chemical attacks on the integrity of the goldfish skin using a pointed structure and a capsule of chemicals found at the front of the parasite. It is after they burrow into the skin that they grow their mouths.

Theronts can survive for a maximum of 4 days without finding a goldfish to feed on, and in most cases they will die after 2 days.

How long does it all take?

It all depends on water temperature. The warmer the water, the quicker the ick life cycle is complete. At a temperature of about 20 Celsius (70 Fahrenheit) the cycle would take up to 4 weeks. Raising the water temperature to 26 Celsius (80 Fahrenheit) would see the process complete in about a week.

As the optimum water temperature for goldfish is at the lower end of the scale, the ick life cycle will take much longer in a goldfish aquarium or pond.