Molly Fish Diseases and Treatments


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Diseases & Treatments

Causes, Symptoms, and Treatment For Mollies

Millions of fish hobbyists around the world have Mollies in their tank community. This species of fish is enjoyable and easy to raise.

Mollies are not typically prone to diseases and are an overall hardy species. If you know ahead of time what to look for with potential problems, you will know how to treat something when it comes up.

50's Vintage Michigan Fishing Artwork Sick Fish

Image By: Donald (Don) Harrison CC by-nc-nd 2.0

Prevention Is The Best Medicine!

A healthy tank is completely dependent upon good maintenance practices that are routinely done. The number one cause of fish disease is poor water quality. When your fish are exposed to water conditions that are less than ideal, it causes stress which leads to disease.

There are things you can do to prevent disease.

  • Perform regular tank maintenance.

    • Water changes

    • Visual checks of filter system and water heater

  • Routinely check water parameters.

  • Don’t overcrowd by placing too many fish in the tank.

  • Always have a hospital tank up and running ready to use at any given time.

  • Feed your fish a high-quality diet and don’t overfeed.

  • Don’t handle your fish.

  • Quarantine new fish and/or plants before introducing into the community tank.

Symptoms

There are specific symptoms that are indicative of a problem. If you notice your Mollies acting strangely or present overall malaise, they may be sick.

Please note that we highly recommend that you consult with a local aquarist before treating your fish.

If Your Fish Is Exhibiting..​​​​.

The Possible Cause Is...

Difficulty breathing (staying at surface and gasping)

  • Poor Water Quality

Refusal to eat

  • Poor Water Quality
  • Internal Parasites
Odd swimming behavior (erratic or upside down)

  • Poor Water Quality
  • Swim Bladder Disease
  • Dropsy
  • Improper Feeding

Listlessness (laying at bottom of tank)

  • Poor Water Quality
  • Infection

Slow reaction to you or stimuli

  • Poor Water Quality
A rubbing behavior against surfaces
  • Parasites
  • Fungal Infection

Lethargy and fins appear closed

  • Poor Water Quality
  • Parasites

Frayed appearance of fins

  • Stress
  • Fin / Tail Rot

Bumps that are raised and fuzzy-like

  • Infection (fungal or bacterial)

White speckle-like appearance (like grains of salt)

  • Infection (fungal or bacterial)

Spots that are black

  • Ammonia burn
  • Parasites

Bloated appearance with raised scales

  • Dropsy
  • Overfeeding

Pale gills

  • Parasites

Appearance of visible lumps

  • Parasites

Protruding, bulging eyes

  • Pop Eye
  • Infection

An overall slimy appearance

  • Velvet (parasite)

Sores that develop on head

  • Parasites

Open sores/ulcers on body

  • Bacterial Infection

Diseases: Indications & Treatment

ICH

This disease is highly contagious to other fish!

Causes

  • Stress
    • The car ride home from a pet store or shipping causes extreme stress on fish. This stress causes the fish to be prone to disease.


  • Introducing new fish into community tank without quarantining in hospital tank for two weeks


    • New fish can be carriers of disease from pet stores. It’s vital that all new fish (and plants as well) be quarantined for a minimum of two weeks before introducing into the community tank.


  • Residual water from container/bag that new fish are placed in from the pet store

    • When bringing new fish home, be very vigilant not to allow water in the carrying bag to get into the tank.


  • Poor water quality

Symptoms

  • Fish having breathing difficulty
  • Small areas develop on the fish that look like grains of salt
  • Fish rubs against surfaces

Treatment


1. Slowly raise the temperature of the water to 75-80 degrees (F.) This will encourage the parasite(s) to fall off the fish.


2. Remove all plants and objects from the tank.


3. Perform a 25% water change.


4. Test water parameters to ensure levels are ideal.


5. Add aquarium salt to tank water:

   

    a. 1 tsp for every 1 gallon of tank water

    b. Use .03% concentration


6. Repeat steps 1-4 every 12 hours for a total of 3 times.


7. After two weeks, perform a 50-75% water change.

Buoyancy Issues 

Causes

Swim Bladder Disease
  • Overfeeding or fed a poor diet
  • Bloating from flatulence
  • Constipation
Symptoms
  • Strange swimming behavior

    • Erratic
    • Sideways
    • Upside down
  • Fish appears enlarged

Treatment For Constipation

  1. Feed fish 1-2 cooked peeled peas a day until symptoms are gone.

Treatment For Swim Bladder

  1. Check water parameters
  2. Clean the tank (this lowers bacteria levels)
  3. Do not feed the fish for 3 days.
  4. If none of the above prove successful, consult with local aquarist for antibiotics.

Fin/Tail Rot 

This disease is highly contagious to other fish!

Causes

  • Stress in fish

  • Water quality is poor

  • Overcrowding in tank

  • Sudden change in water temperature

Symptoms

  • The fins/tail appeared frayed, fringed, torn or raggy

  • Edges of fins/tail develop a white appearance from bacteria that eats away at it

Treatment

  • Quarantine sick fish in the hospital tank for two weeks

  • Perform a 100% water change

  • Thoroughly clean contaminated tank and tank decor with hot water (no soap)

    • Wash gravel with hot water

    • Rinse filter

  • Check water pH and adjust as necessary

  • If symptoms in the sick fish does not improve, consult with local aquarist for fin/tail rot treatment.

Fungal Infection 

This disease is highly contagious to other fish!

Causes

  • Stress

  • Water quality is poor

Symptoms

  • White raised fuzzy bumps appear on fish

Treatment

  1. Quarantine sick fish in the hospital tank for two weeks

  2. Purchase an antifungal treatment from your local pet supply

  3. Treat sick fish per instructions on the bottle.

  4. If the sick fish does not improve after a few days, proceed with a salt bath.

    1. Add aquarium salt to tank water:

      1. 1 tsp for every 1 gallon of tank water

      2. Use .03% concentration

Velvet 

This disease is highly contagious to other fish!

Causes

  • Stress

  • Poor water quality

  • Introduced by new fish that are infected

Symptoms

  • Fish appear to have a slimy film

  • Fish struggle to breath

  • Fins appear clamped

  • Fish begin to run against surfaces

Treatment

  1. Quarantine sick fish in the hospital tank. Other fish in the community tank may be infected as well.

  2. Perform a 100% water change

  3. Thoroughly clean contaminated tank and tank decor with hot water (no soap)

    1. Wash gravel with hot water

    2. Rinse filter

  4. Consult with your local aquarist to proceed with treatment medication called fFormalin. Caution: if not used correctly, this medication will burn your fish’s fins.

Anchor Worm

This disease is highly contagious to other fish!

Causes

  • New fish are carriers of this disease, and when introduced to a community tank (before quarantining,) the other fish become infected

Symptoms

  • Tiny green colored hair-like attachments develop on the fish. The area where it attaches to fish becomes red and inflamed.

  • Fish begin to rub against surfaces

Treatment

  1. Quarantine sick fish in the hospital tank and treat with Dipterex 98% according to instructions.

  2. Monitor other fish in community tank; they may need to be treated as well if symptoms present.

Lice

This disease is highly contagious to other fish!

Causes

  • New fish are carriers of lice, and when introduced to a community tank (before quarantining,) the other fish will become infected

Symptoms

  • Dark olive colored disc-like parasites can be seen on fish attached around the stomach, throat, or base of fins.

  • Fish rubs against surfaces.

Treatment

  1. Quarantine sick fish in the hospital tank and treat with medication from your local pet supply. Follow dosing directions.

  2. Monitor other fish in community tank; they may need to be treated as well if symptoms present.

Dropsy

This disease is fatal and untreatable. This disease is painful, and you may find that making the choice to euthanize your fish is the best humane thing to do

Causes

  • Kidney issues

    • Renal failure

    • Bacteria

    • Parasites

  • Exposure for long periods to low water temperature

Symptoms

  • Fish appears bloated and enlarged with a pinecone look. The fluid retention causes the scales to protrude outwards.

  • The eyes of the fish begin to bulge out.

Setting Up A Hospital Tank

If you plan to have multiple fish, it’s imperative to have a dedicated/separate tank to function as a hospital tank. This tank will serve to quarantine new fish, new plants, and sick fish.

Things You Will Need:

  • 5-10 gallon tank
  • Filter system
  • Plastic plants/decor/rocks (hiding places helps to calm sick fish)
  • Water conditioner
  • Fishnet
  • Thermometer
  • Water heater
  1. Fill tank and allow it to cycle for a minimum of two weeks before using.
  2. Do not use substrate. This will prevent loose food from decaying in this substrate causing poor water quality.
  3. Transfer some of the established bio media from the community tank’s filter into the hospital tank. This will help the hospital tank to maintain a nitrogen cycle.
  4. Limit water movement by putting the filter on the lowest setting. Rapid water movement adds stress to sick fish.
  5. Turn on the water heater.
  6. Check water parameters routinely until the tank has cycled.
  7. Do one last water parameter check before adding sick fish.

Prevention and Your Eyes Are Your Best Tools

If you maintain good water quality, you provide the best measure of defense against disease. By visually checking your fish daily, you will know immediately if they are presenting any symptoms that may indicate a problem.

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