Oxygen deficiency fish disease

Oxygen deficiency fish disease

1. General description

Cause of this disease is rapid or continued over time reduction a concentration of dissolved oxygen in the water below a limit value. This value depends on environmental conditions and fish species. The fish quickly die (within twenty-four hours) after exceeded the limit value.

The sources of oxygen in water are atmospheric air and photosynthesis. Oxygen diffusion from atmosphere happens only on the contact border of two environments. In other words, oxygen concentration reduces with the depth. We need remember that much less oxygen penetrates through standing water compared to rippling water. Water waving causes increase the surface diffusion and then we have more oxygen in the water. The amount of dissolved oxygen in the water depends on temperature and pressure. This amount decreases with increasing temperature. The amount of released oxygen by plants (in photosynthesis) is proportional to their ability to conversion of carbon dioxide and water into other compounds (so-called biological assimilation).

When we configure our aquarium (when we choose equipment, amount and kind of plants, fish, etc.) we should bear in mind that the oxygen balance in aquarium (emission-absorption) was always positive with with advantage for emission. Decomposers (bacteria decomposing dead organic matter) and unlit plants consume the most oxygen in the aquarium.

2. Type of the disease

This disease is caused by environmental factors.

3. Cause of the disease

Cause this disease is rapid reduction dissolved oxygen in aquarium.

4. Favorable circumstances for development of the disease

• too much fish in aquarium
• snails plague
• unsuitable or lack of aeration
• rapid increasing of water temperature
• too small vascular plants compared to amount of the fish
• unsuitable fertilization of the plants (too much fertilisers, especially carbon dioxide)
• too much organic matter in a substrate
• too rapid growth bacterial flora in a filter and its mediums
• completely covered the water surface (e.g. by algae) and lack of possibilities of gases diffusion in both directions: air-water and water-air

5. Common symptoms of the disease

• rapid moves of the fish
• loss of appetite
• fast movements gill covers
• the fish hang under the water surface
• open fish mouth
• excessive secretion of mucus
• dulling and loss of colours
• loss of balance

6. Types of the treatment

We need eliminate main cause of disease occurrence and we need increase water aeration when we have the initial stage of this illness (no fish died yet). Otherwise, when first fish start to die we transfer all fish to a separate aquarium (with properly prepared and well oxygenated water). The fish should rally after a few hours when permanent damage hasn't occurred. Anyway the immune system of the fish is weakened, so we should use adequate vitamin preparations and water treatment conditioners (e.g. Tetra AquaSafe, Sera Aquatan, JBL Atvitol, etc.). We eliminate main causes of disease occurrence in the general tank in this same time. We transfer back the fish to the general aquarium when the situation was brought under control.

7. Comments about this disease

• Oxygen deficiency may be cause of suspension of the spawning, the eggs development or the fry increase.
• The fry needs more dissolved oxygen in the water compared to adult fish.
• This disease causes significant reduction fish immunity and this situation can lead to secondary bacterial, viral or parasitic infections.

8. Prevention

• systematic control oxygen concentration in water
• balanced amount of vascular plants and water animals (fish, snails, shrimps, etc.)
• reasonable plant fertilization
• use adequate lighting and optimal light time
• use additional pump/aeration, especially in the night
• systematic cleaning the substrate and filter
• systematic exchanging of filter mediums, especially in the biological filters
• increase waving on the water surface through use e.g. spray bar