Ornamental Fish Q&A 11
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A 75-L aquarium contains nine neon tetras, two pearl gouramis, two cory catfish, and a Plecostomus. The owner reports that all the fish were purchased six days ago and placed in a newly acquired aquarium with fresh dechlorinated water and fresh filter material.
In the past 24 hours, four of the tetras have died and several others have whitened fin edges.
Filtration consists of an outside power filter with disposable carbon-filled filter packs. No water changes have been performed to date.
Water quality parameters are as follows:
- Temperature = 26°C (68°F)
- pH = 7.4
- Ammonia = 3.0 p.p.m.
- Nitrite = 2.0 p.p.m.
- Nitrate = 2.5 p.p.m.
- Hardness = 130 p.p.m.
| Question | Answer | Article | |
| Based on the history and water quality information, what is the most likely diagnosis? | The likely diagnosis is ‘new tank syndrome.’ When a large number of fish are added to a system with no established bacterial flora, the nitrifying capacity of the system can be quickly overwhelmed, causing increases in the concentrations of toxic nitrogenous compounds. This may result in sluggish or inappetent fish, greatly increased susceptibility to infection, or sudden death. This situation can be averted by ‘priming’ the system with gravel or filter media from an established aquarium, introducing a very small number of fish until the biofilter is established, and daily monitoring of water parameters with water changes as needed to maintain acceptable levels of nitrogenous compounds, especially ammonia and nitrite. |
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| What treatments are indicated? | Immediate treatment may consist of:
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