One of my clinical interests is aquatic animal health. Fish culture, whether fresh or salt water, aquaria or Koi ponds, are extremely popular hobbies. Yet few people really know much about the basics behind aquatic animal health. The most important thing to understand is that the vast majority of aquatic health problems are a result of poor water quality.
Mammals have the ability to eliminate and move away from their waste. On the other hand, fish use the bathroom in the water they live in. Fish in natural environments can eliminate and move away or have the current carry the waste away, unlike captive fish in smaller spaces. Also in most natural aquatic environments the sheer volume of water that the fish lives in can dilute the waste so that it has no toxic effect on the fish.
Most fish eliminate waste in the form of a toxic chemical called ammonia and nitrifying bacteria in aquariums and ponds convert excess food into ammonia. Ammonia is further converted into a toxic metabolite called nitrite. Nitrites are then converted to nitrates which are a nontoxic metabolite. In nature nitrates are assimilated by algae. Even though nitrates are nontoxic a large build up can lead to poor water quality. These nitrates need to be removed by water changes to help keep the aquarium environment healthy. The period of time between when you start a pond or aquarium and when the bacteria can handle processing the ammonia produced by fish is called the conditioning period. Nitrifying bacteria are found in water, soil, and the gravel of an established aquarium. In order to start an aquarium you will ideally seed your aquarium with gravel from a conditioned aquarium. This will help prevent problems with the conditioning period1.
Simple management practices to prevent toxic elevations of ammonia and nitrites include, not overfeeding and gradually introducing fish into the aquarium. If you add too many fish too fast the waste produced by those fish may generate ammonia levels that are higher than the bacteria can metabolize. Another practice that can help the waste management of your aquarium is a filtration system. Nitrification can and will occur without a filtration system but as the process requires oxygen, and oxygen concentration is increased with filtration1, it will therefore increase the level of nitrogen waste breakdown. Filtration can also help remove solid waste.
Paying attention to and maintaining good water quality will prevent a myriad of health problems for your aquatic pets. I suggest regular water quality analysis which you can perform by purchasing an in home water quality kit or taking a sample into a local veterinarian who sees fish.
1. John B. Gratzek Fish Health Management