The so – called water change for fish is actually to replenish oxygen for them. Fish cannot survive without the oxygen in water. Goldfish breathe through their gills, taking in the oxygen dissolved in water to meet the needs of normal metabolic functions. When the oxygen content in water fails to meet the needs of goldfish, their normal life activities will be threatened, and they may even die from suffocation.
The level of dissolved oxygen in water not only directly affects the breathing of goldfish but also severely impacts their appetite, digestion, and absorption abilities, ultimately affecting their growth and development. In water with clean quality and abundant dissolved oxygen, goldfish have a strong appetite, good digestion and absorption, grow relatively fast, have bright colors, and are lively and lovely. On the contrary, in water with deteriorated quality and very low dissolved oxygen, goldfish often have to stick their heads out to gulp down the oxygen – rich surface water to obtain oxygen and get a small amount of oxygen to sustain their lives temporarily. They generally show symptoms such as loss of appetite, dull body color, emaciation, and sluggish movement, thus reducing their ornamental value. Therefore, when keeping fish at home, it should be noted that the oxygen requirement of goldfish is directly proportional to the water temperature.
In the hot summer, special attention should be paid to the problem of oxygen deficiency. In August, when the water temperature is at its highest, goldfish often surface. The dissolved oxygen content in the water should be kept at least 1 milligram per liter to ensure the safety of goldfish.
If the carbon dioxide content in the aquarium is on the high side, it will reduce the ability of goldfish hemoglobin to combine with oxygen. When this happens, even if the dissolved oxygen content in the water is not low, goldfish will still experience breathing difficulties. The carbon dioxide in the water body is mainly produced by the respiration of goldfish, as well as the decomposition of goldfish excreta, uneaten bait and other decaying substances. When keeping fish at home, as long as you pay attention to keeping the water quality clean, generally there will be no situation where excessive carbon dioxide threatens the safety of the fish.
Goldfish have relatively weak adaptability to water pH. They are most likely to get sick and die when the pH is too high or too low. In particular, they cannot tolerate fluctuations in pH. Therefore, for goldfish purchased from other places, never pour them directly into a container filled with local water. Instead, slowly add local water to the container carrying the fish to make the pH values of the two waters gradually consistent, which is safe.
When there are fish in the water, the water will “mature”. The properties of the water will gradually change. In some cases, the dissolved oxygen content decreases while the carbon dioxide content increases. In other cases, the water changes from alkaline to acidic, or the content of ammonia and nitrate increases, and so on. Some water quality remains suitable for goldfish to live in, but some becomes unsuitable.
The fry and young fish of goldfish can still grow when the dissolved oxygen content is around 2 milligrams per liter. Compared with other fish, goldfish are relatively tolerant of low – oxygen conditions. When extremely short of oxygen in water, goldfish will raise their heads to the water surface and keep opening and closing their mouths, swallowing a tiny amount of water from the water surface and the air above it, creating many small bubbles with relatively high oxygen content on the surface, which is beneficial for gas exchange in the gills. When the bubbles in their mouths are too thick and numerous, they will spit out the bubbles from their mouths, and then start to “eat” air to create bubbles again from the beginning.
“Swallowing air” is what people usually call “surface – breathing”. Surface – breathing of goldfish doesn’t necessarily mean oxygen deficiency. It may be caused by illness or other factors. Therefore, breeders should always be cautious.
