Yes, fish can die if the water is too warm. Warm water not only reduces the concentration of dissolved oxygen (DO) but it also increases the metabolism of fish which requires more oxygen. Inappropriate temperature can cause stress to fish, sometimes fish might even die. Therefore it is necessary to maintain an optimal temperature in the fish tank. However, note that the optimal temperature of the surrounding water varies with different species of fish. Tropical fish in general need warmer conditions to thrive and live comfortably.
Every living organism needs basic things such as food, oxygen, and water to produce energy which they use for locomotion and growth. Similarly, fish is also a living thing that needs oxygen to breathe, water to maintain internal state, and food to produce energy. All these essential needs of fish are supplied by their surrounding water. Thus, the surrounding water plays important role in the survival of the fish. Any alteration or contamination in the surrounding water directly affects the fish. In this article, we will learn how the temperature change of the surrounding water affects the survival of the fish.
How temperature affects the dissolved oxygen concentration level?
We know that the fish extracts oxygen from the surrounding water. The amount of gaseous oxygen dissolved in water is known as dissolved oxygen. The ocean or river water gets this dissolved oxygen by direct absorption from the atmosphere, by the rapid movement of water, and in the form of waste product from the photosynthesis which occurs in plants and algae present in the water.
The dissolved oxygen holding capacity of the water depends on the water temperature, salinity, and pressure. This is why the dissolved oxygen varies with different water reservoirs.
The solubility of oxygen or oxygen holding capacity of the water decreases with the increase in temperature. Oxygen is easily soluble in cool water as compared to warm water.
The air-saturated water at sea level pressure ((1 atm or 760 mm of Hg) and temperature of 4 °C (39 °F) can hold 10.92 mg/L of dissolved oxygen. If this temperature is increased to room temperature (21 °C or 70 °F), the dissolved oxygen level will decrease to 8.68 mg/L.
Note that an adequate level of dissolved oxygen is important for the survival of aquatic living organisms. If the dissolved oxygen in the sea or lake water drops below 5 mg/L, it might cause stress to fish.
Read: 🐡 Do fish drink water?
How dissolved oxygen level in freshwater fluctuates with temperature?
The dissolved oxygen in freshwater can fluctuate from 13-14 mg/L to 0 mg/L depending on the temperature. According to a study conducted on the dissolved oxygen level at Crooked Lake in Indiana, the concentration of oxygen varies from 12 mg/L (surface, winter) to 0 mg/L (32 m depth, late summer) depending on the season.
The above graph represents the fluctuation of dissolved oxygen in river water with temperature change. From the above graph, we can clearly infer that the oxygen holding capacity of the river water decreases as temperature increases.
Below table represents the minimum dissolved oxygen required for different fresh water fish to survive.
| Fish Name | Dissolved Oxygen Level (mg/L) |
| Trout | 7 |
| Salmon | 6 |
| Bluegill | 5 |
| Largemouth Bass | 5 |
| Carp | 5 |
| White and yellow Perch | 5 |
| Walleye | 5 |
| Muskie | 4 |
| Pike | 2 |
The dissolved oxygen concentration should be above 7 mg/L for freshwater fish to survive without stress. To achieve this concentration of oxygen in the river, the temperature should be below 25 °C (77 °F).
Read: 👃🏻 Can Fish Smell?
How dissolved oxygen level in saltwater fluctuates?
The dissolved oxygen level in saltwater is comparatively less (20%) than the freshwater due to high salinity. Due to this low DO level, the saltwater fish have a high tolerance for low DO compare to freshwater fish.
Below table gives us an idea about the minimum DO level required by some of the common saltwater fish.
| Fish Name | Dissolved Oxygen Level (mg/L) |
| Clown fish | 7 |
| Striped Bass | 5 |
| White Perch | 5 |
| American Shad | 5 |
| Red Hake | 4 |
| Billfish | 3.5 |
| Marlin | 3 |
| Albacore Tuna | 3 |
| Shark | 2 |
| Sailfish | 1.5 |
| Halibut | 1 |
Are fish cold-blooded?
Yes, fish are cold-blooded which means their body temperature varies with that of the environment. Therefore, changes in surrounding water temperature directly affect the fish. Temperature fluctuations in surrounding water affect the metabolism of the fish. In warmer water, fish needs more oxygen as their metabolic processes occur at a faster rate. As fish are cold-blooded animals and cannot maintain their body temperature, it is important to keep them in a temperature-regulated environment. Some fish might require the same level of DO but they may prefer different temperatures for their optimal growth.
Now we know that fish need a minimum level of dissolved oxygen and this DO level depends on the surrounding water temperature. Therefore, in order to maintain a range of DO levels in a fish tank, the temperature of the tank should be maintained.
Now you must be wondering what is the ideal temperature of an aquarium tank.
Read: 🐳 Do Fish Pee?
Ideal temperature of aquarium
Well, there is no ideal temperature for the fish tank because the different species of fish require different levels of DO which means the required temperature of the tank water also varies with different species. For example, the ideal temperature for goldfish should be maintained around 22-23 oC (71.6 – 73.4 oF) while Betta fish requires warmer water (74 – 79°F). Therefore, it is important to check the ideal dissolved oxygen level and temperature for your pet fish.
Read:🐠 What Do Fish Eat?
Tropical fish temperature
For a tropical fish tank, the temperature should be maintained in the range of 24 to 27 oC (75.2 to 80.6 oF) for their comfort and metabolic efficiency. However, it is better to do some research or take advice from experts to maintain optimal conditions for your pet fish.
We know that saltwater fish are more tolerant of low DO levels. However, note that there are some saltwater tropical fish living near coral reefs that require a higher level of dissolved oxygen. The DO level near coral reefs is high because of the photosynthesis. Depending on species, the minimum level of DO should be maintained in the aquarium tank. The specific range of DO levels can be maintained by various methods such as regulating temperature and adding live plants. Clownfish and angelfish are the best examples of tropical saltwater fish that need a higher level of oxygen.
Read: 🐟 Does Fish Eat Corn? 🌽
Reef tank temperature
The temperature of the reef tank should be ideally maintained in the range of 24-26 oC (75-78 oF) to avoid fish from stress. High fluctuations in the temperature can lead to an algae outbreak and might cause stress to fish as the DO level might also decrease.
Fish that do not need a heater
We know that most of the tropical fish prefer warmer water. Therefore, their aquarium tanks need a heater to regulate temperature. However, there are few fish who do not need a heater such as
- Fancy Goldfish,
- Sunset Variatus Platy,
- Endler’s Livebearer,
- Celestial Pearl Danio,
- Bloodfin Tetras,
- Rainbow Shiner,
- Panda Corydoras,
- Hillstream Loach,
- Clown Killifish,
- Cherry Shrimp,
- Bristlenose Pleco,
- Dojo Loach,
- Odessa barbs,
- White Cloud Mountain Minnow,
- Mosquito Fish,
- Rosy Red Minnow
- Asian Stone Catfish
- Least Killifish
Read: 🦈 Do Fish Blink?
Freshwater fish tank temperature
Freshwater fish tank temperature should be maintained in the range of 24 to 27 oC (75.2 to 80.6 oF). Note that the temperature range might vary from fish to fish. Therefore, always consult experts to maintain ideal conditions for fish to thrive.
Saltwater aquarium temperature
Saltwater aquariums are generally kept in the temperature range of 24 – 25 oC (75 – 77 oF). But we also know that the DO level requirement varies with different species. Saltwater fish living near coral reefs need more DO levels compared to other saltwater fish. Some fish might require the same DO level but prefer the different temperatures to thrive and grow.
Here are some of the popular fish and their ideal temperature.
| Fish tank | Temperature Range |
| Guppies | 72-82 oF |
| Cherry Shrimp | 77-81 oF |
| Betta Fish | 74-79 oF |
| Goldfish | 68-74 oF |
| Platys | 70-77 oF |
| Tetra Fish | 75-80 oF |
| Glofish | 72-82 oF |
| Discus Fish | 82-86 oF |
| Flowerhorn cichlids | 80-85 oF |
| African Cichlid | 78-82 oF |
| Oscar | 74-81 oF |
How to maintain the temperature of the aquarium?
Here are some of the ways to regularly monitor and maintain aquarium temperature.
- Install digital fish tank thermometer to regularly monitor the temperature of fish tank
- Use adjustable fish tank heater to maintain the temperature
- Keep aquarium lights off to reduce the temperature. However, note that fish do require some amount of light to survive.
- Keep fish away from direct sunlight
Read: 🐟 Can Fish See In The Dark?
Key takeaway
The temperature of the fish tank plays important role in the appropriate growth and survival of the fish. It is important to maintain an optimal amount of dissolved oxygen level and temperature of the water.
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