These fish are called bluegill because of the bluish tinge around their gills area. For game fishers, bluegill is quite popular because it bites all around the year. It is also used as bait for larger game fish such as bass.
Other names for this fish include copper nose, sunny, brim and bream. Some people wrongly refer to it as perch, which it is not. The reason for being confused with perch is that they both belong to the same Sunfish family, which collectively has 27 species.
So, can Bluegill live in saltwater?
Bluegill is a freshwater fish, so it can survive for a short time in very cool saltwater, longer in cool brackish water but it cannot live beyond a couple of hours. The solute-concentrated environment of the ocean will draw all water from the cells of the fish, leading to dehydration and eventually, death. We will discuss this in detail later.
The reason why many people ask whether these fish can survive in saltwater is because they are quite tough. They can survive in muddy waters, they evade predators well thanks to their maneuvering speed. They also survive in warm waters and in swift rivers.
That notwithstanding, Bluegill cannot live in saltwater. They might survive for a couple of hours in very cool salty water because it would slow down their metabolic rate.
Unless a fish is euryhaline, that is, from a species that can live in both freshwater and saltwater, it will not survive long in the wrong water. The reason for this is that freshwater or saltwater fish have different chemical compositions.
It boils down to osmosis – really!
Osmosis is the movement of molecules from a less concentrated region to a highly concentrated one, through a semipermeable membrane. To explore this further, we can simply say that the body of a saltwater fish has more salt/solute than the surrounding ocean water. Thus, when the fish is in the water, ocean water flows towards/through the fish, which helps to keep it hydrated.
For a freshwater fish, the opposite happens if it is tossed in saltwater. Since its cells are less concentrated with solute (salt), the salty seawater is the region of high concentration. Thus, water would be drained out of the cells of the freshwater fish to flow to the surrounding seawater. In this case, your bluegill would die of dehydration.
Can you acclimatize bluegill to salt water?
Maybe, but no one knows for sure how long they would live even after acclimatization. Basically, if you are taking fish from freshwater to saltwater, you should introduce it gradually – a few minutes one day, a couple of hours and eventually days. However, since that is not possible for wild fish, just know that freshwater fish such as bluegill would not survive long in salty water. Sooner than later, they would be dehydrated and die.
This brings us to the next point …
All fish urinate, but not all of them drink water. Only saltwater fish drink water. Ocean water is less saline as compared to the water inside their body, so they have to drink to stay hydrated.
Freshwater fish such as bluegill do not drink water, but they urinate for purposes of osmoregulation. Thus, as they lose water from the low salinity conditions of the body to the high salinity of the ocean, they won’t drink to replace what they lose. That is why they dehydrate so fast and die.
By urination, saltwater fish are able to osmoregulate their bodies. Peeing is their survival instinct in such a salty environment.
How long will bluegill survive in salt water?
While it is hard to say specifically how long freshwater fish such as bluegill would live in salty water, certainly, it is not long.
If you are rearing bluegill in your pond at home, maybe you can try to acclimatize them to salty water. To reiterate, you can do that by introducing salty water gradually. It is not known whether they would adapt, so chances are that they would eventually die.
For the bluegill to survive even for several minutes in high salinity conditions, the water would have to be very cool. This would slow the metabolic rate of the fish, thus slowing the rate at which its cells lose water to the surrounding high salinity seawater. Their kidneys cannot handle the heavy filtration that would be required for salty water.
Bluegill can live longer in brackish water
In very cold brackish water, these fish would survive much longer. In fact, some fishermen have caught bluegill in brackish water using shrimp as bait. However, for these fish to survive in brackish water, it must not be too salty. Brackish water is a mix of salty and fresh water found at estuaries where rivers join the ocean.