Bottlenose dolphins are aquatic organisms, but they can be found in two different types of water environments. The first kind of water they can be found in is fresh water. Dolphins that live in fresh water are hypotonic to their surrounding environment (the solution within them is more concentrated then the solution outside of them), which can pose a problem because certain nutrients that dolphins need to survive could theoretically diffuse out of their body, while water could diffuse into them to create an equilibrium. In order to avoid this problem, dolphins take in fresh water (70% diffuses in through their skin, and 30% is inhaled through their mouth) and urinate it right back out. Their ufr (urine flow rate) increases immensely, and their urine is extremely diluted (meaning that it has a very high concentration of water, and a very low concentration of substances, such as chloride and sodium). By urinating often and a diluted urine, dolphins are able to keep their high concentration of nutrients and substances within their body, while getting rid of all the extra water that is being diffused through their skin and inhaled through their mouth.
The second type of water environment that dolphins can be found in is salt water. Bottlenose dolphins are hypertonic in relation to their surrounding salt enriched environment. In order to achieve an equilibrium, the water within the dolphin would diffuse out into the salt water, and the salt water would diffuse in (the same way as fresh water, 70% through their skin, the rest inhaled through their mouth). However, the Bottlenose dolphin is an aquatic animal which needs to retain a certain amount of fresh water in its body to survive. In order to obtain this amount of fresh water they take in the salt water, filter and pee out the salt, and then retain the fresh water. Bottlenose dolphins living in a salt water environment have an increased ufr, and their urine is highly concentrated with salt.
Bottlenose dolphins have to osmoregulate in both fresh and salt water environments to keep the right balance of ions within their body, and the correct amount of fresh water in their body. In both cases they osmoregulate by urinating more often, and they get rid of the unnecessary fluids (in the freshwater environment) and substances (in the salt water environment) through their urine.
