Typically, aquatic anurans excrete ammonia (ammonotelic), because conserving water is not important. Urea-excreting animals (ureotelic), like toads, will have some contact with water. They produce dilute urine when they are in freshwater and typically do not urinate on land (thus, their plasma urea elevates).
hope it helps

Aquatic animals excrete ammonia in gaseous form.

Ammonia is a toxic waste product that is produced during the breakdown of proteins in the body. It is extremely soluble in water and can be easily excreted by aquatic animals. Here is a detailed explanation of why aquatic animals excrete ammonia in gaseous form:

1. Ammonia production: Aquatic animals, such as fish and marine invertebrates, continuously produce ammonia as a byproduct of their metabolism. Ammonia is formed in the liver through the deamination of amino acids, which are the building blocks of proteins. This process releases nitrogen in the form of ammonia.

2. Solubility in water: Ammonia is highly soluble in water. It can dissolve in the surrounding water and form ammonium ions (NH4+) through a reaction with water molecules. This solubility allows aquatic animals to excrete ammonia directly into the water.

3. Aquatic environment: Since aquatic animals live in a water-based environment, they have easy access to large amounts of water that can dilute and carry away the excreted ammonia. The constant flow of water in rivers, lakes, and oceans helps in the removal of ammonia from the vicinity of aquatic organisms.

4. Low energy requirement: Excreting ammonia directly into the water requires minimal energy expenditure by the aquatic animals. They do not need complex specialized structures or metabolic processes to convert ammonia into less toxic forms, as is the case with other animals.

5. Adaptation to high ammonia tolerance: Aquatic animals have evolved to tolerate higher levels of ammonia in their bodies. Their gills and other specialized organs have efficient mechanisms to extract oxygen from water while simultaneously excreting ammonia. This adaptation allows them to thrive in their aquatic habitats.

In contrast, land animals, desert animals, and aerial animals have different mechanisms for excreting waste products. Land animals, including humans, convert ammonia into urea or uric acid, which are less toxic and more concentrated forms of waste. Desert animals, such as reptiles and insects, conserve water by excreting uric acid as a semi-solid paste. Aerial animals, such as birds, excrete uric acid in the form of a white paste or powder, which reduces water loss during excretion.

In conclusion, aquatic animals excrete ammonia in gaseous form due to its high solubility in water, the availability of water in their environment, low energy requirement, and adaptation to high ammonia tolerance.