1) Aquatic biome 2) Branch of biology 
Hydrobiology is the science of life and life processes in water. Much of modern hydrobiology can be viewed as a sub-discipline of ecology but the sphere of hydrobiology includes taxonomy, economic biology, industrial biology, morphology, physiology etc. The one distinguishing aspect is that all relate to aquatic organisms. Much work is closely rel...
study of aquatic organisms
(from the article `limnology`) ...those found in lakes and ponds. The discipline also includes the biological, physical, and chemical aspects of the occurrence of lake and pond ...
hydrobiology 1. The study of life, or living organisms, in aquatic habitats. 2. The study of live forms in bodies of water; such as, lakes or estuaries.
the study of aquatic organisms.