**3.11 Rheotaxis**

Rheotaxis is the movement in response to water or air current. This type of motion is observed in aquatic animals where their movement occurs in response to water current [23]. When movement is towards oncoming water current, it is termed as positive rheotaxis while movement opposite of oncoming water current is termed negative rheotaxis [24]. This type of motion is observed in zebrafish, Crustaceans and American lobsters [25].

## **3.12 Thermotaxis**

Thermotaxis is the movement towards or away from temperature gradient. In this motion, organism move towards temperature source. Slime molds and nematodes are known to move along shallow temperature gradient [26, 27]. Mammalian sperm is also observed to perform theromtaxis to reach towards the oviduct in the female body [28].
