Final answer:
The habitat of the Mexican tetra surface variety is freshwater rivers, where they are uniquely adapted to this ecosystem compared to marine or desert habitats.
Step-by-step explanation:
The habitat of the Mexican tetra surface variety is a) Freshwater rivers. These fish thrive in freshwater environments, which include lakes, ponds, rivers, streams, and wetlands.
It's important to note that these habitats differ significantly from marine environments like the deep ocean, desert regions, or polar ice caps, and they also have different salt content levels compared to oceans.
Biology frequently examines different living environments and the species adapted to them. For instance, while coral reefs are predominantly found in shallow ocean water, the Mexican tetra surface variety does not inhabit such salty waters. Instead, this fish is found in freshwater systems, which are also home to organisms like phytoplankton and are sometimes connected to larger marine ecosystems through estuaries.