Final answer:
The feature that primarily distinguishes most fishes from most amphibians is the presence of scales. Fish are generally covered in scales which aid in protection and movement, while amphibians lack scales and have moist skin for cutaneous respiration.
Step-by-step explanation:
The feature that most distinguishes fishes from most amphibians is 2) scales. This characteristic is an important aspect of the adaptation of fish to aquatic living. Fish, including bony fish and ray-finned fish, are generally covered in scales which provide them with protection and aid in movement.
By contrast, amphibians lack scales and instead have moist skin without scales, a characteristic also connected to their dual life stages - in water, as larvae or tadpoles, and on land, as adults. Their skin further aids in the process of respiration through a process called cutaneous respiration.
Therefore, while both fish and amphibians possess a vertebral column, have a part of life cycle in water with gills assisting in breathing, it is the presence of scales on the body that primarily distinguishes fishes from most amphibians.
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