The limits of sensory evolution in fish are defined very largely by their habitat. Water is physically supportive, carries some kinds of odour well, and is kind to sound - letting it travel several times faster than air will allow, but it inhibits other more personal kinds of communication.

Lyall Watson’s quote delves into the relationship between the sensory evolution of fish and their habitat. He suggests that the way fish have evolved to perceive their environment is deeply influenced by the nature of water. The unique properties of water—its ability to carry certain stimuli like odor and sound—help shape the sensory abilities of fish, but also place limits on how they can interact with the world around them. Watson's observation underscores that the sensory tools fish develop are a direct result of the challenges and advantages their aquatic habitat provides.

Water is described as physically supportive, meaning it provides a stable environment that allows fish to navigate, stay buoyant, and survive. Additionally, water is particularly effective at carrying odor molecules, enabling fish to detect scents in ways that may be less efficient in air. This is a crucial aspect of fish survival, as many species rely on their sense of smell to find food or avoid predators. Similarly, water facilitates the transmission of sound, allowing fish to hear and respond to underwater noises far more effectively than terrestrial animals.

However, Watson also notes that water’s properties present limitations when it comes to other types of communication. While it supports sound and odor, water can hinder other more personal forms of communication, such as visual cues. The murkiness of water, coupled with its refractive qualities, limits the clarity with which fish can see each other, reducing the effectiveness of visual signals. This highlights the trade-offs in how fish rely on their environment to develop specific sensory capabilities.

Ultimately, Watson’s quote reflects the idea that the sensory world of fish is uniquely shaped by the characteristics of their habitat. The limits of their evolutionary development are a direct result of the advantages and constraints presented by water, guiding their sensory systems toward the most useful means of interaction within their environment.