Phenotypic plasticity is a well documented phenomena in biology, this study seems to help confirm it exists in fish. In plants it gets pushed to interesting extremes due to their sessile nature. For instance etiolation occurs when plants are grown in the absence of light. They adapt by growing long thin brittle stems, to optimize the individual's morphology for longer reach, and minimal metabolic impact.

"Personality" in animals is just an extremely variable/adaptable manifestation of this.