Book Description

"One. The organization of a school of Jenkinsia is based on visual cues which become inoperative at just about the visual limit in man under certain conditions or before it under others. 2. Normally a school of Jenkinsia maintains a specified distance from solid vertical objects such as piles, and approaches twice as close to light-colored ones as to dark-colored. 3. The formation of a mill in Jenkinsia, typically based on extrinsic factors, may evidently under certain conditions be based on strictly intrinsic factors. 4. A mill of 3 feet in diameter of about 500 fish had members at the periphery traveling at about 3 inches per second. 5. Such a mill traveling around the wall of a circular tank traveled at the rate of about 1.4 feet per minute. 6. Individual fish near the center of a mill are more closely spaced than are those at its periphery. 7. A mill passing along a wall moves in a direction that a wheel would in rolling along a similar surface but with many more revolutions than a wheel would show without slipping. 8. Isolation of an individual or a small group for as short a time as a week will cause them to show reluctance to join a larger group. 9. Effects of weather such as rippled surface of the water or passing clouds tend to loosen the school, so that it is found in its most striking cohesive form close to the surface on days of clear skies and no wind. 10. Small differences in water temperature control the form and location of a school to a marked extent, certain isothermal lines acting as an effective barrier to the passage of such schools. 11. Within a school of somewhat mixed sizes there appears to be continual self-sorting, resulting in fish of the most nearly similar sizes being found together. 12. Aggressive behavior and aggregating tendencies are considered in theoretical terms in reference to school formation, simple aggregation, and solitary habits. 13. Further analytical suggestions are indicated with reference to future work extending to greater refinement of method than has been possible up to the present"--P. 25.