A black ghost with its sensorium for prey, showing computed flow patterns resulting from two different pitch angles.

<p>As shown by the high degree of flow separation behind the fish pitched at (the orientation it hunts prey in), compared to the laminar flow behind the fish at , there's significant energy costs associated with angling the body downward due to drag. However, the area scanned for prey by its sensorium while swimming forward increases, as shown by the plot at right. The net effect is that the fish needs less energy to get to its next prey when its body is pitched at . While pitch angles of around are best in terms of reducing the energy to get to the next prey, this does not incorporate the diminishing propulsive effectiveness of the ribbon fin as the body pitches more. Propulsion drops by about 25% at (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000769#pcbi-1000769-g006" target="_blank">Figure 6</a>). Because of this effect, the best angle for the fish to swim at will be less than .