PREDATOR-PREY DYNAMICS OF 15-SPINED STICKLEBACK (SPINACHIA-SPINACHIA)AND THE MYSID (NEOMYSIS-INTEGER)

Predatory behaviour of a pelagic fish and escape response of its prey were studied using the fifteen-spined stickleback (Spinachia spinachia ) and the mysid Neomysis integer. Optical methods were applied to quan tify the behaviour of the two species under laboratory conditions. Bef ore the actual attack the sticklebacks approach the mysids to a final attack distance of 6.60 mm (sd +/- 2.20 mm). Within 60 ms the fish acc elerate to a maximum velocity of 846 mm s(-1) equivalent to 8.5 body l engths s(-1) (mean = 633 mm s(-1), i.e. 6.4 body lengths s(-1), sd +/- 98.0 mm s(-1)). Less than 20 ms later the mysids escape with a maximu m velocity of 796 mm s(-1) equivalent to 80 body lengths s(-1) (mean = 670 mm s(-1), i.e. 67.3 body lengths s(-1), sd +/- 100 mm s(-1)), rea ched within 40 ms by tail flipping. The high speed phase of the stickl ebacks lasted about 200 ms, of the mysids about 100 ms. In only 25% of the observations were the prey caught. The energetic costs for the fi sh were estimated as 2.55 mJ per attack. The relatively low capture su ccess of the sticklebacks is discussed in respect to the excellent esc ape capacity and well-developed visual sense of mysids. N. integer can be ranked alongside the euphausiids and copepods as one of the fastes t members of the zooplankton.