Comparison of the prolonged swimming performances of closely related, morphologically distinct three-spined sticklebacks Gasterosteus spp.

Prolonged swimming performances of two as yet unnamed species of three-spined stickleback, Gasterosteus spp., were compared. The two fishes (not yet formally described, referred to here as benthic and limnetic) inhabit different niches within Paxton Lake, Texada Island, British Columbia, Canada, and are recent, morphologically distinct species. Linmetics had longer endurance during prolonged swimming than did benthics. The mean regression of the log(10) of fatigue time (F-t, s) on swimming speed (U, standard length, L-S s(-1)) for limnetics (log(10)F(t) = 7.03 - 0.46U) had a similar slope, but a significantly higher intercept than that for benthics (log(10)F(t) = 5.55 - 0-43U). Adult benthics were larger, heavier and deeper-bodied fish than limnetics. Limnetics, however, had a significantly greater pectoral fin edge:base ratio (mean +/- S.E.: lininetics, 4.58 +/- 0-43; benthics, 3.63 +/- 0.27). In addition, limnetics had significantly lower drag coefficients (CD) than benthics (limnetics, log(10)C(D)) = -0.49log(10)R(e) + 0.66; benthics, log(10)C(D) = -0-26log(10)R(e) - 0-30) where R, is the Reynolds number [(LSU (v(-1)), where U and v are swimming velocity and the kinematic viscosity of the water, respectively]. Compared to their ancestral form, the anadromous three-spined stickleback Gasterosteus aculeatus L., limnetics and benthics had significantly longer and shorter endurance times, respectively. In addition, both these fishes had significantly higher fast-start velocities than their ancestral form. Selection due to differential resource use may have lead to divergence of body form, and, therefore, of steady swimming performance. Therefore predation may be the selective force for the similar high escape performance in these two fishes. (c) 2005 The Fisheries Society of the British Isles.