Carlson Rose L, Lauder George V
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
J Morphol. 2010 Jan;271(1):25-35. doi: 10.1002/jmor.10776.
Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to "hold station" in flowing water. Here, we quantify the station-holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s(-1) in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station-holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s(-1) whereas E. flabellare slipped at 40.2 cm s(-1). On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s(-1) whereas E. flabellare slipped at 23.1 cm s(-1). We measured body and fin positions of the two species from individual frames of high-speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip.
镖鲈是淡水鱼类中的一个重要类群，它们生活在北美溪流和河流中，与水底基质紧密相连。因此，任何镖鲈物种的一个关键特征就是其在流动水中保持原位或“坚守站位”的能力。在此，我们对两种形态不同的镖鲈物种——扇尾镖鲈（Etheostoma flabellare）和密苏里鞍纹镖鲈（Etheostoma tetrazonum）的站位保持性能进行了量化。我们还描述了这两个物种在流水槽中，于有机玻璃或小岩石基质上，在流速从4到56厘米每秒（cm s(-1)）范围内坚守站位时的主要运动学反应。然后，我们提出了一系列假设，涉及观察到的姿势变化的潜在流体动力学和功能后果，以及形态、姿势和站位保持性能之间的联系。在两种基质上，密苏里鞍纹镖鲈都能比扇尾镖鲈在更高流速下保持站位。在岩石上，密苏里鞍纹镖鲈以平均55.7厘米每秒的速度滑动，而扇尾镖鲈以40.2厘米每秒的速度滑动。在有机玻璃上，密苏里鞍纹镖鲈以平均24.7厘米每秒的速度滑动，而扇尾镖鲈以23.1厘米每秒的速度滑动。我们在两个物种于岩石和有机玻璃上坚守站位时，从高速视频的单个帧中测量了它们的身体和鳍的位置。我们发现，在两种基质上，随着水流速度增加，这两个物种通常表现出相似的运动学反应：头部低垂并向下倾斜，背部变得更加拱起，随着水流速度增加，背鳍和尾鳍的鳍条收缩。胸鳍腹侧的一半也会展开，背侧的一半收缩。这些姿势和鳍位置的变化可能会增加负升力，从而增加与基质的接触力，并降低向下游滑动的可能性。
