SUMMARYMembers of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral-caudal gait transition occurs at a threshold speed termed U p-c . The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U p-c in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3Ls , E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above U p-c is associated with anaerobic metabolism in this labriform swimmer.

Using three different swimming velocities and a school size of eight roach Rutilus rutilus, individual intra-school position and tail beat frequency were examined in a flume tank. Tail beat frequency was determined in defined leading and trailing positions. Individual roach showed consistent intra-school positional preferences which implied a sustained positional pattern where certain individuals took up front positions whereas other individuals swam in the rear part of the school. The positional preferences could not be attributed to inter-individual differences of the eight roach in terms of total length, mass or condition factor. At the tested swimming velocities of 2, 3 and 4 L T s À1 , roach in trailing positions swam with tail beat frequencies reduced by 7Á3, 11Á9 and 11Á6%, respectively, compared to roach in leading positions. These results suggested that roach situated in trailing positions experienced energetic savings due to hydrodynamic interactions at a wide range of swimming velocities. This may be important during migrations or when a school of roach is holding its position against the current in a lotic habitat. The observed sustained positional pattern combined with a hydrodynamic advantage in trailing positions would indicate that these energetic savings might not be evenly shared among schoolmates of roach. A positive correlation between swimming velocity and stride length was found. The present study, however, does not support any conclusions concerning these findings.

Acoustic positional telemetry systems (APTs) represent a novel approach to study the behaviour of free ranging aquatic animals in the wild at unprecedented detail. System manufactures promise remarkably high temporal and spatial resolution. However, the performance of APTs has rarely been rigorously tested at the level of entire ecosystems. Moreover, the effect of habitat structure on system performance has only been poorly documented. Two APTs were deployed to cover two small lakes and a series of standardized stationary tests were conducted to assess system performance. Furthermore, a number of tow tests were conducted to simulate moving fish. Based on these data, we quantified system performance in terms of data yield, accuracy and precision as a function of structural complexity in relation to vegetation. Mean data yield of the two systems was 40 % (Lake1) and 60 % (Lake2). Average system accuracy (acc) and precision (prec) were Lake1: acc = 3.1 m, prec = 1.1 m; Lake2: acc = 1.0 m, prec = 0.2 m. System performance was negatively affected by structural complexity, i.e., open water habitats yielded far better performance than structurally complex vegetated habitats. Post-processing greatly improved data quality, and sub-meter accuracy and precision were, on average, regularly achieved in Lake2 but remained the exception in the larger and structurally more complex Lake1. Moving transmitters were tracked well by both systems. Whereas overestimation of moved distance is inevitable for stationary transmitters due to accumulation of small tracking errors, moving transmitters can result in both over- and underestimation of distances depending on circumstances. Both deployed APTs were capable of providing high resolution positional data at the scale of entire lakes and are suitable systems to mine the reality of free ranging fish in their natural environment. This opens important opportunities to advance several fields of study such as movement ecology and animal social networks in the wild. It is recommended that thorough performance tests are conducted in any study utilizing APTs. The APTs tested here appear best suited for studies in structurally simple ecosystems or for studying pelagic species. In such situations, the data quality provided by the APTs is exceptionally high.