A comparison of two methods for estimating critical swimming speed (UCRIT) in larval fathead minnows: the laminar flow assay and the spinning task assay

Critical swimming performance (UCRIT) is considered a good predictor of swimming capabilities in fish. To estimate UCRIT, a fish is exposed to an incrementally-increasing laminar flow of water until it cannot maintain its position against the current. The spinning task assay has been proposed as an alternative method to traditional laminar flow methods; however, these methods have not been directly compared. Thus, the goal of this study was to determine whether the spinning task assay is a suitable alternative to traditional laminar flow assays. To that end, the performance of fathead minnows in each assay was compared at three time points (14, 19 and 24 days post fertilization, dpf). In 14 dpf fish, UCRIT estimates were similar regardless of the assay used. However, at 19 and 24 dpf, UCRIT estimates derived from the two assay types were significantly different. This indicates that the assays are not equivalent to one another and that the spinning task assay is not a suitable alternative to the laminar flow assay for the determination of UCRIT.

A Method for Estimating the Velocity at Which Anaerobic Metabolism Begins in Swimming Fish

Anaerobic metabolism begins before fish reach their critical swimming speed. Anaerobic metabolism affects the swimming ability of fish, which is not conducive to their upward tracking. The initiation of anaerobic metabolism therefore provides a better predictor of flow barriers than critical swimming speed. To estimate the anaerobic element of metabolism for swimming fish, the respiratory metabolism and swimming performance of adult crucian carp (Carassius auratus, mass = 260.10 ± 7.93, body length = 19.32 ± 0.24) were tested in a closed tank at 20 ± 1 °C. The swimming behavior and rate of oxygen consumption of these carp were recorded at various swimming speeds. Results indicate (1) The critical swimming speed of the crucian carp was 0.85 ± 0.032 m/s (4.40 ± 0.16 BL/s). (2) When a power function was fitted to the data, oxygen consumption, as a function of swimming speed, was determined to be AMR = 131.24 + 461.26Us1.27 (R2 = 0.948, p < 0.001) and the power value (1.27) of Us indicated high swimming efficiency. (3) Increased swimming speed led to increases in the tail beat frequency. (4) Swimming costs were calculated via rate of oxygen consumption and hydrodynamic modeling. Then, the drag coefficient of the crucian carp during swimming was calibrated (0.126–0.140), and the velocity at which anaerobic metabolism was initiated was estimated (0.52 m/s), via the new method described herein. This study adds to our understanding of the metabolic patterns of fish at different swimming speeds.

Key factors explaining critical swimming speed in freshwater fish: a review and statistical analysis for Iberian species

Swimming performance is a key feature that mediates fitness and survival in aquatic animals. Dispersal, habitat selection, predator–prey interactions and reproduction are processes that depend on swimming capabilities. Testing the critical swimming speed (Ucrit) of fish is the most straightforward method to assess their prolonged swimming performance. We analysed the contribution of several predictor variables (total body length, experimental water temperature, time step interval between velocity increments, species identity, taxonomic affiliation, native status, body shape and form factor) in explaining the variation of Ucrit, using linear models and random forests. We compiled in total 204 studies testing Ucrit of 35 inland fishes of the Iberian Peninsula, including 17 alien species that are non-native to that region. We found that body length is largely the most important predictor of Ucrit out of the eight tested variables, followed by family, time step interval and species identity. By contrast, form factor, temperature, body shape and native status were less important. Results showed a generally positive relationship between Ucrit and total body length, but regression slopes varied markedly among families and species. By contrast, linear models did not show significant differences between native and alien species. In conclusion, the present study provides a first comprehensive database of Ucrit in Iberian freshwater fish, which can be thus of considerable interest for habitat management and restoration plans. The resulting data represents a sound foundation to assess fish responses to hydrological alteration (e.g. water flow tolerance and dispersal capacities), or to categorize their habitat preferences.

Swimming capability of zebrafish is governed by water temperature, caudal fin length and genetic background

Several zebrafish strains such as AB, Tübingen (TU), Wild India Kolkata (WIK) and Tupfel long fin (TL) have been established for genetic study. Each strain has its morphological and behavioral traits. Motor traits, however, have not been explored in zebrafish strains. We here applied a treadmill for fish (swimmill) and measured swimming capability of adult zebrafish by critical swimming speed, which is the maximum water velocity in which fish can keep swimming. First, we confirmed that swimming capability does not vary between female and male. Second, we found that the appropriate water temperature for swimming was between 16 and 30 °C. Third, our fin clip experiments using long-finned zebrafish revealed that they can exhibit high swimming capability when the caudal fin length was set between 3 and 10 mm, implying that long-finned zebrafish are unfavorable for fast swimming. Finally, we compared swimming capability of several zebrafish strains and demonstrated that WIK fish was significantly less capable of swimming despite that they have short caudal fin (~9 mm). The offspring of WIK fish were less capable of swimming, while hybrids of WIK and TU showed high swimming performance comparable to TU. Thus, lower swimming capability of WIK strain is inheritable as a motor trait.

Swimming Abilities of Temperate Pelagic Fish Larvae Prove that they May Control their Dispersion in Coastal Areas

The Sense Acuity and Behavioral (SAAB) Hypothesis proposes that the swimming capabilities and sensorial acuity of temperate fish larvae allows them to find and swim towards coastal nursery areas, which are crucial for their recruitment. To gather further evidence to support this theory, it is necessary to understand how horizontal swimming capability varies along fish larvae ontogeny. Therefore, we studied the swimming capability of white seabream Diplodus sargus (Linnaeus, 1758) larvae along ontogeny, and their relationship with physiological condition. Thus, critical swimming speed (Ucrit) and the distance swam (km) during endurance tests were determined for fish larvae from 15 to 55 days post-hatching (DPH), and their physiological condition (RNA, DNA and protein contents) was assessed. The critical swimming speed of white seabream larvae increased along ontogeny from 1.1 cm s−1 (15 DPH) to 23 cm s−1 (50 and 55 DPH), and the distance swam by larvae in the endurance experiments increased from 0.01 km (15 DPH) to 86.5 km (45 DPH). This finding supports one of the premises of the SAAB hypothesis, which proposes that fish larvae can influence their transport and distribution in coastal areas due to their swimming capabilities. The relationship between larvae’s physiological condition and swimming capabilities were not evident in this study. Overall, this study provides critical information for understanding the link between population dynamics and connectivity with the management and conservation of fish stocks.