Swimming ability of cyprinid species (subfamily schizothoracinae) at high altitude.

The primary objective of this investigation was to study the effect of altitude on fish swimming ability. Different species were tested to ensure that the differences observed are not associated with a single species. Fish critical swimming speed and burst speed were determined using stepped-velocity tests in a Brett-type swimming respirometer. Based on the effects of water temperature and dissolved oxygen, it is clear that the swimming ability of fish decreases as altitude increases. Further, because the effects of high altitude on fish physiology go beyond the effects of lower temperature and dissolved oxygen, we recommend that fish swimming ability be tested at an altitude similar to the target fishway site to ensure the validity of fish data used for fishway design.

Positive effects of fast growth on locomotor performance in pelagic fish juveniles.

Many laboratory experiments on aquatic vertebrates that inhabit closed water or coastal areas have highlighted negative effects of fast growth on swimming performance. Nonetheless, field studies on pelagic fishes have provided evidence of survival advantages of faster-growing individuals. To reconcile this contradiction, we examined the relationship between growth rate and swimming performance as a continuous function for juveniles of chub mackerel (Scomber japonicus) using 3D tracking analysis. For experiments, 20, 24, 27, and 30 days post-hatch individuals within the size range of 14.5-25.3 mm were used. We found that the growth-swimming (burst speed) relationship in chub mackerel was substantially positive and it was supported by morphological traits such as muscle area, which were also positively related with growth rate. This finding is consistent with field observations showing selective survival of fast-growing individuals of this species, reconciling the current contradiction between laboratory experiments and field observations. A dome-shaped quadratic curve described the relationship between growth rate and burst speed better than a linear or cubic function, suggesting that growth may trade-off with swimming performance, as reported in many previous studies, when it is extremely fast. These results, obtained from the rarely tested offshore species, strongly suggests the importance of experimental verification using animals that inhabit various types of habitats in understanding the principles underlying the evolution of growth-locomotor relationship.

Temperature-mediated trade-off between development and performance in larval wood frogs (Rana sylvatica).

Countergradient variation has been detected in diverse taxa. In a common manifestation, individuals from colder environments develop faster than conspecifics from warmer environments when placed in a common garden. Where such a pattern exists, it implies a trade-off: Individuals from warmer environments have intrinsic rates of development lower than those demonstrated by other individuals of the same species. We explored a trade-off between development rate and locomotor performance in the wood frog (Rana sylvatica), an amphibian for which countergradient variation has been well documented. We reared wood frogs from 10 populations under two temperature regimes, bracketing the temperatures observed in local natural ponds. Individuals reared under warmer conditions developed more rapidly but exhibited burst speeds 20% lower than individuals reared under colder conditions. The slope of the reaction norm was consistent across the 10 populations and thus, we found no evidence of countergradient variation in performance. Burst speed assays of wild-caught tadpoles from the same populations showed a similar but nonsignificant trend, with greater variability among ponds. Overall, our findings support the existence of a development-performance trade-off that may be of broad importance and which may help explain the widespread occurrence of countergradient variation.

Swimming performance of 12 Schizothoracinae species from five rivers.

A series of stepped velocity tests were carried out in a Brett-type swimming respirometer and the overall range in swimming performance for 12 Schizothoracinae species was measured. The relative critical swimming speed Ucrit and burst speed Uburst decreased with body length, while absolute Ucrit and Uburst increased with body length. Ucrit increased with temperature up to approximately 15° C and then decreased. Species with a high Ucrit also displayed a higher Uburst .

THE FUNCTIONAL BASIS OF NATURAL SELECTION FOR VERTEBRAL TRAITS OF LARVAE IN THE STICKLEBACK GASTEROSTEUS ACULEATUS.

Previous studies have demonstrated selective predation for vertebral traits of larvae in the stickleback Gasterosteus aculeatus. I tested the hypothesis that this selection results from a direct functional advantage to particular vertebral phenotypes by direct measurement of the burst swimming performance of larvae. Within a narrow window of lengths, burst speed did depend on vertebral phenotype. As in the previous predation experiments, performance was related more directly to the ratio of abdominal to caudal vertebrae (VR) than to the total number of vertebrae (VN), and the optimal VR decreased as larval length increased. Changes with length in the vertebral phenotype frequencies of wild larvae provided evidence of selection for VR and for VN in the wild. Larvae with particular VR increased in frequency in the wild at just those lengths when their relative performance was superior in the laboratory. The observed pattern of length-dependent selection for vertebral number provides an explanation for the widespread trends in vertebral number that occur among populations of related fishes.