An acute increase in water temperature can decrease the swimming performance and energy utilization efficiency in rainbow trout (Oncorhynchus mykiss).

In order to evaluate the effects of acute temperature exposure on the swimming performance of rainbow trout (Oncorhynchus mykiss), the critical swimming speed (Ucrit) and oxygen consumption rates (MO2) were determined at different temperatures (13.2, 18.4, and 22.5 °C). The Ucrit and MO2 of different body mass (109.44, 175.74, and 249.42 g) fish were also obtained at 13.4 °C. The Ucrit first increased as the temperature increased from 13.2 to 15.2 °C, which was calculated to be the optimal temperature for the Ucrit, and then decreased with increasing temperature. The optimal swimming speed (Uopt) showed a similar trend to the Ucrit. At a given swimming speed, the MO2 and cost of transport (COT) were significantly higher at 22.5 than at 13.2 °C, suggesting the energy utilization efficiency decreased with increasing temperature. The absolute values of Ucrit and Uopt increased as the body mass increased from 109.44 to 249.42 g, whereas the relative values decreased. Although not statistically significant, the maximum metabolic rate (MMR) tended to increase with temperature but decrease with body mass. Results can be of value in understanding the behavioral and physiological response of rainbow trout to acute temperature change.

Ultrastructural and geochemical characterization of Archean-Paleoproterozoic graphite particles: implications for recognizing traces of life in highly metamorphosed rocks.

Abundant graphite particles occur in amphibolite-grade quartzite of the Archean-Paleoproterozoic Wutai Metamorphic Complex in the Wutaishan area of North China. Petrographic thin section observations suggest that the graphite particles occur within and between quartzite clasts and are heterogeneous in origin. Using HF maceration techniques, the Wutai graphite particles were extracted for further investigation. Laser Raman spectroscopic analysis of a population of extracted graphite discs indicated that they experienced a maximum metamorphic temperature of 513 +/- 50 degrees C, which is consistent with the metamorphic grade of the host rock and supports their indigenicity. Scanning and transmission electron microscopy revealed that the particles bear morphological features (such as hexagonal sheets of graphite crystals) related to metamorphism and crystal growth, but a small fraction of them (graphite discs) are characterized by a circular morphology, distinct marginal concentric folds, surficial wrinkles, and complex nanostructures. Ion microprobe analysis of individual graphite discs showed that their carbon isotope compositions range from -7.4 per thousand to -35.9 per thousand V-PDB (Vienna Pee Dee Belemnite), with an average of -20.3 per thousand, which is comparable to bulk analysis of extracted carbonaceous material. The range of their size, ultrastructures, and isotopic signatures suggests that the morphology and geochemistry of the Wutai graphite discs were overprinted by metamorphism and their ultimate carbon source probably had diverse origins that included abiotic processes. We considered both biotic and abiotic origins of the carbon source and graphite disc morphologies and cannot falsify the possibility that some circular graphite discs characterized by marginal folds and surficial wrinkles represent deflated, compressed, and subsequently graphitized organic-walled vesicles. Together with reports by other authors of acanthomorphic acritarchs from greenschist-amphibolite-grade metamorphic rocks, this study suggests that it is worthwhile to examine carbonaceous materials preserved in highly metamorphosed rocks for possible evidence of ancient life.

Doushantuo embryos preserved inside diapause egg cysts.

Phosphatized microfossils in the Ediacaran (635-542 Myr ago) Doushantuo Formation, south China, have been interpreted as the embryos of early animals. Despite experimental demonstration that embryos can be preserved, microstructural evidence that the Doushantuo remains are embryonic and an unambiguous record of fossil embryos in Lower Cambrian rocks, questions about the phylogenetic relationships of these fossils remain. Most recently, some researchers have proposed that Doushantuo microfossils may be giant sulphur-oxidizing bacteria comparable to extant Thiomargarita sp. Here we report new observations that provide a test of the bacterial hypothesis. The discovery of embryo-like Doushantuo fossils inside large, highly ornamented organic vesicles (acritarchs) indicates that these organisms were eukaryotic, and most probably early cleavage stage embryos preserved within diapause egg cysts. Large acanthomorphic microfossils of the type observed to contain fossil embryos first appear in rocks just above a 632.5 +/- 0.5-Myr-old ash bed, suggesting that at least stem-group animals inhabited shallow seas in the immediate aftermath of global Neoproterozoic glaciation.