Changes in age composition and growth characteristics of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) over 400 years

Populations of sturgeon (Acipenseridae) have experienced global declines, and in some cases extirpation, during the past century. In the current era of climate change and over-harvesting of fishery resources, climate models, based on uncertain boundary conditions, are being used to predict future effects on the Earth''s biota. A collection of approximately 400-year-old Atlantic sturgeon spines from a midden in colonial Jamestown, VA, USA, allowed us to compare the age structure and growth rate for a pre-industrial population during a ‘mini-ice age’ with samples collected from the modern population in the same reach of the James River. Compared with modern fish, the colonial population was characterized by larger and older individuals and exhibited significantly slower growth rates, which were comparable with modern populations at higher latitudes of North America. These results may relate to higher population densities and/or colder water temperatures during colonial times.     

Allometric growth of the trunk leads to the rostral shift of the pelvic fin in teleost fishes

The pelvic fin position among teleost fishes has shifted rostrally during evolution, resulting in diversification of both behavior and habitat. We explored the developmental basis for the rostral shift in pelvic fin position in teleost fishes using zebrafish (abdominal pelvic fins) and Nile tilapia (thoracic pelvic fins). Cell fate mapping experiments revealed that changes in the distribution of lateral plate mesodermal cells accompany the trunk-tail protrusion. Presumptive pelvic fin cells are originally located at the body wall adjacent to the anterior limit of hoxc10a expression in the spinal cord, and their position shifts rostrally as the trunk grows. We then showed that the differences in pelvic fin position between zebrafish and Nile tilapia were not due to changes in expression or function of gdf11. We also found that hox-independent motoneurons located above the pelvic fins innervate into the pelvic musculature. Our results suggest that there is a common mechanism among teleosts and tetrapods that controls paired appendage positioning via gdf11, but in teleost fishes the position of prospective pelvic fin cells on the yolk surface shifts as the trunk grows. In addition, teleost motoneurons, which lack lateral motor columns, innervate the pelvic fins in a manner independent of the rostral-caudal patterns of hox expression in the spinal cord.     

Using infrared thermography to assess seasonal trends in dorsal fin surface temperatures of free-swimming bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida

The temperature differential (Δ T ) between a body surface and the environment influences an organism's heat balance. In Sarasota Bay, FL, where ambient water temperature ( T _w) ranges annually from 11° to 33°C, Δ T was investigated in a resident community of bottlenose dolphins ( Tursiops truncatus ). Dorsal fin surface temperatures ( T _dfin) were measured on wild, free-swimming dolphins using infrared thermography. Field and laboratory calibration studies were also undertaken to assess the efficacy of this non-invasive technology in the marine environment. The portability of infrared thermography permitted measurements of T _dfin across the entire range of environmental temperatures experienced by animals in this region. Results indicated a positive, linear relationship between T _dfin and T _w ( r ²= 0.978, P < 0.001). On average, T _dfin was 0.9°C warmer than T _w across seasons, despite the 22°C annual range in T _w. Changes in integumentary and vascular insulation likely account for the stability of Δ T _{dfin − w} and the protection of core temperature ( T _core) across seasons. The high thermal conductivity of water may also influence this Δ T . The use of infrared thermography is an effective, non-invasive method of assessing dorsal fin skin surface temperatures (±1°C) across large numbers of wild, free-swimming dolphins throughout their thermally dynamic aquatic environment.     

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

The concept of convergence, that is, how unrelated animals independently evolve similar morphological traits, is a fundamental aspect of evolution. Hitherto, the Mesozoic ichthyosaurs were regarded as the sole obligate marine reptiles that achieved a fully streamlined body and a semilunate tail fluke. However, analyses of vertebral centrum morphometrics and process orientation have revealed that a subsequent clade of secondarily aquatic reptiles, the mosasaurs (here exemplified by the advanced, mid-Maastrichtian mosasaurine Plotosaurus ), had developed a deep, fusiform body and a probable pursuit-predatory behaviour by the time of their sudden extinction at the Cretaceous–Paleogene boundary. Stringent physical constraints and selection pressures, imposed by the surrounding water, probably were responsible for this spectacular example of large-scale evolutionary convergence.     

The effects of age,sex, and habitat on body size and shape of the blackstripe topminnow,Fundulus notatus (Cyprinodontiformes: Fundulidae) (Rafinesque 1820)

Lake and stream habitats pose a variety of challenges to fishes due to differences in variables such as water velocity, habitat structure, prey community, and predator community. These differences can cause divergent selection on body size and/or shape. Here, we measured sex, age, length, and eight different morphological traits of the blackstripe topminnow, Fundulus notatus, from 19 lake and stream populations across four river drainages in central Illinois. Our goal was to determine whether size and shape differed consistently between lake and stream habitats across drainages. We also considered the effects of age and sex as they may affect size and morphology. We found large differences in body size of age 1 topminnows where stream fish were generally larger than lake fish. Body shape mainly varied as a function of sex. Adult male topminnows had larger morphological traits (with the exception of body width) than females, in particular longer dorsal and anal base lengths. Subtle effects of habitat were present. Stream fish had a longer dorsal fin base than lake fish. These phenotypic patterns may be the result of genetic and/or environmental variation. As these lakes are human‐made, the observed differences, if genetic, would have had to occur relatively rapidly (within about 100 years). © 2013 The Linnean Society of London     

Structure of supporting elements in the dorsal fin of percid fishes

The dorsal fin is one of the most varied swimming structures in Acanthomorpha, the spiny‐finned fishes. This fin can be present as a single contiguous structure supported by bony spines and soft lepidotrichia, or it may be divided into an anterior, spiny dorsal fin and a posterior, soft dorsal fin. The freshwater fish family Percidae exhibits especially great variation in dorsal fin spacing, including fishes with separated fins of varying gap length and fishes with contiguous fins. We hypothesized that fishes with separated dorsal fins, especially those with large gaps between fins, would have stiffened fin elements at the leading edge of the soft dorsal fin to resist hydrodynamic loading during locomotion. For 10 percid species, we measured the spacing between dorsal fins and calculated the second moment of area of selected spines and lepidotrichia from museum specimens. There was no significant relationship between the spacing between dorsal fins and the second moment of area of the leading edge of the soft dorsal fin.     

摄食水平对不同性别食蚊鱼仔幼鱼生长发育的影响

在实验室27℃水温下,研究了少食、中食和饱食三个摄食水平对0至25日龄雌雄食蚊鱼(Gambusia affinis)的生长发育特征和饵料利用效率的影响。26d饲养实验结束后,对试验鱼摄食和生长指标、臀鳍分化、性成熟及饵料转换效率进行分析。结果显示:到臀鳍开始分化时,饱食组雄鱼的累计摄食总能量和生长速度开始小于雌鱼,且随日龄的增加差异加大;随摄食水平的增加,0日龄仔鱼到臀鳍分化和性成熟的时间缩短。至实验结束,各摄食组的雄鱼均形成发育完善的生殖足,性腺都达到成熟状态;而雌鱼性成熟迟于雄鱼,且其性成熟更易受到摄食水平的影响,饱食组只有约50%的个体达到性成熟,少食组的卵母细胞则均处在小生长期。随着摄食水平的增加,雌雄鱼的体长、体重和干物质特定生长率均呈明显上升趋势,而干物质饵料转化效率则呈明显下降趋势;实验结束时,雌鱼的生长指标和干物质饵料转化率均大于雄鱼。以上结果表明,伴随臀鳍的分化,食蚊鱼在摄食、生长、发育、性成熟和应对食物丰度变化上表现出显著的性别差异。       

Ecomorphology of Locomotion in Labrid Fishes

The Labridae is an ecologically diverse group of mostly reef associated marine fishes that swim primarily by oscillating their pectoral fins. To generate locomotor thrust, labrids employ the paired pectoral fins in motions that range from a fore-aft rowing stroke to a dorso-ventral flapping stroke. Species that emphasize one or the other behavior are expected to benefit from alternative fin shapes that maximize performance of their primary swimming behavior. We document the diversity of pectoral fin shape in 143 species of labrids from the Great Barrier Reef and the Caribbean. Pectoral fin aspect ratio ranged among species from 1.12 to 4.48 and showed a distribution with two peaks at about 2.0 and 3.0. Higher aspect ratio fins typically had a relatively long leading edge and were narrower distally. Body mass only explained 3% of the variation in fin aspect ratio in spite of four orders of magnitude range and an expectation that the advantages of high aspect ratio fins and flapping motion are greatest at large body sizes. Aspect ratio was correlated with the angle of attachment of the fin on the body (r = 0.65), indicating that the orientation of the pectoral girdle is rotated in high aspect ratio species to enable them to move their fin in a flapping motion. Field measures of routine swimming speed were made in 43 species from the Great Barrier Reef. Multiple regression revealed that fin aspect ratio explained 52% of the variation in size-corrected swimming speed, but the angle of attachment of the pectoral fin only explained an additional 2%. Labrid locomotor diversity appears to be related to a trade-off between efficiency of fast swimming and maneuverability in slow swimming species. Slow swimmers typically swim closer to the reef while fast swimmers dominate the water column and shallow, high-flow habitats. Planktivory was the most common trophic associate with high aspect ratio fins and fast swimming, apparently evolving six times.     

对胸鳍棘鉴定鱼类年龄方法的技术改进——简易脱钙切片法

用大鳍Hu、粗唇Wei、瓦氏黄颡鱼等的胸鳍棘作为实验材料,用1％－5％的硝酸脱钙切片后,鉴定年龄。为适应大规模的年龄鉴定,对常规的组织切片步骤和时间进行了简化、缩短。与传统的锯片法及磨片法相比,该方法易于操作,有助于准确的年龄鉴定、年轮半径测量和生长推算,特别适用于中、小型无鳞鱼类的年龄鉴定。