A critical appraisal of appendage disparity and homology in fishes

Fishes are both extremely diverse and morphologically disparate. Part of this disparity can be observed in the numerous possible fin configurations that may differ in terms of the number of fins as well as fin shapes, sizes and relative positions on the body. Here, we thoroughly review the major patterns of disparity in fin configurations for each major group of fishes and discuss how median and paired fin homologies have been interpreted over time. When taking into account the entire span of fish diversity, including both extant and fossil taxa, the disparity in fin morphologies greatly complicates inferring homologies for individual fins. Given the phylogenetic scope of this review, structural and topological criteria appear to be the most useful indicators of fin identity. We further suggest that it may be advantageous to consider some of these fin homologies as nested within the larger framework of homologous fin‐forming morphogenetic fields. We also discuss scenarios of appendage evolution and suggest that modularity may have played a key role in appendage disparification. Fin modules re‐expressed within the boundaries of fin‐forming fields could explain how some fins may have evolved numerous times independently in separate lineages (e.g., adipose fin), or how new fins may have evolved over time (e.g., anterior and posterior dorsal fins, pectoral and pelvic fins). We favour an evolutionary scenario whereby median appendages appeared from a unique field of competence first positioned throughout the dorsal and ventral midlines, which was then redeployed laterally leading to paired appendages.     

瓯江鲫鱼胸鳍的波动性不对称、两性异形和生育

研究浙江瓯江鲫鱼胸鳍的波动性不对称、两性异形和生育力。雌雄两性的鳍长、鳍条数的不对称均属波动性不对称。雌雄两性的胸鳍长和鳍条数的不对称指数之间相关关系不显著。雌性个体显著大于雄性个体,特定体长的雄性胸鳍长显著大于雌性,雄性的鳍条数显著大于雌性。鳍长和鳍条数的不对称指数雌雄两性差异不显著,雌雄两性鳍条数对称个体的比例差异不显著。以体长和时间为控制变量,怀卵数量与鳍长和鳍条数的不对称指数具有显著的负相关,与鳍长和鳍条数的相关不显著。以体长和发育时间为控制变量,平均卵重与鳍条数的不对称指数具有显著的正相关,与其他变量的相关不显著。分析表明,雄性较大的胸鳍可能与雄性的性选择有关,胸鳍的波动性不对称可能提供了一种发育历程的指示,间接影响雌性生育力。     

Tbx5基因在漠斑牙鲆（Paralichthys olivaceus）变态前的表达

鲽形目鱼类仔鱼经过变态后形成眼睛和偶鳍等器官左右不对称的稚鱼。Tbx家族成员参与脊椎动物心脏、肢体和眼等器官的发育,而Tbx基因与鲽形目鱼类变态的关系目前尚无报道。我们运用扫描电镜和软硬骨染色等方法对出膜后2d（变态早期）和26d（变态前期）的牙鲆仔鱼的形态进行观察,牙鲆出膜后2d胸鳍原基出现,出膜后26d胸鳍发育成熟,而在出膜后26d胸鳍和腹鳍仍呈现左右对称。我们克隆了牙鲆Tbx5基因的CDS序列,该序列编码的多肽具有部分T-box保守结构域,与斑马鱼Tbx5同源性高达93%。系统进化分析显示：这段CDS序列与硬骨鱼的Tbx5基因聚为一支,但与四足动物Tbx5相分离。整体原位杂交显示出膜后26d的牙鲆仔鱼中,Tbx5基因不仅在胸鳍、眼背侧、脊柱和尿囊表达,且在胸鳍和眼背侧的表达呈现左右不对称,左侧面（有眼侧）的表达量均高于右侧面（无眼侧）的表达量。综上结果暗示,牙鲆Tbx5基因可能参与了变态过程中眼睛与胸鳍左右不对称的形成。 研究亮点： 鲽形目鱼类都经历变态发育过程,产生显著的左右不对称形态,但调控该过程的分子机制尚不清楚。本文对牙鲆变态初期仔鱼进行了形态学观察,并对牙鲆Tbx5进行克隆及其表达分析,并探讨Tbx5与牙鲆仔鱼眼睛与胸鳍不对称变态过程的关系,为进一步研究牙鲆变态机制奠定基础。     

Effects of formalin treatment on epithelial structure and mucous cell densities in rainbow trout, Oncorhynchus mykiss (Walbaum), skin

Formalin bath treatments of rainbow trout are widely used for control of ectoparasitic infections in fish farms and the effects of this chemical on parasite infections have been studied. In addition, tolerance of the host to various concentrations of formalin are also known. However, effects of formaldehyde on the skin epithelium integrity and mucous cell density still need elucidation. The present study revealed that exposure of rainbow trout fry 2 months post-hatching to various concentrations of formalin affected the mucous cell dynamics of the fish. Limited exposure (50 ppm, 1 h) stimulated mucous cell proliferation as indicated by the slight increase in densities of Alcian blue positive cells in tail fin epidermis. In contrast, high concentrations (200-300 ppm, 1 h) or lengthy exposure (24 h) at lower concentrations caused a decrease in mucous cell density. Scanning electron microscopy revealed effects on the epithelial structure of fish fins. Blebbing of epithelial cell membranes was the first sign of injury. The dilated openings of mucous cells indicated increased release of mucus. Highly irregular organization of the cells followed, with regional differences occurring in different parts of fins. The implications of formalin bathing for susceptibility or resistance of fish to subsequent pathogen exposure are discussed.     

鲤鱼三维建模及流场受力数值计算

将鱼体和鱼鳍整体作为研究对象进行流场中受力分析对于研究鱼类本身高游动效率机理和仿生应用具有重要意义。以鲤鱼为研究对象,通过对鱼体的形体模型数学化,将特征数据导入FLUENT三维软件,结合鲤鱼的运动与形体特征进行建模,并将其模型置于来流方向平行于鱼体的流场中进行力学有限元数值计算。计算中物理场采用中心差分插值方法,流动模型采用标准两方程模型,结合具体参数进行了推导计算。通过计算发现X方向上所受阻力贡献度排名前三分别为鱼头部分的45%、鱼主体部分的29%以及鱼胸鳍部分的14%;鱼体部分在Y方向上所受升力贡献度排名前三分别为鱼胸鳍部分的47%、鱼主体部分的29%以及头部的14%;总合力为（-7.88×10-3, 2.00×10-3,-5.87×10-5）N。计算结果表明在设计中考虑升力时应主要着重于鱼的前鳍以及鱼体部分的设计,考虑运行阻力时应着重于鱼头以及鱼体部分的设计。数值计算结果为仿生机器鱼的结构设计提供了一个良好的力学基础,对于提高仿生机器鱼的运动控制水平具有较好的指导价值。     

Reproduction,larviculture and early development of the Bluebanded goby,Lythrypnus dalli,an emerging model organism for studies in evolutionary developmental biology and sexual plasticity

The Bluebanded goby, Lythrypnus dalli, is a popular ornamental aquarium species and a key organism for the study of several fundamental biological questions, most notably reversible sex change in adults. To maximize the tractability of this species as an emerging model system, it is essential to have an optimized propagation system and a detailed developmental staging scheme. One limitation to the larviculture of L. dalli is the relatively small size of the larvae, which makes the transition from yolk to feeding challenging. We developed a protocol and successfully reared three generations of L. dalli in the laboratory. The protocol contains several key innovations for the rearing of diminutive fish larvae, including tank design and co‐culturing of microalgae (Isochrysis galbana) with copepods (Parvocalanus sp.) in the larval rearing tanks. In addition, we describe the embryonic and larval development of L. dalli under controlled conditions and in comparison with the model organism Danio rerio. We found that at 21°C L. dalli larvae hatch in 4 days, reach flexion in 18–25 days and are sexually mature by 3 months. Overall, the embryonic development of L. dalli is remarkably similar to D. rerio with several striking differences, including the position and shape of the blastomere, size of the neuromasts and corresponding cupula, and relative timing of pigmentation and brain subdivision. The ability to rear this species in captivity is a valuable tool that could be utilized for a variety of similarly diminutive species and to address a greater breadth and depth of biological questions.     

Tbx5基因在牙鲆变态初期的表达

鲽形目鱼类仔鱼经过变态后形成眼睛和偶鳍等器官左右不对称的稚鱼。Tbx家族成员参与脊椎动物心脏、肢体和眼等器官的发育,而Tbx基因与鲽形目鱼类变态的关系目前尚无报道。运用扫描电镜和软硬骨染色等方法对出膜后2 d（变态早期）和26 d（变态前期）的牙鲆仔鱼的形态进行观察,牙鲆出膜后2 d胸鳍原基出现,出膜后26 d胸鳍发育成熟,而在出膜后26 d胸鳍和腹鳍仍左右对称。我们克隆了牙鲆Tbx5基因的CDS序列,该序列编码的多肽具有部分T-box保守结构域,与斑马鱼Tbx5同源性高达93%。系统进化分析显示：这段CDS序列与硬骨鱼的Tbx5基因聚为一支,但与四足动物Tbx5相分离。整体原位杂交显示出膜后26 d的牙鲆仔鱼中,Tbx5基因不仅在胸鳍、眼背侧、脊柱和尿囊表达,且在胸鳍和眼背侧的表达呈现左右不对称,左侧面（有眼侧）的表达量均高于右侧面（无眼侧）的表达量。综上结果显示,牙鲆Tbx5基因可能参与了变态过程中眼睛与胸鳍左右不对称的形成。     

滇池鲤4种年龄鉴定材料的比较

为确定鉴定滇池鲤（Cyprinus carpio）年龄的适宜材料,对4种年龄鉴定材料（耳石、鳞片、胸鳍条和鳃盖骨）的形态和年轮标志进行了描述,并对这4种钙化组织鉴定鲤年龄的一致性进行了探讨。2013年5、6、8-11月以及2014年3-7月,使用拖网采集云南滇池鲤584尾,体长范围7.5~50.5 cm,体重范围17.2~3 211.3 g。其中耳石采集于584尾样本,鳃盖骨和鳞片分别采集于276尾样本,胸鳍条采集于274尾样本。微耳石磨片轮纹清晰,在反射光下呈明暗相间的条纹,年龄标志明显。同一鉴定者2次年龄读数的吻合率,微耳石磨片轮最高（88.0%),鳞片次之(84.1%),胸鳍条和鳃盖骨则分别为73.7%和72.1%。2次读龄的平均误差百分比,微耳石磨片和鳞片较小,分别为2.6%和2.9%;胸鳍条和鳃盖骨较高,分别为4.7%和5.9%。以微耳石磨片年龄读数为基准,鳞片年龄读数与其吻合率最高(77.5%),平均变异系数最低(6.14%);鳃盖骨和胸鳍条与其吻合率分别为61.9%和56.2%,平均变异系数均超过12%。综合分析认为,耳石是滇池鲤年龄鉴定的最佳材料,鉴定4龄以下个体年龄时可使用鳞片,鳃盖骨和胸鳍条则不适于滇池鲤的年龄鉴定。