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1.
  1. Isoëtes sabatina is the rarest aquatic quillwort in Europe. Although recently found (2013) in Lake Bracciano (central Italy), the species is just one step away from extinction with an estimated population not exceeding 400 individuals and a spatial range of a few hundred square metres.
  2. Lake Bracciano is a deep, oligo-mesotrophic Mediterranean volcanic lake that has been subjected to human activities. From January to October 2017, the lake experienced a dramatic water level decrease (up to −1.50 m), which significantly affected the littoral zone and the habitat of I. sabatina.
  3. To improve the chances of survival of I. sabatina, the first eco-taxonomic investigation on this species was carried out to describe its genetic distinctness, physical and chemical requirements and companion species.
  4. The phylogenetic position of I. sabatina was investigated by applying standard DNA barcoding methods. Simultaneously, during summer 2019, the physical and chemical features of water and sediments of the I. sabatina population and five small Alpine lakes colonized by Isoëtes echinospora – a supposed close relative – were characterized. These data were then compared with the available data on the trophic requirements of the target obligate aquatic Isoëtes, together with Isoëtes lacustris and Isoëtes malinverniana.
  5. The present survey confirmed the taxonomic and ecological distinctness of I. sabatina – providing the first evidence of genetic differentiation from I. echinospora. Isoëtes sabatina grows in waters with temperature, conductivity and total alkalinity up to 30°C, 561 μS cm−1 and 3.45 meq L−1, respectively.
  6. The edaphic requirements of I. sabatina confirm its outstanding conservation value, and this study offers a basic understanding of how to prevent its extinction. Now, all possible actions must be taken immediately to save this species.
  相似文献   
2.
陆化杰  刘凯  欧玉哲  陈子越  陈新军 《水产学报》2021,45(12):2099-2111
随着微塑料在海洋环境和海洋生物中的发现,海洋微塑料污染问题越来越受到关注。本文对海洋微塑料的来源、类型、分布规律、毒性以及对不同食性、不同栖息地海洋鱼类的影响进行了梳理,对后续研究方向进行了分析和瞻望。结果表明,微塑料来源广泛、种类繁多、分布在海洋的各个角落,其毒性主要由自身毒性和联合毒性两部分组成。微塑料在海洋中垂直分布特点为底层沉积物含量较高,其次为底层、上层水域,中层水域较少;水平方向上分布特点为河口区含量较高,流场区次之,大洋区较少。不同栖息环境的海洋鱼类对微塑料的摄取数量不同,从大到小依次为:近岸底栖性>底层性>大洋性>大洋底栖性;摄取种类也不同,并主要受微塑料密度的影响,中上层鱼类主要摄取密度较小的微塑料,中下层鱼类主要摄取密度较大的微塑料。不同食性鱼类对微塑料摄取量也不相同,滤食性鱼类摄取量最高,植食性和掠食性鱼类摄取量略不相同。海洋鱼类的摄食特性对不同形状、大小、密度的微塑料摄取具有一定的选择性。后续研究应结合渔业生物、生态学,物理海洋,化学海洋等  相似文献   
3.
  1. Freshwater environments host roughly half of the world’s fish diversity, much of which is concentrated in large, tropical river systems such as the Amazon. Fishes are critical to ecosystem functioning in the Amazon River basin but face increasing human threats. The basic biology of these species, and particularly migratory behaviour, remains poorly studied, in part owing to the difficulty associated with conducting tagging studies in remote tropical regions.
  2. Otolith microchemistry can circumvent logistical issues and is an increasingly important tool for studying fish life histories. However, this approach is still new in the Amazon, and its potential and limitations to inform fish conservation strategies remain unclear.
  3. Here, otolith microchemistry studies in the Amazon are reviewed, highlighting current possibilities, and several key factors that limit its use as a conservation tool in the Amazon are discussed. These include the dearth of spatiotemporal elemental data, poor understanding of environment–fish–otolith pathways, and insufficient funding, facilities, and equipment.
  4. A research initiative is proposed to harness the potential of this technique to support conservation in the Amazon. Key aspects of the proposal include recommendations for internal and external funding, which are critical to acquiring and maintaining technical staff, cutting-edge equipment, and facilities, as well as fostering regular scientific meetings and working groups. Meetings can facilitate a systematic approach to investigating environment–otolith pathways, broadening the chemical baseline for most Amazonian tributaries, and exploring potential valuable elements.
  5. These outcomes are urgently needed to conserve biodiversity and ecosystem functioning in the Amazon, especially given threats such as widespread hydroelectric damming. The initiative proposed here could make otolith microchemistry an important, cost-effective tool to inform and foster conservation in the Amazon, and act as a template for other imperilled tropical river basins, such as the Mekong and the Congo.
  相似文献   
4.
  1. Fish assemblages in estuaries have a much lower species richness (number of taxa) when compared with the combined numbers of freshwater and marine species from adjacent aquatic ecosystems. This is primarily because of the relatively harsh and fluctuating physico-chemical conditions in estuaries compared with the more stable freshwater and marine environments.
  2. A comprehensive fish survey of estuaries in South Africa is used as a basis to determine fish species richness in subtropical, warm temperate, and cool temperate systems along the coast, and to assess the degree of redundancy in the different biogeographic regions.
  3. In general, only one or two species belonging to each of the detritivorous, piscivorous, zoobenthivorous, and zooplanktivorous fish guilds are numerically well represented in the larger cool temperate estuaries, but between four and 10 species in each of these guilds are usually recorded in the larger subtropical estuaries.
  4. Although the overall low redundancy of fish species groups in estuaries has already been formally recognized in the literature, this short note highlights the sensitivity of certain trophic guilds in temperate South African estuaries to any form of redundancy, a characteristic that may be equally applicable, based on declining species richness with increasing latitude, to temperate estuaries in other parts of the world.
  相似文献   
5.
通过对贪食迈阿密虫(M. avidus)对4种养殖鱼类组织匀浆液的趋化特性进行研究,以探讨贪食迈阿虫对养殖鱼类的侵染特点。试验结果显示,贪食迈阿密虫对大黄鱼、大菱鲆、黄姑鱼、鲈鱼的眼、脑、脑脊液匀浆液有强烈的趋化效果(P<0.01),对皮肤黏液、鳃、肝、肌肉、肾组织匀浆液的趋化性较弱(P>0.05);对不同鱼类组织匀浆液对贪食迈阿密虫的趋化诱导差异比较结果推测,贪食迈阿密虫对宿主具有一定的选择性。本研究有助于深化贪食迈阿密虫致病性的认识,并为海水养殖鱼类盾纤虫病的预防提供参考资料。  相似文献   
6.
Bovine colostrum, an alternative food of animal origin provided as partial protein source, may constitute an innovative ingredient in fish feeding. Serum insulin‐like growth factor 1 (IGF‐1) and cellular activity of enteric, hepatic and muscle tissues of juvenile pacu Piaractus mesopotamicus fed with lyophilized bovine colostrum (LBC) were evaluated. Pacu (8.46 ± 0.74 g; 7.75 ± 0.27 cm, n = 18 in triplicate) were stocked into 18 tanks (300 L; 18 fish per tank, in triplicate) and fed with control diet containing 0% of LBC or experimental diet containing 10% and 20% of LBC inclusion for either 30 or 60 days of experiment. IGF‐1 serum concentration was not affected (P > 0.05) by the diet containing LBC and experimental period. The intestinal and hepatic cellular activity was not influenced by LBC (P > 0.05); however, intestine protein/RNA decreased at 60 days (P < 0.05). The muscle cellular activity was affected by LBC, highest in fish fed with diet containing 10% of LBC (P < 0.05). Between the periods DNA and protein/RNA increased at 60 days, while RNA, protein/DNA and RNA/DNA ratio decreased in this same period (P < 0.05). Increased DNA muscle content indicates fish growth by hyperplasia. The results of the present study is related with suitable development of enteric, hepatic and muscle tissues and proper condition of juvenile pacu fed with LBC considering the absence of differences in relation to juveniles that consumed diet without colostrum.  相似文献   
7.
8.
针对单品种淡水活鱼数量估计问题,以鲫鱼和鳊鱼为研究对象,采用不同数量淡水鱼的被动水声信号作为样本,通过4~6层小波包分解算法,对比分析了样本的若干特征提取方案,明确了鲫鱼水声信号特征的提取方案为短时平均过零率+6层小波包分解频段能量,而鳊鱼只需提取6层小波包分解频段能量作为其信号特征。根据不同样本集划分方法比较结果,确定了鲫鱼样本集划分方法为Rank-SPXY(m=10),鳊鱼为Rank-SPXY(m=5)。利用竞争自适应重加权采样,筛选出样本的关键特征,并使用多元线性回归和偏最小二乘回归建立了若干淡水活鱼的数量估计模型,结果表明:多元线性回归模型的性能较好,鲫鱼和鳊鱼数量估计模型的复相关系数分别为0.835和0.893,相对分析误差分别为1.79和2.01。  相似文献   
9.
The Lower Mekong Basin is facing unprecedented threats to fish diversity from hydropower development. There is increasing pressure on developers and construction authorities to design solutions to improve fish survival through turbines, thus protecting the resources in regions being developed for hydropower. A hydraulic characteristic of hydropower turbines with known fisheries impacts is fluid shear stress. Elevated shear stress occurs where rapidly flowing water passes near spillways, screens and within turbine draft tubes. Shear stress can have adverse impacts on fish, but no work has assessed whether this holds true for Mekong River species. A flume was used to determine critical tolerances of silver shark, Balantiocheilos melanopterus (Bleeker), to shear stress rates at a high‐velocity jet which simulated a hydropower turbine. Fish were assessed for injury or mortality following exposure. Results were compared against a no‐shear control. Injury and mortality were greater at higher shear stress exposures. Injuries occurred at all shear exposure levels with mortality at shear levels higher than 600/s. This approach should help design future hydropower turbines if data on other species demonstrate similar results. If the likelihood of adverse impact is high, then shear stress will need to be considered in the design of future hydropower facilities.  相似文献   
10.
Preliminary technical baseline information for the inland culture of juvenile red drum, Sciaenops ocellatus, in a freshwater fish hatchery is presented. Three initial stocking densities (d1 = 83, d2 = 167, and d3 = 250 fish/m3) were tested in a semirecirculation system for 575 days using a commercially available feed (48.1% protein, 25% lipids, and 0.13% fiber). Initial and final mean fish weight were 7.11 ± 0.02 g and 287.6 ± 27 g. As carrying capacity appeared to have been reached, only data from Days 1–333 were analyzed. One‐way ANOVA analyses indicated that the survival rate of the smaller density (d1 =40 ± 3.7%) was significantly different from the other two densities (d3 = 21 ± 1.1% and d2 = 23 ± 1.0%), which did not differ between them. Absolute growth rate (0.87 ± 0.02 g/day) was not significantly different between densities (F = 0.23. p = .801). Neither was weight significantly different between treatments. There were significant differences in the feed conversion rate (FCR) between densities (F = 8.54; p = .02). FCR for d1 was significantly lower than for the two other densities, which did not differ from each other. A von Bertalanffy growth model was adjusted (R2 = 0.95), and weight–length relationship presented negative allometric values (b = 2.85, R2 = 0.98).  相似文献   
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