Identifying the spatial pattern of fish assemblages and the correlation between fish assemblages and environmental factors is basic for conserving and managing stream fishes. Based on data collected from 91 sampling segments within first-order through third-order streams of the Xin'an basin, China, we examined the spatial variation of fish assemblages in this area and related it to local, river-network and catchment factors. We found that fish species richness significantly increased from first-order to second- and third-order streams, but assemblage structures showed no among-stream variation. When the independent influence of the three categories of factors was considered, fish assemblages were significantly related to local habitat (e.g. wetted and substrate heterogeneity), tributary spatial position (e.g. confluence link and distance from mouth) and land use (e.g. agriculture and urbanization areas), respectively. However, when the effects of the these factors were considered jointly, local habitat and tributary spatial position were more important in influencing fish assemblages than land use. Our results suggest that fish assemblages in the headwater streams of the Xin'an basin were mainly determined by both local and spatial factors. The landscape data should be further refined in the future to provide more information for assessing how land use influence stream fishes.
确定河流鱼类群落的时空分布格局及其形成机制是开展鱼类物种多样性保护与管理的科学基础.基于2013年10月和2014年5月共2次对太湖流域57个河道样点的调查数据，初步研究太湖流域河流鱼类群落结构及其多样性的季节动态和空间分布特点.共采集鱼类5051尾，计46种，其中鲤科鱼类26种，占全部物种数的57%.10月份的鱼类多样性显著高于5月份，且2个季度的鱼类群落结构存在显著性差异.5个主要水系间的鱼类多样性差异显著，总体上，沿江水系和洮滆水系鱼类多样性较低，黄浦江水系居中，而南河水系和苕溪水系较高；鱼类群落结构也随水系而显著变化，主要表现为黄浦江水系与洮滆、苕溪和沿江水系呈显著差异.在2个一级生态分区之间，鱼类多样性无显著差异但群落结构显著不同，主要因、鲫、似鳊等优势种及宽鳍鱲、尖头鱥、中华青鳉、食蚊鱼等偶见种的空间分布差异所引起；在4个二级生态分区之间，鱼类多样性和群落结构均存在显著的空间变化.;Identifying the distribution of species composition and their abundance of fishes is basic for the conservation and management of fish diversity. Based on the data collected from 57 stream segments within the Taihu Lake Basin during October 2013 and May 2014, we examined how the stream fish assemblages vary spatially and seasonally in this study area. A total of 5051 individuals representing 46 species were collected, among which Cyprinidae fishes are amounted to 26 species. Fish diversity in October was significantly higher than that in May, and fish assemblage structures also significantly differed seasonally. Significant variations among different subbasins were observed for both fish species diversity and assemblage structures. The Yanjiang and Zhaoge subbasins had relatively lower species diversity, while those in the Nanhe and Tiaoxi subbasins were relatively higher. Assemblage structures in the Huangpujiang subbasin showed significantly difference from those in the Zhaoge, Tiaoxi and Yanjiang subbasins. When the spatial variations in fish assemblages among ecoregions were considered, fish assemblage structures, not species diversity, showed significantly variation between two ecoregions at level-1; while both assemblage structures and species diversity differed significantly among four ecoregions at level-2. This among-ecoregion variations in assemblage structures resulted from the spatial distribution of some dominant fishes, such as Hemiculter leucisculus, Carassius auratus and Pseudobrama simoni, and some rare fishes, such as Zacco platypus, Phoxinus oxycephalus, Oryzias latipes sinensis and Gambusia affinis.
As predators are generally larger than their prey, positive body size and trophic position relationships are typically assumed, and these relationships have helped in estimating and predicting the effects of global environmental change on the trophic dynamics of aquatic ecosystems. However, current efforts to confirm the generality of body size-trophic position relationships have focused mainly on interspecific patterns using species-aggregated and averaged data, and little effort has been devoted to assessing how trophic position scales with body size at the intraspecific and community levels as well as exploring its ecological drivers, particularly for fishes in freshwater ecosystems. To fill this gap, we present a broad-scale study of body size-trophic position relationships in freshwater ecosystems at both the intraspecific and community levels using an individual-based body size and isotopic signature dataset that includes 2564 samples of 65 fish species in China. Our results indicate that body size-trophic position patterns at both the intraspecific and community levels can be positive, negative or insignificant. Non-significant patterns predominated at both levels, with slightly more than 30% showing positive relationships, which highlights that the positive body size-trophic position pattern is not universally prevalent and that body size should be used with caution as a proxy for the trophic position of fishes at both the intraspecific and community levels in freshwater ecosystems. No factor was related to body size-trophic position patterns at the community level, while habitat type, elevation, temperature and fishing pressure were identified as the key determinants of body size-trophic position patterns at the intraspecific level, implying that fishing and climate warming can shift the food-web size structure of freshwater ecosystems by affecting population trophic dynamics.
Length-weight relationships (LWRs) were estimated for nine endemic fish species from six trans-border rivers (Sutlej Tsangpo, Niang Chu, Kirong Tsangpo, Poi Chu, Phung Chu and Yadong River) in the southern slope of the Himalaya of China. All specimens were collected using drift gill nets (mesh size: 10, 30 and 50 mm; length: 25 m; depth: 1.2 m) and circle dip nets (diameter: 0.5 m; mesh size: 4 mm; length: 6.5 m) and small backpack electric fishing machines (12 V, 100 Hz) in May and June 2021. Each individual were measured with the precision of 0.1 cm for total length (TL) and 0.01 g for body weight (W). Statistical LWRs for all nine species were highly significant (p < .001), with correlation value r2 > 0.95. Five new maximum total length were recorded.
Teleost otoliths provide a pivotal medium for studying changes in population structure and population dynamics of fish. Understanding the otolith-fish size relationship and intraspecies variation in otolith morphology is essential for the accurate assessment and management of fishery resources. In our study, we aimed to estimate the relationships between otolith morphological measurements and fish length, and detect differences in the otolith morphology of planktivorous and benthivorous morphs of Schizopygopsis thermalis in Lake Amdo Tsonak Co on the Qinghai-Tibet Plateau (QTP). Both morphs exhibited strong linear otolith-fish size relationships; otolith morphology was sexually dimorphic in each morph; the morphs differed significantly in otolith shape and size (e.g., posterior side, the region between the posterior and ventral otolith, otolith length, circularity, and surface density). In addition, we found that the differences in otolith morphology between morphs are related to habitat preferences, diet, and growth. Basic data on the biology of S. thermalis are essential for poorly studied Lake Amdo Tsonak Co, and our study emphasizes that intraspecific variation in otolith morphology should be taken into consideration when differentiating stocks, populations, and age classes based on otolith morphology.
Global environmental change has altered biotic interactions in ecosystems. Trophic structure is a major characteristic of ecosystems, and understanding the factors determining trophic structure is thus important for predicting the response of ecological dynamics and ecosystem services to future environmental change. Different kinds of drivers, including ecosystem size, productivity, and disturbance, have been proposed to explain trophic structure variation in various ecosystems. Much remains unknown about how these drivers operate in determining trophic structure and its underlying mechanisms, particularly in shallow lakes. Here, we evaluated the relative importance of ecosystem size, productivity and disturbance in influencing the trophic structure of fish assemblages in 30 subtropical shallow lakes. We determined that (1) ecosystem size, productivity and disturbance had no effect on food chain length; (2) the mean trophic level increased with increasing ecosystem size and productivity, with productivity contributing the most to explaining the variance in mean trophic level; and (3) ecosystem size, productivity, and disturbance, alone or combined, affected the proportion of species at specific trophic levels. These results indicate the potential for systematic discrepancies in the drivers of trophic structure among different systems and highlight that focusing on food chain length alone may not be sufficient in reflecting the variation in trophic status. Thus, changes in the mean trophic level and specific trophic-level guilds must be considered in future lake management practices.
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