The effect of the cleaner fish Labroides dimidiatus on the capsalid monogenean Benedenia lolo parasite of the labrid fish Hemigymnus melapterus

The cleaner fish Labroides dimidiatus affected the pigmented monogenean parasite Benedenia lolo on the fish Hemigymnus melapterus (Labridae) held in aquaria. The effect of cleaner fish varied with the size class of fish; only small fish [ a posteriori size class <11.5 cm standard length ( L _S)] exposed to cleaner fish had fewer monogeneans compared with fish not exposed to cleaner fish. The abundance of monogeneans on large fish ( a posteriori size class <11.5 cm L _S) was not affected by cleaner fish. The size-frequency distributions of monogeneans on both size-classes of H. melapterus were affected by cleaner fish. Fish exposed to cleaner fish had fewer large (>3 mm) and more small (<1 mm) monogeneans than fish not exposed to cleaner fish, suggesting cleaner fish selectively removed larger monogeneans. This difference was more pronounced on large fish. In the absence of cleaner fish, small fish had almost as many monogeneans as large fish; they also had more small monogeneans than the large fish, suggesting small fish were more vulnerable to infection by monogeneans than larger fish. This suggests that the cleaner fish L. dimidiatus has the potential to control benedeniine monogeneans on captive fish and highlights the importance of taking into account fish size in studies of the effect of cleaner fish on ectoparasites.     

Research on the Swing of the Body of Two-Joint Robot Fish

The disadvantages caused by the swing of a fish body were analyzed. The coordinate system of a two-joint robot fish was built. The hydrodynamic analysis of robot fish was developed. The dynamic simulation of a two-joint robot fish was carried out with the ADAMS software. The relationship between the swing of fish body and the mass distribution of robot fish, the relationship between the swing of fish body and the swing frequency of tail, were gained. The impact of the swing of fish body on the kinematic parameters of tail fin was analyzed. Three methods to restrain the swing of fish body were presented and discussed.     

Effect of the removal of cleaner fish on the abundance and species composition of reef fish

The ecological significance of cleaner fish on coral reefs was investigated. I removed all cleaner fish, Labroides dimidiatus, from eight small reefs, measured the subsequent effect on the abundance and species composition of all reef fish after 3 and 6 months, and compared it with eight control reefs with cleaner fish. The removal of cleaner fish had no detectable effect on the total abundance of fish on reefs and the total number of fish species at both times. Multivariate analysis by non-metric multidimensional scaling and ANOSIM pairwise tests based on 191 fish species revealed no effect of cleaners on the community structure of fish. Similar results were obtained using principal components analysis on subsets of the data using the 33 most common fish species and the 15 most abundant species (≥5 individuals per reef ) with both log10 (x + 1) transformed data and with fish numbers standardized for abundance. This study demonstrates that the removal of cleaner fish for 6 months did not result in fish suffering increased mortality nor in fish leaving reefs to seek cleaning elsewhere. Received: 28 October 1996 / Accepted: 7 February 1997     

塔里木盆地鱼类入侵及区系演变趋势

鱼类入侵是塔里木盆地土著鱼类濒危的关键性影响因素之一,结合历史文献数据及近年调查数据,系统综述了塔里木盆地鱼类入侵现状,并就鱼类入侵引起的鱼类区系均一化问题进行了分析。结果显示,该地区记录鱼类63种,其中土著种19种,入侵种44种。尽管入侵鱼类提升了塔里木盆地鱼类群落属级及科级的多样性水平,但相应的G-F多样性指数却明显下降,表明该区鱼类群落从物种组成简单、分化明显的特点演变为物种成分复杂、分化贫乏的特点。入侵种中源于长江和额尔齐斯河分别有30种(68.2%)和7种(15.9%),源于美欧和亚洲其他区域的有7种(15.9%)。入侵鱼类的进入引起塔里木盆地与其相关区域鱼类区系相似性显著上升(P0.01),并导致该区鱼类区系从单一的中亚高原山区复合体演变为多区系混合体。进一步利用鱼类个体生态矩阵分析方法研究显示,外来种在塔里木盆地适应性广泛,能够占据水域各种栖息生境,显著压缩了土著种的栖息空间,进而通过捕食、食物竞争及其他作用途径严重危及土著鱼类种群的续存,提示须采取有力措施限制入侵种的进一步扩散及对濒危土著物种迅速开展人工保育工作。     

Mathematical analysis of the stimulus for the lateral line organ

Behavioral studies have shown that a blind fish is capable of detecting and recognizing stationary objects in its surroundings. It is proposed that the displacement of water caused by the fish as it moves is the basis for this detection capability. Alterations in the displacement of water around the fish, caused by the obstacle, act as stimuli for the lateral line organ. The question of how these stimuli acting on the skin of the fish, image the environment and what information is thus made available to the fish is the concern of this paper. The stimuli for the lateral line organ are derived mathematically. Two cases are treated: that of a fish gliding past an obstacle and that of one approaching an obstacle.     

Do parasites affect the behavior of the Hawaiian white-spotted toby, Canthigaster jactator (Pisces)?

This study observed differences in behavior associated with parasites in the fish Canthigaster jactator. These fish were observed both within Kaneohe Bay, Oahu, Hawaii, and just outside the bay. Normal (unparasitized) fish behaved similarly to their congeners. Behavior varied by size class and presumed sex. Larger fish (males) patrolled territories and courted medium-sized fish (females), which freely crossed male territories. Smaller fish appeared to be immature and remained in limited home ranges on the edge of male territories. All fish parasitized with a philometrid nematode acted most like immature ”normal” fish, with limited home ranges and few social interactions. However, parasitized fish ate at twice the rate of unparasitized fish. All fish collected from the bay contained some parasites, and none were sexually mature, whereas no parasites were found in fish from outside the bay. These data suggest that parasites affect the behavior of C. jactator. Moreover, parasites may limit the sexual maturation of their hosts.     

Native fish entrapment in irrigation systems: A step towards understanding the significance of the problem

Summary   The Australian irrigation industry diverts significant volumes of water from our rivers, and as such, may also divert and entrain riverine fish. Although it is widely acknowledged that our native fish fauna have been greatly affected by a variety of anthropogenic changes, little is known about the extent or significance of fish entrainment in irrigation systems. This paper presents results from a preliminary investigation into the diversion of fish into irrigation channels undertaken in the Goulburn-Murray Irrigation Network, Victoria, Australia. The case study and our knowledge of the life-history strategies of the Basin's fish fauna suggest that the loss of native fish into irrigation networks may be a substantial problem, which, up until recently, has been largely ignored. We strongly suggest that the impact of diversions on native fish populations requires urgent further investigation and quantification, through the cooperation of water management authorities and fish biologists.     

Modification of the response to high density conditions in the guppy, Poecilia reticulata (Peters)

An examination was made of some of the factors which influence the response to density in the guppy. Water from high density fish was given to fish populations kept at high and low densities. This induced high density behaviour in low density fish by increasing aggression and decreasing courtship. But giving 'fresh' water to high density fish failed to alleviate the response to density. 'High density water' slightly reduced the numbers of young found in low density groups. High density fish kept in the dark had more young than high density groups in the light; and the number of young found was decreased when 'high density water' was given to low density fish. The number of ovarian stages was decreased in the dark in high density and was not overridden by the type of water. Giving 'high density water' to low density fish decreased the number of oocytes stage III, but the interaction between water and 'light' was confounded by the total numbers of ovarian stages. Increasing the 'visual space' of high density fish with mirrors partially decreased aggression and increased courtship and number of young found; but had little affect upon the number of ovarian stages. Decreasing the number of physical contacts by keeping the fish chronically tranquillized reduced the activity of the fish. This reduced the aggression of the high density fish and also reduced the differences between the high and low density fish on the basis of their courtship scores, number of young found and number of stages in the ovary. Fish from differing population sizes were given a choice between varying fish densities. The fish from a 'normal' sized population and with an extended visual field, tended to make a choice conforming to the overall selections compared with fish from populations of extreme size and with a reduced visual field.     

Some differences in the parasitic fauna of three samples of plaice (Pleuronectesplatessa L.) from the southern North Sea

Plaice ( Pleuronectesplatessa L.) from three spawning areas in the southern North Sea were examined for six species of metazoan parasite. Differences of both incidence and level of infestation with particular parasite species were found in fish from the three areas. Neither the incidence nor the level of infestation was associated with the length of fish in the samples except in the case of the larger male fish from Flamborough, which tended to contain more larval nematodes (Anisakidae). All fish contained the intestinal nematode Cucullanus heterochrous , although fewer were found in fish from Flamborough. Southern Bight fish were more likely to contain Capillaria wickinsi than were fish from Flamborough or the German Bight. Flamborough fish were more likely to contain Anisakidae larvae than were fish from the other two areas. Fish from the three areas were similarly infested with Zoogonoides viviparus. Male fish from Flamborough were less likely to be infested with Lepeophtheirus pectoralis than male fish from the German Bight.     

Changes in the lower trophic levels as a consequence of the level of fish manipulation in the ponds

Cyprinid fish of different mature age classes (3+ -4+) and stocks (100, 300 and 500 kg/ha) were introduced into each of three experimental ponds with area of 0.3 ha (average depth ca 1.7 m) while the fourth pond was left free of fish. Bream (Abramis brama L.), white bream (Blicca bjoerkna L.) and roach (Rutilus rutilus L.) made up 75% of the total cyprinid biomass, with wild carp (Cyprinus carpio L.) as the remaining 25%. The introduced fish spawned successfully. The high (above 300 kg/ha) planktivorous and benthivorous fish stocks resulted in several qualitative and quantitative alterations of the food chain structure in our simulation pond experiments. These alterations must primarily be assigned to changes caused by both the zooplanktivory and benthivory nature of the stocked fish populations. At the higher levels of fish biomass, Secchi depth was influenced significantly by chlorophyll-a concentration. Most of the variance in suspended solids concentration could be explained by the biomass ratio of the mature benthivorous fish. There was a clear shift in algal cell size in the ponds with the higher fish stocks: ponds with more fish had larger cells later in the summer. The relative influence of young cyprinid fish on crustaceans species composition and biomass, and mature populations on benthic fauna abundance and biomass, was sufficiently greater at higher (300–500 kg/ha) fish stock rates.     

Insights into the concept of fish welfare

Fish welfare issues are predicated on understanding whether fish are sentient beings. Therefore, we analyzed the logic of the methodologies used for studying this attribute. We conclude that empirical science is unable to prove or to disprove that fish are sentient beings. Thus, we propose a combined ethical-scientific approach for considering fish as sentient beings. The most difficult ongoing question is to determine which conditions fish prefer. Approaches to assess fish preferences should be rigorously and cautiously employed. In light of these considerations, attempts to establish physiological standards for fish welfare are discouraged, and a preference-based definition of fish welfare is proposed.     

Distribution of fish in the complex of floodplain-riverbed biotopes of the Irtysh

Distribution, composition, and movements of fish within the floodplain-riverbed complex of the Lower Irtysh are investigated. The principal working tools were hydroacoustic computerized complexes for the detection of fish aggregations and of their movements in the floodplain water course. Twenty-four-hour hydroacoustic observations revealed the predominantly crepuscular-nocturnal type of activity of most fish and the mass downstream migration of juveniles at the onset of the night. Seasonal traits of formation of fish aggregations on key biotopes of the Irtysh are revealed, and their biological harmony is shown. The necessity that fish distribution should be analyzed as a dynamic phenomenon is shown.     

Histological observation of the urogenital papillae in the bi-directional sex-changing gobiid fish, Trimma okinawae

The gobiid fish Trimma okinawae changes its sex bi-directionally according to its social status. Morphological changes in the urinogenital papillae (UGP) of this fish have been reported during sex change. However, there have been no detailed observations of such changes. Here, we histologically examined the UGP structure of male- and female-phase fish. UGPs of fish in female and male phase contained both oviducts and sperm ducts. Both ducts were coalesced into one duct within the posterior region of the UGP. Female-phase fish had many longitudinal folds in the hypertrophied tunica mucosa of the oviduct, which was found to be responsible for the transport of eggs and the removal of follicular cells from the oocyte. In contrast, male-phase fish had an immature oviduct and a mature sperm duct in the UGP. In the male-phase fish, the co-existence of spermatozoa and fibrillar secretions was observed in the sperm duct during spermiation.     

Distribution of fishes in the floodplain-channel complex of the lower reaches of the Irtysh River

The composition of fish, their location and movements in the channel, channel depressions, and flood waters of the lower reaches of the Irtysh River are investigated. This study is conducted with computer sonar systems used for different purposes. Diurnal and seasonal dynamics of movements of the fish and the abundance and composition of fish aggregations are revealed in the studied sites. The biological unity of the fish community of the floodplain-channel complex is demonstrated.     

Biological significance of the Gornoslinkinskaya Riverbed Depression in the Irtysh

Distribution of fish in the Gornoslinkinskaya Riverbed Depression in the Irtysh is considered in relation to the time of day and to the season. Fish aggregations are characterized quantitatively and by their size and species composition. The major part of the fish population of the depression consists of fish juveniles. The biological significance of the riverbed depression is polyfunctional. The universal traits of the ecosystems of large river basins and mechanisms of their occupation by fish are discussed.     

Spatiotemporal patterns of the fish assemblages downstream of the Gezhouba Dam on the Yangtze River

An explicit demonstration of the changes in fish assemblages is required to reveal the influence of damming on fish species. However, information from which to draw general conclusions regarding changes in fish assemblages is insufficient because of the limitations of available approaches. We used a combination of acoustic surveys, gillnet sampling, and geostatistical simulations to document the spatiotemporal variations in the fish assemblages downstream of the Gezhouba Dam, before and after the third impoundment of Three Gorges Reservoir (TGR). To conduct a hydroacoustic identification of individual species, we matched the size distributions of the fishes captured by gillnet with those of the acoustic surveys. An optimum threshold of target strength of ?50 dB re 1 m² was defined, and acoustic surveys were purposefully extended to the selected fish assemblages (i.e., endemic Coreius species) that was acquired by the size and species selectivity of the gillnet sampling. The relative proportion of fish species in acoustic surveys was allocated based on the composition (%) of the harvest in the gillnet surveys. Geostatistical simulations were likewise used to generate spatial patterns of fish distribution, and to determine the absolute abundance of the selected fish assemblages. We observed both the species composition and the spatial distribution of the selected fish assemblages changed significantly after implementation of new flow regulation in the TGR, wherein an immediate sharp population decline in the Coreius occurred. Our results strongly suggested that the new flow regulation in the TGR impoundment adversely affected downstream fish species, particularly the endemic Coreius species. To determine the factors responsible for the decline, we associated the variation in the fish assemblage patterns with changes in the environment and determined that substrate erosion resulting from trapping practices in the TGR likely played a key role.     

Effects of damming on the biological integrity of fish assemblages in the middle Lancang-Mekong River basin

The Lancang-Mekong River basin contains a diverse assemblage of freshwater fish species; however, their populations are threatened by current and planned dam construction along the river. Fish assemblages are sensitive indicators of environmental degradation and can be used to assess aquatic ecosystem health. This research compared the fish fauna at the Xiaowan hydropower dam located on the middle reaches of the Lancang-Mekong River at three time periods: in 2008 (before impoundment), 2010 (water storage) and 2011 (full operation). A modified fish index of biological integrity (modified F-IBI) was developed and it synthesized information on the taxonomic composition, trophic guilds, and tolerance levels of the fish and habitat diversity to quantitatively assess the condition of fish populations before and after damming. This index also was used to assess the longitudinal diversity of the fish fauna along the river channel and could assess the barrier effect associated with the dam. Jaccard's index of similarity was used as a feasible tool to assess fish diversity loss and biotic homogenization. The analysis clearly showed a homogenization of the fish communities after damming, and the reservoir impoundment region showed much more serious homogenization than the downstream region. The Xiaowan dam had an immediate and profound effect on the fish fauna in this region of the Lancang-Mekong River. A total of eight cascading dams are planned for development in this region, and, unless conservation mitigation efforts are considered, the results could be devastating on the native fish populations of middle reaches of the Lancang-Mekong River basin.     

Foraminifera in the diet of coral reef fish from the lagoon of New Caledonia: Predation, digestion, dispersion

Marine benthic Foraminifera are abundant and thus represent a potential food source for fish. Previous studies of Foraminifera in fish diets have examined only small samples, with significant input reported only for a single surface-feeding species of fish. The present study is the first based on a significant sample (247 fish belonging to 83 species, 291 species of Foraminifera identified from more than 20,000 specimens examined). It provides new information on the contribution of Foraminifera to fish diets, and on the impact of fish predation on Foraminifera. The planktonic Tretomphalus phases, selectively ingested by Pomacentrus amboinensis, were the only significant nutritional input from Foraminifera. Herbivorous fish accidentally ingested living epiphytic Foraminifera, which were still living after digestion, and were defecated, with a significant effect on their dispersion. Carnivorous fish ingested a small number of tests, which were generally altered by the acidic phase of digestion and had no impact on foraminiferal assemblages. Sediment feeders ingested large quantities of empty tests that were released elsewhere, suggesting a possible bias in paleontological interpretations by mixing the thanatocoenoses. Observations on gut contents showed that the fish sometimes fed on a wide range of food, changing with food availability and individual preferences of fish.     

黄河兰州段鱼类多样性与保护

兰州市是黄河唯一穿城而过的省会城市, 是黄河流域综合治理与高质量发展的重要区域, 了解其鱼类多样性现状及变化趋势对黄河流域水生态保护尤为重要。本文于2020年7-10月对黄河干流兰州段及其4条支流(庄浪河、大通河、湟水河和宛川河)开展了鱼类多样性、分布及影响因素调查, 以Shannon-Wiener多样性指数、Pielou均匀度指数、Simpson优势度指数、Cody和Routledge指数、Bray-Curtis相异性系数对黄河兰州段5条河流鱼类群落进行评估, 同时通过相对多度(relative abundance, RA)判定优势种, 利用非度量多维标度排序(non-metric multidimensional scaling, NMDS)展示物种空间分布格局。本次调查获得鱼类20种, 隶属于4目6科15属。其中, 国家II级重点保护野生动物1种, 受威胁鱼类4种, 中国特有鱼类7种, 黄河特有鱼类4种。区系组成属青藏高原区高原西北亚区, 其中鲤形目种类占绝对优势, 优势种为东方高原鳅(Triplophysa orientalis)、粗壮高原鳅(T. robusta)、鲫(Carassius auratus)和麦穗鱼(Pseudorasbora parva)。庄浪河和黄河干流的α多样性较高。β多样性分析结果表明, 黄河干流与庄浪河、大通河、湟水河和宛川河间的鱼类物种明显不相似; 大通河与湟水河之间以及黄河干流与宛川河之间的鱼类物种组成相似性较高。NMDS分析表明, 黄河兰州段鱼类被划分为地理空间上相近的4个地理群。水利设施建设、外来物种和水体污染可能影响了黄河兰州段鱼类多样性和分布。本研究为黄河兰州段鱼类多样性保护和科学管理以及黄河流域生态保护和高质量发展提供了基础调查数据。     

澜沧江-湄公河中上游淡水鱼类多样性

澜沧江-湄公河是东南亚最大的河流, 也是世界上淡水生物多样性最高的三大河流之一。由于特殊的地理位置和国际河流属性, 澜沧江-湄公河淡水鱼类的多样性现状仍缺乏系统的认识。本文在近20年调查的基础上, 系统整理了澜沧江-湄公河中上游32个支流或亚流域的淡水鱼类物种名录, 在此基础上对其种类组成和分布进行了分析, 并利用分类学多样性指数对澜沧江-湄公河中上游流域的物种多样性进行了评估。结果表明, 澜沧江-湄公河中上游共记录了淡水鱼类745种, 分属于2纲17目63科229属, 其中鲤形目鱼类451种, 占物种数的60.5%。分类学多样性指数显示, 从源头到中游, 淡水鱼类在分类阶元上的分布越来越均匀, 亲缘关系越来越远, 分类多样性越来越高。聚类分析(cluster analysis, CA)和多维尺度分析(multi-dimensional scaling, MDS)表明, 当Jaccard相似性系数为8.69时, 澜沧江-湄公河中上游32个亚流域可以分为源区、上游和中游3组; 相似性分析(ANOSIM)结果显示, 各组之间淡水鱼类组成差异显著(R = 0.877, P = 0.001)。相似性百分比分析(similarity percentage analysis, SIMPER)结果表明, 导致3组差异性的鱼类主要是鲤形目和鲇形目鱼类, 且随着地势阶梯的升高出现了科级、属级类群的替代。近几十年来, 随着流域各国人口的增长和经济的快速发展, 澜沧江-湄公河鱼类多样性和渔业资源面临严重威胁, 未来需加强流域内国家间合作, 在流域尺度上制定科学保护计划。