Comparison of inshore and offshore fish larval assemblages within the wider Yangtze River estuary (China)

It is hypothesized that fish larvae undertake vertical movements in estuarine waters. To test this hypothesis, a sampling period was selected during times when many spring‐spawning fish reach maximum abundance in coastal waters so that spring and summer variations in larval fish assemblages could be determined in the Yangtze River estuary. Six oceanographic surveys were conducted across the salinity gradient of an inshore (freshwater) and offshore area (brackish intersection) during spring (May) and summer (August) between 2010 and 2012. The fish larval community was dominated by species of Engraulidae, Gobiidae, Champsodontidae and Mugilidae. The pre‐flexion and flexion larval stages of euryhaline marine species, which are dependent on estuaries as nursery areas, were common. The brackish and marine larval assemblage was the most abundant with taxa such as Coilia mystus and Engraulis japonicus accounting for more than 57.3% of the total catch. Spatial differences in the taxonomic composition of larval fish assemblages were evident between the inshore and offshore areas. Additionally, the Yangtze River runoff regulatory functions as affected by the Three Gorges Reservoir operational mode (hydrological alternating operations) showed weak influences on fish and habitat environments. Low salinities from high freshwater inflow limited bay anchovy production in the inshore area.     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

Arms as areas for larval development of migratory fish species in a Neotropical reservoir and the influence of rainfall over abundances

The aim of the present study was to verify the use of the arms of the Itaipu Reservoir as areas of initial development for migratory fish species and to assess the relationship between rainfall and the spawning of migratory fish. Accordingly, fish larvae were collected from five arms of the reservoir from 2009 to 2016 using 0.5 mm plankton nets. Density was standardized as the number of larvae per 10 m³ filtered water, and the captured larval and juvenile specimens were identified at the lowest-possible taxonomic level. The larvae were also classified according to the degree of development and notochord flexion stage: larval vitelline, pre-flexion, flexion and post-flexion. To evaluate the distribution of larval abundance and the developmental stage along the longitudinal gradients of the arms, the data were evaluated using a set of nested linear models, following the AIC and Bayesian information criteria. In addition, an analysis of covariance was performed to investigate the influence of rainfall on the larval abundance of migratory species. During sampling, several species of economic and conservation interest such as Salminus brasiliensis and Pseudoplatystoma corruscans were collected. The larvae of the migratory fish taxa were captured from all sampled arms, which indicate them as areas of initial development. Nevertheless, it was observed that larval density increases from fluvial towards lacustrine zones inside the arms. Also, the present study verified that species, even in lentic environments, respond positively to rainfall stimuli in a manner similar to that exhibited by conspecifics in lotic environments. Such results reinforce the necessity of the protection of arms aiming at the conservation of this main group of species impaired by the construction of dams.     

Fish Communities Associated with Macrophytes in Brazilian Floodplain Lakes

The composition, diversity and similarity of fish communities associated with macrophytes of two oxbow lakes of Mogi-Guaçu River, São Paulo State, Brazil, were evaluated in the wet and dry seasons of 1994–1995. Fish species composition and relative abundance values were similar for both lakes, despite their difference in connection time to the river and the abundance of macrophytes. The fish communities were predominantly composed by small sized species typical of lentic environments (Characidae), juveniles of large non-migratory species (Erythrinidae and Gymnotidae) and a few juveniles of migratory species (Anostomidae and Curimatidae). These lakes are not characterized as nurseries for the young of migratory species and the zooplankton does not have an important role as food in the ontogenetic development of migratory species of fish.     

The effects of exposure in sandy beach surf zones on larval fishes

The influence of wind and wave exposure on larval fish assemblages within a large bay system was investigated. Larval fishes were sampled from two areas with vastly different exposure to waves and wind, namely the windward and leeward sectors of Algoa Bay. In total, 5702 larval fishes were collected using a modified larval seine. Of these, 4391 were collected in the leeward and 1311 in the windward sector of the bay, representing a total of 23 families and 57 species. Dominant fish families included Clinidae, Engraulidae, Kyphosidae, Mugilidae, Soleidae and Sparidae, similar to the situation elsewhere, highlighting continuity in the composition of larval fish assemblages and the utilization of surf zones by a specific group of larval fishes. Nineteen estuary‐associated marine species occurred within the surf zones of Algoa Bay and dominated catches (86·7%) in terms of abundance. Postflexion larvae comprised > 80% of the catch, indicating the importance of the seemingly inhospitable surf zone environment for the early life stages of many fish species. The greatest species diversity was observed within the windward sector of the bay. Distance‐based linear modelling identified wave period as the environmental variable explaining the largest proportion of the significant variation in the larval fish assemblage. The physical disturbance generated by breaking waves could create a suitable environment for fish larvae, sheltered from predators and with an abundance of food resources.     

Structure and diversity of fishes in a freshwater and coastal subtropical lagoon

This study examined the fish communities of Peri Lagoon in southern Brazil to aid in the development of an effective management plan because the area is under threat from human activities. Sampling of fish fauna, ichthyoplankton and limnological data were compared between sites, differing by habitat type and characteristics such as depth, substratum composition and vegetation type. Results were significantly related to site, with the highest diversity and abundance recorded at shallow vegetated sites. A total of 14 fish species were recorded throughout the lagoon, with the most abundant being Hyphessobrycon luetkenii. Of the 14 species, half were sampled at their larval stage, suggesting a healthy and protected system. Significantly more larvae and eggs were collected during colder months (autumn to winter) and at sites closer to stream flow, possibly owing to increased food sources and habitat protection. This study highlights the importance of Peri Lagoon as a nursery ground for a wide range of fish species, providing essential information for incorporation into the future protection of fish stocks throughout Brazil.     

Year-to-year variation in larval fish assemblages of the Southern North Sea

In order to test the temporal stability within and the reproducibility of larval fish assemblages between years, the larval fish assemblage at Helgoland Roads, North Sea (NE Atlantic) was quantitatively sampled almost daily from January 2003 to December 2005. The survey resulted in a total of 462 samples containing 50,632 larval fish of at least 42 taxa. In winter the larval fish assemblage was mainly dominated by larvae emerging from demersal eggs. This changed gradually to larvae hatching from pelagic eggs. Larvae from pelagic eggs dominated the ichthyoplankton assemblage in summer. A remarkably stable seasonality in terms of dominance patterns with recurring, season-specific fish assemblages was observed over the 3 years, despite substantial variation in environmental conditions such as a temperature difference of almost 20°C between summer and winter. The lesser sandeel (Ammodytes marinus), was the only species which showed significant fluctuations in abundance between the years. After removal of this species from the analysis, the dominance patterns of the remaining fish species were almost identical between years.     

Spatial and temporal variation of the ichthyoplankton in a subtropical river in Brazil

Studies that assess reproduction dynamics and ichthyoplankton distributions are scarce for the upper Uruguay River, especially in environments such as tributary mouths. Therefore, this study aimed to evaluate: (i) ichthyoplankton composition; (ii) spatial and temporal variation in ichthyoplankton abundance; and (iii) relationships between environmental variables and the abundance of ichthyoplankton during one annual cycle in this region. Monthly samples were collected from September 2001 to August 2002 in 48 h cycles at 6 h intervals between each sampling. Samples of eggs and larvae were collected from three of the main tributaries of the region (Ligeiro, Palomas and Chapecó rivers) and from three stretches of the Uruguay River near the confluence of these tributaries. Surface samples were collected with a 0.5 mm mesh cylindro-conical net. In general, reproductive seasonality was well-defined between October and February. It was most intense from November to January, when the photoperiod reached its highest values, flow was decreased, and the water temperature was increased. Based on egg and larval distributions, we found that spawning occurred mainly in the Ligeiro and Chapecó tributaries and in the Uruguay/Chapecó section. In contrast, fish spawning in the sites downstream of dams was more restricted. Finally, a difference was observed between the egg and larval distributions of the main river and its tributaries: the greatest reproductive activity in the tributaries occurred during periods of high flow and increased water temperature, while in the main river, more eggs and larvae were observed when the flow decreased and the water temperature increased.     

溪流大小及其空间位置对鱼类群落结构的影响

2008年10月和2009年10月分别对黄山地区阊江流域与青弋江流域1-3级浅水溪流中鱼类群落结构进行了研究,着重探讨了溪流大小及其空间位置对鱼类群落空间分布的影响。研究共捕获35种鱼类,阊江和青弋江分别为26和29种,其Jaccard相似性系数为57.1%;两流域间每样点的物种数差异显著,个体数差异极显著。在溪流级别梯度(1-3级)下,鱼类的物种数和个体数都呈上升的变动趋势,且物种数的变化相对个体数较显著。综合相关分析、逐步多元回归分析与典范相关分析的结果,阊江和青弋江中鱼类物种数的空间变化主要与下游量级相关,而个体数的空间变化主要与水宽相关。因此,阊江和青弋江1-3级浅水溪流中鱼类群落结构的空间分布格局是溪流大小和空间位置的共同作用结果,且溪流大小和空间位置分别决定鱼类的个体数与物种数的空间分布。       

Depth distribution of nearshore temperate fish larval assemblages near rocky substrates

In this study, we compare the composition, abundance and structureof a temperate fish larval assemblage at different depth intervals(0–4, 4–8 and 8–12 m) in the extreme nearshoreenvironment. We used a plankton net attached to an underwaterscooter to sample in close proximity to the rocky substrate(<50 cm). A total of 868 larvae from 27 taxa in 13 familieswere caught. The majority of larvae belonged to benthic reef-associatedspecies (Blenniidae, Gobiidae, Gobiesocidae and Tripterygiidae),the four most abundant comprising 76% of the total larvae caught.A non-metric multidimensional scaling analysis (MDS) showedthat there was a single multispecific larval patch near thesubstrate in the extreme nearshore up to 12 m depth. Nonetheless,distinct larval abundances were found in this relatively smalldepth range, with the majority of species being more abundantat the deepest interval, particularly Pomatoschistus pictusand Gobius xanthocephalus. Tripterygion delaisi was an exceptionbeing more abundant at the shallowest depth as young larvae.The density of pre-flexion larvae was not significantly differentacross depth intervals, but post-flexion larval density increasedwith depth. The full size range (from hatching to settlement)of P. pictus was present at the extreme nearshore. The innovativesampling technique used here revealed high densities of larvaeclose to the bottom, and depth was found to be an importantfactor influencing the distribution of several taxa and ontogeneticstages. The nearshore component of coastal fish larval assemblagesnear rocky substrates has been poorly studied, and our resultssuggest that the high densities of larvae found to aggregatein these environments must be taken into account when studyingdistribution and functional aspects of these assemblages.     

DNA barcoding reveals the temporal community composition of drifting fish eggs in the lower Hongshui River,China

Determining the temporal community composition of fish eggs in particular regions and understanding the reproductive times of regional fish taxa are key aspects of the management and regulation of regional fish stocks. However, it is extremely difficult to accurately identify fish eggs due to the absence of diagnostic morphological characters. We sampled fish eggs in the lower Hongshuihe River (an upper mainstem of the Pearl River) between May and September 2020. We then used DNA barcoding to determine the species composition of the egg pool and to predict the spawning periods of the identified species. A total of 641 eggs and 17 larvae were chosen for molecular identification; 397 eggs and 17 larvae yielded high‐quality barcoding sequences. The high failure rate (~38%) was most likely due to long‐term storage in low concentrations of ethanol prior to molecular analysis. We successfully classified 392 eggs into 10 species and 13 larvae into four species using public databases. Most of the species identified in the egg pool were small and/or benthic, and migratory species were rare. This may partially reflect the adverse effects of hydropower cascade development in this river section. We also found that spawning periods tended to be species‐specific. Our study provides a reference for the conservation and management of regional fishery stocks.     

Oceanographic and lunar forcing affects nearshore larval fish assemblages from temperate rocky reefs

The influence of oceanographic features and moon phases on ichthyoplankton assemblages in a temperate nearshore rocky reef off El Quisco Bay, central Chile, was assessed during austral spring–summer 2015–2016 using Bongo nets. Wind direction was predominantly south-west, and ocean temperature increased gradually during the study period, fluctuating between 11.6°C and 17.7°C. A relatively cold period (from late September to early December, 12.42?±?0.64°C) was distinguished from a relatively warmer phase (from mid-December to February, 13.56?±?1.08°C). Nearshore ichthyoplankton was composed of 13,700 individuals, belonging to 43 taxa. Larval Strangomera bentincki (Clupeidae) were collected in high numbers between late September and late October with peaks during full moon and first quarter (maximum?=?734 ind. 100?m^?3); larval Engraulis ringens (Engraulidae) was most abundant between late October and late December 2015, with peaks during the third quarter and full moon. Principal Component Analysis of ichthyoplankton data explained more than 44% of total variance and showed the influence of cold/warm periods in the structuring of larval fish assemblages. Water temperature had more influence than lunar phase in the structure and composition of nearshore fish larvae off central Chile. We conclude that larval fish assemblages found in nearshore waters change on a seasonal scale by differences in the reproductive activity among species, and that lunar phase exerts a low, but significant effect on the abundance of fish larvae, but this variability is species-specific.     

Life histories of closely related amphidromous and non‐migratory fish species: a trade‐off between egg size and fecundity

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Spatial and Temporal Patterns of Diversity and Distribution of the Upper Juruá River Fish Community (Brazilian Amazon)

We studied spatial and temporal patterns in fish species composition and diversity at the upper Juruá River located in the west Brazilian Amazon. We collected with gillnet 822 fishes belonging to 90 species in the main Juruá River, its tributaries and the floodplain lakes during wet and dry seasons. Fish abundance and species richness were greater in the dry season. During that season, fishes may be concentrated due to the low water level, being caught more easily by gillnets. There has been a trend towards a greater fish biomass caught in lakes. This might be associated with a greater environmental stability as lakes may be less subject to large variations in water level. The fish communities differed between the two seasons and between lakes and the lotic environments (main river and tributaries). Fish species from the family Curimatidae were most abundant in the lakes, while Pimelodus spp. and Hypostomus spp. predominated in the main Juruá River. Seasonal variations in fish communities may be related to differences in the migratory behavior among fish species. Such spatial and temporal patterns influencing fish community structure at the Upper Juruá Extractive Reserve must be accounted for in management and conservation strategies.     

Veligers of the invasive bivalve Limnoperna fortunei in the diet of indigenous fish larvae in a eutrophic subtropical reservoir

Larval fish development depends largely on their ability to capture and ingest food items, and on food availability. In this context, invasive species, eutrophication and river impoundments have complex impacts on fish larvae. Using samples collected in 2005–2009 in the Salto Grande reservoir (Argentina–Uruguay), periodically affected by cyanobacterial blooms, we studied the impact of the larvae of the exotic bivalve Limnoperna fortunei (Dunker, 1857) (Bivalvia) on larval fish diets. Compared with other nearby waterbodies, the abundance of fish larvae was scarcer in the reservoir, especially during algal bloom periods. Only 20% of the larval fish with gut contents fed on L. fortunei veligers. Seven fish taxa (of a total of 12) consumed veligers of L. fortunei, but only two showed a preference for this prey. Taxonomic changes in the larval fish assemblages due to the river's impoundment, and temporal uncoupling between veliger densities (affected by the toxigenic effects of Microcystis spp.) and ichthyoplankton could account for the comparatively low trophic importance of the invasive bivalve's veligers. These results reflect the complexity of interactions brought about when the same invasive species invades different environments, underscoring that the impacts involved depend as much on the invader, as on the regional and ecological settings of the area invaded.     

Variability in the carbon isotope signature of Prochilodus lineatus (Prochilodontidae, Characiformes) a bottom-feeding fish of the Neotropical region

The spatial and seasonal variability of stable carbon isotopes in detritivorous Prochilodus lineatus , primary producers and particulate organic carbon (POC) were examined to promote a better understanding of the trophic dynamics of food webs in Neotropical ecosystems. Spatial variability in carbon isotope composition in the species showed a decreasing gradient in the Upper Paraná River system, from the Paraná River and Itaipu Reservoir subsystems to the Baía and Ivinheima subsystems. Fish δ¹³C followed the isotopic trend of POC along the Paraná River and Baía subsystem. Seasonal differences were not observed in fish. The analysis of percentile contribution of C₃ and C₄ sources in the species diet revealed the predominance of C₃ plants (phytoplanktonic and periphytic algae and riparian vegetation) in most of the analysed subsystems and seasons. Nevertheless, the considerable participation of riparian vegetation was verified, especially in the Ivinheima subsystem in the dry season. C₄ macrophytes presented a maximum contribution along the Upper Paraná River. These results demonstrate the existence of specific variability for the consumer and their food sources in different environments of the same ecosystem.     

Distribution and abundance of larval fish in the northern Aegean Sea--eastern Mediterranean--in relation to early summer oceanographic conditions

Two ichthyoplanktonic surveys were conducted during June 1995and 1996 along the northern Aegean Sea coast with the aim ofdescribing species composition, abundance and distribution patternsof the assemblages of fish larvae and their relationships tooceanographic regimes. The upper water column was generallycooler, fresher and richer in zooplankton during June 1996.The mean abundance of larvae of the small-sized pelagic fish(anchovy and most mesopelagics) was higher in 1996. In contrast,larvae of the middle-sized pelagics (Sardinella aurita, Trachurusmediterraneus, Scomber jaconicus and Auxis rochei) were moreabundant in 1995. The eastern part of the surveyed area (NEAegean Sea) was colder and less saline during both years becauseof the influence of Black Sea and riverine waters. In the colderJune 1996, larvae of many ‘summer spawners', e.g., themiddle-sized pelagics, were present infrequently and at verylow numbers in the NE Aegean Sea. Cluster analysis using theBray–Curtis similarity index revealed well-defined groupsof stations and assemblages of larvae. Ordination scores derivedfrom non-metric multidimensional scaling were compared by multipleregression with various parameters and the analysis showed thattaxonomic composition and abundance was primarily explainedby bathymetry. In the cooler June 1996, a significant amountof variation in ordination scores was related to longitudinaldifferences in temperature, salinity and the width of the continentalshelf. The membership of station and species groups definedby the cluster analysis differed between 1995 and 1996 and reflectedinterannual differences in the distribution and abundance ofcomponent species. Spatial and temporal spawning patterns ofadults played the key role in the formation of assemblages ofearly larvae.     

The role of relatedness in structuring the social network of a wild guppy population

Parasite avoidance is increasingly considered to be a potential driving factor in animal migrations. In many marine and freshwater benthic fish, migration into a pelagic environment by developing larvae is a common life history trait that could reduce exposure to parasites during a critical window of developmental susceptibility. We tested this hypothesis on congeneric fish (family Galaxiidae, genus Galaxias) belonging to a closely related species complex sampled from coastal streams in southeastern New Zealand. Migratory Galaxias have larvae that migrate to pelagic marine environments, whereas the larvae of non-migratory species rear close to adult habitats with no pelagic larval phase. Both migratory and non-migratory fish are hosts to two species of skin-penetrating trematodes that cause spinal malformations and high mortality in young fish. Using generalized linear models within an Akaike information criterion and model averaging framework, we compared infection levels between migratory and non-migratory fish while taking into account body size and several other local factors likely to influence infection levels. For one trematode species, we found a significant effect of migration: for any given body length, migratory fish harboured fewer parasites than non-migratory fish. Also, no parasites of any kind were found in juvenile migratory fish sampled in spring shortly after their return to stream habitats. Our results demonstrate that migration spares juvenile fish from the debilitating parasites to which they would be exposed in adult stream habitats. Therefore, either the historical adoption of a migratory strategy in some Galaxias was an adaptation against parasitism, or it evolved for other reasons and now provides protection from infection as a coincidental side-effect.     

Distribution and abundance of fish larvae in the northern Ionian Sea (Eastern Mediterranean)

The purpose of this paper was to study the spatial distribution, abundance and composition of fish larvae in the northern Ionian Sea. Samples were collected to the 600 m depth with an electronic multinet BIONESS during the “INTERREG Italia-Grecia” oceanographic cruise carried out in March 2000 off the Apulian Italian coast. A total of 46 species of teleost early stages were collected, belonging to 38 genera and 22 families. Over 52% of the larvae identified were mesopelagic species, almost 27% were demersal and about 21% pelagic. A total of 307 myctophids, 69 clupeids and 61 gadid post-larvae dominated the community. Benthosema glaciale (mean 6.1 mm SL) was the most abundant species (21.6%), the most frequent in the samples (28.8%), and dominant in the whole study area (mean 1.4 ind/100 m³). Particular attention was given to the horizontal and vertical distribution and abundance of the three dominant post-larval species: Benthosema glaciale, Sprattus sprattus sprattus and Notoscopelus elongatus. The Pearson coefficient (R = 0.734) showed a high correlation between total zooplankton and fish larval assemblages in terms of spatial distribution abundance values. Regarding the vertical distribution of fish larvae, Sorensen’s index (S = 0.69) showed that fish larvae and total zooplankton abundance peaks co-occurred along the water column.