Modeling ecosystem impacts of the invasive Japanese smelt Hypomesus nipponensis in Lake Erhai,southwestern China

Introductions or alien species invasions will induce changes in aquatic ecosystems but are rarely reported in Chinese highland lakes. The Japanese smelt (Hypomesus nipponensis) invaded and has become a dominant fish species in Lake Erhai, a highland lake in southwestern China, since 2016. Here, we engineered Ecopath models for two different periods, 2008–2009 (preinvasion) and 2016–2018 (postinvasion), in Lake Erhai to model ecosystem impacts from the Japanese smelt invasion. In the dynamic Ecosim model based on the 2016–2018 Ecopath model, we ran three 50-year scenarios to simulate the potential effects of Japanese smelts on the system. Our results showed competition between invasive and native species as well as changes in trophic structures, highlighting the impacts of the invasive species over time. The lake ecosystem additionally experienced significant degradation after invasion, mainly reflected in several related indicators, such as total biomass/total system throughput (TB/TST), total primary production/total biomass (TPP/TB), total primary production/total respiration (TPP/TR), Finn's mean path length (FML), Finn's cycling index (FCI) and the Connectance Index (CI). The simulation results indicated that the relative biomass of icefish (Neosalanx taihuensis), bighead carp (Hypophthalmichthys nobilis), sharpbelly (Hemiculter leucisculus), and zooplankton were significantly affected by increasing the strength of the top-down control of the Japanese smelt on its prey. It is also important to do ecological regulation of planktivorous fishes in the studied Lake Erhai, especially the Japanese smelt.     

Analyses of growth processes of pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, through the use of daily otolith increments

It has been reported that pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan, appear in small and large size groups during spawning despite being an annual fish. It is hypothesized that pond smelt have a bimodal life history, anadromous for large size groups and resident in the lake for small size groups. We calculated the body length and growth rate of the small and large size groups through the use of daily otolith increments and compared growth parameters between groups. In addition, the growth processes of resident fish in Lake Ogawara and anadromous fish in the adjacent sea were examined and compared with small and large size groups, respectively. We found that the two size groups diverged after 40–50 days from hatching with significant size groups present after 50 days. Through otolith increment analysis the growth processes of the small and large size groups were correlated with resident and anadromous forms respectively. These results revealed the utility of otolith increment analyses to clarify population structure of this species.     

Type II antifreeze protein from a mid-latitude freshwater fish,Japanese smelt (Hypomesus nipponensis)

A lot of reports of antifreeze protein (AFP) from fish have been published, but no report has mentioned of commercialized mid-latitude fresh water fish which producing AFP in its body fluid. We found that the AFP in the body fluid of Japanese smelt (Hypomesus nipponensis) from mid-latitude fresh water was purified and characterized. The N-terminal amino acid sequence of the Japanese smelt AFP was 75.0% identical to Type II AFP from herring. Results of EDTA treatment and ruthenium red staining suggested that the Japanese smelt AFP had at least one Ca2+-binding domain. Interestingly, the antifreeze activity of the Japanese smelt AFP did not completely disappear when Ca2+ ions were removed. The molecular mass of the Japanese smelt AFP was calculated to be 16,756.8 by the TOF-mass analysis. The Open reading flame of the gene coding for the Japanese smelt AFP was 444 bp long and was 85.0% identical with the entire herring AFP gene. The cDNA and amino acid sequence of the Japanese smelt AFP were the same length as those of herring AFP.     

TaqMan assays for the genetic identification of delta smelt (Hypomesus transpacificus) and wakasagi smelt (Hypomesus nipponensis)

We have developed species-specific TaqMan assays for two California fish species, the threatened delta smelt (Hypomesus transpacificus) and the introduced wakasagi smelt (Hypomesus nipponensis). The assays are capable of correctly identifying each species with 100% accuracy, with no cross-species amplification. We anticipate these assays will prove useful for future scientific studies requiring genetic species identification (e.g. predation of smelt) or monitoring (e.g. detection of delta smelt near water diversions).     

Migration flexibility between freshwater and marine habitats of the pond smelt Hypomesus nipponensis

The life histories of the pond smelt Hypomesus nipponensis collected from Japanese fresh waters and brackish (sea) waters were studied by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The pond smelt living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith, averaging 1·2–1·3 × 10⁻³. These samples were identified as a standard freshwater type. In contrast, fish collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated along the growth phase. In addition to the two representative life‐history types of H. nipponensis , i. e . freshwater and anadromous life‐history types, other pond smelts were found to have an estuarine resident life history‐type with no freshwater phase, indicating that the pond smelt has a flexible migration strategy with a high degree of behavioural plasticity and an ability to utilize the full range of salinity in its life history.     

Spawning ecology of Japanese surf smelt, Hypomesus pretiosus japonicus (Osmeridae), in Otsuchi Bay, northeastern Japan

The spawning habits of Japanese surf smelt, Hypomesus pretiosus japonicus (Japanese name chika), were studied from 1992 to 1995 at Akaiso Beach in Otsuchi Bay off the Pacific coast of northern Honshu. Investigations were conducted in relation to time, tidal rhythm, sand grain size on the spawning ground, and sex and age of spawners. Spawning occurred from late March to early May with its peak at the spring tide period during full moon in April. Before dark, fish gathered to school from 1–3 m depth, and 10–20 m off the shoreline of the spawning beach. Just before dark, they repeatedly approached the shoreline and stayed near the shoreline to spawn just after dark. In the spawning process, three intervals, i.e. aggregation, approach, and spawning, were recognized and these intervals are thought to be functionally connected. Mating occurred in a unit or group formed by one female and several males. During 1992–1995, except for 1994, spawning took place in a restricted region of the beach where backwash was stronger than other areas, and most sand grains were more than 1 mm in diameter and coarser than those of other areas. Although spawning was observed near the shoreline (34 to 120 cm tide level), most of the eggs were dispersed by backwash and each became attached to a few sand grains close to a step formed at 1–2 m depth off the spawning site. Spawners were composed mainly of age 0+ fish and some 1+ fish. Males usually outnumbered females on the spawning ground. Their spawning styles are discussed in relation to their ecology and habitat.     

Comparative environmental tolerances of threatened delta smelt (Hypomesus transpacificus) and introduced wakasagi (H. nipponensis) in an altered California estuary

In California’s Sacramento-San Joaquin estuary, environmental protection and habitat restoration efforts directed at a threatened native osmerid, the delta smelt (Hypomesus transpacificus), are complicated by the presence of a morphologically similar non-native congener, the wakasagi (H. nipponensis), transported to the estuary from upstream reservoirs. In order to better define delta smelt critical habitat and to evaluate the potential for habitat overlap by these two species, we compared the tolerances of the two species to temperature, salinity, and water velocity, environmental factors that vary spatially and temporally within the estuary. For fishes acclimated to 17°C and fresh water (0 ppt), we measured critical thermal maxima and minima, chronic upper salinity tolerance limits, and critical swimming velocities. Wakasagi had higher critical thermal maxima (29.1°C vs. 25.4°C for delta smelt), lower critical thermal minima (2.3°C vs. 7.5°C for delta smelt), higher upper salinity tolerances (26.8 ppt vs. 19.1 ppt for delta smelt), and swam faster (for 6–6.9 cm SL fish, 43.3 cm s^–1 vs. 28.2 cm s^–1 for delta smelt) than delta smelt. This suggests that the wide seasonal and year-to-year fluctuations in temperature, salinity, and flow typical in the estuary would not exclude wakasagi, although their eggs and larvae may be less tolerant. With respect to these factors, the native delta smelt may be at a physiological disadvantage, particularly in habitats with suboptimal environmental conditions, and may be excluded from shallow-water habitat restoration sites, which are characterized by poor circulation, low flows, and more environmentally extreme conditions. The low abundance of wakasagi in the estuary recorded to date may indicate that factors other than temperature, salinity, and flow determine wakasagi distribution. Received: 25 August 1999 / Accepted: 22 November 1999     

Characterization of 24 microsatellite loci in delta smelt, Hypomesus transpacificus, and their cross-species amplification in two other smelt species of the Osmeridae family

We characterized 24 polymorphic tetranucleotide microsatellite loci for delta smelt (Hypomesus transpacificus) endemic to the San Francisco Bay Estuary, CA, USA. Screening of samples (n = 30) yielded two to 26 alleles per locus with observed levels of heterozygosity ranging from 0.17 to 1.0. Only one locus deviated from Hardy–Weinberg equilibrium, suggesting these individuals originate from a single panmictic population. Linkage disequilibrium was found in two pairs of loci after excluding the locus out of Hardy–Weinberg equilibrium. Twenty‐two primer pairs cross‐amplified in wakasagi smelt (Hypomesus nipponensis), and 15 primer pairs cross‐amplified in longfin smelt (Spirinchus thaleichthys).     

Analysis of the mitochondrial DNA variation in pond smelt Hypomesus olidus (Osmeridae)

Pond smelt Hypomesus olidus (Pallas, 1814), one of the five species of the genus Hypomesus, family Osmeridae, was examined for intraspecific variation of the mitochondrial DNA cytb (1062 bp) and COI (567 bp) genes. Among the ten single substitutions discovered, only one, leading to the substitution of isoleucine by valine, was nonsynonymous, while the remaining substitutions were synonymous. The degree of genetic divergence among pooled nucleotide sequences in H. olidus populations examined constituted 0.4% on average, ranging from 0.2 to 0.6%. These values were not higher than the levels of divergence between the individuals within the populations. Phylogenetic analysis of the populations examined did not reveal their subdivision depending of their geographic location, and pointed to the absence of intraspecific differentiation of the species.     

Retinal ganglion cell topography and spatial resolution in the smelt Hypomesus japonicus (Brevoort, 1856)

The present study deals with the topography of retinal ganglion cells (GCs) and spatial resolution in the smelt Hypomesus japonicus. The eyes and retinae were examined by light microscopy and computerized tomography. DAPI labelling was used to visualize cell nuclei in the ganglion cell and inner plexiform layers. Two zones of increased GC density in the nasal and temporal retina were bridged by a horizontal streak with the GC density ranging from 5600 to 8000 cells/mm². The maximum cell density (area retinae temporalis) ranged from 9492 to 14,112 cells/mm², and the total number of GCs varied from 286 x 10³ to 326 x 10³ cells in three individuals. The theoretical anatomical spatial resolution (the anatomical estimate of the upper limit of visual acuity) was minimum in the ventral periphery (smaller fish, 1.43 cpd; larger fish, 1.37 cpd) and maximum in area retinae temporalis (smaller fish, 2.83 cpd; larger fish, 2.41 cpd). The relatively high density of GCs and presence of the horizontal streak and area retinae temporalis in the H. japonicus are consistent with its highly visual behaviour. The present findings contribute to better understanding of the factors affecting the topography of retinal ganglion cells and mechanisms of visual adaptation in fish.     

Virus-associated spawning papillomatosis in smelt, Osmerus eperlanus L., in the River Thames

Smelt were collected from the R. Thames, at Lots Road Power Station, Fulham between October 1989 to June 1990. Smooth, white, ovoid tumours were observed on the fins of smelt during their anadromous spring migration and recognized as a form of spawning papillomatosis. Papillomatous fish constituted about 21% of the population in March and about 19% in April but were not present in any other samples. Up to 13 tumours were found on a single fish. Papilloma prevalence and intensity were both raised in larger fish. Ultrastructural examination revealed that a high proportion of tumour cells contained virus particles with herpesvirus group characteristics. Epithelial cells of fins without tumours revealed no such virus particles. Evidence of the herpesvirus as a likely aetiological agent of spawning papillomatosis is discussed.     

A pilot study of the performance of captive-reared delta smelt Hypomesus transpacificus in a semi-natural environment

A captive breeding programme was developed in 2008 for delta smelt Hypomesus transpacificus in reaction to dramatic population decline over several decades. We took 526 sub-adult captive-reared delta smelt and cultured them for 200 days without providing artificial food or water quality management to assess their performance once released in the wild. The results indicated captive-reared sub-adult delta smelt could survive in a semi-natural environment with uncontrolled water quality and naturally produced wild prey through spawning and into their post spawning phase.     

武湖日本沼虾繁殖生物学研究

武湖日本沼虾产卵场位于全湖沿岸带．越冬虾主要繁殖期为春夏季(4月中旬～7月中旬,水温20．5～31℃)。当年虾繁殖期为秋季(7月中旬～9月中旬,水温31～23℃),7月中下旬为新老世代交替期．非繁殖季节雄虾多于雌虾,繁殖季节雌虾多于雄虾．越冬虾绝对繁殖力明显大于当年虾．绝对繁殖力与体长呈幂函数关系,与体重呈直线相关．相对繁殖力RW为常数,其95％置信区间为1067．76±16．94eggs·g^-1。     

Utilization of emergent plants as an aestivation habitat by the Trapa-feeding leaf beetle (Galerucella nipponensis) in Lake Inba,Japan

Limnology - Water chestnuts (Trapa spp.) dominate many shallow eutrophic lakes, and impact aquatic fauna. Use of Trapa beds by animals may vary with the growth stage of Trapa, but little is known...     

Maturation and spawning processes of anadromous and resident pond smelt in lake ogawara

Pond smelt,Hypomesus nipponensis McAllister, in Lake Ogawara demonstrate alternative life history strategies, as evidenced by the coexistence of anadromous and resident fish. However, it is unknown if anadromous and resident groups interbreed. In this study, maturation and spawning processes were examined and compared between anadromous and resident groups. Histological observations indicated negligible variation in the maturational stage composition of oocytes, the frequency of oocyte diameter being unimodal for all specimens at different maturational stages. Oocytes were absent in the ovaries of spent fish. Accordingly, the species can be considered a semelparous spawner with unimodal oocyte diameter distribution. Temporal changes in the proportion of spent fish were compared between anadromous and resident groups. Spawning of both groups began in late March and peaked over April 8–12. Although both groups did not differ significantly in the period of peak spawning, anadromous fish finished spawning earlier than resident ones. Anadromous fish were not able to spawn upon migration into Lake Ogawara, and quickly matured after immigration, contrasting with resident fish.     

Timing and site selection of spawning in a landlocked population of rainbow smelt in Wisconsin

To study the site selection and timing of spawning by rainbow smelt, Osmerus modax, in a freshwater system, smelt were sampled with fyke nets during the spawning run in spring 2002 and 2003. The sex ratio of smelt favored males in the early and late segments of the run, with over 90% of smelt caught being male. At the peak in the catch, females comprised 57% of the smelt collected. The gonadosomatic index of males and females declined significantly on the day of peak catch, signaling the peak in spawning activity. Higher catches of smelt occurred on cobble-dominated substrates during the peak of the run, but no site selection was apparent earlier or later. Groundwater outflow did not appear to affect catches. Our study suggests that smelt come inshore but do not select specific spawning substrates prior to or after the peak in spawning. Smelt do select cobble sites during the highest rates of spawning. The relation between the peak in spawning and site selection could have application in planning removal strategies for the species.     

Coexistence of Anadromous and Resident Life History Styles of Pond Smelt, <Emphasis Type="Italic">Hypomesus nipponensis</Emphasis>, in Lake Ogawara,Japan, as determined by Analyses of Otolith Structure and Strontium:Calcium Ratios

Anadromous and resident forms of pond smelt, Hypomesus nipponensis, were found to occur in sympatry in Lake Ogawara, Japan. Profiles of Sr: Ca ratios from individuals could be grouped to two patterns (1) a resident pattern with low Sr: Ca ratios from core to edge and (2) an anadromous pattern with relatively low Sr: Ca ratios near the core with abrupt increases in ratios at a location approximately 0.3mm from the core. Spawners smaller than 60mm standard length (SL) were resident, between 60 to 80mm were mixed resident and anadromous, and larger than 80mm were anadromous. Anadromous individuals first migrated after 40 to 82 days from hatching (mean±sd, 59.1±13.5d) and 14.6 to 30.9mm SL (22.2±5.3mm). There was no difference in SL between resident and anadromous individuals during age at first migration, suggesting that size may not be the mechanism for divergence of alternative life history styles.     

Interrelation between plankton and benthos in the littoral algal community of Lake Yunoko,Central Japan

To ascertain the floristic interaction between phytoplankton and benthos in the littoral, the composition of each community was investigated and the effect of the substrata on the benthic communities was also examined.The main component of the benthic algal population wasFragilaria pinnata followed byF. pinnata var.lancettula. Although the dominant species of the plankton in the upper layers were similar to those in the limnetic, and those immediately above the bottom contained species of benthic origin, the similarity index of C implied high similarity between these two plankton layers. This index was developed by Morishita (1959) to measure the degree of overlap of component species between two communities. The value of C distributes from 0 to 1. The closer the value approaches 1, the more the communities are similar.For the dominant species, a significant difference was observed between the phytoplankton and benthic communities and in addition, C values indicated low overall similarity in the composition of the communities. These results suggest that there is little interrelation between phytoplankton and benthos even in the shallow littoral zone.     

Seasonal changes in the biomass of floating leaved plant,Trapa spp., and its relation with a leaf beetle,Galerucella nipponensis,in Lake Inba,Japan

Limnology - Trapa spp. dominate many shallow eutrophic lakes in Japan, which must affect the nutrient dynamics in lakes. Trapa spp. are utilized by several animals, in particular the leaf beetle,...