Brackish Water Lake Research Articles

Sources and composition of organic matter as a tool for understanding the complex variation in paleoenvironments and the connectivity of an epicontinental basin: The Miocene in the northern Pannonian Basin

Epicontinental basins are extremely prone to major paleogeographic changes, and this will directly affect any organic matter (OM) preserved in the depositional record. In this study the Middle–Late Miocene successions in the northern Pannonian Basin System were investigated via sedimentological, petrographic, and geochemical analyses of cores from the Danube Basin to reveal the interplay of factors driving the character of the OM. In the late Middle Miocene (~12.3 Ma), the Central Paratethys Sea maintained normal marine salinity, with dysoxic bottom waters in a distal basin floor environment rich in aquatic OM. The last rifting phase followed during the Late Miocene and led to formation of the deep Lake Pannon. Like seawater, the brackish lake water still also contained sulfate. These open lacustrine deposits (~11.6–10.0 Ma) reveal OM sourced from submerged/floating macrophytes and algae, and humid conditions are indicated by the preponderance of deciduous trees and shrubs on shores. The study identifies hybrid event beds (HEBs) on Lake Pannon's floor (~10.0–9.3 Ma), with currents redepositing mud and OM, resulting in similarities between the Middle Miocene and Late Miocene successions. Turbidite deposition (~9.3–9.0 Ma) from the paleo-Danube induced a shift in OM, replacing algae with terrestrial input. Complete isolation from the main water masses of Lake Pannon (~9.0–8.9 Ma) altered its sources of OM, transitioning from algae to macrophytes, and caused a drop in salinity, likely associated with a humidity peak. The subsequent deltaic dominance (~8.9–8.6 Ma) features well-developed topset lakes, swamps, and floodplain forests, reflecting warm temperate to subtropical climates. The Middle–Upper Miocene deposits studied here are source rocks with fair to very good richness and poor to fair generative potential, and contain kerogen types III and IV, while type II is rare. The rapid paleoenvironmental changes observed over the order of ~100 kyr caused the complete switching of OM type and delivery, giving an indication of the complexity of epicontinental basins.

Allometry and condition factor of Faunus ater (Cerithioidea: Pachychilidae) from An Estuarine Habitat of Kerala, Southern India

Faunus ater is a pachychilid gastropod known to inhabit brackish water habi-tats of Western Indo-Pacific countries. This study aimed to analyse the mor-phometric relationships and condition factor of F. ater collected from the Eda-va-Nadayara brackish water lake of Kerala, India. Hydrographic parameters of sampling stations were recorded. A total of 1,522 specimens were collected every month from March 2019 to February 2020. The mean values recorded for total length, shell width, body whorl length, opercular length, opercular width, and total weight were 45.38±13.44 mm, 14.47±3.88 mm, 20.81±5.83 mm, 7.71±3.08 mm, 4.62±1.62 mm, and 6.97±3.72 g, respectively. The length-weight relation was obtained as Log W= -1.005+2.871 Log L. The b value (<3) indicated a negative allometric growth of the organism. Regression analysis of other morphometric measurements also showed a positive correla-tion (P<0.001). The analysis of Fulton’s condition factor indicated a state of well-being of F. ater in this habitat, with condition factors ranging from 5.87 to 6.99 spatially and 5.48 to 7.00 temporally. This study provides the first detailed investigation of morphometric relationships and condition factors in F. ater.

Genome-wide comparative analyses highlight selection signatures underlying saline adaptation in Chilika buffalo.

Chilika, a native buffalo breed of the Eastern coast of India, is mainly distributed around the Chilika brackish water lake connected with the Bay of Bengal Sea. This breed possesses a unique ability to delve deep into the salty water of the lake and stay there to feed on local vegetation of saline nature. Adaptation to salinity is a genetic phenomenon; however, the genetic basis underlying salinity tolerance is still limited in animals, specifically in livestock. The present study explores the genetic evolution that unveils the Chilika buffalo's adaptation to the harsh saline habitat, including both water and food systems. For this study, whole genome resequencing data on 18 Chilika buffalo and for comparison 10 Murrah buffalo of normal habitat were generated. For identification of selection sweeps, intrapopulation and interpopulation statistics were used. A total of 709, 309, 468, and 354 genes were detected to possess selection sweeps in Chilika buffalo using the nucleotide diversity (θπ), Tajima's D, nucleotide diversity ratio (θπ-ratio), and FST methods, respectively. Further analysis revealed a total of 23 genes including EXOC6B, VPS8, LYPD1, VPS35, CAMKMT, NCKAP5, COMMD1, myosin light chain kinase 3 (MYLK3), and B3GNT2 were found to be common by all the methods. Furthermore, functional annotation study of identified genes provided pathways such as MAPK signaling, renin secretion, endocytosis, oxytocin signaling pathway, etc. Gene network analysis enlists that hub genes provide insights into their interactions with each other. In conclusion, this study has highlighted the genetic basis underlying the local adaptive function of Chilika buffalo under saline environment.NEW & NOTEWORTHY Indian Chilika buffaloes are being maintained on extensive grazing system and have a unique ability to convert local salty vegetation into valuable human food. However, adaptability to saline habitat of Chilika buffalo has not been explored to date. Here, we identified genes and biological pathways involved, such as MAPK signaling, renin secretion, endocytosis, and oxytocin signaling pathway, underlying adaptability of Chilika buffalo to saline environment. This investigation shed light on the mechanisms underlying the buffalo's resilience in its native surroundings.

Observations on the Distribution and Effect of Salinity on a Little Known Plant, <I>Mimulus orbicularis</I> Wall. Ex Benth. (Scrophulariaceae)

Mimulus orbicularis Wall, ex Benth., occasionally found in brackish water lakes, ditches, slacks and often in abandoned ricefields near estuaries and the coastal belt of Eastern India, is a rare aquatic plant. Very often the plants have been found to disappear from the habitat due to some ecological or anthropogenic factors. It is observed that the plant has very little potential for modulating its life cycle strategies in the same habitat. Though populations were recorded in three different localities in India, survival of this species in a parmanent habitat is still a question due to its 'nomadic distribution'. On account of this population behaviour, the collection of this species by many workers in the past has been inadequate. Occurrence of this plant in new localities, extent of distribution and some changes in the morphological characteristics with the change of water salinity and some chemical components of water are discussed in this paper.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

New records of a freshwater fish parasite <i>Argulus japonicus</i> (Branchiura: Argulidae) from northern Honshu, Japan, with a note on its occurrence in a brackish water lake

New records of a freshwater fish parasite <i>Argulus japonicus</i> (Branchiura: Argulidae) from northern Honshu, Japan, with a note on its occurrence in a brackish water lake

The bacterial influencing mechanisms of salinity fluctuations in a brackish-water lake on the dissolved organic matter characteristics of pore water

The dissolved organic matter (DOM) components in lake water have been widely studied; however, few previous studies have considered the growth of Phragmites australis in brackish lakes. It has not been well understood how salinity variations influence the DOM compositions in pore water and its bacterial mechanisms in lakes with Phragmites australis. This experiment included three salinity groups (1,200 mg/L, 3,600 mg/L, and 6,000 mg/L) to study the interactions between bacteria and DOM in pore water under a salinity gradient. The results showed that the maximum fluorescence intensity (Fmax) of DOM measured by excitation-emission fluorescence spectroscopy decreased with increasing salinity. Higher salinity reduced the Fmax of protein-like substances and resulted in DOM becoming more aromatic. Salinity affected DOM composition due to the responses of functional bacterial communities. Thiobacillus was salt-tolerant and dominated in the sediments, and its relative abundance was negatively correlated with the Fmax of protein-like components. The relative abundance of Flavobacterium showed a positive correlation with salinity and a negative correlation with the Fmax of the fulvic acid-like component. Pseudomonas, Brevundimonas, and Polaromonas were negatively correlated with salinity and the Fmax of the fulvic acid-like component, while being positively correlated with the Fmax of tyrosine-like and aromatic protein substances. Higher salinity inhibited the metabolism gene modules of tryptophan and tyrosine. The results of this study may offer a novel perspective on comprehending the biochemical cycling of fluorescent DOM, encompassing tryptophan-like, tyrosine-like, and fulvic acid-like components in brackish lakes with fluctuating salinity.

Assessing Impacts of Flood Diversion on the Ecosystem of Brackish-Water Lakes through Simulation-Optimization Model

This study develops and evaluates a simulation-optimization approach to mitigate the environmental impacts of freshwater pulses in brackish-water lakes whilst maximizing flood diversion benefits. Lake Pontchartrain, located downstream of the Mississippi River, Mississippi, United States, is a brackish-water ecosystem threatened by reducing salinity concentrations due to freshwater pulses from the flood diversion project on the Mississippi River. An adaptive neuro-fuzzy-inference-system-based model was developed as a data-driven model for simulating salinity distribution at a representative station of Lake Pontchartrain. Then, the data-driven model was used as the simulator in the optimization system. Both single-objective and multi-objective particle swarm optimizations were used to find the optimal solutions. Results show that the data-driven model is robust at simulating the salinity time series in the brackish-water ecosystem of Lake Pontchartrain. The Nash–Sutcliffe efficiency index of the data-driven model between measured and modelled salinity is 0.85, which means the model is reliable for applying in further simulations. The proposed optimal solutions for the environmental management of the lake indicate that because of the magnitude of the volume of freshwater released, environmental impacts at this location cannot be optimized through varying the timing and volume of the releases. This work presents a novel contribution to science through developing an optimization framework for mitigating the impacts of flood management on changes in salinity in brackish-water systems.

Molecular signatures and diagnostic nucleotides for the fishes of the tropical brackish water lake in South Asia for conservation and management

The Pulicat Lake habitat is one of the most productive and precious ecosystems in India. This study aimed to develop the species-specific molecular signatures and determine the phylogenetic relationship of fish species distributed in the Pulicat Lake. In the present study, a data set of 1008 mtCOI sequences was obtained from the published resources and used to screen character-based molecular diagnostic keys for species in silico. DNA barcodes were generated from 29 fish species fish representing 7 orders, 28 genera, and 21 families. Species-specific probes with a length range of 18–32 bp were designed on the basis of identified diagnostic nucleotide sites. The probes, developed in this study, could be used to develop DNA chips to identify fish species more quickly and accurately. The developed molecular signatures in this study will be helpful in the effective fishery management of these fish genetic resources.

High spatiotemporal resolution reconstruction of suspended particulate matter concentration in arid brackish lake, China

The aquatic ecosystems and regional habitat quality of brackish Ebinur Lake in arid northwest China are significantly affected by suspended particulate matter (SPM). The Landsat series, Sentinel 2 and MODIS remote-sensing data offer a great potential to overcome the issue of the lack of reliable observation data for continuous SPM monitoring, but more accurate SPM inversion models are required for the arid regions. Hence, this research aims to: (1) determine the optimal strategy for applying the SPM inversion model to various time series images, (2) explore the inversion mode of SPM under the missing-image scenario, and (3) analyze the spatiotemporal changes of SPM over the Ebinur Lake lake from May to October during the 2011–2020 period. The findings show that ESTARFM_IVS (Inversion of SPM using images generated by Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model) produces the best inversion accuracy, with the values of R2 ≥ 0.57, RMSE ≤ 44.51 mg/L. Secondly, the exponential model for the Landsat 5/7 and fused images were adopted, while the Quasi-Analytical Algorithms for reference wavelengths of 655 nm and 665 nm (QAA_655(665)) were used for the Landsat 8 and Sentinel 2 images. Thirdly, the SPM fluctuations varied significantly, and the SPM concentrations showed an increasing trend with a widening amplitude over time. The inter-annual SPM increasing trend was significant, while the inter-month SPM variations have not changed much. When compared to the lake's core area, the SPM concentrations in the nearshore area were noticeably higher, and this has been consistent over the years. The results should serve as helpful guides for monitoring brackish lake water environment using satellite technologies.

An Advanced Spatiotemporal Fusion Model for Suspended Particulate Matter Monitoring in an Intermontane Lake

Ebinur Lake is the largest brackish-water lake in Xinjiang, China. Strong winds constantly have an impact on this shallow water body, causing high variability in turbidity of water. Therefore, it is crucial to continuously monitor suspended particulate matter (SPM) for water quality management. This research aims to develop an advanced spatiotemporal fusion model based on the inversion technique that enables time-continuous and detailed monitoring of SPM over an intermontane lake. The findings shows that: (1) the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) fusion in blue, green, red, and near infrared (NIR) bands was better than the flexible spatiotemporal data fusion (FSDAF) model in extracting SPM information; (2) the inversion model constructed by random forest (RF) outperformed the support vector machine (SVM) and partial least squares (PLS) algorithms; and (3) the SPM concentrations acquired from the fused images of Landsat 8 OLI and ESTARFM matched with the actual data of Ebinur Lake based on the visual perspective and accuracy assessment.

U–Pb ages of tuff from the Triassic Yanchang Formation in the Ordos Basin: Constraints on palaeoclimate and tectonics

The Chang 7 member of Triassic Yanchang Formation in the huger Ordos Basin in North China is important economically as a source of oil in the Triassic, but dating the Triassic successions has proved problematic, especially important oil-bearing units such as the Yanchang Formation. Here we analyze depositional ages, palaeoclimate conditions and palaeoenvironments of the Chang 6 to Chang 10 members of Yanchang Formation using SHRIMP U–Pb isotope dating, trace element composition and palynological analyses for samples from well F75 in the northwestern Ordos Basin. The geochronological and palynological data synthetically indicate that the Chang 7 member was deposited in the Ladinian (Middle Triassic) and the Chang 8 to Chang 10 members were deposited in the Anisian (Middle Triassic). Based on the trace element analysis, the palaeoenvironment abruptly changed in the early sedimentary stage of the Chang 7 member, representing warm and humid palaeoclimate, anoxic, brackish lake water and stronger chemical weathering. Therefore a humid paleoclimate event was recorded during the Chang 7 sedimentary period of the Middle Triassic, which provides a basis for the comparison with the global Triassic paleoclimatic event. It was inferred that the paleoclimate event was referred to palaeotopographic (the basin was surrounded by mountains on three sides and low terrain in the east) of the Ordos Basin, which was controlled by the Qinling orogeny and low-latitude warm and humid airflow of the paleo-Pacific Ocean associated with monsoons.

Diatomasinensis: a new diatom species (Bacillariophyta) found in the brackish Lake Qinghai, China.

Lake Qinghai is an ancient brackish water lake in which several endemic diatom species have been discovered. In this study, a species of Diatoma is observed under light and scanning electron microscopy and described as new, Diatomasinensis sp. nov. The living cells of D.sinensis always lie in girdle view due to the cell depth being much larger than valve width (3.3-8.8 vs. 2.0-3.0 μm). The valves of D.sinensis are characterized by their narrow, linear-lanceolate outline, with capitate to subcapitate apices, the presence of two rimoportulae, one at each apex, embedded in the last rib or located among striae and a 4:2 configuration of girdle bands in normal vegetative cells, with four bands assigned to the epivalve and two to the hypovalve. The new taxon is compared with similar species from the genera Diatoma and Distrionella.

<i>Limnotrachelobdella okae</i> (Hirudinida: Piscicolidae) Parasitic on Big-scaled Redfin, <i>Pseudaspius hakonensis</i> (Cypriniformes: Leuciscidae), in Two Brackish Water Lakes, Hokkaido, Japan

Specimens of the coastal marine fish leech Limnotrachelobdella okae (Moore, 1924) were collected from the pelvic fins and lateral body surface of big-scaled redfin, Pseudaspius hakonensis (Günther, 1877), in two brackish water lakes, Lake Tofutsu and Lake Abashiri, on the Sea of Okhotsk coast, Hokkaido, northern Japan. The external morphology of the specimens is briefly described, and the two lakes represent new locality records for the leech. Similarly to coastal marine waters, inshore brackish water lakes are suggested to be a habitat in which L. okae can complete its life cycle. Seasonal occurrence of the species may differ between subarctic Hokkaido and three temperate regions of Japan (Honshu, Shikoku, and Kyushu). The role of big-scaled redfin and its congener, Pacific redfin, Pseudaspius brandtii (Dybowski, 1872), in transporting L. okae alive from the coastal sea to brackish and fresh water bodies is discussed in terms of their diadromous migration ecology.

Spatiotemporal distributions and relationships of phosphorus content, phosphomonoesterase activity, and bacterial phosphomonoesterase genes in sediments from a eutrophic brackish water lake in Chile

Phosphorus (P) cycling by microbial activity is highly relevant in the eutrophication of lakes. In this context, the contents of organic (Po) and inorganic (Pi) phosphorus, the activity of acid (ACP) and alkaline (ALP) phosphomonoesterase (Pase), and the abundances of bacterial Pase genes (phoD, phoC, and phoX) were studied in sediments from Budi Lake, a eutrophic coastal brackish water lake in Chile. Our results showed spatiotemporal variations in P fractions, Pase activities, and Pase gene abundances. In general, our results showed higher contents of Pi (110–144 mg kg−1), Po (512–576 mg kg−1), and total P (647–721 mg kg−1) in sediments from the more anthropogenized sampling sites in summer compared with those values of Pi (86–127 mg kg−1), Po (363–491 mg kg−1) and total P (449–618 mg kg−1) in less anthropogenized sampling sites in winter. In concordance, sediments showed higher Pase activities (μg nitrophenyl phosphate g−1 h−1) in sediments from the more anthropogenized sampling sites (9.7–22.7 for ACP and 5.9 to 9.6 for ALP) compared with those observed in less anthropogenized sampling sites in winter (4.2–12.9 for ACP and 0.3 to 6.7 for ALP). Higher abundances (gene copy g−1 sediment) of phoC (8.5–19 × 108), phoD (9.2–47 × 106), and phoX (8.5–26 × 106) genes were also found in sediments from the more anthropogenized sampling sites in summer compared with those values of phoC (0.1–1.1 × 108), phoD (1.4–2.4 × 106) and phoX (0.7–1.2 × 106) genes in the less anthropogenized sites in winter. Our results also showed a positive correlation between P contents, Pase activities, and abundances of bacterial Pase genes, independent of seasonality. The present study provided information on the microbial activity involved in P cycling in sediments of Budi Lake, which may be used in further research as indicators for the monitoring of eutrophication of lakes.

Assessment of physico-chemical parameters of surface waters of a tropical brackish water lake in South Asia

Brackish lake systems and estuaries are unique aquatic systems that support diversified life forms and strongly influence a region's economy. Major chemical water quality parameters of India's second-largest brackish water lake, Pulicat were assessed. Physico-chemical parameters like pH, temperature, suspended solid concentrates, total dissolved solids, salinity, nitrogenous nutrients, phosphate, silicate, and chlorophyll a were analysed. The results obtained for different parameters were compared and interpreted with statistical software SPSS version 20 and images were plotted using the Arc GIS spatial analyst tool. During the summer months, the nitrogen to phosphorus ratio ranges from a minimum of 1.96 to a maximum of 16.64 (9.55 ± 4.01) while it ranges from a minimum of 7.98 to a maximum of 15.52 (12.47 ± 2) during the pre-monsoon. In the monsoon season, the nitrogen to phosphorus ratio of surface water suggests a range from a minimum of 8.64 to a maximum of 17.58 (13.87 ± 2.14). During the post-monsoon season, the nitrogen to phosphorus ratio ranges from 4.98 to 17.34 (11.77 ± 3.68). The average nitrogen to phosphorus ratios were 9.6, 12.5, 13.9 and 11.8 in summer, pre-monsoon, monsoon, and post-monsoon respectively. The nitrogen to phosphorus ratio was lower than the Redfield ratio for all the seasons. The average concentration of chlorophyll a was 14.9, 13.4, 12.8 and 11.8 in summer, pre-monsoon, monsoon, and post-monsoon respectively. As per the Pearson Correlation Coefficient, there was no significant correlation among nitrogen, phosphorus, and chlorophyll a. This suggests the influence of suspended solid concentrates, and nitrogen and phosphorus flux in the sediment-water interface might be interfering with the nutrient cycles and primary productivity.

A historical record of benthic foraminifera in seasonally anoxic Lake Grevelingen, the Netherlands

Lake Grevelingen is a former branch of the Rhine-Meuse-Scheldt estuary, which was artificially transformed into a salt-water lake by a dam in 1971. This transformation induced profound changes in the biological community of the basin, which have been described as an ecodisaster, with seasonal hypoxia/anoxia occurring in the deepest parts of the lake. Here, we investigate a sediment core sampled in 2012 in the Den Osse Basin (34 m depth) of Lake Grevelingen, recording the last ~50 years and including the transition from an estuary to a salt-water lake. Sediment molybdenum (Mo) concentrations were used to refine an existing age model based on 210Pb, giving us an estimated precision of ±3 years. The benthic foraminiferal succession reflects the anthropogenic modifications in Lake Grevelingen and allows four successive stages to be distinguished: 1) before 1971, when the system was estuarine; 2) from 1971 to 1978, when the system rapidly changed into an enclosed brackish water lake; 3) from 1978 to 1999, when a seaward sluice was opened during winter and 4) the period from 1999 to 2012, with a year-round opening of the sluice and doubling of water exchanges with the North Sea. The foraminiferal record, showing communities mainly dominated by Elphidium selseyense, also highlights the appearance of the putatively exotic Ammonia confertitesta in the mid-1980s, which thereafter progressively replaced the congeneric autochthonous Ammonia aberdoveyensis. Finally, we hypothesise that the activity of cable bacteria, S-oxidising prokaryotes present in the surface sediments of Den Osse Basin in winter and spring, causes dissolution of foraminiferal tests by decreasing the pore water carbonate saturation state in the sediments directly below the oxic zone. This explains the contrast between the abundant living populations and the very low numbers of foraminiferal shells preserved in the top ~15 cm of the sediment.

Physiological, morphological and transcriptomic responses of Tibetan naked carps (Gymnocypris przewalskii) to salinity variations

Gymnocypris przewalskii is a native cyprinid fish that dwells in the Lake Qinghai with salinity of 12–13‰. It migrates annually to the freshwater rivers for spawning, experiencing the significant changes in salinity. In the present study, we performed the physiological, morphological and transcriptomic analyses to understand the osmoregulation in G. przewalskii. The physiological assay showed that the osmotic pressure of G. przewalskii was almost isosmotic to the brackish lake water. The low salinity reduced its ionic concentrations and osmotic pressure. The plasticity of gill microstructure was linked to the salinity variations, including the presence of mucus and intact tight junctions in brackish water and the development of the mitochondria-rich cells and the loosened tight junctions in freshwater. RNA-seq analysis identified 1926 differentially expressed genes, including 710 and 1216 down- and up-regulated genes in freshwater, which were enriched in ion transport, cell-cell adhesion, and mucus secretion. Genes in ion uptake were activated in low salinity, and mucus pathways and tight junction showed the higher transcription in brackish water. The isosmoticity between the body fluid and the environment suggested G. przewalskii was in the metabolic-saving condition in the brackish water. The decreased salinity disrupted this balance, which activated the ion uptake in freshwater to maintain osmotic homeostasis. The gill remodeling was involved in this process through the development of the mitochondria-rich cells to enhance ion uptake. The current finding provided insights into the potential mechanisms of G. przewalskii to cope with salinity alteration.

Revision of the endemic dinoflagellate cyst genus Pontiadinium Stover & Evitt, 1978 from Lake Pannon and the Paratethys realm (Late Miocene–Early Pliocene, Central Europe)

The biota of the brackish-water Lake Pannon in the Pannonian Basin is characterised by remarkable endemism due to the isolated evolution of the lake for 8 myr after the last Miocene marine connection ceased (∼11.6 Ma). A conspicuous feature of this endemism is the large, probably ecophenotypic variation in the morphology of brackish-water dinoflagellate cysts that challenges taxonomy and complicates biostratigraphical and ecological interpretations. We conclude that a widely debated Lake Pannon genus, Pontiadinium, includes several proximate dinoflagellate cyst species with prominent apical and antapical protuberances, and we show how the genus differs from the morphologically similar gonyaulacacean cyst genera Impagidinium, Leptodinium, Cribroperidinium and Komewuia. The generic description of Pontiadinium is emended together with the species descriptions of Pontiadinium inequicornutum, Pontiadinium obesum and Pontiadinium pecsvaradanesis. A new species is described as Pontiadinium szentaiae sp. nov. from Našice (northern Croatia) that is characterised by unique trabeculate sutural septa formed from a beaded tegillum supported by columellae or rod-like luxuriae. The dinoflagellate cyst assemblages of the long-lived brackish-water Lake Pannon clearly demonstrate that dinoflagellate cysts in low-salinity, isolated epicontinental seas display greater morphological plasticity than their normal-marine relatives. The development of an antapical horn appears to be a previously undocumented example of phenotypic morphological features that developed in response to subnormal salinities within at least two dinoflagellate cyst genera endemic to Lake Pannon and the Post-Paratethyan seas of the Ponto-Caspian realm. This ecophenotypic variation resulted in a higher level of morphological adaptation, leading to the evolutionary development of new dinoflagellate cyst species and genera.

A NEW SIZE RECORD OF HILSA, TENUALOSA ILISHA (HAM., 1822) FROM HOOGHLY ESTUARY, WEST BENGAL

The Hilsa shad, Tenualosa ilisha (Hamilton, 1822), occurs in foreshore areas, estuaries, brackish-water lakes and freshwater rivers of the western division of the Indo-Pacific region. It is well known as a delicious, high priced fish of commercial and cultural importance, especially in state of West Bengal and the North Eastern states of India as well as Bangladesh. Along the Indian coast of Bay of Bengal, the Hooghly estuarine system is one of the largest and most productive estuaries and is an important migratory route of the anadromous hilsa. The estuarine system is constituted by the first offshoot of river Gangathe Bhagirathi, which flows southwards through the lower Ganga deltaic plains and joins Bay of Bengal in Sunderbans. Hilsa shad is the most economically significant fishery of the system and it is a major contributor to the total fish landings of this system. Hydrological alterations in the form of barrages and dams built across the major east and west coast rivers, especially along the Ganges and Narmada have blocked its migratory routes to breeding grounds in riverine areas, resulting in the collapse of its fishery in the river stretches above these barrages and as a result, hilsa landing is now concentrated in estuarine part of these rivers (Raja, 1985; De, 1998). After commissioning of the Farakka barrage in 1975, the hilsa fishery is confined to downstream of the barrage, the Hooghly-Bhagirathi system. The indiscriminate exploitation of hilsa adults as well as juveniles during the past years has caused the decline of the once lucrative commercial fisheries of the fish, more particularly along the Hooghly estuary, due to recruitment failure. The comparison of time scale mean size recorded from Hooghly-Bhagirathi river system over past years indicated a declining trend and an increasing contribution of smaller size groups in the catch pointing towards the growth overfishing of hilsa populations. The aim of this paper represents a new record size of hilsa with record fecundity from Hooghly estuarine system