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Induced spawning, larval rearing, and innate diet analysis of Indian black clam, Villorita cyprinoides: An alternative to resource restoration through aquaculture
Abstract
Villorita cyprinoides (Gray, 1825) also called the Indian black clam is a native species from the Indian peninsula
directly related to the livelihood of many beneficiaries. The wild population of this Cyrenid clam is confronted
with substantial challenges, including various climatic stressors and anthropogenic pressures such as overfishing
and habitat destruction. A balance between capture fisheries and aquaculture through the development of
hatchery technology is inevitable for ensuring the sustainable use of resources. The declining population of
V. cyprinoides underscores the urgency of standardizing breeding protocols and implementing proper farming
practices to foster a sustainable black clam fishery, given that Villorita is a potential candidate species for
aquaculture. This paper describes the first successful induced spawning of the clam with successful rearing of
larvae up to the umboned veliger stage and evaluates the efficacy of induced spawning through combined
physical and chemical stimuli. Furthermore, our study employs eDNA metabarcoding to analyze plankton dy-
namics in waters from native clam beds. This sheds light on the potential microalgal dietary preferences of the
species, which can be valuable in preparing diets for larval development and aquaculture in the future.
... Niche fragmentation, climate change, and associated environmental stressors have drastically altered larval development and threatened the existence of this organism 13 . To rejuvenate black clam resources in fishery areas, immediate actions such as re-laying have been undertaken, and initial breeding standardization studies are in progress 14 . However, due to limited genomic resources, it is difficult to ensure the conservation and sustainability of Villorita given the current significant risk in its population. ...
The Indian black clam Villorita cyprinoides Gray, 1825, is an economically valuable estuarine bivalve that faces challenges from multiple stressors and anthropogenic pressures. However, limited genomic resources have hindered molecular investigations into the impact of these stressors on clam populations. Here, we have generated the first transcriptomic reference datasets for V. cyprinoides to address this knowledge gap. A total of 25,040,592 and 22,486,217 million Illumina paired-end reads generated from two individuals were assembled using Trinity and rnaSPAdes. From the 47,607 transcripts identified as Coding Domain Sequences, 37,487 returned positive BLAST hits against six different databases. Additionally, a total of 14,063 Single Sequence Repeats were identified using GMATA. This study significantly enhances the genetic understanding of V. cyprinoides, a potential candidate for aquaculture that supports the livelihoods of many people dependent on small-scale fisheries. The data generated provides insights into broader genealogical connections within the family Cyrenidae through comparative transcriptomics. Furthermore, this transcriptional profile serves as baseline data for future studies in toxicological and conservation genetics.
Bivalve mollusks represent a nutritious source with a low environmental impact; as a result, they are one of the most attractive aquaculture options. Advances in microencapsulation technology offer great potential to face key bivalve nutrition problems, and an alga-based microencapsulated diet can turn enriched bivalves into potential functional foods. The central goal of this study was the evaluation of food intake as a function of particle size and microalga content following the supply of four microencapsulated diets, incorporating as core material Nannochloropsis sp. or Tetraselmis sp. in 20 or 40 µm diameter pellets (diets N20, T20, N40, and T40, respectively) in five bivalve species (Magallana gigas, Solen marginatus, Ruditapes decussatus, Ruditapes philippinarum, and Cerastoderma edule). Overall, all tested diets were easily ingested, although food intake was higher for N20 (except for the S. marginatus, which showed a higher rate for the diet T40). Concerning a size-related analysis, C. edule and S. marginatus favored, respectively, smaller and bigger pellet-sized diets, with no signs of selectivity for microalga species. The diet T20 was the lesser ingested, except for C. edule. This knowledge enables a better selection of feed with appropriate and species-adjusted profiles, contributing to the optimization of microencapsulated diets for bivalve rearing and a better final product.
Understanding the effects of environmental parameters on the reproductive cycle of shellfish is an essential tool for successful hatchery conditioning management and, consequently, for seed supply to the industry. For the tropical oyster, Crassostrea tulipa, little is known about the factors affecting the maturation process and reproduction, but there are indications that salinity may be of importance. Two experiments were carried out to evaluate the effects of salinity on the reproductive cycle of broodstock of C. tulipa. In the first experiment, oysters were reared in five salinities (40, 35, 30, 25, and 20) for 40 days and gonad histological samples were collected regularly. In a follow up experiment, oysters were reared in variable salinity conditions changing from 40 to 30 or from 20 to 30 over a period of 40 days. Salinity was found to affect the reproductive cycle of C. tulipa. Oysters kept in constant salinity of 30 showed a higher condition index compared to animals in other salinities, with most of the animals in the prespawning stage. Salinity variation was also shown to affect C. tulipa maturation. The prespawning stage was the most observed reproductive stage in low salinity, and high salinity induced a resting stage in the female animals. The results are considered the first step towards developing a protocol for the conditioning of C. tulipa in hatchery conditions.
Corbicula has often been reported as one of the most invasive freshwater species in the world. It plays an important role in the food chains of brackish water zones in Korea, where it is predominant. However, detailed information on the Corbicula diet is still lacking. The purpose of this study was to identify the potential prey of Corbicula fluminea in the Seomjin River using a DNA metabarcoding approach, as very little is known about its feeding selectivity in natural conditions. A survey was conducted at two study sites (1 and 2) in the Seomjin River in November 2021. The two sites were selected based on increasing salinity gradient. The dominant operational taxonomic unit in the pseudofeces and gut content of C. fluminea was Microcyclops varicans (Copepoda) and Oncorhynchus mykiss (Fish), respectively. The alpha diversity at site 1 was higher than that at site 2. More diverse potential prey species were identified at the site with low salinity (i.e., site 1). The utilization of this method is strongly recommended for determining specific predator–prey relationships in complex estuarine ecosystem.
Pacific clam, Asaphis violascens is a benthic species present in the Indo‐pacific region. It is very much appreciated as food by the local community and its population is diminishing due to overfishing. The aim of this research is to establish suitable rearing conditions for its spawning and larviculture. Two different spawning induction methods were used, emersion and thermal shock. Two stocking densities of larvae were tested (10 and 20 larvae/mL) and three different microalgae diets, one consisting of Tisochrysis lutea as a single species diet and the other two with Ti. lutea combined with Nannochloropsis oculata and Tetraselmis suecica. Emersion of clams was established as a successful spawning induction method. Larval development of A. violascens is similar to other tropical bivalves, having a 10‐day planktonic period at 28°C. An initial stocking density of 10 larvae/mL showed significantly higher (p < .05) survival rate. No significant differences (p > .05) in growth and survival were found between the diets, proving that the use of Ti. lutea alone or mixed is suitable for their nutrition. The results presented could contribute to the implementation of restorative aquaculture farms in the region, helping to mitigate food security issues in the communities and collaborating with the establishment of healthier coastal ecosystems.
Contaminants of Emerging Concerns (CECs) are defined as chemicals not commonly monitored in aquatic ecosystems, but with the potential to cause adverse effects on biota. CECs include Endocrine Disrupting Chemicals (EDCs) and Neuro-Endocrine disruptors (NEDs) of vertebrates. However, most invertebrates only rely on neuroendocrine systems to maintain homeostatic processes. Although conserved neuroendocrine components have been characterized in ecologically relevant groups, limited knowledge on invertebrate neuroendocrinology makes it difficult to define EDCs and NEDs in most species. The monoamine serotonin (5-hydroxytryptamine, 5-HT) acts both as a neurotransmitter and as a peripheral hormone in mammals. In molluscs, 5-HT is involved in multiple physiological roles and molecular components of the serotonergic system have been identified. This review is focused on the effects of CECs on the serotonergic system of bivalve molluscs. Bivalves are widespread in all aquatic environments, estuarine and coastal areas in particular, where they are exposed to a variety of chemicals. In bivalves, 5-HT is involved in gametogenesis and spawning, oocyte maturation and sperm motility, regulates heart function, gill ciliary beating, mantle/siphon function, the ‘‘catch’’ state of smooth muscle and immune responses. Components of 5-HT transduction (receptors and signaling pathways) are being identified in several bivalve species. Different CECs have been shown to affect bivalve serotonergic system. This particularly applies to antidepressants, among the most commonly detected human pharmaceuticals in the aquatic environment. In particular, selective serotonin reuptake inhibitors (SSRIs) are frequently detected in seawater and in bivalve tissues. Information available on the effects and mechanisms of action of SSRIs on the serotonergic system of adult bivalves is summarized. Data are also reported on the effects of CECs on development of neuroendocrine pathways of early larval stages, in particular on the effects of model EDCs in the marine mussel Mytilus galloprovincialis. Overall, available data point at the serotonergic system as a sensitive target for neuroendocrine disruption in bivalves. The results contribute drawing Adverse Outcome Pathways (AOPs) for model EDCs and SSRIs in larvae and adults. However, basic research on neuroendocrine signaling is still needed to evaluate the potential impact of neuroendocrine disruptors in key invertebrate groups of aquatic ecosystems.
The identification of novel peptides that regulate reproduction is essential for studying reproductive physiology in bivalves. Therefore, we aimed to identify peptides that affect the reproductive physiology of bivalves. We identified an oocyte maturation-, sperm motility-, and spawning-inducing peptide from the visceral ganglia of the pen shell, Atrina pectinata. The peptide consisted of 26 amino acid residues (GFDSINFPGTIDGFKDYSSNKKERLL). This peptide induced oocyte maturation and sperm motility activation at less than 1 nM upon the treatment of gonad fragments and induced spawning at 1 nmol when injected into mature individuals. Mature eggs and sperms artificially spawned by peptide administration were fertilized, and we confirmed that the development proceeded normally to veliger (D-shape) larvae. These results indicated that GFDSINFPGTIDGFKDYSSNKKERLL stimulated the gonads of pen shells and induced oocyte maturation, sperm motility activation, and spawning.
Area-based conservation is essential to safeguard nature’s diversity. In view of expanding human land use, increasing climate change and unmet conservation targets, area-based conservation requires efficiency and effectiveness more than ever. In this review, I identify and relate pressing challenges to promising opportunities for effective and efficient protected area governance and management, to enhance research, decision-making and capacity building in area-based conservation under uncertain future developments. I reveal that protected area management is particularly challenged by human land use, climate change, invasive species, and social, political and economic limitations. Protected area management often lacks the continuous availability of data on current states and trends of nature and threats. Biocultural conservation, climate-smart management and biosecurity approaches help to overcome challenges induced by human needs, climate change and invasive species, respectively. Economic valuation and shifts in funding priorities can boost protected area effectiveness and efficiency. In-situ monitoring techniques, remote sensing and open data infrastructures can fill data and information gaps for protected area planning and management. Moreover, adaptive management is an auspicious concept in the framework of systematic conservation planning to ensure the enduring effectiveness of protected areas despite unpredictable future developments. Post-2020 international biodiversity and sustainable development goals could be met earlier if protected areas were more effective. I consequently conclude with the need for a global information system that is to support area-based conservation by synthesizing challenges and opportunities for protected area management effectiveness and efficiency at the local to global level.
Benthic suspension feeders have significant impacts on plankton communities by depleting plankton or modifying the composition of the plankton through prey selectivity. Quantifying diets of planktivorous animals can be difficult because plankton are frequently microscopic, may lack diagnostic characters, and are digested at variable rates. With DNA metabarcoding, the identification of gut contents has become faster and more accurate, and the technique allows for higher taxonomic resolution while also identifying rare and highly degraded items that would otherwise not be detected. We used DNA metabarcoding to examine the diet of the giant plumose anemone Metridium farcimen, a large, abundant, competitively dominant anemone on subtidal rock surfaces and floating docks in the northeast Pacific Ocean. Gut contents of 12 individuals were compared to 80‐ and 330‐µm filtered plankton samples collected one hour prior between 0.02 and 1.5 km from the anemones. The objectives of this study were to determine if M. farcimen has a selective diet and compare our findings with traditional gut content analyses. Metabarcoding demonstrated that M. farcimen captured a wider range of prey than previously suspected using traditional visual sampling techniques. Individual gut contents had less richness than the 80‐µm filtered plankton samples but had greater richness than the 330‐µm filtered plankton samples. The diet of the anemones was 52% arthropods with a surprisingly high relative abundance of an ant (10%) that has mating flights in August when this study was conducted. The gut contents of M. farcimen likely include all prey that elicit a predation response and that cannot escape. There were no statistically overrepresented taxa in the gut contents compared to the plankton but there were underrepresented taxa. This study highlights the usefulness of the metabarcoding method in identifying prey within the gut of planktivorous animals and the significant terrestrial input into marine food webs. The diet of the competitively dominant and abundant sea anemone Metridium farcimen was compared with available food within the plankton. Metabarcoding showed that these animals captures a wider range of prey than previously suspected based on conventional visual analysis, including terrestrial invertebrates.
When developing a species-specific hatchery protocol it is important to investigate the triggers for spawning, which is the foundation of the production cycle. This study evaluated multiple spawning induction techniques to optimise the spawning success of black-lip rock oyster, Saccostrea echinata, broodstock. Initially, the most effective method for non-destructively opening broodstock was determined, to allow intramuscular injection of chemical stimuli. Following this, the efficacy of seven spawning induction treatments, including two physical shock techniques, three chemical induction techniques, a combination of physical and chemical induction and strip spawning were assessed. Based on the outcomes of these trials, the combined and independent effects of reduced salinity and addition of sperm, as well as the potential of neuropeptides to trigger spawning, were evaluated. Results demonstrated that a concentration of 30 g/L of MgCl2 is an effective muscle relaxant for commercial and research application for S. echinata. It was determined that salinity reduction, rather than temperature increase, is a key factor for spawning induction. Strip spawning is a viable option for S. echinata; however, sperm motility was significantly affected, and fecundity and fertilisation rates were lower (although not significant, P > 0.05) when compared to other induction methods tested. A combination of physical and chemical induction, involving reduced salinity and addition of sperm, was the most successful treatment; 80 % of broodstock spawned within 19 min of salinity drop and addition of sperm. This method delivers significant production improvements for S. echinata, particularly regarding the time taken to induce spawning, and is therefore recommended for application in the hatchery.
The morphology of sperm and early embryo development of shellfish can provide guidance for classification and biological reproduction. In this study, scanning electron microscopy and light microscopy were used to determine the shape of the sperm, characterize the embryonic development, and measured the size of the mature eggs and the D-shape larvae of four different clam species (Paphia schnelliana, Lutraria sieboldii, Antigona lamellaris, and Paphia textzle). The results showed that these four clam species differ in sperm morphology and the size of the mature eggs and the Dshape larvae (P<0.01). There were also differences in embryonic development time and morphology. This analysis of spermatozoa morphology, egg size, D-shaped larvae size, and embryo development in these four different clam species provides the basis for classification and future breeding efforts.
The present study was carried out at the Thycattussery area in Vembanad lake and assessed the ichthyo-diversity, variability in climatic variables, the exploited status of predominant small-scale sector fisheries (SSFs) and impact of climatic variables upon an existing SSF. Fish, as well as clam specimens collected from the study area, were identified. Diversity indices and dominance curves helped to identify monsoon (June–September) as the diverse season in the wetland. SIMPER (similarity percentage) analysis indicated that Villorita cyprinoides (clam) was the predominant species in the wetland with a mean relative abundance of 16.1%. Canonical correspondence analysis (CCA) of variables with clam production identified calcium hardness and rainfall with axis loadings of –0.56 and 0.50 respectively as the variables predominantly contributing to clam production. Stepwise regression indicated that temperature and rainfall were the determinants of clam production. A decrease in rainfall and an increase in temperature at an annual rate of 0.02 and 0.8%, respectively, decreased the clam production by 5.37%/year in the study area. Further, the generalized linear model (GLM) indicated stagnancy in clam production until 2035 below 400,000 kg per year. The study introduced diversification of livelihood systems using clam culture in climate resilient pen structures (CRPS) as an adaptation strategy.
The Indian black clam Villorita cyprinoides (Family: Cyrenidae), an extractive commercially exploited species with aquaculture importance contributing more than 70% of clam fishery in India, is endemic to the Indian peninsula. Currently, there is very sparse information, especially on the molecular data of Villorita. The present study aims to provide a comprehensive knowledge of mitogenome architecture and assess the phylogenetic status of Cyrenidae. This has resulted in reporting the first complete mitogenome of V. cyprinoides using next-generation sequencing technology. The A+T circular mitogenome was 15,880 bp long, exhibiting 13 protein-coding genes (PCGs) including ATP8 (absent in several bivalves), 22 transfer RNA, and two ribosomal RNA genes residing in the heavy strand in a clockwise orientation and a gene order akin to Corbicula fluminea. The molecular phylogeny inferred from a concatenated multi-gene sequence [14 mitochondrial (12 PCGs, rrnS and rrnL) and two nuclear genes (Histone H3, 18S rRNA)] from 47 representative species of superorder Imparidentia, clustered V. cyprinoides and Cyrenid clams to a single clade supporting the monophyly of Cyrenidae. The subsequent mitochondrial gene order analysis substantiates the close relationship of V. cyprinoides and C. fluminea, analogous to phylogenetic output. The multilocus tree topology calibrated with verified fossil data deciphered the origin and diversification of Cyrenid clams during late Triassic-early Jurassic. The data derived from this study shall contribute remarkably for further insights on cryptic species identification, molecular characterization of bivalve mitogenomes and mitochondrial evolutionary history of genus Villorita. Moreover, complete mitogenome can aid in potential marker development for assessing the genetic health of black clam populations.
The global bivalve shellfish industry makes up 25% of aquaculture, is worth USD 220 kg−1, driving highly unsustainable energy and resource use. New advances in algal and microencapsulation technology provide solutions. We developed microencapsulated Schizochytrium algae diets, which can be produced sustainably at < $2 kg−1 from organic side-streams, and are shelf-stable to minimise waste. Physiological, histological, and cutting-edge metabolomic analyses demonstrate that in commercial settings sustainable microencapsulated diets facilitate improved sexual development and 12 × greater omega-3 levels in oysters relative to conventional live algal diets. Every tonne bivalve protein produced instead of fish spares 9 ha, 67 tonnes CO2, and 40,000 L freshwater. Further research into microencapsulated diets could support bivalve industry expansion, and contribute towards a step-change in sustainable global food production through improved aquaculture practices.
Important operational changes that have gradually been assimilated and new approaches that are developing as part of the movement toward sustainable intensive aquaculture production systems are presented via historical, current, and future perspectives. Improved environmental and economic sustainability based on increased efficiency of production continues to be realized. As a result, aquaculture continues to reduce its carbon footprint through reduced greenhouse gas emissions. Reduced use of freshwater and land resources per unit of production, improved feed management practices as well as increased knowledge of nutrient requirements, effective feed ingredients and additives, domestication of species, and new farming practices are now being applied or evaluated. Successful expansion into culture of marine species, both off and on shore, offers the potential of substantial increases in sustainable intensive aquaculture production combined with integrative efforts to increase efficiency will principally contribute to satisfying the increasing global demand for protein and food security needs.
Environmental DNA (eDNA) metabarcoding is a novel method of assessing biodiversity wherein samples are taken from the environment via water, sediment or air from which DNA is extracted, and then amplified using general or universal primers in polymerase chain reaction and sequenced using next-generation sequencing to generate thousands to millions of reads. From this data, species presence can be determined, and overall biodiversity assessed. It is an interdisciplinary method that brings together traditional field-based ecology with in-depth molecular methods and advanced computational tools. As an emerging monitoring method, there are many pitfalls and roadblocks to be considered and avoided, but the method may still have the ability to revolutionize modern biodiversity surveys for the molecular era. In this paper, we review the basic methodology, benefits, and concerns of eDNA metabarcoding, and systematically cover the applications of the method in global ecology thus far, including biodiversity monitoring across all habitats and taxonomic groups, ancient ecosystem reconstruction, plant-pollinator interactions, diet analysis, invasive species detection, pollution responses, and air quality monitoring. We also discuss the future applications of the method as well as expected technological advances and how they may impact the way that eDNA metabarcoding may used in the future. eDNA metabarcoding is a unique method still in development and will likely remain in flux for some time as technology advances and procedures become standardized. However, as metabarcoding is optimized and its use becomes more widespread, it is likely to become an essential tool for ecological monitoring and global conservation study.
Lithophaga lithophaga is one of the commonest bivalves in the Mediterranean Sea and is present in almost every subtidal calcareous rock. Its reproductive cycle is known only from laboratory studies. Herein, we present data on the species reproductive activities based on localised but mass synchronized spawning events. The species reproduces at the end of the northern hemisphere summer and the majority of significant spawning events occur during the period between full moon and its last quarter. Calm seas are an important pre-requisite for the development of such co-ordinated mass spawning events. 'Gamete to gamete' induction seems to be the most likely proximate cue in synchronising gamete release. Spawning begins with a few individuals but spreads progressively along the coastline. In observed situations, reproductive waves finally affect between 10 and >400 m of coastline from 0 to 10 m depth and last longer than three days. In the reproductive zone, dense gamete clouds reduce visibility to zero over tens of metres along the shallow sea bed. No spawning events of such dimensions have been reported upon before for any bivalve.
Background:
Taxonomic classification of marker-gene sequences is an important step in microbiome analysis.
Results:
We present q2-feature-classifier ( https://github.com/qiime2/q2-feature-classifier ), a QIIME 2 plugin containing several novel machine-learning and alignment-based methods for taxonomy classification. We evaluated and optimized several commonly used classification methods implemented in QIIME 1 (RDP, BLAST, UCLUST, and SortMeRNA) and several new methods implemented in QIIME 2 (a scikit-learn naive Bayes machine-learning classifier, and alignment-based taxonomy consensus methods based on VSEARCH, and BLAST+) for classification of bacterial 16S rRNA and fungal ITS marker-gene amplicon sequence data. The naive-Bayes, BLAST+-based, and VSEARCH-based classifiers implemented in QIIME 2 meet or exceed the species-level accuracy of other commonly used methods designed for classification of marker gene sequences that were evaluated in this work. These evaluations, based on 19 mock communities and error-free sequence simulations, including classification of simulated "novel" marker-gene sequences, are available in our extensible benchmarking framework, tax-credit ( https://github.com/caporaso-lab/tax-credit-data ).
Conclusions:
Our results illustrate the importance of parameter tuning for optimizing classifier performance, and we make recommendations regarding parameter choices for these classifiers under a range of standard operating conditions. q2-feature-classifier and tax-credit are both free, open-source, BSD-licensed packages available on GitHub.
Giant clams are the largest extant bivalves and widespread inhabitants of the Indo-Pacific coral reefs. These organisms are particularly sought after by the food industry because of their large mantle and adductor muscle, while also are relevant to the aquarium trade market. The aquaculture of giant clams is dependent of a land-based hatchery divided in several tanks with different purposes for larval rearing. Prior to reproductive events, broodstock are conditioned and gametogensis is stimulated by frequent food additions, increased photoperiod and intense physical-chemical stability at optimum conditions. Several different methods can be employed to induce spawning, most notoriously the intragonadal injection of serotonin, thermal stress and addition of macerated gonadal tissue of a conspecific. The success of the method is based on spawning occurrence, time for response and events of broodstock mortality. After spawning, gametes are fertilized and a succession of planktonic larval stages is cultured in hatching tanks and raceways. Embryonic development lasts for approximately 12 hours until the hatch of free-swimming and non-feeding trochophore larvae. After 24 hours post-fertilization larvae morph into veliger stage, made evident by the presence of calcium carbonate shells and velum. Veliger larva are fed with live or preserved phytoplankton and must also acquire symbiotic zooxanthellae. The last stage is the pediveliger stage at approximately one week post-fertilization, when settlement takes place and metamorphosis is soon attained.
Trace metal concentrations in the muscle of the bivalve Villorita cyprinoides from the Cochin backwaters (southwest coast of India) were investigated during the monsoon, post-monsoon and pre-monsoon periods. The seasonal average ranges of metals (μg g(-1), dry weight) in the bivalve were as follows: Fe (18,532.44-28,267.05), Co (23.25-37.58), Ni (10.56-19.28), Cu (3.58-11.35), Zn (48.45-139.15), Cd (1.06-1.50) and Pb (3.05-4.35). The marginally elevated metal concentrations in bivalve muscles are probably related to high influx of metals as a result of pollution from the industries and agricultural fields with consequent increased bioavailability of metals to the bivalve. Evaluation of the risks to human health associated with consumption of the bivalves suggested that there is no health risk for moderate shellfish consumers. A regular and continuous biomonitoring program is recommended to establish V. cyprinoides as a bioindicator for assessing the effects of trace metal pollution and to identify future changes to conserve the "health" of this fragile ecosystem.
We write to extol the virtues of filter- feeding bivalve shellfish - clams, mus- sels, oysters and scallops - to give them their due as key players in ecologically sustainable aquaculture in the marine en- vironment and as environmentally sensi- tive monitors and water purifiers. Shell- fish are successfully farmed throughout the world and shellfish culture represents a legitimate use of the marine environ- ment for sustainable food production. An equally compelling case can be made for the primary grazers such as abalone and sea urchins. In recent years it has become all too
The reproductive cycle of the cockle Cerastoderma edule was studied by histological techniques and observation of changes in the condition index during three consecutive years in the Ria de Vigo (Northwest Iberian Peninsula). The onset of gametogenesis took place at the end of the summer (September to October), progressed throughout the winter, and the mature stage was finally reached in spring. The first spawning occurred in April and May and, after gonad restoration, another spawning episode took place in May and June. During the summer (July and August), most of the population showed signs of gonad exhaustion, although a less-intensive spawning event was observed at the end of summer and beginning of autumn. This second episode coincided with a phytoplankton bloom, which acted as a stimulus for spawning. Although a simple measure, the condition index proved to be a good indicator of the gonadal cycle, because it reflected adequately the reserve accumulation during gametogenesis, maximum maturity, and gamete emission. The useful information obtained from this study can be applied in shellfishery management.
SILVA (from Latin silva, forest, http://www.arb-silva.de) is a comprehensive web resource for up to date, quality-controlled databases of aligned ribosomal RNA (rRNA) gene sequences
from the Bacteria, Archaea and Eukaryota domains and supplementary online services. The referred database release 111 (July 2012) contains 3 194 778 small subunit
and 288 717 large subunit rRNA gene sequences. Since the initial description of the project, substantial new features have
been introduced, including advanced quality control procedures, an improved rRNA gene aligner, online tools for probe and
primer evaluation and optimized browsing, searching and downloading on the website. Furthermore, the extensively curated SILVA
taxonomy and the new non-redundant SILVA datasets provide an ideal reference for high-throughput classification of data from
next-generation sequencing approaches.
The black clam, Villorita
cyprinoides, is the most important clam
species landed in India. The State of Kerala
has been, by far, the leading producer of
the species. Nearly all the landings, about
25,000 tons (t)/year are harvested in Vembanad
Lake, the largest estuary, 96 km
(54 mi) long, on the west coast of India.
Nearly 4,000 fishermen harvest the black
clams year-round. They harvest most by
hand while diving in waters from 2.1–2.7
m (7–9 ft) deep. Each collects 150–200 kg
(3–5 bushels)/day. Upon returning from
the harvesting beds, the fishermen and
their families cook the clams and separate
their meats from their shells using simple
sieves. Fishermen’s wives sell the meats
within their local villages and save some
for their families to eat. The shells are sold
through organized fishermen societies to
various industries. A substantial quantity
of sub-fossil black clam shells lies buried
from 22–50 cm (9–20 in) beneath the lake
sediments. They are dredged in a controlled
manner and sold to the same industries.
The stocks of black clams seem to be declining
slowly in the southern part of the lake
because the water has been getting fresher,
but they are not declining in the northern
half. A likely threat to the landings may be
a lack of fishermen in the future.
Motivation:
The application of next-generation sequencing (NGS) technologies to RNAs directly extracted from a community of organisms yields a mixture of fragments characterizing both coding and non-coding types of RNAs. The task to distinguish among these and to further categorize the families of messenger RNAs and ribosomal RNAs (rRNAs) is an important step for examining gene expression patterns of an interactive environment and the phylogenetic classification of the constituting species.
Results:
We present SortMeRNA, a new software designed to rapidly filter rRNA fragments from metatranscriptomic data. It is capable of handling large sets of reads and sorting out all fragments matching to the rRNA database with high sensitivity and low running time.
Serotonin (5hydroxytryptamine, 5-HT) and its receptor ligands induce both oocyte maturation and spawning in zebra mussels (Dreissena polymorpha). The selective serotonin reuptake inhibitors (SSRIs) fluvoxa-mine ("Luvox"), fluoxetine ("Prozac"), and paroxetine ("Paxil") are commonly prescribed drugs for the treat-ment of depression in humans. They act to increase 5-HT neurotransmission by inhibiting reuptake transport proteins at synapses. I tested the efficacy of these drugs at inducing spawning in zebra mussels. All three compounds induced spawning in both sexes at concentrations lower than that for 5-HT itself. Fluvoxamine was particularly potent, inducing spawning in 100% of both sexes at lo-' and 10e6 M. The concentration that induced a significant percentage of animals to spawn was as low as lop9 M for males and and lo-' M for females. The lowest concentra-tion of fluvoxamine to induce spawning was lo-* M for females (40%) and lo-" M for males (20%). Gametes spawned in fluvoxamine (10m5 M and lower) were viable, and swimming trochophores were formed within 20 hours. Fluoxetine was also an effective spawning inducer, causing 100% of males to spawn at 5 X 10m6M. The concentration of fluoxetine required to induce a significant percentage of spawning was as low as 5 X 10e8 M for males and 5 X 10m6 M for females. In both fluvoxamine and fluoxetine, more than 60% of the males spawned within the first hour of exposure. In contrast, paroxetine was a weak spawning inducer. At concentrations of 10e5 and 10e6 M it induced significant, but low (50% and 40%, respectively) percentages of males to spawn. Paroxetine did not induce significant spawning in females. Thus, fluvoxamine, fluoxetine, and paroxetine can induce spawning at low concentrations, and fluvoxamine is the most powerful spawning inducer in any bivalve. These may be useful agents for stimulating invertebrate seroto-nergic mechanisms without applying exogenous 5-HT, and they are potentially important in bivalve aquaculture. Moreover, these results suggest, for the first time, the presence of 5-HT reuptake transporters in bivalve mol-lusts.
Worldwide depletion of fish stocks has led fisheries managers to become increasingly concerned about rebuilding and recovery planning. To succeed, factors affecting recovery dynamics need to be understood, including the role of fisheries-induced evolution. Here we investigate a stock’s response to fishing followed by a harvest moratorium by analyzing an individual-based evolutionary model parameterized for Atlantic cod Gadus morhua from its northern range, representative of long-lived, late-maturing species. The model allows evolution of life-history processes including maturation, reproduction, and growth. It also incorporates environmental variability, phenotypic plasticity, and density-dependent feedbacks. Fisheries-induced evolution affects recovery in several ways. The first decades of recovery were dominated by demographic and density-dependent processes. Biomass rebuilding was only lightly influenced by fisheries-induced evolution, whereas other stock characteristics such as maturation age, spawning stock biomass, and recruitment were substantially affected, recovering to new demographic equilibria below their preharvest levels. This is because genetic traits took thousands of years to evolve back to preharvest levels, indicating that natural selection driving recovery of these traits is weaker than fisheries-induced selection was. Our results strengthen the case for proactive management of fisheries-induced evolution, as the restoration of genetic traits altered by fishing is slow and may even be impractical.
Man has a major impact on marine environments through exploitation of fish resources. Fisheries can induce different selective pressures, either directly, i.e., through elevated mortality (which is often highly selective) or through ecosystem-level responses, as exploitation affects food availability and predation risk in both target and nontarget species. Responses to selection can be observed at two levels. First, at the community level, some species may suffer more from effects of harvesting than others; some may even increase in abundance. Responses by species to exploitation are associated with their life histories. In particular, species with late maturation at large size and with low population growth rate tend to undergo more pronounced declines than early-maturing species with rapid growth. Second, the phenotypic composition within species may also change. If phenotypic variability has a genetic basis, then fisheries-induced selection can result in evolutionary change in life-history traits influencing sustainable yields, behavioral traits (e.g., gear-avoidance behavior), and morphological traits. We discuss the possible implications of fisheries-induced adaptive changes for sustainable fisheries management.
Filter-feeder bivalves and phytoplankton are interdependent. Their interaction plays important role in estuarine and coastal ecosystem. The correlation between bivalve feeding and phytoplankton is highly species specificity and environment dependent. In the background of miniature and nondiatom trend of phytoplankton in coastal seawaters, how bivalve respond and how the response play roles in the phytoplankton community are poorly known. In the present study, by applying DNA metabarcoding approach based on plastid 23S rDNA, this question was addressed by comparing the phytoplankton composition in the seston and the stomach content of blood clam Tegillarca granosa sampled during the growth period from March to November 2020 in an experimental farm on tidal flat in Xiangshan Bay, East China Sea. The result showed that, a total of seven phyla, 55 genera and 73 species of phytoplankton were identified for all samples. Chlorophyta, Bacillariophyta, and Cyanobacteria were found to be three dominant phyla both in the stomach contents and seston. High diversity of pico-sized phytoplankton, which was easy overlooked by microscopy, was revealed both in seston and stomach contents. This result indicated that the clam was able to feed on the pico-sized algae. At the genus level, the most abundant genera were the pico-sized green alga Ostreococcus (6.12 %-67.88 %) in seston and Picochlorum (4.07 %-35.33 %) in the stomach contents. In addition, microalgae of high nutritional value showed trend of higher proportion in stomach contents than that in seston, especially in July and September when significant growth of T. granosa was observed during this period (the body size increased 155 %). Biodiversity of phytoplankton in the seston was totally higher than that in stomach content, however, the changes among the months showed respective trend. Especially in July when the biodiversity was the lowest in seston, that in the stomach content showed the highest. The results indicated that blood clam farming might influence the phytoplankton composition, including those of pico-sized level, although the particular species in seston were mainly correlating with the dominant environmental factors such as temperature, salinity, pH respectively. These results extend the understanding of roles that bivalve aquaculture may play in the changing of coastal phytoplankton community.
To investigate biomarkers representing the physiological and biochemical responses of the brackish-water clam Corbicula japonica, we conducted a full factorial-design experiment to test different water-temperature levels (20 °C and 25 °C), salinity levels (5 and 20 psu), and food-availability levels (0.5 and 2.0 mg suspended solids (SS)·ind−1·d−1). Increase in water temperature significantly decreased superoxide dismutase (SOD) and catalase (CAT) activities and oxyradical-absorbance capacity (ORAC), leading to lipid peroxidation (i.e., oxidative damage). Salinity activated or inhibited these biochemical markers. Food availability supported a detoxification mechanism against oxidative stress. Principal-components and cluster analyses revealed that a total of eight experimental conditions fell into three groups related to water temperature and/or salinity. The shift from Group I (20 °C water temperature) to Group II (25 °C water temperature and 5-psu salinity) demonstrated that the condition index, SOD, CAT, and ORAC had significantly decreased. With the further shift to Group III (25 °C water temperature and 20-psu salinity), we found a prominent increase in ORAC, which led to oxidative damage but no mortality. We conclude that future habitat changes driven by global warming should be closely watched, particularly given that local anthropogenic disturbances further add to natural ones.
There is a global need to sustainably increase aquaculture production to meet the needs of a growing population. Bivalve shellfish aquaculture is highly attractive from a human nutrition, economic, environmental and ecosystem standpoint. However, bivalve industry growth is falling behind fish aquaculture due to critical problems in the production process. Feed defects, disease, and quality issues are limiting production. New advances in microencapsulation technology have great potential to tackle these problems. Microencapsulated diets could efficiently deliver high-quality nutrients, disease control agents, and quality enhancers to bivalves. Microencapsulation has the potential to drive improvements in bivalve production, reduce production costs, enhance human nutrition and minimise impacts on the environment.
In the 12 years since Dudgeon et al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in the world's lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only 2.3% of the Earth's surface, these ecosystems host at least 9.5% of the Earth's described animal species. Furthermore, using the World Wide Fund for Nature's Living Planet Index, freshwater population declines (83% between 1970 and 2014) continue to outpace contemporaneous declines in marine or terrestrial systems. The Anthropocene has brought multiple new and varied threats that disproportionately impact freshwater systems. We document 12 emerging threats to freshwater biodiversity that are either entirely new since 2006 or have since intensified: (i) changing climates; (ii) e‐commerce and invasions; (iii) infectious diseases; (iv) harmful algal blooms; (v) expanding hydropower; (vi) emerging contaminants; (vii) engineered nanomaterials; (viii) microplastic pollution; (ix) light and noise; (x) freshwater salinisation; (xi) declining calcium; and (xii) cumulative stressors. Effects are evidenced for amphibians, fishes, invertebrates, microbes, plants, turtles and waterbirds, with potential for ecosystem‐level changes through bottom‐up and top‐down processes. In our highly uncertain future, the net effects of these threats raise serious concerns for freshwater ecosystems. However, we also highlight opportunities for conservation gains as a result of novel management tools (e.g. environmental flows, environmental DNA) and specific conservation‐oriented actions (e.g. dam removal, habitat protection policies, managed relocation of species) that have been met with varying levels of success. Moving forward, we advocate hybrid approaches that manage fresh waters as crucial ecosystems for human life support as well as essential hotspots of biodiversity and ecological function. Efforts to reverse global trends in freshwater degradation now depend on bridging an immense gap between the aspirations of conservation biologists and the accelerating rate of species endangerment.
The marine bivalve mollusk Tapes conspersus is mainly distributed in tropical and subtropical waters of the southwestern Pacific Ocean, including coastal areas of China, Japan, Philippines, India, Indonesia, Australia and New Zealand. The species is relatively new to shellfish mariculture, having potentially high economic value and good prospects for development. This study used biological productivity methods to investigate the species' reproductive cycle, gonad development, fatness, breeding season, embryo development and larval development in the period from August 2013 to July 2014. In the examination of its breeding cycle, the gonadogenesis of T. conspersus presented a unimodal gametogenic cycle, with one spawning season annually. The gonad development of the species could be divided into five stages: proliferating stage, growing stage, maturing stage, spawning stage and resting stage. This shellfish's mode of reproduction is oviparity, with a slightly greater gonad development among males than female. The species displays gonochorism, with a female to male ratio of 1:1. The spawning season was recorded as from October to March. Peaks in spawning occurred in March, October and November, at water temperatures of 20.3-24.6°C. Fatness peaked at 33.43% in August, and the lowest measure of fatness was in April at ~18.31%. The cultivation of embryos and larvae revealed demersal, elliptically shaped eggs, and the egg diameter ranged from 70 to 80 μm. Under the conditions of water temperatures of 24-26°C and salinities of 28-32, the fertilized eggs developed into D-shaped larvae, 90-110 μm in length, within 16 hours of hatching. After 7-8 days, the D-shaped larvae then developed into late-umbo larvae, 210-230 μm in length. Thereafter, the late-umbo larvae developed into juvenile mollusks within 4-5 days. These observations provide a foundation for the artificial breeding and protection of genetic resources of T. conspersus.
ABSTOACT The dam, Meretrix casta (Chemnitz) WM induced to ipawn in the laboratory on 2 occasioni by mcreating wat«' temperature by 3'-7'C from ambient lemfieraturB. Spawning was intense on both the occasions. The fertilized ovum measured 0.08S mm. After passing through early suges of deveiofsnent, the trochophore stage was attained by 6 hr after spawning. D-shaped free-swimming veli^er larva was fomned by 14 hr. The leva started feeding on the microalga, Isoehrysis gaUfana, from the second day after qtawning. The larvae sMtled as spat on dghtfi or nkth day measuring 0.216 mm x 0.201 mm 0ength x height). It attained a size of 2.5 mm x 2.3S mm by SOth day. Pigmentation ctf the periostracum varied leading to muiy mortis, of wbidi S major types could be recognized. Spat numbering about 50000 were produced in each experimmt. The clam, Meretrix casta (Chrannitz) of Family Venwidae, is one of the commercially impOTtant bivalves in India (Al^arswami and Meiyiqjpan 1989). Itiswidelydistributedatong the east and southwest coasts of India and formssustenance fishoy in themmtime states of KamataKa, Kerala, Tamil Nadu and Andhta Pradesh. Besides fishing of Uve cUms, exten-sive quarrying of sub-fossil cteposits of this species is carried out alcMig the coasts. There have not been any attempts on M. casta for developing hatchay techniques. Kqierimaits were conducted on M. casta and the Insults are presented in this paper.
The culture of live microalgae to feed larvae and spat is one of the major bottlenecks in bivalve culture. Consequently, there is a strong need for alternative diets to replace live microalgae as food for bivalves in commercial and research hatcheries. This article initially reviews the literature on the nutritional requirements of bivalves and continues with a review of the development of alternative and artificial diets for bivalves. Although a limited number of such diets have been assessed experimentally, their nutritional value is currently limited by a general lack of knowledge of the nutritional requirements of bivalves. The importance of the development of artificial diets, whose nutritional composition can be precisely manipulated, in order to study bivalve nutrition is emphasized. In the absence of clearly defined artificial diets, dietary vehicles such as microcapsules and spray-dried microalgae are currently the most promising tools to study the nutritional requirements of bivalves.
The effects of salinity on the embryonic development, growth, and survival of D-larvae to plantigrade as well as settling in Placuna placenta were studied. Embryos were developed to D-larvae of shell length (SL) 86±12 μm (SL±S.D.) after 20 h at salinities of 22–34 ppt, but not at lower salinity levels. Percentage production of straight-hinged larvae from fertilized eggs at these salinities ranged from 51% to 63% (P≥0.05). P. placenta larvae survived and settled in salinities of 16–34 ppt. Settlement occurred first (14 days) in salinities of 22–34 ppt and later (19 days) in 16 ppt when SL≥200 μm. Larval size at metamorphosis was not significantly different among these salinities (P≥0.05). Percentage survival of plantigrades at 34 ppt (13%) was significantly higher (P≤0.05) than at 16 ppt (4.5±3%), but not greater than at 22 (6.3±3%) or 28 ppt (7±4%) salinity. The best salinity levels for embryonic development and larval survival at metamorphosis ranged from 22 to 34 ppt and larval growth from 16 to 34 ppt. The tolerance of P. placenta to lower and higher salinities progressively increased as larvae develop from embryo to the plantigrade stage.
Six species of tridacnid clams were induced to spawn by intragonadal injection of 2 mM serotonin solution. Dosages ranging from 0.5 ml to 7.0 ml were tested in situ and in laboratory-held clams. Mean time to first-spawning of sperm in all species ranged from 1.7 to 3.8 min. Egg spawning followed sperm in four species but only reliably in Hippopus hippopus.
Spawning was successfully induced in four bivalves, Saccostrea cuccullata, S. commercialis, Perna viridis, and P. indica, by osmotic and biological stimulation. The response to rapid salinity change is considered to have an adaptive value. The ecological implications of this adaptive response are indicated.
Serotonin induced spawning in six bivalve species using individual spawning techniques without any additional stimuli. Intragonadal injection of serotonin induced spawning in the bay scallop Argopecten irradians, the American oyster Crassostrea virginica, and the surf clam Spisula solidissima. Injection of serotonin into the anterior adductor muscle of the ocean quahog Arctica islandica, the ribbed mussel Geukensia demissa, and the hard clam Mercenaria mercenaria induced spawning. The dosage of 0.4 ml of 2 mM serotonin solution used in this study stimulated bivalves to spawn within 15 min.
T h s study tested the hypothesis that mesozooplankton, particularly crustaceans, inhaled by mussels Myülus eduhs (L.) would be kiiied by ingestion, or by incorporation into pseudofaeces. Crustaceans were expected to be vulnerable because they cannot nd themselves of mucus. Field and laboratory evidence is presented to show that mussels ingest most mesozooplankton present in inhaled sea water. that some of the material is tnturated in the stomach between crystalline style and gastric shield, and that energy can be extracted from a diet of Artemia sp. indicating a degree of carnivory. Gastric processing of 'prey' anirnals is rapid (<40 min at 15 to 20°C). MolIuscs and crustaceans are com-monest 'prey'. Animals < 3 to 6 rnm length are ingested. Inhaled but non-ingested crustaceans become mucus-bound and are expelled in pseudofaecal particles; such animals are dead or moribund.
Age-specific exploitation of a natural population acts as a selective force on genetic variation in life history traits. Evolution arising from this selection may bring about evolutionary changes in the total yield which the population is able to sustain. An analysis of this process is given for a harvested population with densitydependent recruitment, in which selection of life history traits by cropping is independent of density and frequency. Evolution of the total yield depends on an interplay between the yield from an individual over the course of its life and recruitment; whether the total yield increases or decreases depends on the properties of particular populations. Evolution brought about by harvesting does not, in general, lead to the maximization of the total yield. Nonetheless, by appropriate choice of an age-specific harvest pattern, it is possible in principle to select the life history which gives the maximum total yield following evolution; this harvest pattern is called the evolutionarily stable optimal harvesting strategy (ESOHS). Results of the analysis are illustrated with data on the Arcto-Norwegian cod.
The salinity of sea-water, like its temperature, is one of the abiotic factors having a remarka ble innuellce on the development of oysters as is well known from the work of Amemiya (1921. 1926 and 1928), Nelson ( 1921), Seno, Hor; and Kusakabe (1926), Hopkins (1931), Gaarder (1932, 1933), and Gaarder and Bjerkan (1934) on differ~nt species of European, Ja panese, Portuguese and American origin.
The reproductive cycle of Crassostrea madrasensis (Preston) inhabiting an estuarine environment (Mulki, latitude 13°5′N and longitude 74°46′E, southwest coast of India) was investigated from April 1975 to March 1976. The histological study of the gonad revealed two restricted spawning periods. A major spawning activity was evident from mid-April to June. This was followed by a gametogenically inactive phase during late July, August and September. Sex differentiation commenced in mid-September and early October. A minor spawning activity followed and continued until the end of November. From December to March 1976, the popualtion continued to remain in a state of active gametogenesis; no spawning was observed. The southwest monsoon rainfall causes a seasonable decrease in the salinity of this region. The stepping down of salinities to oligohaline conditions, and the subsequent stepping up of salinities to marine conditions during the annual period, synchronizes the gametogenic pattern.