Sameer M. Padhye
Full Text Available The present study is a report on the distribution and assemblages of large branchiopods from the Western Ghats of Maharashtra. Different types of water bodies were sampled including pools on lateritic outcrops. Eight species of large branchiopods were found in 72 samples collected over a period of 4 years. We found 7 large branchiopod species in rock pools, while the cyclestheriid Cyclestheria hislopi was observed only in rivers and water reservoirs. In twenty-five percent of the samples multiple species co-occurred with a maximum of 4 species in a single sample. Streptocephalus dichotomus was the most commonly observed species while Streptocephalus sahyadriensis was noted only in rock pools. Altitude and aquatic vegetation were identified as important factors for the distribution of large branchiopods in the studied area. Triops granarius was the species most commonly found to be co-occurring with other species, followed by S. sahyadriensis. Cyclestheria hislopi and Eulimnadia indocylindrova always occurred alone.
Large branchiopods are considered threatened across much of their global range. However, because several regions, including Zimbabwe in general and its south-eastern lowveld in particular, remain largely unstudied, interpretations of species distribution patterns are often based on limited data. A detailed study of large ...
Full Text Available Temporary ponds are the most peculiar and representative water bodies in the arid and semi-arid regions of the world, where they often represent diversity hotspots that greatly contribute to the regional biodiversity. Being indissolubly linked to these ecosystems, the so-called “large branchiopods” are unanimously considered flagship taxa of these habitats. Nonetheless, updated and detailed information on large branchiopod faunas is still missing in many countries or regions. Based on an extensive bibliographical review and field samplings, we provide an updated and commented checklist of large branchiopods in Tunisia, one of the less investigated countries of the Maghreb as far as inland water crustaceans are concerned. We carried out a field survey from 2004 to 2012, thereby collecting 262 crustacean samples from a total of 177 temporary water bodies scattered throughout the country. Large branchiopod crustaceans were observed in 61% of the sampled sites, leading to the identification of fifteen species. Among these, the halophilic anostracan Branchinectella media is here reported for the first time for the country; conversely, four of the species reported in literature were not found during the present survey. Based on literature and novel data, the known large branchiopod fauna of Tunisia now includes 19 species, showing a noteworthy species richness when the limited extension of the country is considered. For each species, the regional distribution is described and an annotated list of references is provided. Under a conservation perspective, the particular importance of the temporary ponds occurring in the Medjerda river alluvial plain is further stressed. In this location, several large branchiopod taxa with different ecological requirements converge and form unique and species-rich assemblages that should be preserved.
D. Christopher Rogers
Full Text Available The large branchiopod crustaceans (fairy shrimp, tadpole shrimp and clam shrimp of South East (SE Asia have only recently been examined with scientific vigor. Although more than 70 species have been reported for Asia and Indonesia, only six native taxa and one introduced species are known from SE Asia. The majority of records are from Thailand, with fewer than three records each from Laos, Myanmar, Malaysia, Cambodia, Vietnam, and Singapore. Eleven genera reported from adjacent regions may potentially occur in SE Asia. Spinicaudatan clam shrimp have been collected from Thailand and Cambodia, but have not been identified beyond genus. Four of the five native fairy shrimp species are endemic to SE Asia. The limited distributions of these few taxa suggest that this region has a distinct branchiopod fauna. In addition, we present new species and records of clam shrimp from Thailand. Future survey efforts will undoubtedly reveal additional taxa.
Lawrence Livermore National Laboratory (LLNL) requested that Condor Country Consulting, Inc. (CCCI) perform wet season surveys and manage the dry season sampling for listed branchiopods in two ponded locations within the Site 300 Experimental Test Site. Site 300 is located in Alameda and San Joaquin Counties, located between the Cities of Livermore and Tracy. The two pool locations have been identified for possible amphibian enhancement activities in support of the Compensation Plan for impacts tied to the Building 850 soil clean-up project. The Building 850 project design resulted in formal consultation with the U.S. Fish and Wildlife Service (USFWS) as an amendment (File 81420-2009-F-0235) to the site-wide Biological Opinion (BO) (File 1-1-02-F-0062) in the spring of 2009 and requires mitigation for the California tiger salamander (AMCA, Ambystoma californiense) and California red-legged frog (CRLF, Rana draytonii) habitat loss. Both pools contain breeding AMCA, but do not produce metamorphs due to limited hydroperiod. The pool to the southeast (Pool BC-FS-2) is the preferred site for amphibian enhancement activities, and the wetland to northwest (Pool OA-FS-1) is the alternate location for enhancement. However, prior to enhancement, LLNL has been directed by USFWS (BO Conservation Measure 17 iii) to 'conduct USFWS protocol-level branchiopod surveys to determine whether listed brachiopod species are present within the compensation area.' CCCI conducted surveys for listed branchiopods in the 2009-2010 wet season to determine the presence of federally-listed branchiopods at the two pools (previous surveys with negative findings were performed by CCCI in 2001-2002 and 2002-2003 onsite). Surveys were conducted to partially satisfy the survey requirements of the USFWS 'Interim Survey Guidelines to Permittees for Recovery Permits under Section 10(a)(1)(A) of the Endangered Species Act for the Listed Vernal Pool Branchiopods' ('Guidelines, USFWS
Full Text Available A survey of the large branchiopod fauna of the Eastern Cape Karoo region of South Africa was undertaken to provide baseline biodiversity information in light of impending shale gas development activities in the region. Twenty-two waterbodies, including nine dams and thirteen natural depression wetlands, were sampled during November 2014 and April 2015. A total of 13 species belonging to four orders were collected, comprising five anostracans, one notostracan, six spinicaudatans and one laevicaudatan. Cyzicus australis was most common, occurring in 46% of the waterbodies. Species co-occurred in 87% of the waterbodies, with a maximum number of six species recorded from the same waterbody. Our new distribution records for Lynceus truncatus, Streptocephalus spinicaudatus and S. indistinctus represent substantial expansions of the previously known ranges for these species. Tarkastad is now the westernmost record for S. spinicaudatus, while Jansenville now constitutes the southernmost record for S. indistinctus. Large branchiopod distribution data from previous Eastern Cape records were combined with our current data, demonstrating that a total of 23 large branchiopod species have been recorded from the region to date. As the Karoo is one of the few major shale basins in the world where the natural baseline is still largely intact, this survey forms a basis for future reference and surface water quality monitoring during the process of shale gas exploration/extraction.
Lessios, Nicolas; Rutowski, Ronald L; Cohen, Jonathan H; Sayre, Marcel E; Strausfeld, Nicholas J
Animals that have true color vision possess several spectral classes of photoreceptors. Pancrustaceans (Hexapoda+Crustacea) that integrate spectral information about their reconstructed visual world do so from photoreceptor terminals supplying their second optic neuropils, with subsequent participation of the third (lobula) and deeper centers (optic foci). Here, we describe experiments and correlative neural arrangements underlying convergent visual pathways in two species of branchiopod crustaceans that have to cope with a broad range of spectral ambience and illuminance in ephemeral pools, yet possess just two optic neuropils, the lamina and the optic tectum. Electroretinographic recordings and multimodel inference based on modeled spectral absorptance were used to identify the most likely number of spectral photoreceptor classes in their compound eyes. Recordings from the retina provide support for four color channels. Neuroanatomical observations resolve arrangements in their laminas that suggest signal summation at low light intensities, incorporating chromatic channels. Neuroanatomical observations demonstrate that spatial summation in the lamina of the two species are mediated by quite different mechanisms, both of which allow signals from several ommatidia to be pooled at single lamina monopolar cells. We propose that such summation provides sufficient signal for vision at intensities equivalent to those experienced by insects in terrestrial habitats under dim starlight. Our findings suggest that despite the absence of optic lobe neuropils necessary for spectral discrimination utilized by true color vision, four spectral photoreceptor classes have been maintained in Branchiopoda for vision at very low light intensities at variable ambient wavelengths that typify conditions in ephemeral freshwater habitats. © 2018. Published by The Company of Biologists Ltd.
Full Text Available Sex-determining mechanisms are diverse among animal lineages and can be broadly divided into two major categories: genetic and environmental. In contrast to genetic sex determination (GSD, little is known about the molecular mechanisms underlying environmental sex determination (ESD. The Doublesex (Dsx genes play an important role in controlling sexual dimorphism in genetic sex-determining organisms such as nematodes, insects, and vertebrates. Here we report the identification of two Dsx genes from Daphnia magna, a freshwater branchiopod crustacean that parthenogenetically produces males in response to environmental cues. One of these genes, designated DapmaDsx1, is responsible for the male trait development when expressed during environmental sex determination. The domain organization of DapmaDsx1 was similar to that of Dsx from insects, which are thought to be the sister group of branchiopod crustaceans. Intriguingly, the molecular basis for sexually dimorphic expression of DapmaDsx1 is different from that of insects. Rather than being regulated sex-specifically at the level of pre-mRNA splicing in the coding region, DapmaDsx1 exhibits sexually dimorphic differences in the abundance of its transcripts. During embryogenesis, expression of DapmaDsx1 was increased only in males and its transcripts were primarily detected in male-specific structures. Knock-down of DapmaDsx1 in male embryos resulted in the production of female traits including ovarian maturation, whereas ectopic expression of DapmaDsx1 in female embryos resulted in the development of male-like phenotypes. Expression patterns of another D. magna Dsx gene, DapmaDsx2, were similar to those of DapmaDsx1, but silencing and overexpression of this gene did not induce any clear phenotypic changes. These results establish DapmaDsx1 as a key regulator of the male phenotype. Our findings reveal how ESD is implemented by selective expression of a fundamental genetic component that is
Pans are isolated, shallow depressions that are endorheic in nature. Because of the natural hydrological functioning of pans, these systems are usually restricted to arid regions and complete desiccation occurs seasonally. In the eastern provinces of South Africa many pans are perennial in nature often remaining inundated ...
Pirow, Ralph; Buchen, Ina; Richter, Marc; Allmer, Carsten; Nunes, Frank; Günsel, Andreas; Heikens, Wiebke; Lamkemeyer, Tobias; von Reumont, Björn M; Hetz, Stefan K
Recent insights into the allosteric control of oxygen binding in the extracellular hemoglobin (Hb) of the tadpole shrimp Triops cancriformis raised the question about the physico-chemical properties of the protein's native environment. This study determined the cationic composition and acid-base state of the animal's extracellular fluid. The physiological concentrations of potential cationic effectors (calcium, magnesium) were more than one order of magnitude below the level effective to increase Hb oxygen affinity. The extracellular fluid in the pericardial space had a typical bicarbonate concentration of 7.6 mM but a remarkably high CO(2) partial pressure of 1.36 kPa at pH 7.52 and 20 degrees C. The discrepancy between this high CO(2) partial pressure and the comparably low values for water-breathing decapods could not solely be explained by the hemolymph-sampling procedure but may additionally arise from differences in cardiovascular complexity and efficiency. T. cancriformis hemolymph had a non-bicarbonate buffer value of 2.1 meq L(-1) pH(-1). Hb covered 40-60% of the non-bicarbonate buffering power. The specific buffer value of Hb of 1.1 meq (mmol heme)(-1) pH(-1) suggested a minimum requirement of two titratable histidines per heme-binding domain, which is supported by available information from N-terminal sequencing and expressed sequence tags.
Olesen, Jørgen; Pöllabauer, Christina; Sigvardt, Zandra Maria Skandrup
A new species of laevicaudatan branchiopod, Lynceus insularis sp. nov., is described. It is reported from five sinkholes (dolines) in the southern part of New Caledonia. Lynceus insularis sp. nov. is closest to Lynceus species from Australia, but can be separated from these on the basis of clasper...
Semmler, Henrike; Wanninger, Andreas; Høeg, Jens T
of the branchiopod, Artemia franciscana Kellogg, 1906 in our analysis. We describe several characteristic neurons in the brains of the nauplius larvae of both species which are also found in decapod larvae and in adult brains of other crustaceans. Furthermore, our data reveal that the naupliar brain of cirripedes...
Jeffery, Nicholas W; Elías-Gutiérrez, Manuel; Adamowicz, Sarah J
The region of Churchill, Manitoba, contains a wide variety of habitats representative of both the boreal forest and arctic tundra and has been used as a model site for biodiversity studies for nearly seven decades within Canada. Much previous work has been done in Churchill to study the Daphnia pulex species complex in particular, but no study has completed a wide-scale survey on the crustacean species that inhabit Churchill's aquatic ecosystems using molecular markers. We have employed DNA barcoding to study the diversity of the Branchiopoda (Crustacea) in a wide variety of freshwater habitats and to determine the likely origins of the Churchill fauna following the last glaciation. The standard animal barcode marker (COI) was sequenced for 327 specimens, and a 3% divergence threshold was used to delineate potential species. We found 42 provisional and valid branchiopod species from this survey alone, including several cryptic lineages, in comparison with the 25 previously recorded from previous ecological works. Using published sequence data, we explored the phylogeographic affinities of Churchill's branchiopods, finding that the Churchill fauna apparently originated from all directions from multiple glacial refugia (including southern, Beringian, and high arctic regions). Overall, these microcrustaceans are very diverse in Churchill and contain multiple species complexes. The present study introduces among the first sequences for some understudied genera, for which further work is required to delineate species boundaries and develop a more complete understanding of branchiopod diversity over a larger spatial scale.
Strullu-Derrien, Christine; Gora, Tomasz; Longcore, Joyce E.
interpreted as branchiopod resting eggs. Confocal laser scanning microscopy enabled us to reconstruct the fungus and its possible mode of nutrition, the affinity of the resting eggs, and their spatial associations. The new fungus (Cultoraquaticus trewini gen. et sp. nov) is attributed to Chytridiomycota based...... on its size, consistent formation of papillae, and the presence of an internal rhizoidal system. It is the most pristine fossil Chytridiomycota known, especially in terms of rhizoidal development and closely resembles living species in the Rhizophydiales. The spiny resting eggs are attributed...
Swinstrom, Kirsten; Caldwell, Roy; Fourcade, H. Matthew; Boore, Jeffrey L.
We report the first complete mitochondrial genome sequences of stomatopods and compare their features to each other and to those of other crustaceans. Phylogenetic analyses of the concatenated mitochondrial protein-coding sequences were used to explore relationships within the Stomatopoda, within the malacostracan crustaceans, and among crustaceans and insects. Although these analyses support the monophyly of both Malacostraca and, within it, Stomatopoda, it also confirms the view of a paraphyletic Crustacea, with Malacostraca being more closely related to insects than to the branchiopod crustaceans.
Sasaki, Mizuki; Akiyama-Oda, Yasuko; Oda, Hiroki
Classical cadherins are a metazoan-specific family of homophilic cell-cell adhesion molecules that regulate morphogenesis. Type I and type IV cadherins in this family function at adherens junctions in the major epithelial tissues of vertebrates and insects, respectively, but they have distinct, relatively simple domain organizations that are thought to have evolved by independent reductive changes from an ancestral type III cadherin, which is larger than derived paralogs and has a complicated domain organization. Although both type III and type IV cadherins have been identified in hexapods and branchiopods, the process by which the type IV cadherin evolved is still largely unclear. Through an analysis of arthropod genome sequences, we found that the only classical cadherin encoded in chelicerate genomes was the type III cadherin and that the two type III cadherin genes found in the spider Parasteatoda tepidariorum genome exhibited a complex yet ancestral exon-intron organization in arthropods. Genomic and transcriptomic data from branchiopod, copepod, isopod, amphipod, and decapod crustaceans led us to redefine the type IV cadherin category, which we separated into type IVa and type IVb, which displayed a similar domain organization, except type IVb cadherins have a larger number of extracellular cadherin (EC) domains than do type IVa cadherins (nine versus seven). We also showed that type IVa cadherin genes occurred in the hexapod, branchiopod, and copepod genomes whereas only type IVb cadherin genes were present in malacostracans. Furthermore, comparative characterization of the type IVb cadherins suggested that the presence of two extra EC domains in their N-terminal regions represented primitive characteristics. In addition, we identified an evolutionary loss of two highly conserved cysteine residues among the type IVa cadherins of insects. We provide a genomic perspective of the evolution of classical cadherins among bilaterians, with a focus on the Arthropoda
Full Text Available Abstract Background Crustacean Hyperglycemic Hormone (CHH family peptides are neurohormones known to regulate several important functions in decapod crustaceans such as ionic and energetic metabolism, molting and reproduction. The structural conservation of these peptides, together with the variety of functions they display, led us to investigate their evolutionary history. CHH family peptides exist in insects (Ion Transport Peptides and may be present in all ecdysozoans as well. In order to extend the evolutionary study to the entire family, CHH family peptides were thus searched in taxa outside decapods, where they have been, to date, poorly investigated. Results CHH family peptides were characterized by molecular cloning in a branchiopod crustacean, Daphnia magna, and in a collembolan, Folsomia candida. Genes encoding such peptides were also rebuilt in silico from genomic sequences of another branchiopod, a chelicerate and two nematodes. These sequences were included in updated datasets to build phylogenies of the CHH family in pancrustaceans. These phylogenies suggest that peptides found in Branchiopoda and Collembola are more closely related to insect ITPs than to crustacean CHHs. Datasets were also used to support a phylogenetic hypothesis about pancrustacean relationships, which, in addition to gene structures, allowed us to propose two evolutionary scenarios of this multigenic family in ecdysozoans. Conclusions Evolutionary scenarios suggest that CHH family genes of ecdysozoans originate from an ancestral two-exon gene, and genes of arthropods from a three-exon one. In malacostracans, the evolution of the CHH family has involved several duplication, insertion or deletion events, leading to neuropeptides with a wide variety of functions, as observed in decapods. This family could thus constitute a promising model to investigate the links between gene duplications and functional divergence.
Nur Syafiqah Mohamad Ishak
Full Text Available Identifying the genes required for environmental sex determination is important for understanding the evolution of diverse sex determination mechanisms in animals. Orthologs of Drosophila orphan receptor Fushi tarazu factor-1 (Ftz-F1 are known to function in genetic sex determination. In contrast, their roles in environmental sex determination remain unknown. In this study, we have cloned and characterized the Ftz-F1 ortholog in the branchiopod crustacean Daphnia magna, which produces males in response to environmental stimuli. Similar to that observed in Drosophila, D. magna Ftz-F1 (DapmaFtz-F1 produces two splicing variants, αFtz-F1 and βFtz-F1, which encode 699 and 777 amino acids, respectively. Both isoforms share a DNA-binding domain, a ligand-binding domain, and an AF-2 activation domain and differ only at the A/B domain. The phylogenetic position and genomic structure of DapmaFtz-F1 suggested that this gene has diverged from an ancestral gene common to branchiopod crustacean and insect Ftz-F1 genes. qRT-PCR showed that at the one cell and gastrulation stages, both DapmaFtz-F1 isoforms are two-fold more abundant in males than in females. In addition, in later stages, their sexual dimorphic expressions were maintained in spite of reduced expression. Time-lapse imaging of DapmaFtz-F1 RNAi embryos was performed in H2B-GFP expressing transgenic Daphnia, demonstrating that development of the RNAi embryos slowed down after the gastrulation stage and stopped at 30-48 h after ovulation. DapmaFtz-F1 shows high homology to insect Ftz-F1 orthologs based on its amino acid sequence and exon-intron organization. The sexually dimorphic expression of DapmaFtz-F1 suggests that it plays a role in environmental sex determination of D. magna.
Mabidi, Annah; Bird, Matthew S; Perissinotto, Renzo
Salinity is an important factor affecting freshwater aquatic species distribution and diversity. The semi-arid Eastern Cape Karoo region of South Africa has been earmarked for shale gas development through hydraulic fracturing. The process uses large amounts of water and produces briny wastewater. When not managed properly, these wastewaters may lead to salinisation of surface freshwater bodies in the region. Therefore, the effect of salinity on the hatching success of crustacean resting eggs was examined using sediments from four depression wetlands found in the region. The sediments were exposed for 28 days to salinity levels of 0.5 g L -1 , 2.5 g L -1 , 5 g L -1 and 10 g L -1 . Control aquaria in which no salt was added were also set up. There was a significant decrease in the emerged taxa richness and abundances at salinities of 2.5 g L -1 and above. Anostraca, Notostraca and Spinicaudata hatchlings were abundant at salinities of 0.5 g L -1 and below, while Copepoda, Daphniidae (Cladocera) and Ostracoda were observed in the highest salinity, but their densities were still lower with increased salinities. Given the importance of large branchiopods in the trophic balance of depression wetlands, their loss may alter the ecological balance and function of these ecosystems.
Wong, Yue Him
The most recent phylogenomic study suggested that Bryozoa (Ectoprocta), Brachiopoda, and Phoronida are monophyletic, implying that the lophophore of bryozoans, phoronids and brachiopods is a synapomorphy. Understanding the molecular mechanisms of the lophophore development of the Lophophorata clade can therefore provide us a new insight into the formation of the diverse morphological traits in metazoans. In the present study, we profiled the transcriptome of the Bryozoan (Ectoproct) Bugula neritina during the swimming larval stage (SW) and the early (4 h) and late (24 h) metamorphic stages using the Illumina HiSeq2000 platform. Various genes that function in development, the immune response and neurogenesis showed differential expression levels during metamorphosis. In situ hybridization of 23 genes that participate in the Wnt, BMP, Notch, and Hedgehog signaling pathways revealed their regulatory roles in the development of the lophophore and the ancestrula digestive tract. Our findings support the hypothesis that developmental precursors of the lophophore and the ancestrula digestive tract are pre-patterned by the differential expression of key developmental genes according to their fate. This study provides a foundation to better understand the developmental divergence and/or convergence among developmental precursors of the lophophore of bryozoans, branchiopods and phoronids.
Suzuki, Masataka G; Tochigi, Mayuko; Sakaguchi, Honami; Aoki, Fugaku; Miyamoto, Norio
The transformer (tra) gene is an intermediate component of the sex determination hierarchy in many insect species. The homolog of tra is also found in two branchiopod crustacean species but is not known outside arthropods. We have isolated a tra homolog in the acorn worm, Saccoglossus kowalevskii, which is a hemichordate belonging to the deuterostome superphylum. The full-length complementary DNA (cDNA) of the S. kowalevskii tra homolog (Sktra) has a 3786-bp open reading frame that encodes a 1261-amino acid sequence including a TRA-CAM domain and an arginine/serine (RS)-rich domain, both of which are characteristic of TRA orthologs. Reverse transcription PCR (RT-PCR) analyses demonstrated that Sktra showed no differences in expression patterns between testes and ovaries, but its expression level was approximately 7.5-fold higher in the testes than in the ovaries. TRA, together with the protein product of the transformer-2 (tra-2) gene, assembles on doublesex (dsx) pre-messenger RNA (mRNA) via the cis-regulatory element, enhancing female-specific splicing of dsx in Drosophila. To understand functional conservation of the SkTRA protein as a dsx-splicing activator, we investigated whether SkTRA is capable of inducing female-specific splicing of the Drosophila dsx. Ectopic expression of Sktra cDNA in insect cultured cells did not induce the female-specific splicing of dsx. On the other hand, forced expression of Sktra-2 (a tra-2 homolog of S. kowalevskii) was able to induce the female-specific dsx splicing. These results demonstrate that the function as a dsx-splicing activator is not conserved in SkTRA even though SkTRA-2 is capable of functionally replacing the Drosophila TRA-2. We have also found a tra homolog in an echinoderm genome. This study provides the first evidence that that tra is conserved not only in arthropods but also in basal species of deuterostoms.
Full Text Available Studying the species distribution of Limnadiidae, a family of crustaceans, in environments favourable to their growth and reproduction is made difficult by their extremely short life cycle and the transient existence of adult forms. However, the eggs of these branchiopods are highly resistant to environmental extremes and persist in the soil of humidified and dried pools. We therefore studied the capacity to detect populations of Limnadiidae and identify them at the species level using egg morphology. We investigated influences of pool sediments on Eulimnadia (clam shrimp egg morphology and asked whether we could rely on this morphology after various lengths of time in the soil to recognise species. We studied sediment collected from temporary pools in four Neotropical areas: Minas Gerais and Bahia (Brazil, French Guiana, and Martinique. These samples represented diverse geographical regions and climates and allowed us to study the four most widely distributed Eulimnadia species in the Neotropics: E. colombiensis, E. cylindrova, E. geayi, and E. magdalensis. Our results indicated that soil abrasion is superficial and does not affect the general shape of the eggs (cylindrical or spherical. However, details of egg ornamentation can be severely affected by the combined effects of erosion and filling with sediments, which can lead to difficulties in species identification. In the particular case of the spherical eggs of E. magdalensis, this species cannot be unequivocally identified without clean eggs collected from adults after breeding or from eggs recently deposited in the field. This work and the investigative methods described herein should facilitate identification of Eulimnadia species and promote further study of Limnadiidae crustaceans in the field.
Full Text Available L'approvisionnement quotidien en nourriture est, en règle générale, le principal facteur limitant de productions à grande échelle de jeunes poissons marins.La pêche de plancton dans la nature a été, et reste, le moyen d'expérimentation le plus immédiat, et le plus satisfaisant sur le plan qualitatif. Mais la récolte des quantités nécessaires, au moment voulu, devient très délicate dès que l'on dépasse l'échelle de l'aquarium. Le développement, ces dernières décennies, de techniques de production en masse d'animaux-proies a permis le lancement d'élevages à grande échelle. Parmi ces proies, le Branchiopode Artemia salina et le Rotifère Brachionus plicatilis dominent incontestablement ; tandis que l'élevage des Copépodes, part la plus intéressante du plancton naturel, reste encore mal maîtrisé. Cependant , l'élevage et l'emploi de proies vivantes, quelles qu'elles soient, imposent la réalisation d'installations coûteuses et l'emploi d'un abondant personnel qualifié. Il en est résulté récemment un important effort de recherche en direction de nourritures inertes, broyats , poudres et aliments composés, généralement abandonnés après les échecs enregistrés pendant les premières années du siècle. Quelques résultats encourageants ont été obtenus, mais ils restent limités et soulèvent de délicats problèmes d'hygiène des bacs d'élevage. L'emploi de proies vivantes , au moins pendant le premier mois des élevages , reste donc encore une obligation. Dans ce contexte, l'essentiel de l'effort actuel tend , d'une part à réduire leur durée d'emploi au minimum possible et, d'autre part, à rendre leur production plus rationnelle , en recherchant des méthodes qui évitent, pour leur alimentation , de faire appel à des algues planctoniques vivantes.