Apocyclops Royi Research Articles

Transcriptomic and Microbiome Analyses of copepod Apocyclops royi in Response to an AHPND-causing strain of Vibrio parahaemolyticus

Copepods are small crustaceans that live in microorganism-rich aquatic environments and provide a key supply of live food for fish and shellfish larviculture. To better understand the host-pathogen interaction between the copepod and Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VPAHPND), the comparative transcriptome and microbiome analyses were conducted in copepod Apocyclops royi-TH following VPAHPND infection. Transcriptome analysis identified a total of 836 differentially expressed genes, with 275 upregulated and 561 downregulated genes. Subsequent analysis showed that a total of 37 differentially expressed genes were associated with the innate immune system, including 16 upregulated genes related to Toll-like receptor signaling pathway, antimicrobial peptides, and stress response genes, and 21 downregulated genes associated with immunological modulators, signaling molecules, and apoptosis-related proteins. Analysis of the copepod microbiome following VPAHPND infection showed that the microbes changed significantly after bacterial infection, with a reduced alpha diversity accompanied by the increased level of Proteobacteria and decreased levels of Bdellovibrionota, Bacteroidota, and Verrucomicrobiota. The population of Vibrio genera were increased significantly, while several other genera, including Denitromonas, Nitrosomonas, Blastopirellula, Fusibacter, Alteromonas, KI89A_clade, and Ruegeria, were decreased significantly after infection. These findings suggest that VPAHPND infection has a significant impact on the immune defense and the composition of the copepod microbiota.

Coping with salinity change: How does the cyclopoid copepod Apocyclops royi (Lindberg 1940) do it?

The cyclopoid copepod species Apocyclops royi has attracted significant attention due to its importance in marine food webs and its role as a vital food source for many marine organisms, particularly marine fish larvae. This study aims to understand the activity patterns, osmoregulation mechanisms, and physiological adaptations of A. royi in response to acute decreasing salinities. In total three experiments were conducted. The first two experiments both investigated behavioural change and survival as a function of acute decreasing salinities in the range from 32 to 0, with steps of salinity reductions of five. The third experiment investigated the correlation between internal and external osmolality in A. royi, by using a novel method developed for the experiment. The first experiment indicated that A. royi behaviour and survival were not affected at salinities from 20 and higher. Surprisingly, some copepods were able to survive an acute decrease in salinity from 32 to 0. The second experiment utilized, for the first time for this copepod species, an in situ Multispecies Freshwater Biomonitoring system, to further observe A. royi's behaviour. The results showed that the system was able to monitor A. royi activity level. The system both documented that A. royi exhibit a statistically significant increase in activity levels in response to light. Furthermore, it provided knowledge about the temporal activity level of A. royi as a function of acute decreases in salinities, providing insights into that A. royi has an ~3 h acclimatization time to an acute decrease from 32 to 0 salinity. In the third experiment, the osmolality of the copepods' body fluids with relation to external osmolality was examined using a vapor pressure osmometer. In this context a new method to extract body fluids from A. royi was developed. The body fluid osmolality of copepods exposed to three different salinities 10, 20 and 32 was examined. The results showed that A. royi is an osmoconformer at a higher salinity 32 but initiates hyperregulation at a lower salinity 10. Furthermore, it was observed that when copepods were exposed to a salinity of 10, 1000 individuals (stage: C5 or adults) were needed to obtain one sample of body fluid (10 μL) whereas when exposed to a salinity of 32, 3000 individuals were required to extract the same amount of body fluid. Overall, the findings demonstrated that A. royi has a high tolerance for acute decreases in salinity, showcasing behavioural adaptations and osmoregulatory capabilities, at extreme salinities. These results contribute to our understanding of copepod physiology and their ability to thrive in various habitats. Further research is needed to fully comprehend the physiological mechanisms underlying A. royi's adaptation abilities to acute decreases in salinity.

First feeding of a marine ornamental fish, the White‐barred Goby Amblygobius phalaena: Investigating the optimal initial live feed organisms and optimal feeding density

AbstractObjectiveThe White‐barred Goby Amblygobius phalaena is a popular ornamental fish in the marine aquarium market. To achieve successful commercial production, efficient larval rearing techniques are crucial. Previous studies have achieved successful cultivation of White‐barred Goby larvae by using a combination of three live feed organisms—the ciliate Euplotes sp., the rotifer Brachionus rotundiformis, and the copepod Apocyclops royi nauplii—during the first feeding stage. However, the specific contributions of these live feed organisms to larval survival and growth remain unclear. Moreover, the optimal feeding density for the critical initial live feed organism has not been determined experimentally. In this study, we aimed to enhance the larviculture protocol for White‐barred Goby by introducing Portuguese oyster Crassostrea angulata trochophores and by addressing these knowledge gaps.MethodsLarvae were initially cultured through individual and combined feeding with four live feed organisms: Euplotes sp., Portuguese oyster trochophores, B. rotundiformis, and A. royi nauplii. The objective was to identify the optimal initial live feed organism during the first feeding stage by assessing the survival and growth performance of larvae. Subsequently, using this optimal live feed organism, larvae were cultured at four feeding densities (2, 5, 10, and 20 individuals/mL). Through evaluating feeding incidence, feeding intensity, survival, and growth performance, the aim was to determine the optimal feeding density for the selected live prey.ResultOur experiments revealed that White‐barred Goby larvae could consume both oyster trochophores and Euplotes sp. during the first feeding stage. However, larvae exhibited superior survival and growth performance when fed oyster trochophores. The optimal feeding density of oyster trochophores was determined to be 10 individuals/mL, while a feeding density as high as 20 individuals/mL resulted in decreased larval feeding incidence.ConclusionThese findings have significant implications for enhancing larval production programs for marine ornamental gobies and promoting their sustainable commercialization.

Efficacy of Apocyclops royi (Cyclopoida, Copepoda) Nauplii as Live Prey for the First Feeding Larvae of Silver Pompano, Trachinotus blochii (Lacepède, 1801)

In the rearing of first exogenous feeding, marine finfish larvae availability of live prey with suitable size and nutritive content is vital for their growth and survival. Copepods represent an important alternative food to present traditional live feed organisms used in marine fish hatcheries. Use of copepods is known to improve survival, growth, and development of fish larvae. The silver pompano, Trachinotus blochii (Lacepède, 1801) is one of the suitable candidate species for aquaculture due to its fast growth, good meat quality and high market demand. The present study aimed to investigate the efficacy of Apocyclops royi nauplii in the rearing of first feeding larvae of T. blochii. The feeding experiments were conducted from 3 to 7 Day Post Hatch (DPH) using A. royi nauplii and Brachionus plicatilis (s type) diets. Higher growth of T. blochii larvae was evident with A. royi nauplii than that of rotifer diet. The A. royi nauplii fed experimental group of T. blochii larvae showed significantly different length (p <0.05) compared to rotifer fed larvae and the specific growth rate recorded was 29.42% and 24.28% in A. royi and rotifers fed experimental groups, respectively. On 7 DPH, A. royi nauplii fed T. blochii larvae showed higher mortality than rotifer fed group. With A. royi feed T. blochii larvae produced higher pigmentation which gradually started on the head and dorsal surface of the body from 3 DPH onwards and spread all over the body and became intense as the larvae grew to 7 DPH. Our results suggest the A. royi nauplii are suitable live prey for the T. blochii larvae during the initial feeding phase for better growth and pigmentation.

Resolving the paradox of the ambush feeding cyclopoid copepod Apocyclops royi being microphageous

Abstract The cyclopoid copepod Apocyclops royi is assumed to be an ambush feeder that passively waits for its prey and captures it by a fast surprise attack. This feeding strategy requires an acute sensibility to hydromechanical signals generated by moving prey. However, A. royi in long-term cultures is able to survive microphageously fed solely on Baker’s yeast (Saccharomyces cerevisae), a small, non-motile prey. In this study, we investigate the feeding behavior of A. royi and how it senses S. cerevisae cells. Using high-speed video, we find that A. royi still exhibits an ambush feeding behavior when fed S. cerevisae. Moreover, we characterize the distance and the duration of attack jumps and evaluate the sensitivity of A. royi to fluid disturbances by filming its escaping behavior when caught in a suction flow simulating a predator, e.g. a fish larva. We demonstrate that its sensitivity to fluid disturbances is very similar to that of other copepod species. Thus, we find that remote detection of S. cerevisae cells due to hydromechanical signals is unlikely as the particles are small (3.8 ± 1.3 μm) and non-motile, and that A. royi likely senses S. cerevisae cells by randomly touching them with setae on their first antennae.

An Individual-Based Model to Quantify the Effect of Salinity on the Production of Apocyclops royi (Cyclopoida, Copepoda)

In this study, an individual-based model (IBM) was established and applied to simulate the effects of salinity variations on the productivity of a promising live feed cyclopoid copepod Apocyclops royi for aquaculture applications. The model integrates the effect of salinity on the different reproductive traits and temperature on female longevity. To calibrate the model developed on the Mobidyc platform, we collected data from previous literature and conducted complementary experiments. The model outputs on total nauplii production match the experimental results. Both showed a progressive increase in nauplii production from 0 up to 21 PSU, beyond which the production decreases. There were no significant differences between the estimated nauplii production and the observed ones for most salinity conditions. We then used the model to estimate the egg and nauplii production of a population initiated with 1,000 females along a salinity gradient from 0 to 39 PSU during 20-d cultivation. Around the optimal salinity of 21 PSU, the egg and nauplii production peaked at 1.8x105 eggs and 1.39x105 nauplii, respectively. A deviation of 7 PSU from the optimal salinity range would lead to a loss of 22 to 25% in egg and nauplii production. The results indicate that implementing the IBM into a life-cycle model provides useful tool for managing the risks of salinity variation on the copepod productivity in aquaculture conditions.

RNA-seq transcriptome analysis and identification of the theromacin antimicrobial peptide of the copepod Apocyclops royi

Copepods, including Apocyclops royi, are small aquatic crustaceans and one of the important foods for fish and shellfish larvae. However, studies of the host-pathogen interactions and understanding of infectious disease in copepods are still very limited, yet they are likely to be a significant factor in the sustainable development of copepod aquaculture. In the present study, we performed de novo RNA sequence analysis of A. royi-TH (a Thai isolate of A. royi), which yielded 4.80 Gb bases of clean data and a total of 29,786 unigenes. Annotation was then performed by comparison against seven functional databases, yielding 17,617 (NR: 59.15%), 2,969 (NT: 9.97%), 15,023 (SwissProt: 50.44%), 14,543 (KOG: 48.82%), 15,077 (KEGG: 50.62%), 6,763(GO: 22.71%), and 15,841 (InterPro: 53.18%) unigenes. In comparison to the components of the shrimp Toll pathway, LGBP, Spätzle, Toll receptors, MyD88, Pelle, TRAF6, Dorsal, and Cactus homologs were successfully identified in A. royi-TH. Additionally, a novel antimicrobial peptide (Theromacin-like) was characterized in A. royi (ArTM-like). The ArTM-like ORF was 279 bp and predicted to encode for 92 amino acid residues, with a mature peptide of 75 amino acids and a molecular mass of 8.56 kDa. The genomic organization of the ArTM-like gene consisted of three exons and two introns. Expression analysis indicated that ArTM-like mRNA was abundantly expressed in copepodid and adult stages as an immune responsive gene after infection with the pathogenic Vibrio parahaemolyticus-(AHPND)-causing strain. Altogether, the knowledge obtained in this study will provide a basis for future functional studies of the molecular mechanisms in copepod immunity that may eventually be applied for disease prevention in copepod aquaculture.

Molecular characterization of biosynthesis of polyunsaturated fatty acids during different developmental stages in the copepod Apocyclops royi

Copepod Apocyclops royi can biosynthesize long-chain polyunsaturated fatty acids (LC-PUFAs) when fed low-PUFA precursors. Previously, two elongases and two desaturases in the n-3 PUFA biosynthetic pathway were identified from A. royi. However, the complete PUFA biosynthesis pathway in this copepod species is poorly understood. Here, we report 13 genes, of which nine are novel genes, encoding PUFA biosynthesis-related enzymes belonging to the fatty acid desaturases (ArD6D, ArD5D, ArD4D, ArO3D-1, and ArO3D-2) and elongases (Elovl1, 2, 3, 4, 5, 6, 7, and 8) families identified from a Thai culture of A. royi (A. royi-TH). Identification of the fatty acid contents using gas chromatography/mass spectroscopy analysis indicated that the copepodid and adult stages were high in PUFAs, with omega-3 fatty acids, while the nauplius stage had the lowest level of PUFAs. Moreover, all copepod stages of A. royi-TH fed Tetraselmis suecica contained higher levels of LC-PUFAs, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), than the microalgae fatty acid content, which was deficient in omega-3 DHA. Changes in transcript expression levels were determined in three developmental stages of A. royi-TH. Interestingly, the increased gene expression of the fatty acid desaturases (ArD6D, ArD5D, ArD4D, ArO3D-1, and ArO3D-2) and elongases (ArElovl3, 4, 5, 6, and 7) in the adult stages was reflected in the increased fatty acid concentration of DHA and EPA in the adult stages compared with the other developmental stages, suggesting the possible function of these genes for LC-PUFA synthesis in the different copepod developmental stages. These results indicate that the nauplius, copepodid, and adult stages are capable of synthesizing DHA from low PUFA through a LC-PUFA biosynthesis pathway.

Can we adjust a marine cyclopoid copepod to freshwater?—First step towards a ‘universal’ live feed product for fish and shrimp larvae

The copepod Apocyclops royi tolerates very low salinity while being highly capable of synthesizing n-3 fatty acids based on PUFA-poor diets. The feasibility of culturing A. royi in freshwater fed with baker's yeast was evaluated. The copepods were adjusted for 8 days by decreasing stepwise from salinity 20 to freshwater diluting with deionized water. Initially, the cultures exhibited adequate survival and reproduction. However, after 10 days in freshwater, they stopped reproducing presumably due to the lack of vital ions in the medium. Therefore, before continuing the freshwater cultures, we tested the survival of a batch of salinity 1 pre-acclimated adults and copepodites in various types of freshwater: deionized, bottled ‘mineral’ and tap water for 48 h. All copepods died in deionized water, but a significantly higher survival, 29% ± 11%, was found in mineral water versus 11% ± 8% in tap water. Hence, we continued culturing the copepods in freshwater using ‘Maglekilde spring’ water as diluter. The copepods regained and kept reproducing until day 71 where the experiment was terminated. After a 48 h freshwater versus salinity 20 exposure, nauplii survival was significantly less in freshwater 25 ± 12 versus 79 ± 20 (±STD) at salinity 20 but not different in mean body length. For the first time, we conducted NMR metabolomics revealing a large decrease in glycine betaine and a large increase in lactate in the copepods when challenged by freshwater versus salinity 20. There is obviously a ‘price to pay’ when culturing not only the copepods in freshwater, but also perspectives in developing a ‘universal’ A. royi live-feed product.

Evaluation of high-density tank cultivation of the live-feed cyclopoid copepod Apocyclops royi (Lindberg 1940)

Copepods are considered relevant live feed for fish larval marine aquaculture. They promote fish larval survival and growth rate and reduce deformities when used as food source. The cyclopoid copepod Apocyplops royi are among others used in extensive Taiwanese aquaculture. However, knowledge on its performance in intensive cultures is limited. This study investigates parameters that are relevant prerequisites before initiating intensive tank cultures with A. royi. We found that the biochemical profile of A. royi is promising and relevant when used as live feed with a C:N ratio of 4.7 and a fatty acid ratio (DHA/EPA 3.2 ± 0.7) that fulfil the minimum quantitatively dietary requirement of essential FAs for marine fish larvae and early juveniles. The size range of nauplii (78 - 245 μm) is evaluated to be a feasible size for small mouthed first feeding marine fish larvae. The copepod exhibits similar specific growth rates as other cyclopoids (10% DW d−1). Further, we tested A. royi populations relative composition (nauplii, copepodites, males, females and ovigerous females) as an effect of culture densities and found no change within the test range (300 to 3800 ind. L−1). To evaluate the recruitment into the population we conducted an experiment with densities from a few hundred to 10,000 ind. L−1. We observed no density limitation on the female ovigerous rate = ((ovigerous females) / copepodites + adults) x 100) ~6%) even at very high densities. We demonstrated, that A. royi is a promising candidate for intensive copepod cultures and a relevant live feed for marine larval fish culture.

Biochemical adaptation by the tropical copepods Apocyclops royi and Pseudodiaptomus annandalei to a PUFA-poor brackish water habitat

The cyclopoidApocyclops royi(Lindberg 1940) and the calanoidPseudodiaptomus annandalei(Sewell 1919) are 2 tropical copepods suspected of having the capability to biosynthesize the physiologically important n-3 polyunsaturated fatty acids (n-3 PUFAs) eicosapentaenoic acid (C20:5n-3, EPA) and docosahexaenoic acid (C22:6n-3, DHA). We demonstrated this suspected ability using13C18α-linolenic acid (C18:3n-3, ALA) fed to the copepods through liposomes and a subsequent fatty acid (FA) analysis by GC-MS at 3 different time points (0, 24, and 48 h). Two different diets were applied post liposome exposure: baker’s yeastSaccharomyces cerevisiaeand the microalgaDunaliella tertiolecta.For both copepods, further elongated and desaturated13C n-3 PUFAs were found at all time points. At T48h,A. royiandP. annandaleicontained13C-labelled DHA contents (±SD) of 1.3 ± 0.2 and 0.7 ± 0.3 µg13C-FA mgCcopepod-1when fed baker’s yeast, respectively, and 1.2 ± 0.1 and 1.6 ± 0.5 µg13C-FA mgCcopepod-1when fedD. tertiolecta, respectively, with significant differences observed only betweenP. annandaleidiet treatments. The13C-labelled EPA content ofA. royiandP. annandaleiat T48hwas 0.6 ± 0.4 and 0.7 ± 0.4 µg13C-FA mgCcopepod-1when fed baker’s yeast and 0.8 ± 0.2 and 0.3 ± 0.1 µg13C-FA mgCcopepod-1when fedD. tertiolecta, with significant differences only between copepods fedD. tertiolecta.A. royiandP. annandaleiexhibited an ability to produce n-3 PUFAs from the precursor ALA in comparatively large quantities. This ability enables these 2 species to inhabit habitats characterized by PUFA-poor particulate material.

Does resource availability influence the vital rates of the tropical copepod Apocyclops royi (Lindberg, 1940) under changing salinities?

Abstract The physiology of invertebrates inhabiting many coastal ecosystems is challenged by strong temporal fluctuations in salinity. We investigated how food availability influences vital rates in the tropical cyclopoid copepod Apocyclops royi subjected to different salinities (5–32 PSU). We hypothesized that (i) mortality decreases and egg production rate increases with food availability; (ii) under suboptimal salinity, mortality increases and the egg production rate is reduced and (iii) the threshold concentration for egg production (the lowest food concentration where egg production is initiated) shifts to higher food concentrations when challenged by salinity. Surprisingly, A. royi survived, ingested food and produced eggs at all tested salinities. Mortality rate was, however, dependent on salinity level, but not on food availability. Mortality increased (~12% h−1) during short-term (1 h) salinity acclimatization to 5 PSU and during the following 24-h incubations (~5% d−1) compared with higher salinities. Feeding and egg production rates increased with food availability up to an optimum at all salinity levels, with no effect of salinity on the lowest food concentration initiating egg production. This reveals a high-salinity tolerance by A. royi and may partly explain why this particular copepod is so successful compared with its congeners in occupying extreme habitats.

The Whole Genome Sequence and mRNA Transcriptome of the Tropical Cyclopoid Copepod Apocyclops royi.

Copepoda is one of the most ecologically important animal groups on Earth, yet very few genetic resources are available for this Subclass. Here, we present the first whole genome sequence (WGS, acc. UYDY01) and the first mRNA transcriptome assembly (TSA, Acc. GHAJ01) for the tropical cyclopoid copepod species Apocyclops royi. Until now, only the 18S small subunit of ribosomal RNA gene and the COI gene has been available from A. royi, and WGS resources was only available from one other cyclopoid copepod species. Overall, the provided resources are the 8th copepod species to have WGS resources available and the 19th copepod species with TSA information available. We analyze the length and GC content of the provided WGS scaffolds as well as the coverage and gene content of both the WGS and the TSA assembly. Finally, we place the resources within the copepod order Cyclopoida as a member of the Apocyclops genus. We estimate the total genome size of A. royi to 450 Mb, with 181 Mb assembled nonrepetitive sequence, 76 Mb assembled repeats and 193 Mb unassembled sequence. The TSA assembly consists of 29,737 genes and an additional 45,756 isoforms. In the WGS and TSA assemblies, >80% and >95% of core genes can be found, though many in fragmented versions. The provided resources will allow researchers to conduct physiological experiments on A. royi, and also increase the possibilities for copepod gene set analysis, as it adds substantially to the copepod datasets available.

N-3 PUFA biosynthesis by the copepod Apocyclops royi documented using fatty acid profile analysis and gene expression analysis.

ABSTRACTThe cyclopoid copepod Apocyclops royi (Lindberg 1940) is one of two dominant mesozooplankton species in brackish Taiwanese aquaculture ponds. Periodically low n-3 polyunsaturated fatty acid (PUFA) content in seston could potentially be a limiting factor for zooplankton diversity. Apocyclops royi’s potential ability to biosynthesize n-3 PUFA was investigated through a short-term feeding experiment on four species of microalgae. Furthermore, we analyzed the expression of genes encoding putative fatty acid elongase (ELO) and desaturase (FAD) enzymes in A. royi on long-term diets of the PUFA-poor Dunaliella tertiolecta and the PUFA-rich Isochrysis galbana. The copepods exhibited high contents of docosahexaenoic acid (DHA, C22:6n-3) (>20% of total fatty acid) even when DHA-starved for two generations, and no significant differences were found in absolute DHA content between treatments. Transcripts correlating to the four enzymes Elovl4, Elovl5, Fad Δ5 and Fad Δ6 in the n-3 PUFA biosynthetic pathway were identified. Gene expression analysis revealed a significantly higher expression of two desaturases similar to Fad Δ6 in copepods fed PUFA-lacking algae compared to copepods fed algae with high PUFA content. These findings suggest a highly active n-3 PUFA biosynthesis and capability of DHA production in A. royi when fed low-PUFA diets.

Assessment of the fecundity, population growth and fatty acid composition ofApocyclops royi(Cyclopoida, Copepoda) fed on different microalgal diets

The brackish cyclopoid copepod Apocyclops royi is used in Taiwanese aquaculture industry as a prey for fish larvae. This study investigated the effects of seven microalgal diets, namely single-species diets of Isochrysis galbana (ISO), Nannochloropsis oculata (NAN), and Tetraselmis chui (TET), two-species diets (ISO+NAN, ISO+TET and TET+NAN), and a three-species diet (ISO+NAN+TET), on the population growth, female fecundity and fatty acid composition of A. royi. For reproductive traits, the combination ISO+NAN was found to be the most supportive diet for both population growth and female fecundity. For nutritional value, copepods fed ISO and ISO+NAN were detected to have the highest content of docosahexaenoic acid (DHA) (18.99% and 10.73% total fatty acid, respectively) and, more importantly, a high DHA/EPA ratio (6.09 and 4.09, respectively). Additionally, a comparison of fatty acid composition between copepods and microalgae gives a tentative indication that A. royi may have the ability to synthesize long-chain polyunsaturated fatty acids (PUFA) from short-chain PUFA. Our findings illustrate that ISO+NAN is the most suitable microalgal diet for mass culturing A. royi because it increases productivity and enhances the nutritional value of the copepods for use as fish larvae prey.

Effects of cold selective breeding on the body length, fatty acid content, and productivity of the tropical copepod Apocyclops royi (Cyclopoida, Copepoda)

Effects of cold selective breeding on the body length, fatty acid content, and productivity of the tropical copepod Apocyclops royi (Cyclopoida, Copepoda)

An analysis of how to improve production of copepods as live feed from tropical Taiwanese outdoor aquaculture ponds

The motivation for this study was to analyse the productivity of Taiwanese aquaculture ponds while providing recommendations for a more effective copepod harvesting. Hence, variations in copepod species composition, biomass and productivity were investigated during four separate 3weeks of intensive sampling campaigns across an annual season. The ponds showed seasonal changes, with relatively colder water at 20°C and lower chlorophyll-a in the winter (January 2014) compared to warm water 32°C and higher chlorophyll-a during the long summer season (April, July, October 2013). Differences between seasons were found for phytoplankton pigments concentration in the seston. Inorganic nutrients were never limited, and the average availability of phytoplankton such as diatoms and haptophytes was sufficient to support maximal growth of zooplankton. The copepod community was characterized by low species diversity with Pseudodiaptomus annandalei and Apocyclops royi as main species. Adult copepods and copepodite stages showed total maximum biomass in October and January with 383±35μgCL−1 and 352±74μgCL−1, respectively, where the farmers harvesting effort was minimal. The secondary production, evaluated by the nauplii and copepodites carbon specific growth, was stable at 0.36±0.10d−1 and 0.50±0.05d−1, respectively. The fatty acid composition in the copepods was highly favourable during the winter campaign of which also coincided with a favourable phytoplankton composition. Lastly, this study shows evidence on the yearlong availability of copepods to the pond managers, which, based on standing stock and secondary productivity, easily could improve and intensify their harvest effort. Nauplii could be harvested all year long and adult copepods and copepodites could also be collected during the winter, allowing the pond managers to expand the sales period and thereby increase their revenue.

Natural resource landscapes of a marine bacterium reveal distinct fitness-determining genes across the genome.

Heterotrophic bacteria exploit diverse microhabitats in the ocean, from particles to transient gradients. Yet the degree to which genes and pathways can contribute to an organism's fitness on such complex and variable natural resource landscapes remains poorly understood. Here, we determine the gene-by-gene fitness of a generalist saprophytic marine bacterium (Vibrio sp. F13 9CS106) on complex resources derived from its natural habitats - copepods (Apocyclops royi) and brown algae (Fucus vesiculosus) - and as reference substrates, glucose and the polysaccharide alginate, derived from brown algal cell walls. We find that resource complexity strongly buffers fitness costs of mutations, and that anabolic rather than catabolic pathways are more stringently required, likely due to functional redundancy in the latter. Moreover, while carbohydrate-rich algae requires several synthesis pathways, protein-rich Apocyclops does not, suggesting this ancestral habitat for Vibrios is a replete medium with metabolically redundant substrates. We also identify a candidate fitness trade-off for algal colonization: deletion of mshA increases mutant fitness. Our results demonstrate that gene fitness depends on habitat composition, and suggest that this generalist uses distinct resources in different natural habitats. The results further indicate that substrate replete conditions may lead to relatively relaxed selection on catabolic genes.

Effects of salinity on the reproductive performance of Apocyclops royi (Copepoda, Cyclopoida)

The cyclopoid copepod Apocyclops royi is a dominant species in inland saline ponds and estuarine areas in southern Taiwan. Although it is an ideal live prey candidate for larval fish feed because of its short life cycle, small body size, and easy maintenance, the ecology of the species is poorly documented. In this study, we conducted a series of individual and population experiments to investigate the effects of salinity on the reproductive performance of A. royi. In the population experiments, 8 ovigerous females were cultivated in an 800-mL culture medium at designated salinities (0, 5, 10, 15, 20, 25, 30, and 35) for 14days, after which the population growth, composition of different developmental stages, and clutch size of adult females were quantified. Subsequently, individual experiments were conducted to test the salinity effects (0, 10, 20, and 30) on the nauplii and clutch production of 12 pairs of copepods over 14days. The results showed that salinity significantly affected the reproduction of A. royi, and that 20 was the optimal salinity for attaining their highest productivity. In the population experiments, significantly lower population growth rates were obtained at the extreme salinity treatments (0 and 5, and 30 and 35). However, a reduced clutch size was revealed only at salinities 0 and 5. In the individual experiments, a significantly lower nauplii and clutch production was found at salinities 0 and 30. Salinity had varying influences on A. royi across its different developmental stages. Our findings revealed the reproductive patterns of A. royi under different salinity conditions and indicated how salinity may affect A. royi in their natural habitat. The results offer a crucial recommendation on the manipulated processes for larval feeding in marine and brackish aquaculture hatcheries.

Predation by Apocyclops royi (Cyclopoid: Copepod) on Ciliates and Rotifers

We studied the prey consumption rates in Apocyclops royi on neonate and adult rotifers, Brachionus rotundiformis and ciliate, Euplotes sp. in the presence and absence of algae, the smaller Isochrysis galbana and the larger Tetraselmis chui. Both males and females of A. royi were able to successfully ingest neonate and adult rotifers and ciliate. The prey consumption rates were significantly lower in males than in females of A. royi. Regardless of sex and reproductive state of the copepod, prey consumption rates were higher on neonates rotifer than on adults. However, the prey consumption rates were significantly lower on ciliate than rotifer in the female copepods. Further, the prey ingestion rates did not differ statistically between ovigerous and non-ovigerous adults of A. royi females. The ovigerous rotifer was ingested at lower rates than either non-ovigerous or neonates rotifer by both males and females of A. royi. The presence of algae (no matter I. galbana or T. chui) negatively influenced the rotifer and ciliate consumption rates. The present study provides first information on predatory efficiency of A. royi, and attests its omnivory feeding habit. Our results suggest that A. royi can utilize heterotrophic food efficiently and can derive nutrients during periods of low primary production. The present study points to the role of A. royi in forming a link between the microbial loop and classical food chain, which expedites the flow of bacterial carbon to higher trophic levels in estuarine ecosystems.