Physiological stress responses of two species of coral trout (Plectropomus leopardus and Plectropomus maculatus)

Validation of the HemoCue Hb 801 portable haemoglobin analyser for fish blood

Haemoglobin concentration ([Hb]) assessment in fish blood has become a routine parameter to measure the health and welfare status of the animals. The original method (haemoglobincyanide method, best known as the Drabkin method) for measuring Hb in human and animals is not well suited for work outside of a laboratory setting. It is relatively time consuming, contains hazardous cyanide elements, and requires specific laboratory material. As an alternative to the Drabkin method, portable analysers have been developed for human blood, but they need to be first validated for fish blood before being used in experiments. In this study, the performance of the new HemoCue Hb 801 portable haemoglobin analyser was compared to the validated Drabkin method to determine [Hb] in three fish species. Hb readings between the two methods were not different for any of the species tested (rainbow trout, Onchorynchus mykiss, Atlantic wolffish, Anarhichas lupus, and Nile tilapia, Oreochromis niloticus). Therefore, this new portable device can be readily used to measure Hb in fish blood. Unlike the previous model from HemoCue, the Hb 201+, this device does not need an incubation time or a correction factor, representing a major gain of time and precision.

De novo sequencing and chromosomal-scale genome assembly of leopard coral grouper, Plectropomus leopardus

The leopard coral grouper, Plectropomus leopardus, belonging to the family Epinephelinae, is a carnivorous coral reef fish widely distributed in tropical and subtropical waters of the Indo-Pacific. Due to its appealing body appearance and delicious taste, P. leopardus has become a popular commercial fish for aquaculture in many countries. However, the lack of genomic and molecular resources for P. leopardus has hindered study of its biology and genomic breeding programmes. Here we report the de novo sequencing and assembly of the P. leopardus genome using a combination of 10 × Genomics, high-throughput chromosome conformation capture (Hi-C) and PacBio long-read sequencing technologies. The genome assembly has a total length of 881.55 Mb with a scaffold N50 of 34.15 Mb, consisting of 24 pseudochromosome scaffolds. busco analysis showed that 97.2% of the conserved single-copy genes were retrieved, indicating the assembly was almost entire. We predicted 25,248 protein-coding genes, among which 96.5% were functionally annotated. Comparative genomic analyses revealed that gene family expansions in P. leopardus were associated with immune-related pathways. In addition, we identified 5,178,453 single nucleotide polymorphisms based on genome resequencing of 54 individuals. The P. leopardus genome and genomic variation data provide valuable genomic resources for studies of its genetics, evolution and biology. In particular, it is expected to benefit the development of genomic breeding programmes in the farming industry.

Variation in DNA methylation is associated with migratory phenotypes of lake sturgeon Acipenser fulvescens in the St. Clair River, MI, USA

Lake sturgeon Acipenser fulvescens populations show a variety of movement patterns that are poorly understood. To compare two migratory phenotypes of A. fulvescens in the St. Clair River, MI, USA, multiple data types were analysed. Individual fish were classified into migratory phenotypes based on acoustic telemetry data collected 2012-2015. Acipenser fulvescens consistently showed movement from the St. Clair River upriver into Lake Huron or downriver into Lake St. Clair. The two migratory phenotypes were then compared for differences in morphometrics, genetics and epigenetics. Morphological differences based on linear measurements were not detected between phenotypes. Microsatellite data from 11 loci suggested one population with no genetic differentiation between migratory phenotypes. Our epigenetic results indicated that the migratory phenotypes are differentially methylated (P < 0.05), thus epigenetics may be associated with migratory differences in A. fulvescens. Only one restriction site was identified to be driving the differential methylation (P < 0.05). While little evidence at neutral loci occurred for genetic differentiation of A. fulvescens, DNA methylation may play a role in the observed movement pattern variation. When combined with microsatellite and morphometric analyses, our results suggested that different migratory patterns may reflect phenotypic plasticity, allowing A. fulvescens to acclimate to short-term environmental variability. Without an integrated approach, the role of epigenetics in the migratory phenotype of A. fulvescens may have been overlooked. Further characterization of migratory phenotypes could be important for management to conserve behavioural variation across the distribution of A. fulvescens and for design of stocking guidelines.

Widespread hybridization and bidirectional introgression in sympatric species of coral reef fish

Coral reefs are highly diverse ecosystems, where numerous closely related species often coexist. How new species arise and are maintained in these high geneflow environments have been long-standing conundrums. Hybridization and patterns of introgression between sympatric species provide a unique insight into the mechanisms of speciation and the maintenance of species boundaries. In this study, we investigate the extent of hybridization between two closely related species of coral reef fish: the common coral trout (Plectropomus leopardus) and the bar-cheek coral trout (Plectropomus maculatus). Using a complementary set of 25 microsatellite loci, we distinguish pure genotype classes from first- and later-generation hybrids, identifying 124 interspecific hybrids from a collection of 2,991 coral trout sampled in inshore and mid-shelf reefs of the southern Great Barrier Reef. Hybrids were ubiquitous among reefs, fertile and spanned multiple generations suggesting both ecological and evolutionary processes are acting to maintain species barriers. We elaborate on these finding to investigate the extent of genomic introgression and admixture from 2,271 SNP loci recovered from a ddRAD library of pure and hybrid individuals. An analysis of genomic clines on recovered loci indicates that 261 SNP loci deviate from a model of neutral introgression, of which 132 indicate a pattern of introgression consistent with selection favouring both hybrid and parental genotypes. Our findings indicate genome-wide, bidirectional introgression between two sympatric species of coral reef fishes and provide further support to a growing body of evidence for the role of hybridization in the evolution of coral reef fishes.

In Silico Comparative Transcriptome Analysis of Two Color Morphs of the Common Coral Trout (Plectropomus Leopardus)

The common coral trout is one species of major importance in commercial fisheries and aquaculture. Recently, two different color morphs of Plectropomus leopardus were discovered and the biological importance of the color difference is unknown. Since coral trout species are poorly characterized at the molecular level, we undertook the transcriptomic characterization of the two color morphs, one black and one red coral trout, using Illumina next generation sequencing technologies. The study produced 55162966 and 54588952 paired-end reads, for black and red trout, respectively. De novo transcriptome assembly generated 95367 and 99424 unique sequences in black and red trout, respectively, with 88813 sequences shared between them. Approximately 50% of both trancriptomes were functionally annotated by BLAST searches against protein databases. The two trancriptomes were enriched into 25 functional categories and showed similar profiles of Gene Ontology category compositions. 34110 unigenes were grouped into 259 KEGG pathways. Moreover, we identified 14649 simple sequence repeats (SSRs) and designed primers for potential application. We also discovered 130524 putative single nucleotide polymorphisms (SNPs) in the two transcriptomes, supplying potential genomic resources for the coral trout species. In addition, we identified 936 fast-evolving genes and 165 candidate genes under positive selection between the two color morphs. Finally, 38 candidate genes underlying the mechanism of color and pigmentation were also isolated. This study presents the first transcriptome resources for the common coral trout and provides basic information for the development of genomic tools for the identification, conservation, and understanding of the speciation and local adaptation of coral reef fish species.

Contrasting stress responses of two co-occurring chipmunk species (Tamias alpinus and T. speciosus)

Glucocorticoid (GC) hormones are important mediators of responses to environmental conditions. Accordingly, differences in GC physiology may contribute to interspecific variation in response to anthropogenically-induced patterns of climate change. To begin exploring this possibility, we validated the use of fecal cortisol/corticosterone metabolites (FCM) to measure baseline glucocorticoid levels in two species of co-occurring chipmunks that have exhibited markedly different patterns of response to environmental change. In Yosemite National Park, the alpine chipmunk (Tamias alpinus) has undergone a significant upward contraction of its elevational range over the past century; in contrast, the lodgepole chipmunk (Tamiasspeciosus) has experienced no significant change in elevational distribution over this period. To determine if GC levels in these species vary in response to external stimuli and to assess whether these responses differ between species, we compared FCM levels for the same individuals (1) at the time of capture in the field, (2) after a short period of captivity, and (3) after adrenocorticotropic hormone (ACTH), (4) handling, and (5) trapping challenges conducted while these animals were held in captivity. Our analyses indicate that T. alpinus was more responsive to several of these changes in external conditions. Although both species displayed a significant FCM response to ACTH challenge, only T. alpinus showed a significant response to our handling challenge and to captive housing conditions. These findings underscore the importance of species-specific validation studies and support the potential for studies of GC physiology to generate insights into interspecific differences in response to environmental change.

Exploration of the mechanisms of protein quality control and osmoregulation in gills of Chromis viridis in response to reduced salinity

Fish gills are the vital multifunctional organ in direct contact with external environment. Therefore, activation of the cytoprotective mechanisms to maintain branchial cell viability is important for fish upon stresses. Salinity is one of the major factors strongly affecting cellular and organismal functions. Reduction of ambient salinity may occur in coral reef and leads to osmotic stress for reef-associated stenohaline fish. However, the physiological responses to salinity stress in reef-associated fish were not examined substantially. With this regard, the physiological parameters and the responses of protein quality control (PQC) and osmoregulatory mechanisms in gills of seawater (SW; 33-35 ‰)- and brackish water (BW; 20 ‰)-acclimated blue-green damselfish (Chromis viridis) were explored. The results showed that the examined physiological parameters were maintained within certain physiological ranges in C. viridis acclimated to different salinities. In PQC mechanism, expression of heat-shock protein (HSP) 90, 70, and 60 elevated in response to BW acclimation while the levels of ubiquitin-conjugated proteins were similar between the two groups. Thus, it was presumed that upregulation of HSPs was sufficient to prevent the accumulation of aggregated proteins for maintaining the protein quality and viability of gill cells when C. viridis were acclimated to BW. Moreover, gill Na(+)/K(+)-ATPase expression and protein amounts of basolaterally located Na(+)/K(+)/2Cl(-) cotransporter were higher in SW fish than in BW fish. Taken together, this study showed that the cytoprotective and osmoregulatory mechanisms of blue-green damselfish were functionally activated and modulated to withstand the challenge of reduction in salinity for maintaining physiological homeostasis.

Confinement during field studies may jeopardize antioxidant and physiological responses of Nile tilapia to contaminants

This work evaluates the effects of caging, a known confinement stress, in Nile tilapia (Oreochromis niloticus) during an environmental study in Cubatão river, southern Brazil. Caging animals for 7 days, regardless of being at the reference or at a contaminated site, resulted in lower levels of antioxidant-related defenses (glutathione, glutathione S-transferase, glucose-6-phosphate dehydrogenase) in liver and physiological parameters (blood glucose and lactate) as compared with free-swimming animals. Higher hepatic glutathione reductase activity and elevated Hb content could be associated to contaminant exposure. In conclusion, the confinement stress in caged Nile tilapia biochemical and physiological disturbances, acting as a confounding factor in field studies.

Individual variation in glucocorticoid stress responses in animals

When stimuli from the environment are perceived to be a threat or potential threat then animals initiate stress responses, with activation of the hypothalamo-pituitary-adrenal axis and secretion of glucocorticoid hormones (cortisol and corticosterone). Whilst standard deviation or standard error values are always reported, it is only when graphs of individual responses are shown that the extensive variation between animals is apparent. Some animals have little or no response to a stressor that evokes a relatively large response in others. Glucocorticoid responses of fish, amphibian, reptiles, birds, and mammals are considered in this review. Comparisons of responses between animals and groups of animals focused on responses to restraint or confinement as relatively standard stressors. Individual graphs could not be found in the literature for glucocorticoid responses to capture or restraint in fish or reptiles, with just one graph in mammals with the first sample was collected when animals were initially restrained. Coefficients of variation (CVs) calculated for parameters of glucocorticoid stress responses showed that the relative magnitudes of variation were similar in different vertebrate groups. The overall mean CV for glucocorticoid concentrations in initial (0 min) samples was 74.5%, and CVs for samples collected over various times up to 4 h were consistently between 50% and 60%. The factors that lead to the observed individual variation and the extent to which this variation is adaptive or non-adaptive are little known in most animals, and future studies of glucocorticoid responses in animals can focus on individual responses and their origins and significance.

Species specificity in the magnitude and duration of the acute stress response in Mediterranean marine fish in culture

The aim of the present study was to examine the species-specific stress response for seven Mediterranean fishes in culture. Also, to evaluate the method of measuring free cortisol concentration in the rearing water as a non-invasive and reliable indicator of stress in marine species, of aquaculture importance. Gilthead sea bream, Sparus aurata (Sparidae); common dentex, Dentex dentex (Sparidae); common Pandora, Pagellus erythrinus (Sparidae); sharpsnout sea bream, Diplodus puntazzo (Sparidae); dusky grouper, Epinephelus marginatus (Serranidae); meagre, Argyrosomus regius (Sciaenidae) and European sea bass, Dicentrarchus labrax (Moronidae) were subjected to identical acute stress (5-6 min chasing and 1-1.5 min air exposure) under the same environmental conditions and samples were analyzed by the same procedures. Results indicated that there was a clear species-specificity in the magnitude, timing and duration of the stress response in terms of cortisol, glucose and lactate. European sea bass showed a very high response and dusky grouper and meagre a very low response, except plasma glucose concentrations of dusky grouper which was constantly high, while sharpsnout sea bream presented a protracted stress response, up to 8h. The present study confirmed that free cortisol release rate into the water can be used as a reliable stress indicator.

The endocrinology of stress in fish: an environmental perspective

Much of the understanding of the endocrine basis of stress in fish comes from studies of cultured stocks of teleosts; there is comparatively little information on stress responses in wild stock, and less still on chondrosteans and elasmobranchs. This understanding is being refined through increasing understanding of molecular processes underlying endocrine events, with molecular tools offering ready examination of parts of the endocrine pathway that have been resistant to easy measurement of hormone products. An assessment of the timecourse of activation of the hypothalamic-pituitary-interrenal axis shows generally strong independence of temperature, with most teleosts showing measurable increase in plasma cortisol within 10 min of stress. Chondrostean and elasmobranch responses are less well described, but in chondrosteans at least, the response pattern appears to be similar to teleosts. The short latency for increases in corticosteroids following exposure to a stressor means that sampling of wild fish needs to occur rapidly after encounter. Several techniques including underwater sampling and rapid line capture are suitable for this, as is measurement of steroid release to the water by undisturbed fish, albeit possibly with a reduced range of applications. Basal cortisol values in wild teleosts are typically <10 ng mL(-1), but a number of species show values orders of magnitude higher in unstressed fish. Variability in corticosteroid levels arises from a range of factors in addition to stress including, sex and maturity, time of day or since feeding, and season. These factors need to be understood for the sensible assessment of stress responses in wild fish. Studies on free-living birds suggest that environmental stress resides mainly around unpredictable change, and the limited data available for fish support this view. The effect of unpredictable event such as floods or storms are difficult to assess in wild fish due to the difficulty in sampling at these times, and would be predicted to impose environmental stress as in terrestrial systems; however, this has yet to be demonstrated. There is scope for use of stress responses to be used as a measure of environmental quality but only if the basic response to environmental stress is well understood first. Development of this understanding remains a priority for this field of research.

Transgenerational marking of marine fish larvae: stable-isotope retention, physiological effects and health issues

This study examined the toxicological and physiological responses of a commercially important coral-reef grouper, Plectropomus leopardus (Serranidae), to injection of enriched stable-isotope barium chloride (BaCl(2)) solution. Thirty adult P. leopardus were subject to one of two (138)BaCl(2) injection treatment groups (corresponding to dosage rates of 2 and 4 mg (138)Ba kg(-1) body mass), and a control group in which fish were injected with 0.9% sodium chloride (NaCl) solution. Fish from each group were sampled at post-injection intervals of 48 h and 1, 3, 5 and 8 weeks, at which time blood and tissue samples were removed from each fish. Residual concentrations of Ba and (138)Ba:(137)Ba ratios were measured in muscle, gonad, liver and bone tissues of each experimental fish. Elevated Ba concentrations were detected in all treatment fish tissue samples within 48 h post injection. Residual Ba concentrations decreased throughout the remainder of the 8 week experimental period in all tissues except bone. The BaCl(2) injection had no significant effects on measured whole blood variables or on the plasma concentrations of steroid hormones. Enriched Ba stable isotopes can therefore be used at low dosages to mark larvae of commercially important marine fishes, without adverse effects on the health of the fishes or on humans who may consume them.

Stress responses of the fish Nile tilapia subjected to electroshock and social stressors

Plasma cortisol and glucose levels were measured in 36 adult Nile tilapia males, Oreochromis niloticus (standard length, mean +/- SD, 14.38 +/- 1.31 cm), subjected to electroshock and social stressors. Pre-stressor levels were determined 5 days after the adjustment of the fish to the experimental aquaria (1 fish/aquarium). Five days later, the effects of stressors on both cortisol and glucose levels were assessed. The following stressors were imposed for 60 min: pairing with a larger resident animal (social stressor), or a gentle electroshock (AC, 20 V, 15 mA, 100 Hz for 1 min every 4 min). Each stressor was tested in two independent groups, one in which stress was quantified immediately after the end of the 60-min stressor imposition (T60) and the other in which stress was quantified 30 min later (T90). Pre-stressor values for cortisol and glucose were not statistically different between groups. Plasma cortisol levels increased significantly and were of similar magnitude for both electroshock and the social stressor (mean +/- SD for basal and final samples were: electroshock T60 = 65.47 +/- 15.3, 177.0 +/- 30.3; T90 = 54.8 +/- 16.0, 196.2 +/- 57.8; social stress T60 = 47.1 +/- 9.0, 187.6 +/- 61.7; T90 = 41.6 +/- 8.1, 112.3 +/- 26.8, respectively). Plasma glucose levels increased significantly for electroshock at both time points (T60 and T90), but only at T90 for the social stressor. Initial and final mean (+/- SD) values are: electroshock T60 = 52.5 +/- 9.2, 115.0 +/- 15.7; T90 = 35.5 +/- 1.1, 146.3 +/- 13.3; social stress T60 = 54.8 +/- 8.8, 84.4 +/- 15.0; T90 = 34.5 +/- 5.6, 116.3 +/- 13.6, respectively. Therefore, electroshock induced an increase in glucose more rapidly than did the social stressor. Furthermore, a significant positive correlation between cortisol and glucose was detected only at T90 for the social stressor. These results indicate that a fish species responds differently to different stressors, thus suggesting specificity of fish stress response to a stressor.

Black porgy (Acanthopagrus schlegeli) prolactin cDNA sequence: mRNA expression and blood physiological responses during freshwater acclimation

To investigate the consequences of freshwater (FW) transfer, we studied the prolactin (PRL) cDNA sequence and its mRNA expression, and physiological responses in the black porgy (Acanthopagrus schlegeli). We cloned and characterized cDNA encoding its PRL from the pituitary gland. Black porgy PRL cDNA consists of 1492 bp and encodes a protein of 212 amino acids including 24 signal peptides. Reverse transcription-PCR showed the PRL mRNA expression in the pituitary gland. Expression of pituitary gland PRL mRNA was significantly higher during FW acclimation. Furthermore, we studied the stress responses and osmoregulatory abilities of black porgy in changing salinities. Plasma cortisol, glucose, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) significantly increased in the fish immediately after transfer to FW. We also identified significant changes in the fish in terms of plasma ions (Na(+), Cl(-), Ca(2+)) and osmolality during the acclimation period. These results suggests that PRL plays an important role in hormonal regulation in osmoregulatory organs, thereby improving the hyperosmoregulatory ability of black porgy in freshwater.

Plasma lactate and glucose flushes following burst swimming in silver trevally (Pseudocaranx dentex: Carangidae) support the “releaser” hypothesis

Silver trevally (Pseudocaranx dentex) are highly athletic marine teleosts inhabiting the tropical waters of the Great Barrier Reef, Australia. Burst swimming increased plasma lactate from 1.6 +/- 0.4 S.D. to 21.6 +/- 3.3 mM (N = 6), among the highest values reported for functional hypoxia in fish. These data support the hypothesis that elite swimmers release lactate produced in the myotome into the circulation following anaerobic burst activity. The fish further developed a hyperglycaemic response to burst exercise with plasma glucose increasing from 6.6 +/- 2.0 to 13.2 +/- 2.3 mM (N = 6). Post-exercise erythrocyte swelling also occurred, but nucleoside triphosphate levels remained unaltered and do not provide a mechanism to modulate haemoglobin function during exercise. Metabolism of the blood cells appeared to be fuelled by both lactate and glucose.