Marine Teleost Research Articles

Avoidance threshold to oil water-soluble fraction by a juvenile marine teleost fish.

When oil spills occur, behavior is the first line of defense for a fish to avoid being contaminated. We determined the avoidance threshold of the European seabass (Dicentrarchus labrax) to the water-soluble fraction (WSF) of oil using a dual-flow choice box. The results showed that a plume of 20%-diluted WSF (total polycyclic aromatic hydrocarbon [PAH] concentration: 8.54 μg L-1 ) triggered a significant avoidance response that was detected within 7.5 min of introducing WSF-contaminated water into the experimental setup. However, the ecological relevance of seabass capacity to detect and avoid WSF remains to be established. In the short term, such a response is indeed liable to reduce seabass contact time with oil-contaminated water and thus preserve their functional integrity. In the long term, however, avoidance may contribute to the displacement of a population into a possibly less auspicious environment, with consequences very similar to those of contaminant exposure, that is, disturbed population dynamics and demography. Environ Toxicol Chem 2018;37:854-859. © 2017 SETAC.

Sex-specific differences in growth, mortality and migration support population resilience in the heavily exploited migratory marine teleost Mugil cephalus (Linnaeus 1758)

Understanding mechanisms supporting the resilience of exploited fish populations is fundamental to sustainable management. Herein we identify sex-specific differences in life history traits that confer resilience in the heavily exploited population of Mugil cephalus along eastern Australia. M. cephalus in this region emigrate from estuaries and undergo an annual northerly spawning migration that is dominated by males. Males mature, on average, at younger ages than females and were most abundant in the spawning migration at age-4, whereas females were most abundant at age-5. Females grew significantly faster and larger than males, with both sexes being aged up to 14 years. These sex-specific differences relate directly to the population stability of M. cephalus under the reproductive strategy of a spawning migration. Males participate in the spawning migration at younger ages and in greater numbers than females to ensure a sufficient number of males for successful spawning. Females partition more energy to growth than males, maturing and participating in the spawning migration at older ages and larger sizes. The larger body size of females is related to increased fecundity, increased survivorship and more efficient swimming ability. These traits, combined with population strategies of both delayed and skipped spawning, convey substantial resilience.

Under control: how a dietary additive can restore the gut microbiome and proteomic profile, and improve disease resilience in a marine teleostean fish fed vegetable diets

BackgroundThe constant increase of aquaculture production and wealthy seafood consumption has forced the industry to explore alternative and more sustainable raw aquafeed materials, and plant ingredients have been used to replace marine feedstuffs in many farmed fish. The objective of the present study was to assess whether plant-based diets can induce changes in the intestinal mucus proteome, gut autochthonous microbiota and disease susceptibility of fish, and whether these changes could be reversed by the addition of sodium butyrate to the diets. Three different trials were performed using the teleostean gilthead sea bream (Sparus aurata) as model. In a first preliminary short-term trial, fish were fed with the additive (0.8%) supplementing a basal diet with low vegetable inclusion (D1) and then challenged with a bacteria to detect possible effects on survival. In a second trial, fish were fed with diets with greater vegetable inclusion levels (D2, D3) and the long-term effect of sodium butyrate at a lower dose (0.4%) added to D3 (D4 diet) was tested on the intestinal proteome and microbiome. In a third trial, the long-term effectiveness of sodium butyrate (D4) to prevent disease outcome after an intestinal parasite (Enteromyxum leei) challenge was tested.ResultsThe results showed that opposed forces were driven by dietary plant ingredients and sodium butyrate supplementation in fish diet. On the one hand, vegetable diets induced high parasite infection levels that provoked drops in growth performance, decreased intestinal microbiota diversity, induced the dominance of the Photobacterium genus, as well as altered the gut mucosal proteome suggesting detrimental effects on intestinal function. On the other hand, butyrate addition slightly decreased cumulative mortality after bacterial challenge, avoided growth retardation in parasitized fish, increased intestinal microbiota diversity with a higher representation of butyrate-producing bacteria and reversed most vegetable diet-induced changes in the gut proteome.ConclusionsThis integrative work gives insights on the pleiotropic effects of a dietary additive on the restoration of intestinal homeostasis and disease resilience, using a multifaceted approach.

Effects of temperature and host species on the life cycle of Cryptocaryon irritans

Cryptocaryon irritans, an important protozoan ciliate, infects almost all species of marine teleosts and causes heavy economic losses in aquaculture. In industrial aquaculture, culture container rotation is an effective method to control cryptocaryoniasis. However, the accurate frequency and times of container rotation for different temperatures or fish species has not been reported but is very important information for the application of the method. In the present study, we investigated the duration of C. irritans trophont residence and theront production in three fish species at temperatures from 18°C to 32°C with 2°C intervals. The results indicate that duration of trophont residence and theront excystment was shorter with rises in temperature, especially from 18°C to 22°C. In different fish species, the length of trophont residence varied whereas the length of theront excystment was very similar at the same temperature. In line with these data, we determined the frequency and times that tomonts were removed, and results demonstrated that all the tomonts can be completely removed with 2 or 3days interval for 2 or 3 times (from 22°C to 32°C), and the removal of tomonts was identical in three fish species at the same temperature. At 18°C and 20°C, however, the interval of tomont removal was >4days. Lastly, we verified the removal of tomonts with Trachinotus ovatus as host at 22°C and 30°C by a placemat removal method. In conclusion, these data provide an important basis for defense against C. irritans infection by the interruption of its life cycle in an intensive aquaculture system.

Dormancy induced by a hypoxic environment in tomonts of Cryptocaryon irritans, a parasitic ciliate of marine teleosts

We incubated tomonts of Cryptocaryon irritans in a hypoxic seawater environment (1.4–1.7mg/L O2) (low dissolved oxygen; DO) and examined their development using a acetocarmine whole-mount staining method we developed for nuclear staining. They showed little development and stayed in the dormant phase in the hypoxic environment. When transferred into the hypoxic environment after incubation in an oxic environment (air-saturated, 8.7–8.9mg/L O2) for 1–4days, their development stopped in 1day. However, when dormant tomonts generated in the hypoxic environment were transferred to the oxic environment, they resumed development and released theronts. These results indicate that tomonts can become dormant when exposed to a hypoxic environment, but can resume development when exposed to an oxic environment at any developmental stage. When exposed to the oxic environment, tomonts recovered from 1-month dormancy and released as many theronts as control tomonts constantly incubated in the oxic environment. The infectivity of theronts from the recovered tomonts was similar to the control tomonts. Thermoclines prevent oxygen-rich surface seawater from reaching the bottom of water column and create a hypoxic sea floor environment in summer; these thermoclines are broken down in autumn or after typhoons. The long-term viability of dormant tomonts in hypoxic environments may be a key factor in the autumn outbreaks of cryptocaryoniasis in floating net cages in temperate waters.

Eosinophilic Granulocytes: A New Bio-Marker of Sexual Maturity in Fishes?

A microscopic morphological feature (eosinophilic granulocytes, eG) was recently detected in the gonads of two species of economically important and broadly distributed, tropical Indo-Pacific eteline snappers, primarily in the ovaries of mature but reproductively inactive female Ruby Snapper Etelis carbunculus. Eosinophilic granulocytes have been known for more than a century to occur in diverse tissues (e.g., liver, kidney, gill, gonad) of a variety of freshwater and marine teleosts and have usually been recognized as bio-markers of immune response to environmental toxins or pathogens. Until now, they have been mostly overlooked as indicators of natural atresia in gonads and evidence of prior reproductive function in healthy fishes. The eG feature is herein suggested as a bio-marker of sexual maturity that might be useful when combined with an existing suite of largely qualitative markers of maturity in mature females that lack direct signs of maturity such as atretic yolked oocytes and post-ovulatory fo...

Philometrid nematodes (Philometridae) of marine teleosts from Balinese waters, Indonesia, including the description of Philometra damriyasai sp. nov.

Based on light and scanning electron microscopy, one new species of philometrid nematodes, Philometra damriyasai sp. nov. (Nematoda: Dracunculoidea: Philometridae) from the body cavity of Tylerius spinosissimus (Regan, 1908) (Tetraodontiformes, Tetraodontidae), and five known species are reported in different marine teleosts from South Bali, Indonesia. The new species can be distinguished from the most closely related P. javensis Moravec, Walter & Juniar, 2012 by the absence of sclerotized denticles on the cuticle of the anterior oesophageal lobes of the mouth and smaller larvae. Philometra nemipteri Luo, 2001 of Nemipterus japonicus (Bloch, 1791), P. otolithi Moravec & Manoharan, 2013 of Otolithes ruber (Bloch & Schneider, 1801) (both from gonads) and Philometroides marinus Moravec & Buron, 2009 from the body cavity of Rachycentron canadum (Linnaeus, 1766) are reported for the first time from Indonesian waters, thus extending their range of distribution into the tropical Indo-Pacific Ocean. Philometra lobotidis Moravec, Walter & Yuniar, 2012 from the body cavity of Lobotes surinamensis (Bloch, 1790) and P. ocularis Moravec, Ogawa, Suzuki, Miyaki & Donai, 2002 from the eye cavity of Variola louti (Forsskål, 1775) represent new geographical records, and Philometra sp. was recorded for the first time from Cephalopholis sexmaculata (Rüppell, 1830). A total of 14 philometrids have been so far identified from marine fishes in Indonesia.

Differences in neurochemical profiles of two gadid species under ocean warming and acidification

BackgroundExposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO2-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO2 under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience.ResultsWe found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In B. saida, changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO2, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO2 induced behavioural impairments. In contrast to B. saida, such temperature limitation was not detected in G. morhua; however, at 8 °C, CO2 induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in G.morhua. Further, increased availability of energy-rich substrates was detected under these conditions.ConclusionsOur results indicate a change of GABAergic metabolism in the nervous system of Gadus morhua close to the optimum of the temperature range. Since a former study showed that juvenile G. morhua might be slightly more behaviourally resilient to CO2 at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to B. saida in a future warmer, more acidified polar ocean.

Characterization of the ligand binding of PGRP-L in half-smooth tongue sole ( Cynoglossus semilaevis ) by molecular dynamics and free energy calculation

Background: Peptidoglycan (PGN) recognition proteins (PGRPs) are important pattern recognition receptors of the host innate immune system that are involved in the immune defense against bacterial pathogens. PGRPs have been characterized in several fish species. The PGN-binding ability is important for the function of PGRPs. However, the PGRP-PGN interaction mechanism in fish remains unclear. In the present study, the 3-D model of a long PGRP of half-smooth tongue sole (Cynoglossus semilaevis) (csPGRP-L), a marine teleost with great economic value, was constructed through the comparative modeling method, and the key amino acids involved in the interaction with Lys-type PGNs and Dap-type PGNs were analyzed by molecular dynamics and molecular docking methods. Results: csPGRP-L possessed a typical PGRP structure, consisting of five β-sheets and four α-helices. Molecular docking showed that the van der Waals forces had a slightly larger contribution than Coulombic interaction in the csPGRP-L-PGN complex. Moreover, the binding energies of csPGRP-L-PGNs computed by MM-PBSA method revealed that csPGRP-L might selectively bind both types of MTP-PGNs and MPP-PGNs. In addition, the binding energy of each residue of csPGRP-L was also calculated, revealing that the residues involved in the interaction with Lys-type PGNs were different from that with Dap-type PGNs. Conclusions: The 3-D structure of csPGRP-L possessed typical PGRP structure and might selectively bind both types of MTP- and MPP-PGNs, which provided useful insights to understanding the functions of fish PGRPs.

Inorganic, organic, and encapsulated minerals in vegetable meal based diets for Sparus aurata (Linnaeus, 1758).

Substituting fishmeal (FM) with vegetable meal (VM) can markedly affect the mineral composition of feeds, and may require additional mineral supplementation. Their bioavailability and optimal supplementation levels depend also on the form of delivery of minerals. The aim of the study was to determine the effect of different delivery forms of three major trace elements (Zn, Mn and Se) in a marine teleost. Gilthead sea bream juveniles of 22.5 g were fed a VM-based diet for 12 weeks that was either not supplemented with these minerals or supplemented with inorganic, organic, or encapsulated inorganic forms of minerals in triplicate and compared to a FM-based diet. Our results showed that mineral delivery form significantly affected the biochemical composition and morphology of posterior vertebrae. Supplementation of VM-based diets with inorganic forms of the target minerals significantly promoted growth, increased the vertebral weight and content of ash and Zn, enhanced bone mineralization and affected the vertebral shape. Conversely, encapsulation of inorganic minerals reduced fish growth and vertebral mineral content, whereas supplementation of organic minerals, enhanced bone osteogenesis by upregulating bone morphogenetic protein 2 (bmp2) gene and produced vertebrae with a larger length in relation to height. Furthermore, organic mineral forms of delivery downregulated the expression of oxidative stress related genes, such as Cu/Zn superoxide dismutase (Cu/Zn sod) and glutathione peroxidase 1 (gpx-1), suggesting thus that dietary minerals supplemented in the organic form could be reasonably considered more effective than the inorganic and encapsulated forms of supply.

İhtiyoplanktonun dağılım dinamikleri ve stoka katılım hipotezleri

Planktonic eggs and larvae of marine teleost fishes are considered as ichthyoplankton until they improve active locomotion. These fishes usually produce a large number of propagules however, the great majority of them die before recruitment due to the extrinsic conditions such as predation, starvation and aberrant drift. In this period, small variations in survival rates may cause important differences in recruitment success. On the other hand, the presence of the ideal habitats which can sustain maximal survival for propagules, can significantly change in space and time. Therefore, it is critically important that emergence of propagules should match with the appearance of ideal habitats. To ensure this match, fishes have advanced different spawning strategies. In this review, intrinsic (spawning strategies) and extrinsic (environmental factors) conditions affecting the spatio-temporal distribution of ichthyoplankton have been evaluated on a theoretical basis by discussing match-mismatch dynamics and recruitment hypotheses.

RNA-seq analysis of the head-kidney transcriptome response to handling-stress in the red cusk-eel (Genypterus chilensis)

Stress is a primary contributing factor of fish disease and mortality in aquaculture. We have previously reported that the red cusk-eel (Genypterus chilensis), an important farmed marine fish, demonstrates a handling-stress response that results in increased juvenile mortality, which is mainly associated with skeletal muscle atrophy and liver steatosis.To better understand the systemic effects of stress on red cusk-eel immune-related gene expression, the present study assessed the transcriptomic head-kidney response to handling-stress. The RNA sequencing generated a total of 61,655,525 paired-end reads from control and stressed conditions. De novo assembly using the CLC Genomic Workbench produced 86,840 transcripts and created a reference transcriptome with a N50 of 1426bp. Reads mapped onto the assembled reference transcriptome resulted in the identification of 569 up-regulated and 513 down-regulated transcripts. Gene ontology enrichment analysis revealed a significant up-regulation of the biological processes, like response to stress, response to biotic stimulus, and immune response. Conversely, a significant down-regulation of biological processes is associated with metabolic processes. These results were validated by RT-qPCR analysis for nine candidate genes involved in the immune response. The present data demonstrated that short term stress promotes the immune innate response in the marine teleost G. chilensis. This study is an important step towards understanding the immune adaptive response to stress in non-model teleost species.

Molecular characterisation, ontogeny and expression analysis of melanoma differentiation-associated factor 5 (MDA5) from Asian seabass, Lates calcarifer

MDA5 is the pivotal member of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) and is reported to play a crucial role in type I IFN-mediated responses against pathogen-associated molecular patterns (PAMPs), especially nucleic acids. In this study, we have identified and cloned the full-length cDNA sequence of MDA5, which comprises 3398 nucleotides and encodes for a putative protein of 978 AA length, in Asian seabass, Lates calcarifer. From the putative amino acid sequence of AsMDA5, four different conserved domains could be predicted: two N-terminal CARD domains, a DExDc domain, a HELICc domain and a C-terminal RIG-1_C-RD domain. The mRNA transcript of AsMDA5 could be detected in all the 11 tissues tested in healthy animals with the highest expression in heart followed by gill and skin. The ontogenetic expression profile showed constitutive expression in developmental stages starting from unfertilized eggs, which implies the possibility of maternally acquired immunity of RLRs in offspring. The viral analogue poly I:C could modulate the AsMDA5 expression both in vivo and in vitro. In all the tissues, AsMDA5 expression was found to be highly regulated following injection with poly I:C with the highest expression observed in kidney. The expression level of AsMDA5 was found to be modulated at different time-points following challenge with Gram-negative bacterium, Vibrio alginolyticus, and Gram-positive bacterium, Staphylococcus aureus. Similarly, noticeable change in AsMDA5 expression was detected in SISK cell line induced with either LPS or PGN. The observations made in this study suggest that in euryhaline marine teleosts like Asian seabass, MDA5 gene serves as one of the pivotal receptor for the detection of viral and bacterial PAMP, and might play an important antimicrobial role during early embryonic development.

Effects of dietary LNA/LA ratios on growth performance, fatty acid composition and expression levels of elovl5, Δ4 fad and Δ6/Δ5 fad in the marine teleost Siganus canaliculatus

Rabbitfish Siganus canaliculatus is a crucial cultured herbivorous marine teleost, and the first marine teleost demonstrated to have the ability of biosynthesizing long-chain polyunsaturated fatty acids (LC-PUFA) from linolenic (LNA) and linoleic acid (LA) precursors, suggesting the application potential of vegetable oils (VO), rich in LNA or LA but lack of LC-PUFA, as the dietary lipid resources. In the present study, seven diets (D1–D7) were prepared for the culture of rabbitfish juveniles lasting 12weeks. D1 (control diet) contained fish oil (FO) as the sole lipid, while D2–D7 contained a blend of glycerol trioleate and perilla oil with an ALA/LA ratios ranging from 0.05 to 2.45. The results showed that fish fed D3 or D5–D7 displayed as good growth performance as that fed D1. The fatty acid (FA) composition of liver and fillet reflected dietary FA profiles, and relatively higher levels of n-3 LC-PUFA was observed in D5–D7 groups. While the hepatic mRNA levels of ∆4 and ∆6/∆5 fatty acyl desaturase (Fad) and elongation of very long-chain fatty acids (Elovl) genes were affected by dietary LNA/LA ratios, with the highest expression of all three genes in fish fed D6 with an LNA/LA ratio of 1.93. Take the above results together, it can be concluded that diet contained a blend of VO with around 1.93 LNA/LA ratio is suitable for rabbitfish culture concerning the growth performance and LC-PUFA biosynthesis.

Pop-up satellite archival tag (PSAT) temporal data resolution affects interpretations of spawning behaviour of a commercially important teleost

BackgroundThe effects of temporal data resolution on the interpretation of fish behaviours are questions fundamental to research programs using electronic tags with finite data storage and data transmission capacities. However, understanding these effects requires sub-sampling high-resolution data at multiple temporal resolutions. In pop-up satellite archival tags (PSATs), data transmissions via satellite are limited, so temporal resolution is a decreasing function of the deployment duration. Physical recovery of PSATs overcomes this limitation, providing data on temperature, depth, etc., at rates at least 15–30 times greater than transmitted data.ResultsUsing PSATs physically recovered from Atlantic halibut (Hippoglossus hippoglossus), we evaluated the effects of data resolution (2, 30, 60 min) on interpreting vertical movements including rapid ascents during the expected spawning season. Putative ‘spawning rises’ of 6–20 min were only present within highest temporal resolution data. Vertical movement rates during spawning rises identified with high-resolution data exceeded rates in all other periods; such movement rates were virtually absent in all other tagged fish within the spawning period. Mean maximum ascent rates were 13 and 23 times higher when the sampling interval was 2 versus 30 or 60 min, respectively.ConclusionsWe illustrate the limitations of using satellite-transmitted data to quantify vertical movement rates and detect potential spawning events in marine teleosts. Such low temporal resolution data suggest spurious results by masking important behaviours that archived data reveal as occurring at high frequencies. We highlight new technologies that facilitate PSAT recoveries at sea to overcome these limitations and facilitate analyses of high-frequency archived data.

†Sorbinicharax verraesi: An unexpected case of a benthic fish outside Acanthomorpha in the Upper Cretaceous of the Tethyan Sea.

†Sorbinicharax verraesi is a marine teleostean fish from the Upper Cretaceous of Nardò (Italy). It was first attributed to the otophysan order Characiformes, which represents potential evidence for the controversial marine origin of the clade. Through a review of all the available material, we demonstrate that this species is not an otophysan since it lacks key structures that would allow for its inclusion in this group. †Sorbinicharax has a body shape that recalls ground fishes classically assigned to Acanthomorpha. However, no unambiguous feature allows us to relate it to this clade. In fact, the presence of cellular bony tissue supports its exclusion from Eurypterygii. Since no feature permits the definitive attribution of †Sorbinicharax to any teleost group, it remains as Teleostei incertae sedis. We infer that the morphology of †Sorbinicharax indicates a benthic ecology. It displays: an anteriorly wide body with enlarged ribs; large pectoral fins, while anal and dorsal fins are reduced; a large head measuring ¼ of the total body length; and a mouth opening dorsally in a high position. Such morphology was so far undescribed in Nardo. It is surprisingly displayed by a non-eurypterygian teleost fish which means by a fish which does not belong to the clades that diversify since the upper Cretaceous and include the extant families that show ground ecomorphologies.

The impact of acute PAH exposure on the toadfish glucocorticoid stress response

The objective of the present study was to determine whether the polycyclic aromatic hydrocarbons (PAHs) associated with the Deepwater Horizon (DWH) oil spill impacted the stress response of teleost fish. The hypothesis was that intraperitoneal (IP) treatment with PAHs associated with the DWH oil spill or waterborne exposure to DWH oil high energy water-accommodated fraction (HEWAF) would result in the downregulation of the stress response of Gulf toadfish, Opsanus beta, a benthic marine teleost fish that resides in the Gulf of Mexico. In vivo plasma cortisol levels and adrenocorticotropic hormone (ACTH)-mediated cortisol secretion by in vitro isolated kidney tissue were measured. Toadfish at rest IP-treated with naphthalene had higher plasma cortisol compared to fluorene-treated and control fish; phenanthrene-treated fish tended to have higher plasma cortisol levels that fluorene-treated and controls. When subjected to an additional crowding stress, naphthalene and phenanthrene-treated fish were no longer able to mount a stress response compared to fluorene-treated and control fish, suggesting exhaustion of the stress response. Supporting this in vivo data, there tended to be less cortisol released by the kidney in vitro from naphthalene and phenanthrene-treated fish in response to ACTH compared to controls. In contrast, toadfish at rest exposed to 3% Slick A HEWAF did not have significantly different plasma cortisol levels compared to controls. But, exposed fish did have significantly less cortisol released by the kidney in vitro in response to ACTH. When toadfish were subjected to an additional stress, there were no significant differences in plasma cortisol or ACTH, suggesting the action of a secondary secretagogue to maintain plasma cortisol in vivo. Combined, these data suggest that in response to acute PAH exposure, there may be internalization or downregulation of the melanocortin 2 receptor (MC2R) that mediates the action of ACTH.

Characterizing egg quality and larval performance from captive mahi-mahiCoryphaena hippurus(Linnaeus, 1758) spawns over time

Mahi-mahi Coryphaena hippurus is a promising species for aquaculture development and has been used as a model species for oil toxicology and physiology studies. This species has one of the fastest growth rates of any marine teleost and a unique reproductive biology due to its high spawning frequency and reproductive energy allocation. These characteristics lend the species to being an excellent model for understanding broodstock nutrition for other high energetic pelagic species. In this study, egg morphometrics and larval survival were tracked over a 10-week period from the initial capture of wild mahi-mahi broodstock. Larval quality from subsequent spawns collected over time was quantified using larval survival activity indices (SAIs) as a metric to assess egg quality. Larval SAIs were maintained and did not significantly decrease (p < .05) over the time course of this study. A multiple linear regression based on the elapsed time in captivity of the broodstock, egg diameter and larval SAI at 1 dph provided the most accurate prediction of larval SAI at 3 dph (R2 = 0.996 p < .05). There were strong positive correlations with larval SAIs at 1 and 3 dph and the key nutrients: eicosapentaenoic acid (C20: 5n-3, EPA) and related fatty acid ratios, vitamin E and nearly all amino acids under investigation. This study demonstrated that larval survival was maintained over time due to the supply of these key nutrients in the broodstock diet.

The genetic structure of a marine teleost, Chrysophrys auratus, in a large, heterogeneous marine embayment

There is considerable interest in the processes that generate genetic divergence in marine species and the spatial and temporal scales over which these processes operate. Shark Bay, a large embayment (~13,000 km2) on the arid west coast of Australia, has been described as a focal point for genetic divergence in marine species due to its heterogeneous environment. This study represents the first DNA-based analysis of the genetic structure of a marine species with pelagic early life stages (ELS) in this region. Twelve microsatellite loci were used to compare the genetic composition of the teleost Chrysophrys auratus from five areas within Shark Bay, and from near-by shelf waters approximately 250 km to the south. The results suggest that the microsatellite composition of C. auratus is homogeneous across most of Shark Bay and near-by shelf waters. This genetic homogeneity is probably maintained via small amounts of contemporary gene flow, which may reduce the potential for C. auratus to locally adapt to the Shark Bay environment. A weakly differentiated assemblage in Freycinet Estuary in the Western Gulf of Shark Bay provided an important exception to the otherwise homogeneous microsatellite composition of C. auratus in the study area. This weak differentiation probably reflects restrictions to gene flow into and/or out of this site due to the temporal isolation of breeding adults, selective mortality of immigrants and/or the presence of hydrological barriers to larval transport. Each of these factors can be linked to environmental heterogeneity in Shark Bay.

Complete Genome Sequence of Mycobacterium stephanolepidis.

ABSTRACTMycobacterium stephanolepidis is a rapid-growing nonpigmented species isolated from marine teleost fish (Stephanolepis cirrhifer) and is closely related to Mycobacterium chelonae. Here, we report the complete sequence of its genome, comprising a 4.9-Mb chromosome. The sequence represents essential data for future phylogenetic and comparative genome studies of this fish pathogen.