Dorsal White Muscle Research Articles

Postmortem Muscle Proteome Characteristics of Silver Carp (Hypophthalmichthys molitrix): Insights from Full-Length Transcriptome and Deep 4D Label-Free Proteomic.

The coverage of the protein database directly determines the results of shotgun proteomics. In this study, PacBio single-molecule real-time sequencing technology was performed on postmortem silver carp muscle transcripts. A total of 42.43 Gb clean data, 35,834 nonredundant transcripts, and 15,413 unigenes were obtained. In total, 99.32% of the unigenes were successfully annotated and assigned specific functions. PacBio long-read isoform sequencing (Iso-Seq) analysis can provide more accurate protein information with a higher proportion of complete coding sequences and longer lengths. Subsequently, 2671 proteins were identified in deep 4D proteomics informed by a full-length transcriptomics technique, which has been shown to improve the identification of low-abundance muscle proteins and potential protein isoforms. The feature of the sarcomeric protein profile and information on more than 30 major proteins in the white dorsal muscle of silver carp were reported here for the first time. Overall, this study provides valuable transcriptome data resources and the comprehensive muscle protein information detected to date for further study into the processing characteristic of early postmortem fish muscle, as well as a spectral library for data-independent acquisition and data processing. This batch of muscle-specific dependent acquisition data is available via PRIDE with identifier PXD043702.

Mercury and amino acid content relations in northern pike (Esox lucius) in subarctic lakes along a climate-productivity gradient

Mercury is a highly toxic element for consumers, but its relation to amino acids and physiology of wild fish is not well known. The main aim of this study was to evaluate how total mercury content (THg) of northern pike (Esox lucius) is related to amino acids and potentially important environmental and biological factors along a climate-productivity gradient of ten subarctic lakes. Linear regression between THg and sixteen amino acids content [nmol mg−1 dry weight] from white dorsal muscle of pike from these lakes were tested. Lastly, a general linear model (GLM) for age-corrected THg was used to test which factors are significantly related to mercury content of pike. There was a positive relationship between THg and proline. Seven out of sixteen analysed amino acids (histidine, threonine, arginine, serine, glutamic acid, glycine, and aspartic acid) were significantly negatively related to warmer and more productive lakes, while THg showed a positive relationship. GLM model indicated higher THg was found in higher trophic level pike with lower cysteine content and inhabiting warmer and more productive lakes with larger catchment containing substantial proportion of peatland area. In general, THg was not only related to the biological and environmental variables but also to amino acid content.

Promoting the use of non-lethal sample collection for analysing the trophic relationships of inshore flatfish populations using stable isotope analysis

Trophic studies on inshore flatfish populations usually rely on stomach content analyses and/or stable isotope analysis (SIA) of dorsal white muscle that involves the collection of samples from euthanised fishes. To promote the use of non-lethal sampling methods in inshore flatfish populations of relatively high intrinsic angling and/or ecological value, the applicability of using fin tissue and/or epidermal mucus as non-lethal alternatives to muscle in SIA studies was assessed for European flounder Platichthys flesus, plaice Pleuronectes platessa and common sole Solea solea. In all species, the results indicated that there were significant differences in the δ13C and δ15N values of dorsal muscle versus their fin and mucus samples. These significant differences were, however, predictable by linear regression, with regression coefficients produced for converting fin and mucus SI values to the equivalent muscle SI values. The use of combined data across the species also provided regression coefficients for converting fin and mucus SI to equivalent muscle values for flatfish populations more generally. These results indicated that there are tissue alternatives to dorsal muscle that can be applied to the SIA of flatfish populations, with these tissues able to be collected using non-lethal sampling methods.

Cytokine Pattern of Peripheral Blood Mononuclear Cells Isolated from Children Affected by Generalized Epilepsy Treated with Different Protein Fractions of Meat Sources.

The objective of the present study was the evaluation of cytokine patterns in terms of TNF-α, IL-10, IL-6, and IL-1β secretion in peripheral blood mononuclear cell (PBMC) supernatants isolated from blood of children affected by generalized epilepsy and treated in vitro with myofibrillar, sarcoplasmic, and total protein fractions of meat and fish sources. Children with generalized epilepsy (EC group, n = 16) and children without any clinical signs of disease, representing a control group (CC group n = 16), were recruited at the Complex Structure of Neuropsychiatry Childhood-Adolescence of Policlinico Riuniti (Foggia, Italy). Myofibrillar (MYO), sarcoplasmic (SA), and total (TOT) protein fractions were obtained from longissimus thoracis muscle of beef (BF) and lamb (LA); from pectoralis muscle of chicken (CH); and from dorsal white muscle of sole (Solea solea, SO), European hake (Merluccius merluccius, EH), and sea bass fish (Dicentrarchus labrax, SB), respectively. PBMCs were isolated from peripheral blood of EC and CC groups, and an in vitro stimulation in the presence of 100 μg/mL for each protein fraction from different meat sources was performed. Data were classified according to three different levels of cytokines produced from the EC group relative to the CC group. TNF-α, IL-10, and IL-6 levels were not affected by different meat fractions and meat sources; on the contrary, IL-1β levels were found to be significantly affected by the tested proteins fractions, as well as different meat sources, in high-level cytokine group. On average, the protein fractions obtained from LB, BF, and CH meat sources showed a higher level of IL-1β than the protein fractions obtained from EH and SB fish samples. When all cytokine classes were analyzed, on average, a significant effect was observed for IL-10, IL-1β, and TNF-α. Data obtained in the present study evidence that the nutritional strategy based on protein from fish and meat sources may modulate the immunological cytokine pattern of infants with generalized epilepsy.

Differences in free amino acid compositions in liver and dorsal white muscle of juvenile Pacific bluefin tuna Thunnus orientalis fed raw fish and artificial feeds

Differences in free amino acid compositions in liver and dorsal white muscle of juvenile Pacific bluefin tuna <I>Thunnus orientalis</I> fed raw fish and artificial feeds

Multi-elemental composition of white and dark muscles in swordfish

Concentrations of 16 elements (K, Na, Mg, Ca, Fe, Zn, Hg, Se, As, Cu, Cd, Mn, Ni, Cr, Pb and Co) were determined in dorsal white and dark muscle of Xiphias gladius, sampled at various positions of a single swordfish and at the same position of eight specimens. Hg was quantified by thermal decomposition atomic absorption spectrometry (LECO AMA-254) and the rest of the elements by inductively coupled plasma optical emission spectrometry (ICP OES) or mass spectrometry (ICP MS). Element partitioning differed in dark and white muscle. Dark muscle was particularly enriched in Fe (median 13 times) and Cu (9) and moderately enhanced in Se, Mn, Zn and Cd (2.8–4.0). Dark:white ratios of the potentially toxic elements (As, Cr, Hg, Ni and Pb) varied from 0.9 to 1.4, pointing to a similar distribution between the two muscles types and indicating no additional risk in the consumption of dark muscle.

Legacy persistent organic pollutants (POPs) in archive samples of wild Bluefin tuna from the Mediterranean Sea

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were quantified in archive samples of dorsal white muscle of the wild Bluefin tuna (BFT) (n = 9) collected in the central Adriatic. PCBs were the predominant organochlorine (OC) compounds (60.8–69.4% of the total OC load) found. The contribution of HCB and ΣHCHs was significantly lower, ranging from <LOD (α- and β-HCH) to 1.5% (γ-HCH). p,p′-DDE was the predominant OCP compound (60–89% of the ΣOCPs). PCB and DDT levels were comparable to the values previously found for tuna from the Mediterranean Sea, known as one of the areas most polluted by PCBs.

Prevalence of pelagic dependence among coral reef predators across an atoll seascape.

Coral reef food webs are complex, vary spatially and remain poorly understood. Certain large predators, notably sharks, are subsidized by pelagic production on outer reef slopes, but how widespread this dependence is across all teleost fishery target species and within atolls is unclear.North Malé Atoll (Maldives) includes oceanic barrier as well as lagoonal reefs. Nine fishery target predators constituting ca. 55% of the local fishery target species biomass at assumed trophic levels 3–5 were selected for analysis. Data were derived from carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S) stable isotopes from predator white dorsal muscle samples, and primary consumer species representing production source end‐members.Three‐source Bayesian stable isotope mixing models showed that uptake of pelagic production extends throughout the atoll, with predatory fishes showing equal planktonic reliance between inner and outer edge reefs. Median plankton contribution was 65%–80% for all groupers and 68%–88% for an emperor, a jack and snappers.Lagoonal and atoll edge predators are equally at risk from anthropogenic and climate‐induced changes, which may impact the linkages they construct, highlighting the need for management plans that transcend the boundaries of this threatened ecosystem.

Effects of Different Iron Sources on the Growth and Iron Concentrations of Tissues, Organs, and Blood of Genetically Improved Farmed Tilapia (Oreochromis niloticus)

A 70-day feeding trial was conducted to elucidate the effects of different iron (Fe) sources on growth and Fe concentrations in the tissues, organs, and blood of genetically improved farmed tilapia (Oreochromis niloticus). Five experimental diets (45.0% crude protein, 3.7% crude lipid) with the same Fe concentration (100 mg/kg of feed) were formulated from different Fe sources: ferrous sulfate (FeSO4), ferric chloride (FeCl3), ferrous chloride (FeCl2), ferrous citrate (C6H5FeO7), and iron porphyrin (Fe-porphyrin). The results showed that the percent weight gain (%WG) of fish in the FeCl2 group was the greatest among all five groups (p &lt; 0.05). With %WG as the main indicator, FeCl2 was the most suitable source of dietary Fe for O. niloticus．In the FeCl2 group, the content of Fe in the spleen was significantly greater than that in the C6H5FeO7 group on day 28, and that of the FeSO4 group on day 56. The Fe concentrations in the liver, spleen, gill, vertebra, blood, whole intestine, and dorsal white muscle of O. niloticus were not significantly affected by different dietary sources of Fe on day 70. There were only slight dynamic changes to the Fe content of tissues and organs during the experimental period. The Fe contents in different tissues and organs were as follows: spleen &gt; mid-hind intestine &gt; liver &gt; gill, muscle, foregut &gt; spine. The spleen had the highest Fe content in all groups on day 70. These results suggest that FeCl2 is the best source of dietary Fe for O. niloticus with %WG as the main indicator.

Methods for Extraction of Muscle Proteins from Meat and Fish Using Denaturing and Nondenaturing Solutions

The objective of the present study was to test two extraction methods including solutions with different ionic strengths on the extraction and separation of the myofibrillar proteins from meat and fish muscles of different species. Meat samples from longissimus thoracis muscle of beef and lamb, pectoralis major muscle of chicken, and dorsal white muscle of fish from sole (Solea solea), European hake (Merluccius merluccius), and sea bass (Dicentrarchus labrax) were analyzed. The extraction method using nondenaturing solution led to a major extraction of high molecular-weight proteins as myosin heavy chain, α-actinin, and desmin; on the contrary, the denaturing method provided a good protein extractability of proteins and fragments with low molecular-weight as actin, troponin-T, tropomyosin, and myosin light chain 1 and 2 proteins for the most meat and fish samples. The nondenaturing extraction method showed several advantages resulting in time and labour saving and in minimizing the use of toxic and polluting agents.

Trace elements in a Mediterranean scorpaenid fish: Bioaccumulation processes and spatial variations

The black scorpionfish Scorpaena porcus, a carnivorous sedentary species, was studied as an indicator of local trace element (TE) contamination of coastal fish species in the northwestern Mediterranean Sea. Fish were collected in seagrass meadows in winter 2012 at four sampling sites: three were located near Marseille, a highly urbanized and industrial area that is subjected to various types of contaminant inputs, and one was located near Hyères, a less urbanized area. Size, sex, age and diet of fish were determined before stable isotope and TE analyses. C and N isotopic compositions and concentrations of nine TEs (As, Ba, Cd, Cu, Cr, T-Hg, Ni, Pb, and Zn) were determined in dorsal white muscle. Most TEs did not bioaccumulate in S. porcus, as no increase in TE concentrations with increasing size, age or trophic level of fish was evident. Total mercury (T-Hg) was the only element to bioaccumulate and biomagnify, displaying strong positive correlations of its concentration with age (r = 0.88, p < 0.01), length (r = 0.84, p < 0.01) and δ15N value (r = 0.68, p < 0.01). Compared with the reference site, higher concentrations of As, Ba, Cd, T-Hg, Pb, and Zn were recorded in fish collected at one or all of the Marseille site. In contrast, no difference was observed for Cr, Cu, and Ni concentrations with site. Spatial differences in TE concentrations in S. porcus were related to differences in isotopic composition and to the primary environmental characteristics and human activities prevailing at each site. Concentrations of Cd, T-Hg and Pb in fish muscle (priority substances for monitoring) were all below the maximum permitted European values.

Effects of euthanasia methods on stable carbon (δ13 C value) and nitrogen (δ15 N value) isotopic compositions of fry and juvenile rainbow trout Oncorhynchus mykiss.

Carbon and nitrogen stable isotope analyses of fish tissues are now commonly used in ecological studies but mostly require the sacrifice of the animal. Ethical considerations recommend the use of anesthetics for tissue sampling. This study examines how anesthetics affect stable isotope ratios of fish compared with other euthanasia methods. Rainbow trout fry and juveniles were sacrificed using ice-freezing (as this common method used to kill fish does not affect natural isotopic ratios), electronarcosis or an overdose of chemical anesthetics (2-phenoxyethanol, benzocaine and clove oil). For fry, we sampled the whole animal whereas, for juveniles, white dorsal muscle, liver, red blood cells, plasma, external tegument and pectoral fin were sampled. Isotopic ratios and the elemental compositions of carbon and nitrogen were then measured. The δ15 N values, and the C and N contents of all considered tissues as well as δ13 C values of muscle, liver, red blood cells and plasma, were not affected by the use of chemical anesthetics. Clove oil and to a lesser extent 2-phenoxyethanol and benzocaine decreased δ13 C values of whole fry and juvenile external tegument and pectoral fin. The use of electronarcosis drastically affects the δ13 C and δ15 N values of all fish tissues. Anesthetics should be avoided for δ13 C analysis when tissues are in contact with the water containing the anesthetic. Ice-immersion has to be preferred when approved by guidelines. If not, benzocaine and 2-phenoxyethanol should be preferred over clove oil. Electronarcosis should not be used to kill fish until further investigations are performed.

Combined stomach content and δ13C/δ15N analyses of oilfish, escolar, snake mackerel and lancetfish in the western North Atlantic

AbstractLarge, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length‐at‐maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ13C and δ15N. Escolar were the most depleted in δ13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ15N = 10.20), followed by snake mackerel (δ15N = 9.66), adult oilfish (δ15N = 9.32), lancetfish (δ15N = 9.05) and juvenile oilfish (δ15N = 7.83). A marked change in oilfish δ13C and C/N at 30–35 cm fork length coincided with a presumed length‐at‐maturity.

Trophic overlap between blue sharks (Prionace glauca) and shortfin makos (Isurus oxyrinchus): Trophic linkages between two shark species in the Eastern Pacific Ocean food web

Trophic interactions in food webs must be considered in order to assess the trophic role of different species in the ecological network structure as well as the relationship between resource use and interactions between different organisms. Such studies provide important information for ecosystem-based fisheries management. Thus, our goal was to analyze the trophic overlap between blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) off the west coast of Baja California Sur, Mexico, in order to infer their diet preferences and spatial distribution. We sampled the dorsal white muscle of 39 P. glauca and 35 I. oxyrinchus in December 2009 and March 2011. No significant differences between sexes or maturity stage were identified for P. glauca from either sampling location, indicating similar foraging preferences. For I. oxyrinchus, there was a significant difference in the δ13C values for males and females, suggesting different foraging preferences or movement patterns. The trophic positions and the SIBER analysis assigned to both tertiary predators in this study indicate that P. glauca is a specialist, while I. oxyrinchus is a generalist. Significant differences were also identified in the δ15N and δ13C values for P. glauca and I. oxyrinchus, indicating low overlap between these two shark species. These patterns suggest that these two sharks have different trophic preferences and migratory histories; thus, each species plays a unique trophic role off the west coast of Baja California Sur, Mexico.

Quantification of major allergen parvalbumin in 22 species of fish by SDS–PAGE

Fish is an important causative material of food allergy. Although the allergenicity of fish is considered to correlate with the content of parvalbumin, the major fish allergen, available information about the parvalbumin content in fish is limited. In this study, a simple and reliable quantification method for fish parvalbumin by SDS–PAGE was first established. Application of the SDS–PAGE method to 22 species of fish revealed a marked variation in parvalbumin content among fish. Furthermore, the parvalbumin content was found to be higher in dorsal white muscle than in ventral white muscle, in rostral part of white muscle than in caudal part of white muscle and in white muscle than in dark muscle. IgE reactivity of fish was roughly proportional to parvalbumin content. Interestingly, large-sized migratory fish, such as salmon, swordfish and tuna, were commonly very low in both parvalbumin content and IgE reactivity.

Stable isotope signatures and trophic-step fractionation factors of fish tissues collected as non-lethal surrogates of dorsal muscle

Dorsal white muscle is the standard tissue analysed in fish trophic studies using stable isotope analyses. As muscle is usually collected destructively, fin tissues and scales are often used as non-lethal surrogates; we examined the utility of scales and fin tissue as muscle surrogates. The muscle, fin and scale δ(15) N and δ(13) C values from 10 cyprinid fish species determined with an elemental analyser coupled with an isotope ratio mass spectrometer were compared. The fish comprised (1) samples from the wild, and (2) samples from tank aquaria, using six species held for 120 days and fed a single food resource. Relationships between muscle, fin and scale isotope ratios were examined for each species and for the entire dataset, with the efficacy of four methods of predicting muscle isotope ratios from fin and scale values being tested. The fractionation factors between the three tissues of the laboratory fishes and their food resource were then calculated and applied to Bayesian mixing models to assess their effect on fish diet predictions. The isotopic data of the three tissues per species were distinct, but were significantly related, enabling estimations of muscle values from the two surrogates. Species-specific equations provided the least erroneous corrections of scale and fin isotope ratios (errors < 0.6‰). The fractionation factors for δ(15) N values were in the range obtained for other species, but were often higher for δ(13) C values. Their application to data from two fish populations in the mixing models resulted in significant alterations in diet predictions. Scales and fin tissue are strong surrogates of dorsal muscle in food web studies as they can provide estimates of muscle values within an acceptable level of error when species-specific methods are used. Their derived fractionation factors can also be applied to models predicting fish diet composition from δ(15) N and δ(13) C values.

Effects of dietary glucose and dextrin on activity and gene expression of glucokinase and fructose-1,6-bisphosphatase in liver of turbot Scophthalmus maximus.

Glucokinase (GK) and fructose-1,6-bisphosphatase (FBPase) play crucial role in glucose metabolism. In the present study, the cDNA encoding GK and FBPase was cloned from the liver of turbot Scophthalmus maximus by rapid amplification of cDNA end technique. Effects of dietary glucose and dextrin on the activities and gene expressions of these two enzymes were also studied. Results showed that the full length of GK cDNA was 2226bp, consisting of an open reading frame (ORF) of 1434bp. The full-length cDNA coding FBPase was 1314bp with a 1014bp ORF encoding 337 amino acids. Analyses of gene expression of GK and FBPase were conducted in gill, liver, the whole intestine, the whole kidney, heart, the dorsal white muscle and brain. The highest expression of GK was found in liver, followed by muscle. The expression of FBPase was found higher in liver than heart and gill. Both hepatic GK activity and mRNA expression were highly induced in turbot after being fed with dietary carbohydrates (p<0.05). However, the GK activity and mRNA expression in the group with dietary glucose did not significantly differ from those in the group with dietary dextrin (p>0.05). Compared with the control group, there were no significant differences in FBPase activity and mRNA expression in the glucose as well as dextrin group (p>0.05). The increased hepatic GK activity and gene expression indicated that the first step of glycolysis was activated in turbot by dietary carbohydrates.

Lead accumulation pattern and molecular biomarkers of oxidative stress in seabream (Sparus aurata) under short-term metal treatment

The present work aimed to look at the distribution and accumulation pattern of Lead (Pb) within the fish body after 2 h, 4 h and 24 h of waterborne exposure to the metal at 0.75 mg/L. Tests of lead acute toxicity and bioaccumulation were performed in the common fish species Sparus aurata. In our study, we assessed the oxidative stress damages extent after 2 h, 4 h and 24 h of exposure to lead using the enzymatic stress biomarkers: Superoxide Dismutase (SOD), Catalase (CAT) and Gluthathione (GSH). The lipid peroxidation (LPO) was also investigated by dosing Malondyhaldéhyde (MDA) quantities in the liver tissue. The acute neurotoxicity of Pb was evaluated in the dorsal white muscle using the Acethylcholenesterase (AchE) activity. The liver tissue accumulates preferentially the metal, followed by the intestines, the gills and finally the dorsal muscle. The antioxidant response failed to prevent the lipid peroxidation and the neurotoxic effect of lead after 24 h of exposure.

Reliability of non-lethal assessment methods of body composition and energetic status exemplified by applications to eel (Anguilla anguilla) and carp (Cyprinus carpio)

Non-lethal assessments of proximate body composition of fish can help unravelling the physiological and condition-dependent mechanisms of individual responses to ecological challenges. Common non-lethal methods designed to index nutrient composition in fish include the relative condition factor (Kn), bioelectric impedance-based assessments of body composition (BIA), and microwave-based “fat” meters (FM). Previous studies have revealed mixed findings as to the reliability of each of these. We compared the performance of Kn, BIA and FM at different temperatures to predict energetic status of the whole bodies of live eel (Anguilla anguilla) and carp (Cyprinus carpio) and the dorsal white muscle of carp. Homogenized fish flesh was used for calibration. Relative dry mass was strongly correlated with relative fat content (R2 up to 96.7%) and energy density (R2 up to 99.1%). Thus, calibrations were only conducted for relative dry mass as an index of energetic status of a fish. FM readings were found to predict relative dry mass of whole body in eel (R2=0.707) and carp (R2=0.676), and dorsal white muscle of carp (R2=0.814) well. By contrast, BIA measurements and Kn were much less suited to identify variation in relative dry mass. BIA-based models were also temperature-dependent. As a result, a regression model calibrated at 10°C and applied to BIA measurements at 20°C was found to underestimate energetic status of a fish. By contrast, no effects of temperature on FM calibration results were found. Based on our study, the FM approach is the most suitable method to non-lethally estimate energetic status in both, carp and eel, whereas BIA is of limited use for energetic measurements in the same species, in contrast to other reports in the literature.

Stable Isotope Differences Between Blue Marlin (&lt;I&gt;Makaira Nigricans&lt;/I&gt;) and Striped Marlin (&lt;I&gt;Kajikia Audax&lt;/I&gt;) in the Southern Gulf of California, Mexico

Stable isotope values of Kajikia audax (Philippi, 1887) and Makaira nigricans (Lacepede, 1802) were analyzed to detect differences associated with trophic segregation influenced by their feeding habits in the southern Gulf of California, Mexico. We sampled the dorsal white muscle of 47 M. nigricans and 35 K. audax collected from 2005 to 2007. No relationship was found between billfish body size and isotopic values. Significant differences in (delta connection)15N and (delta connection)13C values were found among genders, years, or areas for K. audax. The significant differences in (delta connection)15N and (delta connection)13C values found between areas for M. nigricans suggested differences in foraging preferences or movement patterns. Significant differences were also found in (delta connection)15N and (delta connection)13C values between K. audax and M. nigricans, possibly placing these two billfish species at different trophic levels. These patterns appear to correspond to each species' known foraging ecology and suggest that these two billfishes have different trophic preferences or migratory histories.