Marine Teleost Research Articles

Correlation of proline, hydroxyproline and serine content, denaturation temperature and circular dichroism analysis of type I collagen with the physiological temperature of marine teleosts

Fish products are a promising source of collagen; however, these extracts are biochemically unstable. Acid-soluble collagen (ASC) was isolated from the skin of eleven fish species at various physiological temperatures (Tp). Structural features of these samples were analysed in detail using Circular Dichroism (CD) and compared to their biochemical characteristics. Positive correlation (r = 0.74, p < 0.01) between the Tp and ratio of positive peak intensity to negative peak intensity (Rpn) in CD analysis suggested a higher thermal stability of ASC from warm-water fish, owing to a higher content of cyclic imino acids, such as proline and hydroxyproline (Hyp). Conversely, cold-water fish ASCs contain significantly higher levels of acyclic, hydroxyl groups carrying Ser. These results indicated that CD spectrum techniques including Rpn measurement are concise and helpful for direct detection of the triple helix structure of fish collagens, and that this structure is tightly linked to thermostability of this molecule.

The requirements for sterol regulatory element-binding protein (Srebp) and stimulatory protein 1 (Sp1)-binding elements in the transcriptional activation of two freshwater fish Channa striata and Danio rerio elovl5 elongase.

Fish are a major source of beneficial n-3 LC-PUFA in human diet, and there is considerable interest to elucidate the mechanism and regulatory aspects of LC-PUFA biosynthesis in farmed species. Long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis involves the activities of two groups of enzymes, the fatty acyl desaturase (Fads) and elongase of very long-chain fatty acid (Elovl). The promoters of elovl5 elongase, which catalyses the rate-limiting reaction of elongating polyunsaturated fatty acid (PUFA), have been previously described and characterized from several marine and diadromous teleost species. We report here the cloning and characterization of elovl5 promoter from two freshwater fish species, the carnivorous snakehead fish (Channa striata) and zebrafish. Results show the presence of sterol-responsive elements (SRE) in the core regulatory region of both promoters, suggesting the importance of sterol regulatory element-binding protein (Srebp) in the regulation of elovl5 for both species. Mutagenesis luciferase and electrophoretic mobility shift assays further validate the role of SRE for basal transcriptional activation. In addition, several Sp1-binding sites located in close proximity with SRE were present in the snakehead promoter, with one having a potential synergy with SRE in the regulation of elovl5 expression. The core zebrafish elovl5 promoter fragment also directed in vivo expression in the yolk syncytial layer of developing zebrafish embryos.

Global responses to tris(1-chloro-2-propyl)phosphate (TCPP) in rockfish Sebastes schlegeli using integrated proteomic and metabolomic approach

As alternatives of brominated flame retardants, organophosphate flame retardants (OPFRs) can be detected in multiple marine environmental media. Tris(1-chloro-2-propyl)phosphate (TCPP) was one of the most frequently and abundantly detected OPFRs in the Bohai Sea. Exposure to TCPP has been shown to induce abnormal behavior in zebrafish as well as neurotoxicity in Caenorhabditis elegans. However, there is a lack of mechanism investigations on the toxic effects of TCPP at molecular levels. In this work, proteomics and metabolomics were integrated to analyze the proteome and metabolome responses in rockfish Sebastes schlegeli treated with TCPP (10 and 100 nM) for 15 days. A total of 143 proteins and 8 metabolites were significantly altered in rockfish following TCPP treatments. The responsive proteins and metabolites were predominantly involved in neurotransmission, neurodevelopment, signal transduction, cellular transport, cholesterol metabolism, bile acid synthesis, and detoxification. Furthermore, a hypothesized network of proteins, metabolites, and pathways in rockfish was summarized based on the combination of proteomic and metabolomic results, showing some key molecular events in response to TCPP. Overall, the present study unraveled the molecular responses at protein and metabolite levels, which provided a better understanding of toxicological effects and mechanisms of TCPP in marine teleost.

Molecular characterization and expression of arginine vasotocin V1a2 receptor in Atlantic croaker brain: Potential mechanisms of its downregulation by PCB77.

The arginine vasotocin (AVT)-V1a receptor mediates critical reproductive behaviors of the nonapeptide vasotocin in the teleost brain. In this study, we report the molecular characterization of the AVT-V1a2 receptor and its messenger RNA (mRNA) and protein expressions in the Atlantic croaker brain after exposure to the planar polychlorinated biphenyl congener 3,3',4,4'-tetrachlorobiphenyl (PCB77). The full-length sequence of croaker AVT-V1a2 receptor complementary DNA (cDNA) is highly homologous to other teleost AVT-V1a2 receptor cDNAs. Double-labeled immunohistochemistry showed coexpression of AVT-V1a2 receptor and gonadotropin-releasing hormone-I (GnRH-I, a neuropeptide that regulates gonadotropin secretion) in hypothalamic neurons, thereby providing the anatomical basis for possible AVT modulation of croaker reproduction through alterations in GnRH-I secretion. AVT-V1a2 receptor mRNA and protein levels as well as GnRH-I mRNA levels were markedly decreased in hypothalamic tissues of croaker exposed to PCB77 (dose: 2 and 8 µg/g body weight for 4 weeks) compared with levels in untreated (control) fish. In contrast, hypothalamic cytochrome P450 1A (CYP1A, a monooxygenase enzyme) and interleukin-1β (IL-1β, a cytokine indicator of inflammation and response to neuronal damage) mRNA levels, and plasma protein carbonyl (PC, an indicator of reactive oxygen species) contents, important biomarkers of neural stress, were increased in PCB77-exposed fish compared with controls. Collectively, these results suggest that the downregulation of hypothalamic AVT-V1a2 receptor and GnRH-I transcripts due to PCB77 exposure is associated with induction of CYP1A, cellular inflammation and oxidative stress in Atlantic croaker, a marine teleost that inhabits estuaries along the US Atlantic coast and the Gulf of Mexico that are often contaminated with persistent organic pollutants such as PCBs.

Comments on "The marine teleost fishes of the Sea of Marmara; an updated and annotated checklist" by Artüz amp; Fricke (2019).

The recent paper by Artüz Fricke (2019) is focused on the analysis of marine teleost fishes of the Sea of Marmara, where they have tried to correct doubtful species occurrences and presented an annotated checklist. In a few cases, the authors have provided convincing data for the removal of some species from the regional inventory, such as Apogon imberbis (Linnaeus, 1758), Scomberesox saurus (Walbaum, 1792) and Polyprion americanus (Bloch Schneider, 1801), and pointed out revision-seeking genera (i.e. Alosa spp., Pegusa spp., etc.), which should certainly be taken into consideration. However, the paper also raises several doubts resulting from mistranslations of some previous research, misinterpretation and incomplete examination of certain published biodiversity data related to the Sea of Marmara. Despite the authors presented a number of mistaken first record data (for example Sardinella aurita Valenciennes, 1837, for full account see Bilecenoglu et al. 2002), included some unsubstantiated/questionable species (such as Symphodus melops (Linnaeus, 1758), Gobius vittatus Vinciguerra, 1883, etc.), and unexpectedly neglected the occurrence of some common coastal and deepsea species from the area, such as Arnoglossus kessleri Schmidt, 1915, Gobius bucchichi Steindachner, 1870, Labrus merula Linnaeus, 1758, Parablennius zvonimiri (Kolombatović, 1892) and Argyropelecus hemigymnus Cocco, 1829, I herein concentrate solely on the erroneous/invalid records (totaling 42 fish species) with appropriate explanations.

The complete mitochondrial genome of black sea bass, Centropristis striata

The complete mitochondrial genome was sequenced from the marine teleost fish Black Sea Bass, Centropristis striata. The genome sequence is 16,986 bp in size and has a base composition of A (26.65%), T (26.44%), C (28.63%), and G (18.28%). The phylogenetic analysis showed that C. striata belongs to Serranidae family and is most closely related to Hypoplectrus. The complete mitochondrial genome sequences provided here was the first one in Centropristis, which would be useful for further understanding the evolution and conservation genetics of C. striata.

Spatial distribution and activity patterns as welfare indicators in response to water quality changes in European sea bass, Dicentrarchus labrax

In aquaculture, fish are exposed to unavoidable stressors that can be detrimental for their health and welfare. However, welfare in farmed fish can be difficult to assess, and, so far, no standardized test has been universally accepted as a welfare indicator. This work contributes to the establishment of behavioural welfare indicators in a marine teleost in response to different water quality acute stressors. Groups of ten fish were exposed to high Total Ammonia Nitrogen concentration (High TAN, 18 mg.L-1), Hyperoxia (200 % O2 saturation), Hypoxia (20 % O2 saturation), or control water quality (100% O2 saturation and TAN < 2.5 mg.L-1) over 1 hour. Fish were then transferred in a novel environment for a group behaviour test under the same water quality conditions over 2 hours. Videos were recorded to assess thigmotaxis, activity and group cohesion. After this challenge, plasma cortisol concentration was measured in a subsample, while individual behavioural response was measured in the other fish using novel tank diving test. Prior to this study, the novel tank diving test was validated as a behavioural challenge indicative of anxiety state, by using nicotine as anxiolytic drug. Overall, all stress conditions induced a decrease in activity and thigmotaxis and changes in group cohesion while only fish exposed to Hypoxia and High TAN conditions displayed elevated plasma cortisol concentrations. In post-stress condition, activity was still affected but normal behaviour was recovered within the 25 minutes of the test duration. Our work suggests that the activity, thigmotaxis and group cohesion are good behavioural indicators of exposure to degraded water quality, and could be used as standardized measures to assess fish welfare.

Plastic intake does not depend on fish eating habits: Identification of microplastics in the stomach contents of fish on an urban beach in Brazil

This study aims to identify, classify, quantify the ingested microplastic by marine teleost fish, in order to analyze the relationship between microplastic and trophic guilds. Food items of 214 individuals of Opisthonema oglinum, Bagre marinus, Cathorops spixii, Sciades herzbergii, Chloroscombrus chrysurus, Conodon nobilis, Haemulopsis corvinaeformis were analyzed. The species were classified according to their trophic guilds (zoobenthivorous or opportunistic/omnivorous). All species ingested microplastic and contamination occurred independently of the trophic guild. Of the sampled fish, 55% were contaminated by microplastic. The most consumed categories were blue (28%) and transparent filaments (20%). Raman spectroscopy measurements detected that most sampled filament corresponds to blue synthetic fiber (polyester). This study can contribute by filling gaps in knowledge regarding sandy beach impacts, which are environments so highly threatened by human activities around the world and are neglected in terms of use and conservation plans.

Leptin stimulates gonadotropin release and ovarian development in marine teleost chub mackerel

Leptin transmits information about energy stored in the periphery to the reproductive axis and is an essential signal for puberty initiation in mammals; however, to date, few studies have focused on the direct effects of leptin stimulation on reproductive factors in fish. This study demonstrated the effect of leptin stimulation on important reproductive factors and ovarian development in the marine teleost chub mackerel (Scomber japonicus). We prepared recombinant leptin and conducted functional analyses through in vitro bioassays using primary pituitary cells, long-term leptin treatment administered to pre-pubertal females, and intracerebroventricular (ICV) administration. The results showed that leptin stimulation strongly induced gonadotropin (follicle-stimulating hormone: FSH and luteinizing hormone: LH) secretion from pituitary cells collected from pre-pubertal females, and that long-term leptin treatment significantly promoted ovarian development and triggered pubertal onset. Furthermore, ICV administration of leptin did not affect kisspeptin gene expression but significantly upregulated gonadotropin-releasing hormone 1 (gnrh1), fshb and lhb gene expression in sexually immature females. These results strongly suggest leptin as an important signal for reproductive-axis activation in chub mackerel.

Hypoosmotic stress induced tissue-specific immune responses of yellowfin seabream (Acanthopagrus latus) revealed by transcriptomic analysis

Salinity is a limiting factor for many marine organisms, including fishes. The shift in the ambient salinity can cause osmotic stress and arouse immune responses in fish. In this study, yellowfin seabream (Acanthopagrus latus), a euryhaline marine teleost, was used to investigate immune responses of different tissues (gill, liver, and muscle) under hypoosmotic stress. Comparative transcriptomic and physiological analyses of three tissues were conducted after fish exposed to the fresh water (FW, salinity = 0 ppt), low-saline water (LW, salinity = 3 ppt), and brackish water (BW, salinity = 6 ppt) for 8 days. The results showed that hypoosmotic stress dramatically altered the gene expression of three tissues in yellowfin seabream; The investigation of differentially expressed genes (DEGs) related to osmoregulation and immune response indicated that T cell-mediate immunity pathways were essential to tackle such stress. In terms of tissues, gill was found to be the most sensitive tissue under hypoosmotic stress by enhancing of Na+K+-ATPase activity and preventing the loss of Na+ and K+; Liver, on the other hand, was under the most sever oxidative stress indicated by the fluctuation of SOD, CAT activities and the MDA content; In contrast, muscle had the least osmoregulation and immune related response. We also identified several potential candidate genes, which may serve as gene indicators to identify the stressor. Overall, this study provides preliminary mechanistic insights into hypoosmotic stress adaption of aquatic organism.

Genome wide identification and functional characterization of two LC-PUFA biosynthesis elongase (elovl8) genes in rabbitfish (Siganus canaliculatus)

Elongases of very long-chain fatty acids (Elovls) catalyze the rate-limiting step of the elongation pathway that results in net two‑carbon elongation of pre-existing fatty acyl chains. As a set of crucial enzymes involved in the long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis, Elovls of fish have been investigated extensively in recent years. In the present study, we first identified two novel fish-specific elovl genes (named as elovl8a and elovl8b) from the herbivorous marine teleost rabbitfish (Siganus canaliculatus) by genomic survey and molecular cloning methods. Subsequently, their functional characteristics, tissue distribution patterns and transcriptional changes in response to different nutritional states were investigated. Full-length coding sequences of the elovl8a and elovl8b genes were 804 and 792 bp, encoding 267 and 263 amino acids, respectively. Multiple alignment, genomic synteny and phylogenetic analyses further suggested that elovl8 genes were unique to teleosts. Functional characterization by heterologous expression in yeast showed that Elovl8b could elongate C18 (18:2n-6, 18:3n-3 and 18:4n-3) and C20 (20:4n-6 and 20:5n-3) polyunsaturated fatty acids (PUFAs) to longer-chain polyunsaturated fatty acids (LC-PUFAs) whereas Elovl8a lacked this ability. In vitro, the expression of elovl8b but not elovl8a in rabbitfish hepatocytes was significantly up-regulated by incubation with 18:2n-6, 18:3n-3, 20:4n-6 and 20:5n-3, respectively. In vivo, compared with fish oil, dietary vegetable oil enriched in C18 PUFA enhanced the expression of elovl8b in rabbitfish brain, liver, intestine and gill tissues. These findings suggest that elovl8b but not elovl8a is a novel active member of the Elovl protein family involved in the LC-PUFAs biosynthesis pathway in rabbitfish, and provide novel insight into the mechanisms of LC-PUFAs biosynthesis in teleost.

Induction of oocyte maturation and changes in the biochemical composition, physiology and molecular biology of oocytes during maturation and hydration in the orange-spotted grouper (Epinephelus coioides)

In aquaculture, oocyte maturation, ovulation and spawning are important for successful breeding and seed production. Most marine teleost fish can be induced to spawn regularly using intramuscular injections of human chorionic gonadotropin (HCG). In this study, an intra-ovarian injection method was developed in orange-spotted grouper to deal with the broodstocks unresponsive to HCG. Successful oocyte maturation and ovulation in the unilateral injected ovary was induced within 35 h of treatment. An in vitro method was then established to induce HCG-primed oocyte maturation. HCG or maturation-inducing hormones (MIHs) induced the maturation of oocytes with a diameter between 490 and 560 μm. Biochemical, physiological and molecular changes during oocyte maturation and hydration were also characterized. The concentration of free amino acids except the cysteine increased during oocyte maturation, whereas Na+ decreased steadily and K+ increased. The expression of genes encoding cathepsin B, D, L, and the subunits of Na+, K+-ATPase were upregulated during hydration. Specific inhibitors for cathepsin and Na+, K+-ATPase were used to further confirm their crucial roles in oocyte hydration both in vivo and in vitro. These results provide valuable data for inducing oocyte maturation and evaluating oocyte quality in marine teleost fish.

Dietary taurine stimulates the hepatic biosynthesis of both bile acids and cholesterol in the marine teleost, tiger puffer (Takifugu rubripes).

Taurine (TAU) plays important roles in the metabolism of bile acids, cholesterol and lipids. However, little relevant information has been available in fish where TAU has been identified as a conditionally essential nutrient. The present study aimed to investigate the effects of dietary TAU on the metabolism of bile acids, cholesterol and lipids in tiger puffer, which is both an important aquaculture species and a good research model, having a unique lipid storage pattern. An 8-week feeding trial was conducted in a flow-through seawater system. Three experimental diets differed only in TAU level, that is, 1·7, 8·2 and 14·0 mg/kg. TAU supplementation increased the total bile acid content in liver but decreased the content in serum. TAU supplementation also increased the contents of total cholesterol and HDL-cholesterol in both liver and serum. The hepatic bile acid profile mainly includes taurocholic acid (94·48 %), taurochenodeoxycholic acid (4·17 %) and taurodeoxycholic acid (1·35 %), and the contents of all these conjugated bile acids were increased by dietary TAU. The hepatic lipidomics analysis showed that TAU tended to decrease the abundance of individual phospholipids and increase those of some individual TAG and ceramides. The hepatic mRNA expression study showed that TAU stimulated the biosynthesis of both bile acids and cholesterol, possibly via regulation of farnesoid X receptor and HDL metabolism. TAU also stimulated the hepatic expression of lipogenic genes. In conclusion, dietary TAU stimulated the hepatic biosynthesis of both bile acids and cholesterol and tended to regulate lipid metabolism in multiple ways.

Cloning and Characterization of Cholesterol 25-Hydroxylase (ch25h) From a Marine Teleost, Chinese Tongue Sole (Cynoglossus semilaevis), and Its Gene Expressions in Response to Dietary Arachidonic Acid

Our previous studies have shown that ARA regulated the gonadal steroidogenesis and the synthesis of gonadotrophin-releasing hormone (GnRH) in the brain in a gender-dependent manner in Chinese tongue sole, a marine teleost with typical sex dimorphism. As a following up-study, the current study aimed to clone and characterize a gene responding to dietary ARA differently between males and females, cholesterol 25-hydroxylase (ch25h), which has important roles in cholesterol and lipid metabolism of mammals, but is rarely investigated in fish. The full-length cDNA of Chinese tongue sole ch25h was cloned and characterized, and its transcription in the gonads, brain and liver of both males and females in response to dietary ARA levels (0.34%, 2.53%, and 9.63% of TFA) was investigated. The Chinese tongue sole Ch25h, which putatively is Ch25h subtype B, shared moderate identity to its known orthologs of other teleost and lower identity to human Ch25h. It has high transcription levels in the gonads, followed by skin and muscle, but low levels in the intestine, spleen, and kidney. High ARA levels significantly increased the ch25h transcription in the gonads and brain of male fish, but did not affect the transcription in the females. However, the effect of dietary ARA on ch25h transcription in the liver showed an opposite gender-difference pattern to those in the gonads and brain. To our knowledge, this is the first study in marine teleost investigating the nutritional regulation of ch25h expression.

Molecular characterisation of acanthocephalans from Australian marine teleosts: proposal of a new family, synonymy of another and transfer of taxa between orders.

We provide molecular data (cox1, 18S rDNA and 28S rDNA) for 17 acanthocephalan species and 20 host-parasite combinations from Australian marine teleosts collected from off Queensland, Australia. Fourteen of these acanthocephalans are characterised with molecular data for the first time and we provide the first molecular data for a species of each of the genera Heterosentis Van Cleave, 1931, Pyriproboscis Amin, Abdullah & Mhaisen, 2003 and Sclerocollum Schmidt & Paperna, 1978. Using 18S and 28S rDNA sequences, the phylogenetic position of each newly sequenced species is assessed with both single-gene and concatenated 18S+28S maximum likelihood and Bayesian inference analyses. Additional phylogenetic analyses focusing on the genus Rhadinorhynchus Lühe, 1912 and related lineages are included. Our phylogenetic results are broadly consistent with previous analyses, recovering previously identified inconsistencies but also providing new insights and necessitating taxonomic action. We do not find sufficient evidence to recognise the Gymnorhadinorhynchidae Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014 as distinct from the Rhadinorhynchidae Lühe, 1912. The family Gymnorhadinorhynchidae and its sole genus, Gymnorhadinorhynchus Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014, are here recognised as junior synonyms of Rhadinorhynchidae and Rhadinorhynchus, respectively. The two species currently assigned to Gymnorhadinorhynchus are recombined as Rhadinorhynchus decapteri (Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014) n. comb. and Rhadinorhynchus mariserpentis (Steinauer, Garcia-Vedrenne, Weinstein & Kuris, 2019) n. comb. In all of our analyses, Rhadinorhynchus biformis Smales, 2014 is found basal to the Rhadinorhynchidae + Transvenidae Pichelin & Cribb, 2001, thus resulting in a paraphyletic Rhadinorhynchidae. It appears that R. biformis may require a new genus and family; however, morphological data for this species are currently insufficient to adequately distinguish it from related lineages, thus we defer the proposal of any new higher-rank names for this species. Species of the genus Sclerocollum, currently assigned to the Cavisomidae Meyer, 1932, are found nested within the family Transvenidae. We transfer the genus Sclerocollum to the Transvenidae and amend the diagnosis of the family accordingly. The genera Gorgorhynchoides Cable & Linderoth, 1963 and Serrasentis Van Cleave, 1923, currently assigned to the Rhadinorhynchidae, are supported as sister taxa and form a clade in the Polymorphida. We transfer these genera and Golvanorhynchus Noronha, Fabio & Pinto, 1978 to an emended concept of the Isthomosacanthidae Smales, 2012 and transfer this family to the Polymorphida. Lastly, Pyriproboscis heronensis (Pichelin, 1997) Amin, Abdullah & Mhaisen, 2003, currently assigned to the Pomphorhynchidae Yamaguti, 1939, falls under the Polymorphida in our analyses with some support for a sister relationship with the Centrorhynchidae Van Cleave, 1916. As this species clearly does not belong in the Pomphorhynchidae and is morphologically and molecularly distinct from the lineages of the Polymorphida, we propose the Pyriprobosicidae n. fam. to accommodate it.

Swimming performance of marine fish larvae: review of a universal trait under ecological and environmental pressure

The larval phase of marine teleost fishes is characterized by important morphological and physiological modifications. Many of these modifications improve the larvae’s ability to swim, which satisfies a suite of crucial biological and ecological functions. Indeed, larval fish swimming performance has been considered a good proxy for overall condition, a predictor for growth and survival, and particularly helpful in assessing effects of natural and anthropogenic stress. Several methodologies have been developed to test larval fish swimming performance; however, measured swimming capabilities can strongly depend on the methodology utilised and developmental stage investigated. The aims of this review were, therefore, to link the ontogenetic development of swimming performance in early life stages of marine fishes, particularly the anatomical and physiological processes around the fins, muscles, and gills, with both the experimental methodologies used and the environmental stressors tested. We conducted a literature search and found 156 research papers relevant to swimming performance of marine teleost fish larvae. We found swimming performance to be highly variable among species and driven by temperature. In a meta-analysis focusing on the impacts of environmental stress on larval swimming performance, we found that prey reduction had the greatest impact on swimming. Methods used to evaluate swimming should keep the ontogenetic stage a focus, as forced swimming experiments are unfit for larvae prior to flexion of the notochord. Overall, while the data are deficient in some areas, we are able to highlight where the field of larval fish swimming could be directed and provide insight into which methods are best used under certain ecological scenarios, environmental stressors, and developmental stages.

Occurrence of Caligus asperimanus Pearse, 1951 (Copepoda: Caligidae) parasitic Lutjanus spp. (Perciformes: Lutjanidae) in the western South Atlantic.

Sea lice are widespread copepods in marine teleost around the world. In this paper the first record of Caligus asperimanus Pearse, 1951 in the Western South Atlantic is documented parasitizing Lutjanus jocu and Lutjanus vivanus caught from coastal zones of Espírito Santo and Rio de Janeiro State, respectively.

The teleost fish intestine is a major oxalate-secreting epithelium.

Oxalate is a common constituent of kidney stones, but the mechanism of its transport across epithelia is not well understood. With prior research on the role of the intestine focused on mammals, the present study considered oxalate handling by teleost fish. Given the osmotic challenge of seawater (SW), marine teleosts have limited scope for urinary oxalate excretion relative to freshwater (FW) taxa. The marine teleost intestine was hypothesized as the principal route for oxalate elimination, thus demanding epithelial secretion. To test this, intestinal 14C-oxalate flux was compared between FW- and SW-acclimated sailfin molly (Poecilia latipinna). In SW, oxalate was secreted at remarkable rates (367.90±22.95 pmol cm-2h-1), which were similar following FW transfer (387.59±27.82 pmol cm-2h-1), implying no regulation by salinity. Nevertheless, this ability to secrete oxalate at rates 15-19 times higher than the mammalian small intestine supports this proposal of the teleost gut as a major, previously unrecognized excretory pathway.

Auditory evoked potentials of utricular hair cells in the plainfin midshipman, Porichthys notatus.

The plainfin midshipman, Porichthys notatus, is a soniferous marine teleost fish that generates acoustic signals for intraspecific social communication. Nocturnally active males and females rely on their auditory sense to detect and locate vocally active conspecifics during social behaviors. Previous work showed that the midshipman inner ear saccule and lagena are highly adapted to detect and encode socially relevant acoustic stimuli, but the auditory sensitivity and function of the midshipman utricle remain largely unknown. Here, we characterized the auditory evoked potentials from hair cells in the utricle of non-reproductive type I males and tested the hypothesis that the midshipman utricle is sensitive to behaviorally relevant acoustic stimuli. Hair cell potentials were recorded from the rostral, medial and caudal regions of the utricle in response to pure tone stimuli presented by an underwater speaker. We show that the utricle is highly sensitive to particle motion stimuli produced by an underwater speaker positioned in the horizontal plane. Utricular potentials were recorded across a broad range of frequencies with lowest particle acceleration (dB re. 1 m s-2) thresholds occurring at 105 Hz (lowest frequency tested; mean threshold -32 dB re. 1 m s-2) and highest thresholds at 605-1005 Hz (mean threshold range -5 to -4 dB re. 1 m s-2). The high gain and broadband frequency sensitivity of the utricle suggest that it likely serves a primary auditory function and is well suited to detect conspecific vocalizations including broadband agonistic signals and the multiharmonic advertisement calls produced by reproductive type I males.

Fishmeal can be replaced with a high proportion of terrestrial protein in the diet of the carnivorous marine teleost (Trachinotus ovatus)

In general, over 30% fishmeal (FM) is required in diets for marine teleosts, which limits the sustainable development of aquaculture. Here, seven isonitrogenous (46%) and isolipidic (12%) diets (namely D1-D7) were formulated with three compound proteins (CPro I, CPro II and CPro III), which consisted of terrestrial animal and plant proteins, as substitutes for FM. Diet D1 (control) contained 30% FM, while diets D2-D3, D4-D5 and D6-D7 were formed by replacing 40% and 60%, 40% and 60%, and 60% and 80% FM with CPro I, CPro II, and CPro III, respectively. Juveniles of the carnivorous marine teleost Trachinotus ovatus were fed the seven diets in floating sea cages for 8 weeks. Growth performance including weight gain (WG) and specific growth rate (SGR), serum biochemical indices alkaline phosphatase (AKP) and glutamic pyruvate transaminase (GPT) activities, serum and liver antioxidant indices catalase (CAT) activities and total antioxidant capacity (T-AOC), fish proximate composition, muscle cooking percentage (CP) and textural properties of fish fed diets D2-D7 showed no difference or improved values compared with those of fish fed diet D1, suggesting no negative effects produced with 40–80% replacement of dietary FM by the compound proteins. Significantly higher contents of essential amino acids (EAA), non-essential amino acids (NEAA) and flavour amino acids (FAA) in muscle, as well as higher liver antioxidant capacity were found in fish fed diets D6 (12% FM) or D7 (6% FM) compared with those fed diet D1. The results demonstrated that 40–80% replacement of dietary FM by terrestrial compound proteins is feasible in T. ovatus, moreover 60% or 80% replacement brought a positive influence on antioxidant capacity and nutritional value.