Marine Teleost Research Articles

Submissions of diagnostic samples of two critically endangered species of handfish (Branchionichthys hirsutus and Thymichthys politus) from a public aquarium from 2018 to 2024.

Handfish (Family Brachionichthyidae) is the most threatened marine teleost fish family, however, there is little information on handfish health. We reviewed the results of submissions of mortalities from captive and captive bred spotted handfish (Branchionichthys hirsutus (Lacepède, 1804)) and red handfish (Thymichthys politus (Richardson, 1844)) from a public aquarium from January 2018 to February 2024. Seventeen cases for spotted handfish (comprising 33 individuals) and five cases for red handfish (one individual each) were submitted for mortality investigation. In 2018-2019, six of seven cases were diagnosed with scuticociliatosis. Other conditions included epitheliocystis (1 of 17), infections with metazoan parasites (2 of 17 for spotted handfish and 2 of 5 for red handfish) and hepatic lipidosis (4 of 17). Most submissions were fixed samples for histology with only one fish suitable for microbiology. We recommend development of a coordinated health program for all captive breeders and aquaria, which should include sampling protocols, collection, and preservation in a range of fixatives of all the dying or dead handfish and adapting sublethal sampling, including tank water to assess presence of pathogens and other microorganisms. Risk factors for handfish health in captivity should be assessed. Handfish health database should be established to avoid loss of corporate knowledge in this area.

Deep Dive Into Noninvasive Biometrics: A Pilot Journey Using Stereo-Video in a Public Aquarium.

Accurate collection of biometric data is important for understanding the biology and conservation of marine organisms, including elasmobranch and teleost fish, both in nature and controlled environments where monitoring marine specimens' health is mandatory. Traditional methods involving specimen capture and handling are invasive, stressful, and disruptive. Some techniques like underwater visual census or laser photogrammetry have been used for noninvasive data collection, but they have limitations and biases. The application of stereo-video photogrammetry through the use of diver-operated stereo-video systems (stereo-DOV) is a noninvasive method that overcomes these challenges, providing highly accurate measurements. It has become popular for species monitoring, studying anthropogenic impacts, and assessing length distributions. However, this technique is still uncommon and barely reported in aquarium settings. This study describes an innovative pilot study targeting multiple species carried out in a Public Aquarium, using a low-cost house-made device. The results revealed that measuring more than 100 individuals in approximately 1 day's work is possible. Total and fork lengths were estimated using specific software for 31 teleost and 16 elasmobranch species and compared with real measurements for the available species. Despite technical limitations that must be reviewed for application in future studies that resulted in high root mean square (RMS) values (> 20 mm), differences between methodological approaches revealed a minimal discrepancy (1.37%-5% in large sharks and rays and 1.8%-5.5% in teleost fish). This technique has time and cost requirements, but might represent a major advance in husbandry and in the contribution to conservation that ex situ studies can provide.

Gulf toadfish (Opsanus beta) urinary bladder ion and water transport is enhanced by acclimation to higher salinity to serve water balance.

Marine teleosts experience ion gain and water loss in their natural habitats. Among other tissues, the urinary bladder epithelium of marine fishes has been shown to actively transport ions to facilitate water absorption. However, transport properties of the urinary bladder epithelium of marine fishes and its plasticity in altered ambient salinities is relatively under-investigated. We describe urinary bladder epithelium electrophysiology, water flux, and expressions of ion transporters in urinary bladder tissue of Gulf toadfish (Opsanus beta) acclimated to either 35 ppt or 60 ppt seawater. Water absorption in bladder sac preparations increased ~ 350% upon acclimation to 60 ppt. Increases in water transport coincided with a significant ~ 137% increase in urinary bladder tissue mucosal-to-serosal short circuit current (Isc) and a ~ 56% decrease in tissue membrane resistance. Collectively, these metrics indicate that an active electrogenic system facilitates water absorption via Na+ (and Cl-) transport in urinary bladder tissue. Furthermore, pharmacological inhibition of urinary bladder tissue Isc and expression of a suite of ion transporters and channels previously unidentified in this tissue provide mechanistic insights into the transport processes responsible for water flux. Analysis of water transport to overall Gulf toadfish water balance reveals a modest water conservation role for the urinary bladder of ~ 0.5% of total water absorption in 35 ppt and 1.9% in 60 ppt acclimated toadfish. These results emphasize that electrogenic ion transport facilitates water-absorptive properties of the urinary bladder in Gulf toadfish - a process that is regulated to facilitate water homeostasis.

Aquaporin-3a Dysfunction Impairs Osmoadaptation in Post-Activated Marine Fish Spermatozoa.

Spermatozoon volume regulation is an essential determinant of male fertility competence in mammals and oviparous fishes. In mammals, aquaporin water channels (AQP3, -7 and -8) have been suggested to play a role in spermatozoon cell volume regulatory responses in the hypotonic female oviduct. In contrast, the ejaculated spermatozoa of marine teleosts, such as the gilthead seabream (Sparus aurata), experience a high hypertonic shock in seawater, initially resulting in an Aqp1aa-mediated water efflux, cell shrinkage and the activation of motility. Further regulatory recovery of cell volume in post-activated spermatozoa is mediated by Aqp4a in cooperation with the Trpv4 Ca2+ channel and other ion channels and transporters. Using a paralog-specific antibody, here, we show that seabream spermatozoa also express the aquaglyceroporin AQP3 ortholog Aqp3a, which is highly accumulated in the mid posterior region of the spermatozoon flagella, in a similar pattern to that described in mouse and human sperm. To investigate the role of Aqp3a in seabream sperm motility, we used a recently developed AQP3 antagonist (DFP00173), as well as the seabream Aqp3a-specific antibody (α-SaAqp3a), both of which specifically inhibit Aqp3a-mediated water conductance when the channel was heterologously expressed in Xenopus laevis oocytes. Inhibition with either DFP00173 or α-SaAqp3a did not affect sperm motility activation but did impair the spermatozoon motion kinetics at 30 s post activation in a dose-dependent manner. Interestingly, in close resemblance to the phenotypes of AQP3-deficient murine sperm, electron microscopy image analysis revealed that both Aqp3a inhibitors induce abnormal sperm tail morphologies, including swelling and angulation of the tail, with complete coiling of the flagella in some cases. These findings suggest a conserved role of Aqp3a as an osmosensor that regulates cell volume in fish spermatozoa under a high hypertonic stress, thereby controlling the efflux of water and/or solutes in the post-activated spermatozoon.

Sirt1 Mitigates Hepatic Lipotoxic Injury Induced by High-Fat-Diet in Fish Through Ire1α Deacetylation

BackgroundSilent information regulator protein 1 (Sirt1) is crucial in regulating lipid metabolism, but its specific role and mechanism in fish hepatic lipotoxic injury remain undefined. ObjectivesThis study aimed to elucidate the regulatory role of Sirt1 and the underlying mechanisms in dietary lipid-induced hepatic lipotoxic injury in a marine teleost black seabream. MethodsBlack seabream were fed a control diet (12% lipid level), high-fat diet (HFD) [18% lipid level, oleic acid (OA)-rich], or HFD supplemented with 0.25%, 0.50%, or 1.00% resveratrol (RSV) for 8 wk. The cultured hepatocytes were stimulated by OA (200 μM), OA supplemented with RSV (20 μM), or transfection with sirt1-small interfering RNA (sisirt1). Biochemical indices, gene expression (qPCR), histology, transmission electron microscope, immunofluorescence, Western blot, flow cytometry, and immunoprecipitation assays were conducted to evaluate hepatic lipid deposition, lipid metabolism, endoplasmic reticulum stress, inflammation and apoptosis, and determine protein interactions between Sirt1 and Ire1α. ResultsIn vivo, RSV supplementation increased mRNA and protein expression levels of sirt1 (236.2% ± 16.1% and 53.1% ± 14.3%) and downregulated the mRNA and phosphorylated protein expression levels of ire1α/Ire1α (46.0% ± 7.6% and 38.6% ± 7.0%), jnk/Jnk (57.6% ± 7.3% and 122.1%), and nuclear factor κ B (nf-κb/Nf-κb) p65 (41.7% ± 7.1% and 24.6% ± 0.8%) compared with the HFD group. Similar patterns were found in the in vitro experiments; however, after knockdown of sirt1, although the cells were incubated with RSV, the expression levels of ire1α/ Ire1α, jnk/Jnk, and nf-κb/Nf-κb p65 showed no significant differences compared with the OA treatment. Moreover, we found that mutation of K61 to arginine to mimic Ire1α deacetylation confers protection against Ire1α-mediated OA-rich HFD-induced inflammation and apoptosis. ConclusionsThe findings revealed that Sirt1 protects against OA-rich HFD-induced hepatic lipotoxic injury via the deacetylation of Ire1α on K61, hence reducing Ire1α autophosphorylation level, and suppressing Jnk and Nf-κb p65 activation. This mechanism is elucidated for the first time in fish.

Hypoxia-acclimation adjusts skeletal muscle anaerobic metabolism and burst swim performance in a marine fish

Red drum, Sciaenops ocellatus, are a marine teleost native to the Gulf of Mexico that routinely experiences periods of low oxygen (hypoxia). Recent work has demonstrated this species has the capacity to improve aerobic performance in hypoxia through respiratory acclimation. However, it remains unknown how hypoxia acclimation impacts anaerobic metabolism in red drum, and the consequences of exhaustive exercise and recovery. Juvenile fish were acclimated to normoxia (n = 15, DO 90.4 ± 6.42 %) or hypoxia (n = 15, DO 33.6 ± 7.2 %) for 8 days then sampled at three time points: at rest, after exercise, and after a 3 h recovery period. The resting time point was used to characterize the acclimated phenotype, while the remaining time points demonstrate how this phenotype responds to exhaustive exercise. Whole blood, red muscle, white muscle, and heart tissues were sampled for metabolites and enzyme activity. The resting phenotype was characterized by lower pHe and changes to skeletal muscle ATP. Exhaustive exercise increased muscle lactate, and decreased phosphocreatine and ATP with no effect of acclimation. Interestingly, hypoxia-acclimated fish had higher pHe and pHi than control in all exercise time points. Red muscle ATP was lower in hypoxia-acclimated fish versus control at each sample period. Moreover, acclimated fish increased lactate dehydrogenase activity in the red muscle. Hypoxia acclimation increased white muscle ATP and hexokinase activity, a glycolytic enzyme. In a gait-transition swim test, hypoxia-acclimated fish recruited anaerobic-powered burst swimming at lower speeds in normoxia compared to control fish. These data suggest that acclimation increases reliance on anaerobic metabolism, and does not benefit recovery from exhaustive exercise.

Further diversity in the origins of fish antifreeze proteins.

Shifts in environmental conditions can impose strong selection for adaptive traits. During the Cenozoic era, as the oceans cooled, many marine teleost fish species were at risk of freezing. This led to the independent emergence of distinct ice-binding antifreeze proteins (AFPs). The report in this issue by Graham and Davies reveals the development of AFP genes in shorthorn and longhorn sculpin from a copy of the lunapark gene. The predicted sculpin AFP sequences are unrelated to that of lunapark; the coding sequences for the AFPs appear to have arisen from small portions of the lunapark gene by codon frameshifting along with a series of mutations.

Inferring the extinction risk of marine fish to inform global conservation priorities.

While extinction risk categorization is fundamental for building robust conservation planning for marine fishes, empirical data on occurrence and vulnerability to disturbances are still lacking for most marine teleost fish species, preventing the assessment of their International Union for the Conservation of Nature (IUCN) status. In this article, we predicted the IUCN status of marine fishes based on two machine learning algorithms, trained with available species occurrences, biological traits, taxonomy, and human uses. We found that extinction risk for marine fish species is higher than initially estimated by the IUCN, increasing from 2.5% to 12.7%. Species predicted as Threatened were mainly characterized by a small geographic range, a relatively large body size, and a low growth rate. Hotspots of predicted Threatened species peaked mainly in the South China Sea, the Philippine Sea, the Celebes Sea, the west coast Australia and North America. We also explored the consequences of including these predicted species' IUCN status in the prioritization of marine protected areas through conservation planning. We found a marked increase in prioritization ranks for subpolar and polar regions despite their low species richness. We suggest to integrate multifactorial ensemble learning to assess species extinction risk and offer a more complete view of endangered taxonomic groups to ultimately reach global conservation targets like the extending coverage of protected areas where species are the most vulnerable.

Mass mortality event of round sardinella Sardinella aurita Valenciennes associated with Glugea Thélohan, 1891 microsporidian infection off the southern Italian coast.

Intracellular parasites of the genus Glugea Thélohan, 1891 (Microsporidia) comprise about 34 putative species capable of causing high morbidity and mortality in freshwater and marine teleost fishes. In this study, we report on the first mass mortality event associated with Glugea sp. infecting free-ranging round sardinella Sardinella aurita in the southern Tyrrhenian Sea (Italy). Here, we describe the ultrastructure of mature spores of this microsporidian and characterize it molecularly, as well as report its phylogenetic position. Most of the affected fish showed an irregular swelling of its abdomen. At necropsy, a variable number of xenomas, spherical to ellipsoidal in shape, were found in the peritoneal cavity strongly attached to the viscera of all fish. Histological analysis revealed varying severity of chronic inflammation along with occasional necrosis in visceral organs associated with multiple xenoma proliferation. These pathological findings were considered the main cause of this mass mortality event. Morphologically, the present material was closely related to G. sardinellesis and G. thunni. The phylogenetically closest taxa to the newly SSU rDNA sequence were G. thunni and an erroneusly identified G. plecoglossi, which were very closely related to each other, also suggesting that all these sequences might belong to the same species.

Embryonic and early larval development of Florida pompano, Trachinotus carolinus

AbstractThe Florida pompano, Trachinotus carolinus, is an ideal species for commercial aquaculture because of its rapid growth, tolerance to a range of environmental parameters, and high demand in the seafood market. This study detailed embryonic and early larval development of this species. Florida pompano followed similar developmental sequences to those observed in other marine teleosts, and embryos hatched between 22 and 28 h post‐fertilization. Significant brain lobe differentiation occurred prior to hatching. Pectoral fins were functional within 1‐day post‐hatch (dph). Substantial eye development occurred within 3 dph, indicating visual acuity prior to the onset of exogenous live feeding. Intestinal segments were differentiated by 3 dph, and rotifers were seen in the digestive tract by 4 dph. Digestive functions were limited through the first 7 dph because of the absence of functional gastric glands and gastric mucous cells in the rudimentary stomach, lipid vacuoles in the anterior intestines, and the persistence of acidophilic supranuclear vesicles in the posterior intestines. Within 7 dph, the pharyngeal arches differentiated, and hematopoietic tissue and mesonephric tubules were visible in the larval kidney. Their rapid larval development and organogenesis are additional factors that make Florida pompano an ideal species for aquaculture production and should encourage continued efforts toward commercialization.

Estimation of effective number of breeders and effective population size in an abundant and heavily exploited marine teleost.

Obtaining reliable estimates of the effective number of breeders (N b) and generational effective population size (N e) for fishery-important species is challenging because they are often iteroparous and highly abundant, which can lead to bias and imprecision. However, recent advances in understanding of these parameters, as well as the development of bias correction methods, have improved the capacity to generate reliable estimates. We utilized samples of both single-cohort young of the year and mixed-age adults from two geographically and genetically isolated stocks of the Australasian snapper (Chrysophrys auratus) to investigate the feasibility of generating reliable N b and N e estimates for a fishery species. Snapper is an abundant, iteroparous broadcast spawning teleost that is heavily exploited by recreational and commercial fisheries. Employing neutral genome-wide SNPs and the linkage-disequilibrium method, we determined that the most reliable N b and N e estimates could be derived by genotyping at least 200 individuals from a single cohort. Although our estimates made from the mixed-age adult samples were generally lower and less precise than those based on a single cohort, they still proved useful for understanding relative differences in genetic effective size between stocks. The correction formulas applied to adjust for biases due to physical linkage of loci and age structure resulted in substantial upward modifications of our estimates, demonstrating the importance of applying these bias corrections. Our findings provide important guidelines for estimating N b and N e for iteroparous species with large populations. This work also highlights the utility of samples originally collected for stock structure and stock assessment work for investigating genetic effective size in fishery-important species.

Orca (Orcinus orca) and shark predator-prey interactions within Cabo Pulmo National Park in the Gulf of California, Mexico

Orcas (Orcinus orca) have a worldwide distribution and as apex predators feed on a wide variety of prey, including marine mammals, seabirds, sea turtles, cephalopods, teleost fish and elasmobranchs. Historically, there have been few observations of orca predation on large elasmobranch species nor are they commonly identified in the stomach contents of deceased orcas. In recent years there has been an increase in observational records of orca predation, such as on white sharks (Carcharodon carcharias) in South Africa, which could indicate that elasmobranchs serve a greater importance in their diet than previously considered. These events are often documented by members of the public due to the development and affordability of innovative cameras, including the use of the drones (unoccupied aerial vehicles). Here we describe new predator-prey interactions between orcas and large shark species in Cabo Pulmo National Park (CPNP), a small no-take marine protected area located in the Gulf of California. In this paper, we were able to successfully identify individuals from the described orca pods in the region; specifically, the same individuals hunting sharks over a period of nearly two years. We discuss the potential implications of these new ecological interactions, given the importance of tourism to sustain the management of CPNP, as cascading impacts have been documented elsewhere in light of orca predations on sharks.

Long-distance migrations and seasonal movements of meagre (Argyrosomus regius), a large coastal predator, along the Iberian Peninsula coast

BackgroundThe meagre, Argyrosomus regius, is a large coastal predatory fish inhabiting waters from the north-eastern Atlantic and Mediterranean Sea, where it is targeted by commercial and recreational fisheries. Previous genetic studies have found an unexpectedly high population differentiation not only between the Atlantic and the Mediterranean, but also along the Atlantic coast. However, the reasons underpinning this genetic barrier remained unclear. Likewise, even though the species is amongst the world’s largest marine teleosts, knowledge about its movement ecology and migratory behaviour remains notably scarce, and primarily reliant on fisheries-dependent data.MethodsIn this study, we used a combination of acoustic telemetry and pop-up satellite archival tags to investigate the movements of 22 adult meagre (70–143 cm total length) along the Southwestern coast of the Iberian Peninsula.ResultsOur results strongly suggest that the previously reported genetic differentiation is not maintained by limited adult dispersal/movement, as hypothesized. On the contrary, we documented some of the longest individual annual migrations ever recorded for a coastal teleost, up to > 2000 km, with frequent back-and-forth movements between the West and Southern Iberian coasts. Moreover, their detected regional movement patterns support the existence of a marked seasonal behavioural shift, with individuals being less active and moving to deeper waters during winter, and are consistent with spawning philopatry associated to their summer reproductive movements. Finally, we identified putative aggregation areas that may harbour important feeding/overwintering grounds.ConclusionsThese findings shed new light on the movement and behaviour patterns of meagre that may be of particular importance for the conservation and spatial management of this species throughout its range, and open the door to further research on functional connectivity.

Alternative splicing plays a nonredundant role in greater amberjack (Seriola dumerili) in acclimation to ambient salinity fluctuations

Alternative splicing (AS) is an important post-transcriptional mechanism for adaptation of fish to environmental stress. Here, we performed a genome-wide investigation to AS dynamics in greater amberjack (Seriola dumerili), an economical marine teleost, in response to hypo- (10 ppt) and hyper-salinity (40 ppt) stresses. Totally, 2267–2611 differentially spliced events were identified in gills and kidney upon the exposure to undesired salinity regimes. In gills, genes involved in energy metabolism, stimulus response and epithelial cell differentiation were differentially spliced in response to salinity variation, while sodium ion transport and cellular amide metabolism were enhanced in kidney to combat the adverse impacts of salinity changes. Most of these differentially spliced genes were not differentially expressed, and AS was found to regulate different biological processes from differential gene expression, indicative of the functionally nonredundant role of AS in modulating salinity acclimation in greater amberjack. Together, our study highlights the important contribution of post-transcriptional mechanisms to the adaptation of fish to ambient salinity fluctuations and provides theoretical guidance for the conservation of marine fishery resources against increasingly environmental challenges.

Intraperitoneal administration of arginine vasotocin (AVT) induces anorexigenic and anxiogenic actions via the brain V1a receptor-signaling pathway in the tiger puffer, Takifugu rubripes

Arginine vasotocin (AVT) is produced mainly in the hypothalamus and as a neurohypophyseal hormone peripherally regulates water-mineral balance in sub-mammals. In addition, AVT-containing neurons innervate several areas of the brain, and AVT also acts centrally as both an anorexigenic and anxiogenic factor in goldfish. However, it is unclear whether these central effects operate in fish in general. In the present study, therefore, we investigated AVT-like immunoreactivity in the brain of the tiger puffer, a cultured fish with a high market value in Japan and also a representative marine teleost species, focusing particularly on whether AVT affects food intake and psychomotor activity. AVT-like immunoreactivity was distributed higher in the ventral region of the telencephalon, the hypothalamus and midbrain. Intraperitoneal (IP) administration of AVT at 100 pmol g−1 body weight (BW) increased the immunoreactivity of phosphorylated ribosomal proteinS6 (RPS6), a neuronal activation marker, in the telencephalon and diencephalon, decreased food consumption and enhanced thigmotaxis. AVT-induced anorexigenic and anxiogenic actions were blocked by IP co-injection of a V1a receptor (V1aR) antagonist, Manning compound (MC) at 300 pmol g−1 BW. These results suggest that AVT acts as an anorexigenic and anxiogenic factor via the V1aR-signaling pathway in the tiger puffer brain.

Systematic analysis of ocular features and responses of cultured spotted wolffish (Anarhichas minor).

A better understanding of unique anatomical and functional features of the visual systems of teleost fish could provide key knowledge on how these systems influence the health and survival of these animals in both wild and culture environments. We took a systematic approach to assess some of the visual systems of spotted wolffish (Anarhichas minor), a species of increasing importance in North Atlantic aquaculture initiatives. The lumpfish (Cyclopterus lumpus) was included in these studies in a comparative manner to provide reference. Histology, light and electron microscopy were used to study the spatial distribution and occurrence of cone photoreceptor cells and the nature of the retinal tissues, while immunohistochemistry was used to explore the expression patterns of two photoreceptor markers, XAP-1 and XAP-2, in both species. A marine bacterial infection paradigm in lumpfish was used to assess how host-pathogen responses might impact the expression of these photoreceptor markers in these animals. We define a basic photoreceptor mosaic and present an ultrastructural to macroscopic geographical configuration of the retinal pigment tissues in both animals. Photoreceptor markers XAP-1 and XAP-2 have novel distribution patterns in spotted wolffish and lumpfish retinas, and exogenous pathogenic influences can affect the normal expression pattern of XAP-1 in lumpfish. Live tank-side ophthalmoscopy and spectral domain optical coherence tomography (SD-OCT) revealed that normal cultured spotted wolffish display novel variations in the shape of the retinal tissue. These two complementary imaging findings suggest that spotted wolffish harbour unique ocular features not yet described in marine teleosts and that visual function might involve specific retinal tissue shape dynamics in these animals. Finally, extensive endogenous biofluorescence is present in the retinal tissues of both animals, which raises questions about how these animals might use retinal tissue in novel ways for visual perception and/or communication. This work advances fundamental knowledge on the visual systems of two economically important but now threatened North Atlantic teleosts and provides a basic foundation for further research on the visual systems of these animals in health versus disease settings. This work could also be useful for understanding and optimizing the health and welfare of lumpfish and spotted wolffish in aquaculture towards a one health or integrative perspective.

Reproductive Characteristics and Suitability of Sterile dead end Knockout Nibe Croaker as a Recipient for Intraperitoneal Germ Cell Transplantation.

The use of sterile recipients is crucial for efficiently producing donor-derived offspring through surrogate broodstock technology for practical aquaculture applications. Although knockout (KO) of the dead end (dnd) gene has been used in previous studies as a sterilization method, it has not been reported in marine fish. In this study, nibe croaker was utilized as a model for marine teleosts that produce small pelagic eggs, and the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system was utilized to produce dnd KO fish. The F1 generation, which carried a nonsense mutation in the dnd gene, was produced by mating founder individuals with wild-type counterparts. Subsequently, the F2 generation was produced by mating the resulting males and females. Among the F2 generations, 24.0% consisted of homozygous KO individuals. Histological analysis revealed that primordial germ cells (PGCs) were present in homozygous KO individuals at 10days post-hatching (dph), similar to wild-type individuals. However, by 20 dph, PGCs were absent in KO individuals. Furthermore, no germ cells were observed in the gonads of both sexes of homozygous KO individuals at 6months old, which is the typical maturity age for wild-type individuals of both sexes. In addition, when cryopreserved donor nibe croaker testicular cells were transplanted, only donor-derived offspring were successfully obtained through the spontaneous mating of homozygous KO recipient parents. Results indicate that dnd KO nibe croaker lacks germ cells and can serve as promising recipients, producing only donor-derived gametes as surrogate broodstock.

Reports of Pennellidae Burmeister, 1835 (Copepoda: Siphonostomatoida) post metamorphosed females off the coast of southern Africa

Seven species belonging to Pennellidae are reported from marine teleosts caught off southern Africa. Additionally, complete re-descriptions are provided for Propeniculus stromatei and Sarcotretes scopeli. Examination of Lernaeenicus gonostomae, deposited in the Iziko South African Museum, indicated that it has the morphological features of Sarcotretes rather than Lernaeenicus and thus should be moved to Sarcotretes i.e. S. gonostomaen. comb. for which a re-description is also provided. Reports of new host records include those of Pennella instructa from Seriola lalandi; Propeniculus stromatei from Rhabdosargus holubi and Pomadasys commersonnii; Sarcotretes scopeli from Nansenia tenera, and Sarcotretes longirostris from Centrolophus niger. New geographical records include those of P. instructa, P. stromatei, S. scopeli, S. longirostris, and L. longiventris off southern Africa. Additionally, an attempt to estimate the evolutionary relationships amongst some genera is done from partial COI sequences deposited in Genbank.

Physiological responses of European sea bass (Dicentrarchus labrax) exposed to increased carbon dioxide and reduced seawater salinities.

The iono- and osmoregulatory capacities of marine teleosts, such as European sea bass (Dicentrarchus labrax) are expected to be challenged by high carbon dioxide exposure, and the adverse effects of elevated CO2 could be amplified when such fish migrate into less buffered hypo-osmotic estuarine environments. Therefore, the effects of increased CO2 on the physiological responses of European sea bass (Dicentrarchus labrax) acclimated to 32 ppt, 10 ppt and 2.5 ppt were investigated. Following acclimation to different salinities for two weeks, fish were exposed to present-day (400 µatm) and future (1000 µatm) atmospheric CO2 for 1, 3, 7 and 21 days. Blood pH, plasma ions (Na+, K+, Cl-), branchial mRNA expression of ion transporters such as Na+/K+-ATPase (NKA), Na+/K+/2Cl- co-transporters (NKCC) and ammonia transporters (e.g. Rhesus glycoproteins Rhbg, Rhcg1 and Rhcg2) were examined to understand the iono- and osmoregulatory consequences of elevated CO2. A transient but significant increase in the blood pH of exposed fish acclimated at 10 ppt (day 1) and 2.5 ppt (day 21) was observed possibly due to an overshoot of the blood HCO3- accumulation while a significant reduction of blood pH was observed after 21 days at 2.5ppt. However, no change was seen at 32 ppt. Generally, Na + concentration of control fish was relatively higher at 10 ppt and lower at 2.5 ppt compared to 32 ppt control group at all sampling periods. Additionally, NKA was upregulated in gill of juvenile sea bass when acclimated to lower salinities compared to 32 ppt control group. CO2 exposure generally downregulated NKA mRNA expression at 32ppt (day 1), 10 ppt (days 3, 7 and 21) and 2.5ppt (days 1 and 7) and also a significant reduction of NKCC mRNA level of the exposed fish acclimated at 32 ppt (1-3 days) and 10 ppt (7-21 days) was observed. Furthermore, Rhesus glycoproteins were generally upregulated in the fish acclimated at lower salinities indicating a higher dependance on gill ammonia excretion. Increased CO2 led to a reduced expression of Rhbg and may therefore reduce ammonia excretion rate. Juvenile sea bass were relatively successful in keeping acid base balance under an ocean acidification scenario. However, this came at a cost for ionoregulation with reduced NKA, NKCC and Rhbg expression rates as a consequence.

Twenty years later: Biodiversity of marine symbiotic Siphonostomatoida (Copepoda) off Southern Africa.

Siphonostomatoida (Copepoda) consists of 40 families of symbionts infecting vertebrates (17 families) and invertebrates (23 families) found mostly in marine habitats. In 2004, a list was compiled of all the reported families, genera and species symbiotic with marine fish in Southern African waters. Since this was done 20 years ago, it is necessary to re-evaluate the progress made in 20 years regarding our knowledge of the diversity of marine siphonostomatoids. To assess the current knowledge, the 2004 list was updated with reports published since 2004 as well as with new host and locality records including species with changes in taxonomy. Additionally, species collected but unreported as well as species previously reported but with new hosts and/or localities were also added. Currently reports include 16 families, 75 genera and 234 species. However, amongst these are reports of only two families (3 species) infecting invertebrates. Even though the report includes 71 additional species it still compares poorly with the about 2 274 accepted species, especially regarding species infecting invertebrates. Considering South Africas wealth in possible marine host species, examination of more hosts (especially marine teleosts and invertebrates) will definitely result in an increase in the current knowledge about the biodiversity of marine siphonostomatoids off Southern Africa.