Adult Fish Research Articles

Updating the zooplankton species list for the Belgian part of the North Sea

Many marine species are threatened, and given the importance of biodiversity indices in the current European marine policy, taking stock of existing species and species diversity is crucial. Zooplankton form the basis of the pelagic food web, acting as staple food for fish larvae and adult pelagic fish, but are very susceptible to a changing climate. Inventorying zooplanktonic diversity is therefore important. Based on monthly sampling campaigns in 2009 and 2010, an update is provided on the zooplankton species list for the Belgian part of the North Sea. A total of 137 taxa are listed, some of which had rarely or never been observed in the area. This inventory revealed several species new to the Belgian marine species list: the calanoid copepod Metridia lucens, the cyclopoids Oithona similis and Giardella callianassae, the hydrozoans Amphinema dinema and Eutima gracilis, the mysid Acanthomysis longicornis, the polychaete worm Tomopteris helgolandica, the cladoceran Penilia avirostris and the monstrilloid copepod Cymbasoma germanicum. Additionally, we identified several males of C. germanicum, which have never been described before. Brief discussions are presented on spatial distribution and abundance of all taxa.

Toxic effects and comparison of common amino antioxidants (AAOs) in the environment on zebrafish: A comprehensive analysis based on cells, embryos, and adult fish

The ubiquity of amino antioxidants (AAOs) in the environment has attracted increasing attention, given their potential toxicity. This investigation represents a pioneering effort, systematically scrutinizing the toxicological effects of four distinct AAOs across the developmental spectrum of zebrafish, encompassing embryonic, larvae, and adult stages. The results indicate that four types of AAO exhibit varying degrees of cell proliferation toxicity. Although environmentally relevant concentrations of AAOs exhibit a comparatively circumscribed impact on zebrafish embryo development, heightened concentrations (300 μg/L) of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD) distinctly evoke developmental toxicity. Behavioral analysis results indicate that at concentrations of 20 and 300 μg/L, the majority of AAOs significantly reduced the swimming speed and activity of larvae. Moreover, each AAO triggers the generation of reactive oxygen species (ROS) in larvae, instigating diverse levels of oxidative stress. The study delineates parallel toxicological patterns in zebrafish exposed to 300 μg/L of 6PPD and IPPD, thereby establishing a comparable toxicity profile. The comprehensive toxicity effects among the four AAOs is as follows: IPPD >6PPD > N-Phenyl-1-naphthylamine (PANA) > diphenylamine (DPA). These findings not only enrich our comprehension of the potential hazards associated with AAOs but also provide data support for structure-based toxicity prediction models.

Total mercury in three small tunas from southeastern Brazil: Stable isotope relations and human risk assessment

Mercury (Hg) bioaccumulation can be highly variable in marine species. Its concentration is influenced by several physico-chemical and biotic processes, including size, age, diet composition and foraging habitats. Herein, we addressed total mercury (THg) concentrations in three small tuna species in Brazil: the frigate tuna Auxis thazard, the little tunny Euthynnus alletteratus and the skipjack tuna Katsuwonus pelamis. Samples were collected from commercial landings in the SE Brazilian coast from 2017 to 2019. The influence of trophic ecology and habitat preference on Hg accumulation was assessed through stable isotope [carbon (δ13C) and nitrogen (δ15N)] measurements. Additionally, the human health risk regarding the species consumption was assessed by the estimated weekly intake (EWI) and the provisional tolerable weekly intake (PTWI) for total consumers, adult men and adult women. Variables such as size and age were positively correlated to Hg, due to the bioaccumulation process. Trophic position appears to positively influence the mercury concentrations for A. thazard and K. pelamis, since relationship between δ15N and THg was significant. For E. alletteratus, the lack of relationship suggests that δ15N values do not vary much among adult fish (> 300 mm). Muscle THg concentrations in the three species did not exceed the established tolerable limit for mercury by Brazilian and international organs, as indicated by the %PTWI. This finding suggests that the consumption of those species caught off southeast Brazil at the considered amounts does not present a risk for healthy adults.

Trace elemental and stable isotopic signatures to reconstruct the large-scale environmental connectivity of fish populations

Animal movements and connectivity across different environments constitute essential components of virtually all ecological and evolutionary processes. In the present study, we measured multiple trace-element profiles and stable isotopes to reconstruct life cycle patterns of Eleutheronema rhadinum, and patterns of connectivity among populations of E. rhadinum across 3 distinct ecoregions in the eastern China Sea. Our results indicated that E. rhadinum larvae from different regions exhibited distinct otolith core levels of trace elements and stable isotopes, serving as discriminative markers of geographical origin. We used the maximum likelihood approach and linear discriminant analysis to trace back the origins of the mixed adult fish stocks. After leaving their nursery areas, juvenile fish from colder northern regions migrated south to overwinter in the South China Sea, where they mixed with the local populations. After overwintering, the adult fish began their long journey north, with the migrating population including individuals of both East China Sea and South China Sea origins. Meanwhile, fish in the Beibu Gulf exhibited a lower degree of interaction with the South China Sea populations and minimal interaction with those in the East China Sea. Trace elements and stable isotopes revealed the spatiotemporal connectivity of E. rhadinum across the 3 different ecoregions. This study provides critical information on how marine connectivity supports temperature-mediated fish community movement patterns within coastal ecosystems.

Ontogeny and tissue specific expression profiles of recombination activating genes (RAGs) during development in Nile tilapia, Oreochromisniloticus

Recombination activating genes (RAGs) mediates the process of rearrangement and somatic recombination (V(D)J) to generate different antibody repertoire. Studies on the expression pattern of adaptive immune genes during ontogenic development are crucial for the formulation of fish immunization strategy. In the present study, Nile tilapia was taken to explore the relative expression profile of RAG genes during their developmental stages. The developmental stages of Nile tilapia, i.e., unfertilized egg, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30 days post-hatch (dph) and kidney, blood, gill, liver and spleen tissues from adult fish were collected and the cDNA synthesis was carried out. Gene specific primers for RAG-1 and RAG-2 of Nile tilapia were designed and their annealing temperature (Tm) was optimized by gradient PCR. Consequently, PCR was performed to confirm the specific amplification of RAG-1 and RAG-2 genes. Quantitative real-time PCR (qRT-PCR) gene expression of RAG-1 and RAG-2 were noticed in all the developmental stages; however, a significant increase was observed after 12 dph and peaked at 24 dph, followed by a gradual decrease until 30 dph. Tissue-specific gene expression profiling revealed that the highest expression of RAG-1 and RAG-2 was observed in the kidney, followed by spleen, gill, liver and blood. The findings of the study explored the suitable timing of lymphoid maturation that could be technically used for the adoption of strategies to improve disease resistance of fish larvae for mitigating larval mortality.

The length-weight relationship and condition factors of coastal small-sized adult and juvenile fish species following dense mucilage in the Sea of Marmara, Türkiye

The length-weight relationship and condition factors of coastal small-sized adult and juvenile fish species following dense mucilage in the Sea of Marmara, Türkiye

Diversity of Fish and Decapod Fry in the Coastal Zone of Amvrakikos Gulf

Amvrakikos Gulf and its surrounding coastal lagoons are of primary importance for the local biodiversity and fishing activities. Fish species inhabited the coastal lagoons based on the seasonal ongoing migration movements of fry and adult fish individuals from the sea towards the lagoons. Information on the early stages of fish and decapod species in the Amvrakikos Gulf is limited only to the planktonic ontogenetic stages and reproduction biology, respectively. The aim of this study was to describe the spatial distribution of fry from commercially important fish and decapod species in the coastal zone of Amvrakikos Gulf. The seasonal appearance of the early stage of the most commercially important fish species caught in the coastal zone of the gulf ranged from one to four seasons, depending on the species. Individuals of all ontogenetic stages (fry, juveniles, and adults) were reported for several species (A. boyeri, A. fasciatus, S. abaster, S. tyfle, and B. ocellaris), indicating that these species may be regarded as residents in the coastal zone, providing habitats for their entire life cycle. The average relative abundance of the species/genera exhibited no differences compared to other Greek brackish waters. The species composition in the Amvrakikos Gulf at 10 cm and above was in agreement with the transitional nature of the area, with permanent and occasional species present. The present study emphasizes the importance of the coastal zone as a nursery habitat for commercially important species.

Abstract PR-010: Asc1lb progenitor-specific RB conditional inactivation in zebrafish models rare CNS primitive neuroectodermal tumors

Abstract PR-010: Asc1lb progenitor-specific RB conditional inactivation in zebrafish models rare CNS primitive neuroectodermal tumors

Comparisons of donor stray percentages between hatchery‐ and natural‐origin Chinook Salmon and steelhead in the upper Columbia watershed

AbstractObjectiveArtificial propagation of Pacific salmon Oncorhynchus spp. is commonly used to achieve conservation and harvest goals. However, unintended effects of artificial propagation, such as high donor stray percentages, can reduce numbers of adults that return to target areas and also contribute spawners to different populations where they are undesirable. Until recently, it was difficult to assess if hatchery‐origin fish stray rates were atypical because few estimates of stray rates of natural‐origin fish were available. We sought to fill that gap by comparing donor stray percentages of hatchery‐ and natural‐origin Chinook Salmon O. tshawytscha and steelhead O. mykiss from the same locations.MethodsWe used 29,885 last passive integrated transponder tag detections of adult fish to estimate and compare donor stray percentages of hatchery‐origin and natural‐origin Chinook Salmon and steelhead in the upper Columbia River watershed between 2002 and 2018.ResultDonor stray percentages of hatchery‐origin spring, summer, and fall Chinook Salmon and steelhead were <0.3% at the upper Columbia basin scale and similar to natural‐origin donor stray percentages. Only steelhead donor stray percentages were higher for hatchery‐origin adults at the subbasin scale than natural‐origin counterparts and were <22% for all taxa. The percentage of hatchery‐origin steelhead and spring Chinook Salmon released in tributaries were detected at nontarget areas at higher percentages (<63%) than natural‐origin counterparts born in these tributaries. Returning hatchery‐origin and natural‐origin Chinook Salmon and steelhead generally strayed in an upstream direction in similar proportions. Juvenile spring Chinook Salmon that were moved 14–391 km from centralized hatcheries to tributaries for overwintering or final acclimation strayed at a much higher rate than those that completed their incubation, rearing, and acclimation at a single location, but this did not occur with steelhead. Other adaptive management actions that were implemented to reduce straying produced mixed results. A high proportion of stray hatchery‐origin spring Chinook Salmon initially homed to tributary weirs.ConclusionDonor stray percentages of hatchery‐origin Chinook Salmon and steelhead were generally not higher than natural‐origin donor stray percentages at larger spatial scales (e.g., upper Columbia basin and subbasin) but were higher at smaller spatial scales (e.g., tributaries). A variety of approaches can be considered to reduce undesirable production of strays, but most of them involve difficult management trade‐offs.

Trophic niche partitioning of golden cuttlefish (Sepia esculenta) during ontogeny revealed by stable isotope analysis and DNA metabarcoding

Cephalopods are becoming more important in global fishery. Understanding the trophic ecology partitioning during their ontogeny is critical to the stock assessment and fishery management. The golden cuttlefish (Sepia esculenta), one of commercially important cephalopod species has been found at different life-history stages that co-inhibit in the coastal waters of Qingdao, China. In the present study, the trophic ecology of S. esculenta was assessed by using stable isotope analysis (SIA: based δ13C and δ15N from muscle and liver tissue) and DNA metabarcoding of the stomach contents through high-throughput sequencing (HTS). SIA uncovered the variation in isotope niche and trophic position of S. esculenta during ontogeny. DNA metabarcoding showed a higher resolution of prey identification than before. The combined analysis of SIA and DNA metabarcoding indicated that diet shifts occurred in the ontogeny of S. esculenta. Paralaval and juvenile prefer zooplankton, while sub-adult and adult prefer demersal fishes. The standard ellipse area (SEAc) indicated that low isotope niche overlaps among paralaval, juvenile and sub-adult of S. esculenta, which reflect the squid foraging strategy during ontogeny. The study confirmed that S. esculenta resources can be partitioned into different life stages, suggesting a survival strategy to maintain population dynamics.

Study on the Impact of Brick-kiln Effluent on Histomorphology of Gill and Hepatopancreas of Channa punctata Bloch. with Reference to Mobilization of Thyroid Hormones

This study deals with the effect of sublethal exposure of brick kiln effluent on lipid and protein peroxides, Aspartate Transferase (AST), Alanine Transferase (ALT) and Alkaline Phosphatase (ALP) activities and mobilization of thyroid-stimulating and thyroid hormones in gill and hepatopancreas of Channa punctata Bloch., with supporting histochemical investigations in these tissues. Acclimatized adult fishes of either sexes of three groups were reared separately in three aquaria. Aquarium-I comprised the normal control group, and the other two aquariums, i.e. Aquarium-II and Aquarium-III, comprised experimental groups of fishes exposed to 20ppm/L and 30ppm/L of brick kiln effluents, respectively. Before these, the LC50 value of the Fish for brick kiln effluent was evaluated as 55±0.50 ppm/L for 28 days. Increased lipid and protein peroxides, decreased transaminase activities with hypothyroidic conditions were observed both in gills and hepatopancreas on treatment. Significant alternations of these biochemical parameters were recorded, with some drastic changes in the histo-architecture regarding treatment issues. Gills showed hypertrophy with fusion and curving of gill lamellae. Spiked secondary gill lamellae were also observed to have several degenerative features. Decreasing hepatocytes and vacuolation at several places were recorded in hepatopancreas with necrosis of the tissues and patchy degeneration.

Effects of stocking density during simulated transport on physiology and behavior of largemouth bass (Micropterus salmoides)

AbstractThe live transport of farmed fish is an important practice in Chinese aquaculture due to consumer preferences in its domestic market. However, live transport can be stressful for fish and may cause many welfare issues. This study aimed to examine the effects of transport density on the welfare of largemouth bass (Micropterus salmoides). Adult fish were allocated to four experimental treatments in a two‐factor design (N = 5 groups per treatment). Factor one was stocking density of either 39 (low density) or 78 (high density) g L−1. Factor two was transport, with half of the fish groups exposed to simulated transport stress for 3 h using a motion platform, and the other half kept in static tanks for the same length of time. Baseline behavior and physiology were determined from a subset of fish after acclimation but before selection into groups and application of transport. To determine the effects of transport, stocking density, and their interaction on the experimental groups, physiological sampling and behavioral recording were carried out immediately after simulated transport, and water quality was measured both before and after transport. Changes in water quality were observed between two timepoints, with decreased dissolved oxygen levels and increased water temperature. Total ammonia nitrogen levels significantly increased in all treatments over time, particularly in the high‐density groups. Fish ventilation rates were significantly elevated in the groups kept at a high stocking density regardless of whether they also experienced transport stress. Fish transported at a high stocking density also showed more fear‐related behaviors such as freezing and thigmotaxis than non‐transported groups. Serum cortisol, catalase, and aspartate transaminase levels were significantly higher in the transported treatment groups compared to the baseline fish, but no difference was found for serum glucose, lactate, and glutathione peroxidase. We concluded that 3 h of simulated transport was stressful to largemouth bass kept at 78 g L−1, as evidenced by altered fish physiological and behavioral indicators of stress, as well as deteriorated water quality. Additionally, we identified a positive correlation between serum and skin mucus samples for cortisol, glucose, and lactate in transported fish, providing important information for developing less invasive methods for the welfare assessment of largemouth bass.

Assessing entrainment of larval fish in the Hogback Diversion Canal, San Juan River

AbstractWater diversions worldwide may entrain or impinge fish and have population‐level impacts, but barriers like fish screens can reduce such threats. Traditional barriers are ineffective in the San Juan River, USA, due to high sediment and debris loads, so the Hogback Diversion Canal, NM, employs a novel weir wall design to reduce entrainment of sub‐adult and adult fishes. We evaluated the effectiveness of the weir wall in reducing the entrainment of larval fish using a combination of experimental and overnight trials. Larval fish densities were compared between the irrigation canal that delivers water to irrigators and subsequently entrains fish and the bypass canal that conveys water and fish back to the river. The density of hatchery‐produced larval fish collected in the irrigation canal during the experimental trial (0.74 fish/m3) was 52% of their density in the bypass canal (1.43 fish/m3), suggesting entrainment reduction. The density of wild‐produced larvae during overnight trials indicated some minor, mostly nonsignificant, differences between catch rates in irrigation and bypass canals, ontogenetic phases, and sampling dates. Though entrainment rates of wild‐produced larvae were not significantly reduced, density differences among postflexion mesolarvae and metalarvae suggest possible entrainment reduction of more developed ontogenetic phases. More intensive research is necessary to better elucidate the efficacy of the novel weir wall for reducing the entrainment of larval fish. However, our larval fish results and the results from prior large‐bodied entrainment studies suggest the novel weir wall may reduce fish entrainment in water diversions and benefit fluvial ecosystems in which traditional screens are unfeasible.

The crucial role of fish mucus in regulating progeny inflammation and microbial homeostasis

Maternal immunity plays a vital role in protecting offspring from pathogen invasion, and it is present in nearly all vertebrates. As the most ancient vertebrates, teleost fish continuously secrete a substantial amount of mucus due to their unique living environment, and often exhibit schooling behavior. Previous studies have highlighted the presence of numerous immune components in the mucus of fish, that plays a crucial role in resisting pathogens. We hypothesize that this represents a distinctive maternal immune response mechanism in fish. In this study, we established a dextran sulfate sodium (DSS)-induced injury model by immersing zebrafish larvae in 0.5% DSS. This elicited robust inflammatory responses and showed DSS-induced alterations in microbial abundance via 16S rRNA sequencing. These changes included the disruption of normal gut structure; an increase in goblet cells; increased expression of inflammatory cytokines; and infiltration of neutrophils and macrophages into the gut, as well as an increase in pathogenic bacteria and a decline in probiotic bacteria. Furthermore, we conducted a mucus protection test by adding adult zebrafish mucus in fish tank water containing 0.5% DSS to test our hypothesis. As suspected, the mucus from adult zebrafish exhibited a protective role in defending zebrafish larvae against DSS-induced enteritis by alleviating excessive inflammatory responses and increasing probiotic abundance. In conclusion, our results confirm a significant role of adult fish mucus in the immune response of teleost fish to DSS-induced inflammation. Collectively, our findings show that the mucus of adult zebrafish may represent a novel form of maternal immunization, playing roles analogous to mammalian milk in immune regulatory functions.

Elovl4b knockout zebrafish as a model for ocular very-long-chain PUFA deficiency

Very-long-chain PUFAs (VLC-PUFAs) are a group of lipids with chain lengths >24 carbons, and the ELOVL4 (elongation of very-long-chain FA-4) enzyme is responsible for vertebrate VLC-PUFA biosynthesis. Studies on the role of VLC-PUFAs in vision have been hindered because of the need for adequate animal models to capture the global loss of VLC-PUFAs. Since homozygous Elovl4 ablation is lethal in neonatal mice because of catastrophic drying from the loss of their protective skin barrier, we established a zebrafish (Danio rerio) model of Elovl4 ablation. We generated Elovl4b KO zebrafish by creating a 56-bp deletion mutation in exon 2 of the Elovl4b gene using CRISPR-Cas9. We used GC-MS and LC-MS/MS to analyze the VLC-PUFA and lipid profiles from wild-type and Elovl4b KO fish eyes. We also performed histology and visual-behavioral tests. We found that heterozygous and homozygous Elovl4b KO zebrafish eyes had altered lipid profiles and a significantly lower C30 to C36 VLC-PUFA abundance than wild-type fish. Moreover, Elovl4b+/− and Elovl4b−/− KO larvae had significantly lower motor activity in response to light-dark cycles than their age-matched controls. Elovl4b−/− adult fish showed no obvious differences in gross retinal morphology and lamination compared with wild type, except for the presence of lipid droplets within the retinal pigment epithelial cell layer of Elovl4b−/− fish. Our data indicate that the loss of Elovl4b in zebrafish changes ocular lipid profiles and leads to visual abnormalities and subtle retinal changes. These findings highlight the use of zebrafish as a model for VLC-PUFA depletion and ELOVL4-related dysfunction.

Metabonomics and Transcriptomics Analyses Reveal the Development Process of the Auditory System in the Embryonic Development Period of the Small Yellow Croaker under Background Noise.

Underwater noise pollution has become a potential threat to aquatic animals in the natural environment. The main causes of such pollution are frequent human activities creating underwater environmental noise, including commercial shipping, offshore energy platforms, scientific exploration activities, etc. However, in aquaculture environments, underwater noise pollution has also become an unavoidable problem due to background noise created by aquaculture equipment. Some research has shown that certain fish show adaptability to noise over a period of time. This could be due to fish's special auditory organ, i.e., their "inner ear"; meanwhile, otoliths and sensory hair cells are the important components of the inner ear and are also essential for the function of the auditory system. Recently, research in respect of underwater noise pollution has mainly focused on adult fish, and there is a lack of the research on the effects of underwater noise pollution on the development process of the auditory system in the embryonic development period. Thus, in this study, we collected embryo-larval samples of the small yellow croaker (Larimichthys polyactis) in four important stages of otic vesicle development through artificial breeding. Then, we used metabonomics and transcriptomics analyses to reveal the development process of the auditory system in the embryonic development period under background noise (indoor and underwater environment sound). Finally, we identified 4026 differentially expressed genes (DEGs) and 672 differential metabolites (DMs), including 37 DEGs associated with the auditory system, and many differences mainly existed in the neurula stage (20 h of post-fertilization/20 HPF). We also inferred the regulatory mode and process of some important DEGs (Dnmt1, CPS1, and endothelin-1) in the early development of the auditory system. In conclusion, we suggest that the auditory system development of L. polyactis begins at least in the neurula stage or earlier; the other three stages (tail bud stage, caudal fin fold stage, and heart pulsation stage, 28-35 HPF) mark the rapid development period. We speculate that the effect of underwater noise pollution on the embryo-larval stage probably begins even earlier.

An equatorial mid-Atlantic Ocean archipelago as nursery area for the cookiecutter shark: Investigating foraging strategies of neonates through bite mark inferences.

This study delves into the foraging ecology of the cookiecutter shark (Isistius brasiliensis) in the Saint Peter and Saint Paul Archipelago (SPSPA), assessing bite marks on pelagic fishes collected between March and September 2018. Examination of 200 individuals from five species revealed the shark's predilection for targeting adult fish, ensuring efficient removal of energy-rich tissue layers. However, a notable exception is Thunnus albacares, preyed on predominantly during its juvenile stage, possibly due to vertical spatial segregation. Recent bites were pervasive across species, with wahoo displaying a distinctive pattern. Cookiecutter shark bites predominantly targeted the lateral body portion (>55%) except for yellowfin tuna, which exhibited a preference for the ventral region (95%). The estimated length distribution suggests the SPSPA as a potential nursery area for cookiecutter sharks. Bite mark positions and frequencies may be linked to fish behavior, swimming velocity, and fishing gear strategy, highlighting the complex interplay in pelagic ecosystems.

Hatchery supplementation provides a demographic boost but alters age composition of sockeye salmon in Auke Lake, Southeast Alaska.

Evaluating salmon hatchery supplementation programs requires assessing not only program objectives but identifying potential risks to wild populations as well. Such evaluations can be hampered by difficulty in distinguishing between hatchery- and wild-born returning adults. Here, we conducted 3 years (2011-2013) of experimental hatchery supplementation of sockeye salmon in Auke Lake, Juneau, Alaska where a permanent weir allows sampling and genotyping of every returning adult (2008-2019). We identified both hatchery- and wild-born returning adults with parentage assignment, quantified the productivity (adult offspring/spawner) of hatchery spawners relative to that of wild spawners, and compared run timing, age, and size at age between hatchery- and wild-born adults. Hatchery-spawning females produced from approximately six to 50 times more returning adults than did naturally spawning females. Supplementation had no discernable effect on run timing and limited consequences for size at age, but we observed a distinct shift to younger age at maturity in the hatchery-born individuals in all three brood years. The shift appeared to be driven by hatchery-born fish being more likely to emigrate after one, rather than two, years in the lake but the cause is unknown. In cases when spawning or incubation habitat is limiting sockeye salmon production, hatchery supplementation can be effective for enhancing the number of returning adult fish but not without the risk of phenotypic change in the recipient population, which can be an undesired outcome of hatchery supplementation. This study adds to a growing body of evidence suggesting that phenotypic change within a single generation of captive spawning might be widespread in salmon hatchery programs.

Molecular Characterization, Expression Pattern, DNA Methylation and Gene Disruption of Figla in Blotched Snakehead (Channa maculata)

Figla is one of the earliest expressed genes in the oocyte during ovarian development. In this study, Figla was characterized in C. maculata, one of the main aquaculture species in China, and designated as CmFigla. The length of CmFigla cDNA was 1303 bp, encoding 197 amino acids that contained a conserved bHLH domain. CmFigla revealed a female-biased expression patterns in the gonads of adult fish, and CmFigla expression was far higher in ovaries than that in testes at all gonadal development stages, especially at 60~180 days post-fertilization (dpf). Furthermore, a noteworthy inverse relationship was observed between CmFigla expression and the methylation of its promoter in the adult gonads. Gonads at 90 dpf were used for in situ hybridization (ISH), and CmFigla transcripts were mainly concentrated in oogonia and the primary oocytes in ovaries, but undetectable in the testes. These results indicated that Figla would play vital roles in the ovarian development in C. maculata. Additionally, the frame-shift mutations of CmFigla were successfully constructed through the CRISPR/Cas9 system, which established a positive foundation for further investigation on the role of Figla in the ovarian development of C. maculata. Our study provides valuable clues for exploring the regulatory mechanism of Figla in the fish ovarian development and maintenance, which would be useful for the sex control and reproduction of fish in aquaculture.

Distribution of myctophid fishes in the Eastern Pacific Ocean off northern Chile (18°30´ TO 30°30'S)

Thejuvenile and adult myctophid fishes from two cruises off northern Chile (from 18°30' to 30°30’S) captured with a HPN midwater trawl in oblique tows and a Bongo net in double oblique tows, 0 to 200 m and a CalCOFl net in surface tows, were identified and their distributions plotted. Eleven species were caught during the winter cruise and fourteen during the summer cruise. Triphoturus mexicanus was the most numerous and widespread species in both cruises. Diogenichthys atlanticus, D. latematus, Hygophum bruuni and Myctophum nitidulum were alsocommon. Almost ail specimens of all species were caught during night-time sampling, suggesting different day and night vertical distributions. The length-frecuency distribution of most of the species captured is analyzed.The apparent relationship between northward or southward extensions of the seasonal distributions of several speciesand the physical parameters recorded during the cruises is discussed.