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Tributyltin (TBT), an antifouling biocide frequently detected in aquatic systems, is generally considered to be an environmental obesogen. However, alterations in lipid metabolism in aquatic animals that are exposed to TBT are scarcely known. This study examined the effects of in vitro exposure to TBT on hepatic lipid homeostasis in the lined seahorse (Hippocampus erectus). Primary seahorse hepatocyte cultures were established for the first time. TBT exposure (100 and 500 nM for 24 h) significantly promoted lipid accumulation in seahorse hepatocytes and drastically reduced the number of active intracellular lysosomes. Furthermore, exposure to TBT significantly upregulated the gene expression of lipogenic enzymes and transcription factors but downregulated that of genes involved in the catabolism of lipid droplets in seahorse hepatocytes. These results indicate that TBT disrupts hepatic lipid homeostasis by simultaneously promoting lipid synthesis and inhibiting lipid droplet breakdown in seahorses. The present study extends our understanding of the utilization of primary hepatocytes from marine animals for toxicological research, and the molecular evidence of the effects of TBT on hepatic lipid homeostasis in teleost fishes. [Display omitted] • Seahorse primary hepatocyte cultures were established for the first time. • TBT-induced hepatic lipid accumulation was related to exposure concentrations. • Lipid droplets increased while lysosomes decreased in TBT-exposed hepatocytes. • TBT altered the expression of lipid metabolism genes in seahorse hepatocytes. [ABSTRACT FROM AUTHOR]

Seahorse conservation has been performed utilizing various strategies for many decades, and the deeper understanding of genomic information is necessary to more efficiently protect the germplasm resources of seahorse species. However, little genetic information about seahorses currently exists in the public databases. In this study, high-throughput RNA sequencing for two seahorse species, Hippocampus erectus and H. mohnikei, was carried out, and de novo assembly generated 37,506 unigenes for H. erectus and 36,113 unigenes for H. mohnikei. Among them, 17,338 (46.23%) unigenes for H. erectus and 17,900 (49.57%) for H. mohnikei were successfully annotated based on the information available from the public databases. Through comparing the unigenes of two seahorse species, 7,802 candidate orthologous genes were identified and 5,268 genes among them could be annotated. In addition, gene ontology analysis of two species was similarly performed on biological processes, cellular components, and molecular functions. Twenty-four and twenty-one unigenes in H. erectus and H. mohnikei were annotated in the biosynthesis of unsaturated fatty acids pathways, and both seahorses lacked the Δ12 and Δ15 desaturases. Total of 8,992 and 9,116 SSR loci were obtained from H. erectus and H. mohnikei unigenes, respectively. Dozens of SSR were developed and then applied to assess the population genetic diversity, as well as cross-amplified in a related species, H. trimaculatus. The HO and HE values of the tested populations for H. erectus, H. mohnikei, and H. trimaculatus were medium. These resources would facilitate the conservation of the species through a better understanding of the genomics and comparative genome analysis within the Hippocampus genus. [ABSTRACT FROM AUTHOR]

Abstract: Seahorse performing attractive skin color under sensitive environmental conditions has been of favor for aquarists and aquaculturists. This study investigated the skin coloration and fading process, and the effects of broodstock, background and substrate color on the skin coloration of the three-spotted seahorse Hippocampus trimaculatus Leach, 1814. The formation of skin coloration was in the sequence of abdomen, tail, back and head, respectively. Seahorse color changed from black to yellow within 26.41±6.28s in response to sudden tactile stimuli, and then faded to the original black color within 259±147.5s. Skin coloration negatively correlated with seahorse body size: the smaller the seahorse, the easier seahorse changed skin color. Compared among six background color treatments (white, red, brown, yellow, blue and clear, respectively), the skin coloration rate (% changed from black to yellow) was the highest in the blue background (86.4±11.6%, P <0.001). Seahorses derived from three broodstock origin (A, B and C) had different skin coloration rates of 44.2, 41.6 and 17.1%, respectively (P =0.012). When cultured with four different substrate colors (yellow, green, red and the mixture, respectively) for 5days, 77.8% of the seahorses with the yellow substrate changed their skin color to yellow (P =0.007), and all seahorses with the red became yellow or yellow-black skin. As a novelty, this is the first report of the instantaneous skin color change in seahorses, and this study will be of interest for the behavior study and ornamental aquaculture of H. trimaculatus. [Copyright &y& Elsevier]

Abstract: Seahorses are popular ornamental fish for marine aquaria, with more colorful individuals commanding higher prices. We investigated the effects of substrate color, light intensity and water temperature on the survival and skin color change of the juvenile seahorse, Hippocampus erectus. During the 6-week study, the juveniles cultured with substrates of mixed colors (green and orange, green and red) had higher survival and color change rates than those with a single color substrate (green, orange, red, or black, F 5, 18 =2.764, F 5, 18 =56.225, P <0.05). Color change rate of the juveniles increased with increasing light intensity (500, 1000, 1500, 2000, 2500 and 3000lx) with juveniles cultured at 500lx had the highest survival rate (85.35±5.18%). The wet weight, standard body length and age of the juveniles that began to change their skin color ranged from 0.054±0.007g, 3.12±0.31cm and 17.26±2.23days post partum (green and orange substrate mixture) to 0.082±0.013g, 3.68±0.59cm and 25.66±6.21days post partum (black) among the substrate color treatments; and from 0.043±0.009g, 3.09±0.62cm, and 14.57±2.35days post partum (3000lx) to 0.067±0.008g, 3.87±0.49cm, and 18.41±3.73days post partum (500lx) among the light intensity treatments. Survival rate and color change rate of the juveniles cultured at three temperatures (23°C, 26°C, and 29°C) differed significantly after 5weeks (F 2, 9 =11.053, P <0.05). The juveniles cultured at the temperature of 29°C had the highest color change rate of 80.43±4.27%. These results demonstrate that appropriate mixed color substrate, light intensity and temperature can improve the survival and skin color change rates of the juvenile H. erectus, thus affecting their market value. [Copyright &y& Elsevier]

Abstract: This investigation examined the effects of light intensity, stocking density, feeding frequency and salinity on the growth of sub-adult seahorses, Hippocampus erectus and the development of the brood pouch in male seahorses. During the 8-week study, seahorses cultured at a light intensity of 1000 lx had higher incremental wet weight and standard length than those at 100 lx and 2500 lx. Seahorse growth rate decreased with increasing stocking density (0.25, 0.5, 1 and 1.5 inds/L, respectively) during the 10-week study. Male seahorses grew much faster than females, with incremental wet weights of male and female seahorses of 6.64±1.601 g and 5.87±1.173 g, respectively, in the 0.25 inds/L treatment. The brood pouches of the males emerged earlier, and the ratio between the pouch length and standard length was higher at the higher stocking densities (1 and 1.5 inds/L). The final body weight, weight gain (WG) and specific growth rate (SGR) of the male and female seahorses that were fed 4 times per day were the highest, while those fed 3 times per day had the highest standard length after 10 weeks of culture. The ratio of the length of male brood pouch to standard length was the highest in the low feeding frequency treatment (fed once a day). The incremental wet weight and standard length of sub-adult seahorses differed significantly among the different salinities (35, 33, 31, 29 and 27‰) after 8 weeks of culture (F 4,60 =18.950, F 4,60 =9.225, P <0.05) with greatest growth at 31–33‰. Results demonstrated that appropriate light intensity, stocking density, feeding frequency and salinity can improve the growth rate of the sub-adult seahorses and affect the development of the brood pouch in male seahorses. [Copyright &y& Elsevier]

Abstract: In this study, the weaning of juvenile seahorses Hippocampus erectus from live Artemia to frozen Mysis spp. at different ages and sizes was evaluated as a means of improving commercial culture efficacy. The incremental increases in wet weight and standard length of the 42, 49, 56, 63 and 70 day-post-partum juvenile seahorses over a 14-day period were significantly different (F 4, 45 =47.359, F 4, 45 =32.108, P <0.05), with 70 day-post-partum juveniles having highest specific growth rate (SGR) and weight gain (WG), at 5.7±1.2 and 122.3±18.7%, respectively. Wet weight decreased in juveniles of 42 and 49 day-post-partum at 4–6 days after being weaned. The incremental growth rate of the same age juveniles of different body sizes also differed significantly (F 3, 36 =27.185 in wet weight, F 3, 36 =19.424 in standard length, P <0.05); the larger the juveniles, the higher their SGR and WG. The difference in body size and wet weight between the large size and small size juveniles increased after weaning to Mysis spp., with daily growth rate in wet weight 0.07±0.003 g/day in large juveniles and 0.02±0.004 g/day in small juveniles from 63 to 112 days post-partum. Body size and wet weight of the juveniles appear to be an important factor in deciding an appropriate time for weaning in commercial seahorse culture. The present study suggests that for juvenile H. erectus, weaning to frozen food should occur at approximately 0.54–0.70 g in wet weight or 6.59–7.46 cm in standard length. [Copyright &y& Elsevier]

The biochemical composition of wild and cultured seahorses Hippocampus kuda Bleeker and Hippocampus trimaculatus Leach was analysed in this study. The crude protein contents (% dry weight) of wild seahorses were high: 72.7±2.5% in H. kuda and 78.5±4.2% in H. trimaculatus. The crude lipid contents (% dry weight) of wild and cultured seahorses (1.1±0.1 vs. 1.4±0.2 for H. kuda and 1.2±0.1 vs. 1.2±0.2 for H. trimaculatus) were low and did not differ significantly ( F3, 12=1.461, P=0.12). The essential amino acids and flavour-enhancing amino acids in wild seahorses were higher than those in cultured seahorses, although the essential amino acid index in wild and cultured H. kuda and H. trimaculatus were generally low. The total amino acid content decreased with growth in cultured H. trimaculatus ( F3, 12=14.927, P<0.05). The poly-unsaturated fatty acid (PUFA) contents in wild and cultured H. kuda and H. trimaculatus were 21.69%, 37.72%, 21.39% and 33.89% respectively. The fatty acid content in seahorses first decreased and then increased with growth both in wild and in cultured H. trimaculatus. The PUFA/saturated fatty acid ratio was 1.31 in cultured H. kuda and 0.87 in cultured H. trimaculatus. The trace metal concentrations in the wild seahorses were relatively low. The results presented in this study provide biochemical information necessary for understanding the medicinal value of H. kuda and H. trimaculatus and for elucidating the potential dietary requirements for their culture. [ABSTRACT FROM AUTHOR]

Abstract: All seahorse species worldwide have been placed under CITES Appendix II since 2004, because they have been over-exploited for traditional Chinese medicine and aquarium trades. Aquaculture has been recognized as a long-term solution for sustaining the seahorse trade while minimizing wild collection. In this study, we evaluated the breeding and juvenile culture of an important aquarium seahorse species, the lined seahorse Hippocampus erectus, Perry 1810. Pairing, mating and copulation behavior were observed. Gestation time and brood size were 17.33±2.94 days and 272.33±66.45 individuals/brood, respectively. Growth rates differed among juveniles from different broods. Effects of temperature on the growth rates and survivorship of the juveniles during the first two weeks were compared. The highest growth rate and survivorship of the juveniles occurred at 28–29 °C among the temperatures tested (24–33 °C). Growth rate and survivorship of the juveniles during the first 9 weeks at 28 °C were investigated. The final standard length and survivorship of the juveniles were 6.32±0.52 cm and 71.11±10.18%, respectively, and the relationship between the wet weight and the standard length of the juvenile seahorses can be expressed as: W =0.0034 L2.5535 (r 2 =0.9903, n =12, P <0.01). These findings suggest that H. erectus is a good candidate for commercial aquaculture. [Copyright &y& Elsevier]

Abstract: The effect of different food (live Acetes spp., live Mysis spp., frozen Mysis spp., and mixed food of 50% live Acetes spp. and 50% frozen Mysis spp.) on gonad development of seahorses, Hippocampus kuda Bleeker, was evaluated in this experiment. The developmental durations of testes and ovary of seahorses were significantly different among the four experimental treatments. The live Acetes spp. treatment presented the shortest developmental durations to stage V, which were 87.6±3.84 days and 89.2±3.71 days, respectively, for ovary and testes. The frozen Mysis spp. treatment had the longest developmental durations (F 3,15 =13.284, P <0.05). The relationship between developmental duration of the ovary and gonad developmental stages could be formulated: Y 1 =12.04x +24.36 (r 2 =0.9722, n =16, P <0.05). The gonadosomatic index (GSI) of parent seahorses among the four treatments differed significantly (F 3,15 =18.364, P <0.05). The standard GSI of seahorses fed live Acetes spp. was 15.64±1.65%, which was the highest. Feeding live food had a significant effect on the fecundity and spawning of seahorses. The fecundity and spawning number of the live Acetes spp. treatment were 598±45.49 and 552±49.19 individuals, respectively, which were dramatically higher than those of frozen treatment (F 3,19 =34.152, P <0.05). Live food also had a similar effect on the fertilization and hatching rate during the embryonic development of seahorses (F 3,19 =11.386, P <0.05). Food treatment could also induce an indirect effect on survival rate of juveniles through gonadal and embryonic development of the parents (F 3,15 =14.519, P <0.05). In this experiment, the mortality within parent seahorses in the frozen Mysis spp. treatment was the highest (15.1±6.55%), and the survival of juveniles was the highest in the live Acetes spp. treatment (90.4±2.26% at 10 days). In conclusion, feeding live Acetes spp. significantly benefited the gonadal and embryonic development of H. kuda. The effect of temperature (22 °C, 24 °C, 26 °C, 28 °C, 30 °C and 32 °C) on the hatching time of H. kuda was also studied. We demonstrated that the higher the temperature, the shorter the hatching time, as well as the higher the hatching speed. The relationship between hatching time and temperature could be expressed: T =−39.337 t +677.75 (r 2 =0.9755, n =30, P <0.05). In this finding, we provided the sum of effective temperature (SET) and threshold temperature of embryonic development of H. kuda (14066.9 °C h−1 and 13.7 °C, respectively). This new information on the effect of feeding type and culture temperature is beneficial for the commercial rearing and breeding industry of this species. [Copyright &y& Elsevier]

Abstract: Seahorses are an important commercial and cultural commodity for medicinal and ornamental use. The effects of food, temperature and light intensity on the feeding behavior of juvenile seahorses, Hippocampus trimaculatus Leach, were investigated. All four age groups of juveniles (5-day, 10-day, 15-day and 30-day groups) tested had only one feeding peak in the afternoon, but the time of the peak differed significantly among groups. The major feeding peak of the 5-day and 30-day groups was at 1430h, the 10-day group at 1630–1830h and the 15-day group at 1630h (P <0.05). For the first 3days, the juveniles preferred copepod (Pseudodiaptomus annandalei) nauplii and Moina (Moina mongolia) nauplii. They altered their feed to copepodites from 4days to 10days and, over 10days, they began to eat copepod adults and Moina. The abilities of juveniles to digest and assimilate their feed were related to developmental stages. It took to digest the feed entirely, 2.5h at 5days postpartum, 3.5h at 10days postpartum and 4h at 15days postpartum. Water temperature affected significantly the feeding rate of juveniles (P <0.01) with an optimum temperature at 26°C. Light intensity also affected the feeding rates of different juvenile groups (P <0.01): 1834lx was the best light intensity to feed juveniles of the 1-day group, 1014lx in the 5-day group and 510lx in the 10-day group. The relationship between the standard length and the wet weight of juveniles was found to be exponential: W =10−2.72211SL2.690562 (R 2 =0.984064, P <0.01). The results obtained in this investigation contribute to the aquaculture potential of H. trimaculatus. [Copyright &y& Elsevier]

Abstract: This investigtion examined the effect of varying temperatures on the gonad development and the reproduction efficiency of Hippocampus kuda Bleeker. We demonstrated that gonad development, gonadosomatic index (GSI), female and male fecundity, fertilization rate, hatching rate, and survival rate of juvenile seahorses varied significantly at different temperatures (18, 20, 22, 24, 26, 28, 30 and 32 °C). The periods of gonad development also differed significantly at different temperatures (F 7, 32 =154.065, P <0.01). The optimal temperature was 28 °C based on the shortest developmental duration to stage V (mean±standard deviation) (85.2±6.37 days). The GSI peaked at 28 °C (16.60±0.43%) and it displayed significantly higher than those of other seven trials (P <0.01). The relationship between the GSI and the temperatures can be expressed by the following formula: Y =−1.0737t2 +8.0768t+1.013 (r 2 =0.9894, n =30, P <0.01). In contrast, the treatments could not develop successfully at 18 and 20 °C, ending before stage II and stage III, respectively. The range from 26 to 28 °C was suggested as the optimal temperature for fecundity and spawning of H. kuda because of the large number of eggs in the ovaries. The relationship between fecundity number and temperature can also be formulated: Y =−30.536t2 +209.24t+237.8 (r 2 =0.886, n =30, P <0.01). There were dramatic differences for fertilization and hatching rate among different treatments (F 5, 24 =53.675; F 5, 24 =101.897, P <0.01). Compared with control seahorses, the results indicated that the condition indices such as the GSI, fecundity, spawning, fertilization, and hatching during the early development could affect in part the survival rate of the newborn juveniles (which was also an indirect effect of temperature). However, there were no marked differences at temperatures from 24 to 28 °C with the similar high survival rate. Based on this, the temperature range from 26 to 28 °C was recommended for gonad development and artificial reproduction of H. kuda. [Copyright &y& Elsevier]

• Zn increases growth but causes gonadal dysfunction in male and female seahorses. • Zn causes a polycystic ovary syndrome (PCOS)-like phenotype in female seahorses. • Zn impacts serum testosterone and estradiol levels, leading to gonadal dysplasia. • Zn regulates gene expression with androgen receptor as the hub gene. • Caution should be exercised for Zn supplementation in aquaculture. Seahorses are characterized by unique characteristics such as a male pregnancy reproductive strategy and grasping preferences, which make these species vulnerable to various environmental risks. Zinc (Zn) is one of the most frequently occurring toxic elements in coastal waters; however, little is known about the effect of Zn exposure on seahorses. In the present study, line seahorses (Hippocampus erectus) were exposed to waterborne Zn (0.2 and 1.0 mg/L) and the impact on growth and gonadal development was investigated. Zn exposure induced growth improvement, but also led to gonadal dysfunction in the lined seahorse. Female seahorses exhibited high testosterone levels, immature follicles, and weight increase after Zn exposure, which is the typical characteristics of a polycystic ovary syndrome (PCOS)-like phenotype. Transcriptomic data suggested that the Zn-induced growth promotion resulted from the dysregulated expression of fat accumulation genes. Further investigation of gene expression profiles in the brain, ovaries, and testes indicated that Zn affected the expression of genes involved in growth, immunity, tissue remodeling, and gonadal development by regulating serum steroid hormone levels and androgen receptor expression. This study not only clarifies the complex impact of Zn on seahorses using physiological, histological, and molecular evidence but can also provide new insights into the mechanism underlying PCOS in reproductive-aged women. Moreover, this work demonstrates the risk of the common practice of Zn supplementation in the aquaculture industry as the consequent growth yield may not represent a healthy condition. [ABSTRACT FROM AUTHOR]

Considering that the intestine is always in close contact with microorganisms and is vulnerable to pathogen invasion (Lawley & Walker, 2013; Li et al., 2015), the highest expression pattern implied that the two seahorse sPLA2-XIIBs might play an important role in intestinal immunity. Keywords: antibacterial response; intestine; seahorse; secretory phospholipase A2 group XIIB EN antibacterial response intestine seahorse secretory phospholipase A2 group XIIB 1059 1063 5 06/10/22 20220701 NES 220701 Aquatic diseases caused by pathogenic bacteria have seriously hindered the development of seahorse aquaculture, which is supposed to bridge the gap between the increasing demand for medicinal markets and decreasing wild seahorse populations (Jiang et al., 2020; Li et al., 2020; Qin et al., 2017). Therefore, the two sPLA2-XIIBs identified in seahorses are homologous to the sPLA2-XIIBs in teleosts. The qPCR results showed that the expression levels of the two sPLA2-XIIB genes in the intestine of the I Vibrio i -infected seahorses were significantly higher than those of healthy seahorses (Figure 3a). [Extracted from the article]

Seahorse embryos are brooded in the enclosed nutrient-rich environment of the male brood pouch, which may be prone to bacterial infection. The immune responses of interleukin (IL) genes in the brood pouch have not been well studied. We identified 13 interleukins in the lined seahorse Hippocampus erectus. Tissue-specific expression analysis revealed increased mRNA expression levels of il-1β, il-18, and il-8 in the brood pouch. When challenged with lipopolysaccharide or Vibrio parahaemolyticus, il-1β and il-18 were active as part of the acute and chronic inflammatory responses, respectively. Importantly, il-8 may be involved in powerful antibacterial immune responses and may be induced by il-1β and il-18 via a process involving the nuclear factor-κB signaling pathway. These results suggest that il-1β, il-18, and il-8 may play key roles in the antibacterial immune defense of the brood pouch in male seahorses. [ABSTRACT FROM AUTHOR]

Seahorses have evolved many unique biological traits, including a male brood pouch, the absence of caudal and pelvic fins, and the lack of spleen and gut-associated lymphatic tissue. The mitogen-activated protein kinases (MAPKs) are known to be involved in various important biological processes including growth, differentiation, immunity, and stress responses. Therefore, we hypothesized that the adaptive evolution and expression of the MAPK gene family in seahorse may differ from those of other teleost species. We identified positive selection sites in the erk2, erk5, jnk1, and p38α MAPK genes of the lined seahorse Hippocampus erectus and tiger-tailed seahorse Hippocampus comes. A novel expression profile of MAPK cascade genes was found in seahorse larvae during the first day after birth based on the RNA-seq data of H. erectus, which reflected vital signs of immune response to its parental immune system. The expression patterns of the four positively selected MAPK genes were analyzed following the bacterial challenge of Vibrio fortis, revealing their upregulation pattern in brood pouch and other immune tissues. This study enriched our knowledge of the evolution of the H. erectus MAPK subfamilies, and could help better understanding the functional role of MAPKs in teleosts. [ABSTRACT FROM AUTHOR]

• The sequences of seahorse LPXRFa-1 and LPXRFa-2 are unique among vertebrates. • The synteny blocks of GnIH gene loci are conserved among the vertebrates. • The seahorse GnIH mRNA expressed highly in the hypothalamus and brood pouch. • The GnIH mRNA expression reduced significantly at the early puberty stage of the male seahorse. • The GnIH gene was up-regulated at the pregnancy stage of the male seahorse. The gonadotropin-inhibitory hormone (GnIH) plays a negative role in the hypothalamic-pituitary-gonadal (HPG) axis by inhibiting gonadotropin secretion in vertebrates. Male pregnancy and ovoviviparous behavior are unique phenomena among vertebrates. To better understand the neuroendocrine regulatory mechanisms in ovoviviparous fish with male pregnancy, we identified the orthologous GnIH gene in the lined seahorse (Hippocampus erectus). The full-length cDNA of the GnIH precursor was 658 base pairs with an open reading frame of 528 base pairs that encoded a 175-amino acid prepro-GnIH peptide. The seahorse GnIH precursor contained two putative LPXRFamide peptides. Both seahorse LPXRFa-1 and LPXRFa-2 were found to be unique among vertebrates. The synteny blocks of GnIH gene loci were conserved in mammals and teleosts. Tissue distribution analysis revealed that seahorse GnIH mRNA was mainly expressed in the hypothalamus, with relatively high levels observed in the brood pouch. The expression patterns of seahorse GnIH during different reproductive stages and pregnancy stages were also detected, and GnIH mRNA expression was significantly reduced during the early puberty stage. In addition, GnIH mRNA expression was significantly increased during the pregnancy stage compared to non-pregnancy stages. In summary, our results reveal the existence of GnIH in ovoviviparous fish and suggest its involvement in regulation of reproductive behavior and male pregnancy in the male seahorse. [ABSTRACT FROM AUTHOR]

The article discusses a study that screens the key toll-like receptor (TLR) gene that plays a functional role in lined seahorse brood pouch immune systems. Highlights include the use of qualitative reverse transcription-polymerase chain reaction to detect the expression patterns of nine TLR genes, gene expression patterns after LPS stimulation, and a schematic of TLR2-triggered immune responses in the seahorse brood pouch.

Background: The evolution of male pregnancy is the most distinctive characteristic of syngnathids, and their specialized life history traits make syngnathid species excellent model species for many issues in biological evolution. However, the origin of syngnathids and the evolutionary divergence time of different syngnathid species remain poorly resolved. Comprehensive phylogenetic studies of the Syngnathidae will provide critical evidence to elucidate their origin, evolution, and dispersal patterns. Results: We sequenced the mitochondrial genomes of eight syngnathid species in this study, and the estimated divergence times suggested that syngnathids diverged from other teleosts approximately 48.8 Mya during the Eocene period. Selection analysis showed that many mitochondrial genes of syngnathids exhibited significantly lower Ka/Ks values than those of other teleosts. The two most frequently used codons in syngnathid fishes were different from those in other teleosts, and a greater proportion of the mitochondrial simple sequence repeats (SSRs) were distributed in non-coding sequences in syngnathids compared with other teleosts. Conclusions: Our study indicated that syngnathid fishes experienced an adaptive radiation process during the early explosion of species. Syngnathid mitochondrial OXPHOS genes appear to exhibit depressed Ka/Ks ratios compared with those of other teleosts, and this may suggest that their mitogenomes have experienced strong selective constraints to eliminate deleterious mutations. [ABSTRACT FROM AUTHOR]

Seahorse is characterized by its male pregnancy and sex-role reversal. To better understand the sexual dimorphism of male and female seahorses based on essential genes, we performed systematic transcriptome studies for both genders. A total of 157,834,590 cleaned reads were obtained and assembled into 129,268 transcripts and 31,764 could be annotated. Results showed that 176 up-regulated and 391 down-regulated transcripts were identified in the male seahorses compared with those in females. Genes involved in sex differentiation, such as dmrt1, sox9, fem1 and vasa , were identified and characterized. Moreover, the essential genes involved in reproductive molecular pathway were identified and analyzed in seahorses. In conclusion, the present study provides an archive for the future systematic research on seahorse sex differentiation. • Sexual dimorphism of male and female seahorses was studied through transcriptome comparison. • 176 up-regulated transcripts were identified in male seahorses. • Genes involved in sex differentiation, such as dmrt1, sox9 and fem1 , were characterized. [ABSTRACT FROM AUTHOR]

The unique body morphology and specialized life history traits make seahorses excellent flagship species for many issues in marine conservation and biological evolution. In this study, the complete mitochondrial genome of Hippocampus fuscus was determined. Phylogenetic analyses showed that H. fuscus had a close genetic relationship to Hippocampus reidi, which give us a new insight into the speciation and dispersal among seahorse genus. A total of 843 base pairs of cytochrome b (Cytb) gene and a 646 base pairs of cytochrome oxidase I (COI) gene were obtained from 36 H. fuscus and 26 H. reidi from three populations. Population genetic analysis revealed a relatively high genetic diversity across the populations of H. fuscus compared with H. reidi. Neighbour-joining (NJ) tree of COI and Cytb gene sequences showed that H. fuscus haplotypes formed one cluster. The result of median-joining network of haplotypes based on COI and Cytb indicated a lack of structure in populations of H. fuscus. This study addressed the information about the evolution history and genetic structure of an Arabian seahorse H. fuscus, which provides insight into the genetic conservation and sustainable management for this species. [ABSTRACT FROM AUTHOR]

The article presents a study which reveals that Seahorse TLR5 gene responses to Vibrio vulnificus infection, in combination with scuticociliates causes heavy reductions in seahorse aquaculture. Topics include decline in wild seahorse population due to habitat destruction and heavy trade; isolation of pathogenic bacteria with the thiosulfate citrate bile salts sucrose agar culture medium; and significance of TLR5 for recognizing V. vulnificus in seahorse immune systems.

Seahorses are one of the most amazing ovoviviparous fishes in the ocean because males, and not females, have evolved a brood pouch for incubating embryos. During male pregnancy, paternal seahorses need to develop effective immune protection for embryos in the brood pouch from potential infection by pathogens. Lysozymes (Lyz) are a group of antibacterial enzymes of the innate immune system that play an important role in resisting pathogen invasion. However, the immune function of lysozymes in the brood pouch of the pregnancy-lined seahorse (Hippocampus erectus) remains unknown. In this study, we found three different lysozymes in the lined seahorse: HeLyzC , HeLyzG1 , and HeLyzG2. Synteny analysis revealed that HeLyzG1 and HeLyzG2 were generated by species-specific expansion rather than tandem duplication. Tissue expression patterns showed that the highest mRNA expression levels of the three lysozymes occurred in the brood pouches. Immunostimulation-induced expression analysis showed that all three HeLyzs in the brood pouches up-regulated their mRNA expression levels after Vibrio parahaemolyticus infection, but only the HeLyzG2 was upregulated after Poly(I:C) injection. Similarly, except for HeLyzC , upregulated expressions of HeLyzG1 and HeLyzG2 were found quickly in brood pouches injected with LPS. The upregulated levels of HeLyzC and HeLyzG2 in brood pouches during pregnancy were significantly higher than those in non-pregnancy, implying that seahorse lysozymes might function in the immune defense in brood pouches during pregnancy. In addition, the expression levels of HeLyzs were low in embryos in the brood pouch but significantly increased in neonates. This implies that embryos in the brood pouch might not necessarily express more lysozymes by themselves due to paternal immune protection. In conclusion, our study demonstrated that HeLyzs play an important role in immune protection during male seahorse gestation, and the synergistic effect of multiple HeLyzs may contribute to improved neonatal survival. • Three isoforms of seahorse lysozyme were highly expressed in the brood pouch. • Immunostimulation induced up-regulations of lysozymes proved defense against pathogen. • Higher expressions in pregnant brood pouch indicated functions in male pregnancy. • Low expressions in embryos suggested dependence on paternal immune protection. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome sequence of the pacific seahorse Hippocampus ingens was determined using long polymerase chain reactions. The total length of H. ingens mitogenome is 16,526 bp and consists of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a control region. The gene order and composition of H. ingens were similar to those of most other vertebrates. The overall base composition of H. ingens is 32.6% A, 29.3% T, 23.5% G and 14.6% C, with a slight A+T rich feature (61.9%). [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome sequence of the lined seahorseHippocampus erectuswas first determined in this article. The total length ofH. erectusmitogenome is 16,529 bp, which consists of 13 protein-coding genes, 22 tRNA and 2 rRNA genes and 1 control region. The features of theH. erectusmitochondrial genome were similar to the typical vertebrates. The overall base composition ofH. erectusis 31.8% A, 28.6% T, 24.3% C and 15.3% G, with a slight A + T rich feature (60.4%). [ABSTRACT FROM PUBLISHER]

The peptide cholecystokinin (CCK) plays an important role in the regulation of vertebrate appetite and feeding behaviour. In the present study, the full-length cDNA and genomic DNA sequences of two CCK precursors were cloned and analysed in the Syngnathidae fish, the lined seahorse ( Hippocampus erectus ). Both CCK1 and CCK2 in the seahorse consist of four exons. The sequence of the octapeptide of seahorse CCK1 (DYMGWMDF) was the same as that of the chicken and human, while the octapeptide of seahorse CCK2 (DYEGWMDF) was unique among vertebrates. According to the phylogenetic analysis, two types of CCKs were produced by teleost-specific genome duplication (TGD). Both CCK1 and CCK2 were highly expressed in the brain, while detectable amounts of CCK1 mRNA in the brood pouch and CCK2 mRNA in the intestine were also found. Both CCK1 and CCK2 mRNA levels significantly increased during the transition from endogenous to exogenous nutrition. Additionally, fasting induced a significant increase in the CCK1 mRNA expression in the brain of juvenile seahorses but had no effect on CCK2 transcript levels. In addition, the CCK1 and CCK2 mRNA levels in the seahorse brain significantly increased after a high-temperature treatment. Thus, the mRNA expression of CCK had obvious tissue specificities and this preliminary study opens new avenues for further functional studies on the endocrine regulations of CCK in the transition from endogenous to exogenous nutrition, food intake regulation and metabolism in the seahorse. [ABSTRACT FROM AUTHOR]

The unique morphology and life history characteristics make seahorses excellent flagship species for marine ecosystems. The ecological rarity of seahorses has made it difficult to address fundamental demographic processes of seahorses, such as seasonal migration and ecological characteristics. This 3-year investigation evaluated, for the first time, the seasonal distribution of a wild seahorse, Hippocampus mohnikei, and its ecological significance. The results revealed a significant difference in the abundance of wild H. mohnikei populations between warm and cold seasons, indicating that seahorses might undertake a seasonal inshore-offshore migration every year. A total of 42 794 samples were taken during the 3-year survey in the Laizhou Bay, and migratory seahorses had the highest reproductive rates from July to September each year, suggesting that seahorse reproduction might be an important trigger for variation in distribution and migration. Moreover, water temperature might also affect the temporal and spatial abundance of migratory seahorses. There was no genetic subdivision among the different geographical populations of H. mohnikei along China's coast. In conclusion, this study confirmed that large-scale seasonal seahorse migrations occur periodically and that reproduction is one of the important drivers, suggesting that closed-season fishing of breeding grounds is essential and applicable for seahorse conservation. [ABSTRACT FROM AUTHOR]

The major histocompatibility complex (MHC) genes are crucial in the adaptive immune system, and the gene duplication of MHC in animals can generally result in immune flexibility. In this study, we found that the lined seahorse ( Hippocampus erectus ) has only one gene copy number (GCN) of MHC IIα and IIβ, which is different from that in other teleosts. Together with the lack of spleen and gut-associated lymphatic tissue (GALT), the seahorse may be referred to as having a partial but natural “immunodeficiency”. Highly variable amino acid residues were found in the IIα and IIβ domains, especially in the α1 and β1 domains with 9.62% and 8.43% allelic variation, respectively. Site models revealed seven and ten positively selected positions in the α1 and β1 domains, respectively. Real-time PCR experiments showed high expression levels of the MHC II genes in intestine (In), gill (Gi) and trunk kidney (TK) and medium in muscle (Mu) and brood pouch (BP), and the expression levels were significantly up-regulated after bacterial infection. Specially, relative higher expression level of both MHC IIα and IIβ was found in Mu and BP when compared with other fish species, in which MHC II is expressed negligibly in Mu. These results indicate that apart from TK, Gi and In, MU and BP play an important role in the immune response against pathogens in the seahorse. In conclusion, high allelic variation and strong positive selection in PBR and relative higher expression in MU and BP are speculated to partly compensate for the immunodeficiency. [ABSTRACT FROM AUTHOR]

The article focuses on a study where HC2 strain of genus Pseudomonas is isolated in Hippocampus japonicus with enteritis and its pathogenicity was approved by means of experimental infection. Topics discussed include the extensive use of seahorses in traditional medicine particularly traditional Chinese medicine, vulnerability of seahorses for infection and disease as they are extremely prone to stress, and bacteriosis as the leading cause of mortality during the rearing of seahorses.

Seahorses (genus Hippocampus ) are flagship species for marine conservation and evolutionary studies. Wild seahorse populations have declined sharply because of overfishing or other disrupting activities, which are attracting increasing global concern for their threatened status. For study of their population status, the identification of young seahorses by morphological examination has been controversial and remains a difficult task due to overlapping of meristic and morphological characters. Here we reported a simple and sensitive method to identify seahorse species from China based on cross-species microsatellites. The cross-species amplification success rate varied from 40.0% to 90.0% depending on the species, with a mean value of 59.6%. According to allele presence/absence of cross-species microsatellites, all the individuals representing 10 seahorse species could be accurately identified using one or more loci. In addition, we found both genome size and genetic distance between the source and target species negatively correlated with microsatellite cross-species amplification success. Moreover, a Neighbor-Joining dendrogram was constructed based on genetic similarity and suggested that the 10 seahorse species could be divided into four groups. These results demonstrate our method could improve the identification of seahorses, providing data to understand seahorse stock structure and recruitment dynamics, and therefore resources conservation. [ABSTRACT FROM AUTHOR]

Seahorse is a specialized animal due to its male pregnant strategy in the brood pouch, which can evidently provide immune protection, nutrition, and osmoregulation to the offspring. Secretory phospholipase A2 group IB (sPLA2-IB), which encodes a secreted phospholipase A2 that functions for metabolic regulation and antibacterial defense, plays a vital role for immune regulation in teleost, but its potential immune functions in seahorse remain unknown. Here, we aimed to evaluate the characteristics and functional profiles of sPLA2-IBs in lined seahorse (Hippocampus erectus), which is one of the most important breeding seahorse species in the world. Results showed that most teleost species have only one sPLA2-IB gene, while the seahorses presented two tandem repetitive copies (sPLA2-IBa and sPLA2-IBb). This finding showed that the highest expression levels of sPLA2-IBs in seahorses were in the liver, and significant up-regulation could be induced by lipopolysaccharide (LPS), polyinosinic-polycytidylic acid (Poly[I:C]), as well as the seahorse's common pathogen Vibrio parahaemolyticus. Interestingly, the expression levels of sPLA2-IBs in the brood pouch showed an upward trend during pregnancy, compared with that in non-pregnancy stage, and peaked in the late pregnancy stage, implying that seahorse sPLA2-IBs in brood pouch might function for immune defense during pregnancy. In addition, seahorse sPLA2-IBa was significantly highly expressed in early developing embryos in brood pouch, but sPLA2-IBb expression dramatically increased in new-born juveniles, which implies the functional divergence between the two sPLA2-IBs by different ontogenetic expression. In conclusion, this study indicated that seahorse sPLA2-IBs play an important role in the immunoprotection during male pregnancy, and functional co-option of seahorse sPLA2-IBs might be conducive to improving the survival rate of its offspring. • Seahorses presented two lineage-specific tandem repetitive sPLA2-IB genes. • Challenge induced up-regulation proved their immune defense against pathogen. • Higher expressions during pregnancy suggest potential immune function in the brood pouch. [ABSTRACT FROM AUTHOR]

Seahorses are poor swimmers, and their dispersion is a topic of increasing interest for their conservation. In the present study, the swimming performance, ventilation, and feeding behavior of the young seahorses Hippocampus erectus Perry, 1810 under simulated water currents (control-, low-, mid-, and high velocities) were investigated. Between 25.0% and 33.9% of the seahorses in the experimental groups (3, 10, and 30 days post birth [DPB]) stayed attaching to the substrate, and the rest swam if there was no water current; however, the attachment rates of the 10 and 30 DPB seahorses increased significantly in the high velocity treatment ( P < 0.05). The ventilation rates decreased significantly with the increase of seahorse age under the high water current, regardless of whether they were swimming or attaching ( P < 0.05). For all of the groups, the high water current could significantly decrease the total feeding frequency (TFF) and effective feeding frequency (EFF), with the swimming seahorses having a higher feeding frequency than that of the attaching seahorses. The young seahorses in the high water current treatment had lower growth rates and suffered total mortality by the end of 30 day experiment. [ABSTRACT FROM AUTHOR]

Population genetic of seahorses is confidently influenced by their species-specific ecological requirements and life-history traits. In the present study, partial sequences of mitochondrial cytochrome b (cytb) and control region (CR) were obtained from 50 Hippocampus mohnikei and 92 H. trimaculatus from four zoogeographical zones. A total of 780 base pairs of cytb gene were sequenced to characterize mitochondrial DNA (mtDNA) diversity. The mtDNA marker revealed high haplotype diversity, low nucleotide diversity, and a lack of population structure across both populations of H. mohnikei and H. trimaculatus. A neighbour-joining (NJ) tree of cytb gene sequences showed that H. mohnikei haplotypes formed one cluster. A maximum likelihood (ML) tree of cytb gene sequences showed that H. trimaculatus belonged to one lineage. The star-like pattern median-joining network of cytb and CR markers indicated a previous demographic expansion of H. mohnikei and H. trimaculatus. The cytb and CR data sets exhibited a unimodal mismatch distribution, which may have resulted from population expansion. Mismatch analysis suggested that the expansion was initiated about 276,000 years ago for H. mohnikei and about 230,000 years ago for H. trimaculatus during the middle Pleistocene period. This study indicates a possible signature of genetic variation and population expansion in two seahorses under complex marine environments. [ABSTRACT FROM AUTHOR]

The innate immune system plays an important role in the immune responses of fish, particularly in immunodeficient seahorses, which are vulnerable to infection. In this study, we investigated the evolutionary adaptation of the Toll-like receptor 5 signaling in the lined seahorse (Hippocampus erectus) and the physiological and molecular responses of seahorse to bacterial and parasitic tapeworm infections. Four sites under positive selection among three genes, hsp70 , tlr5 , and tak1 , showed Bayes Empirical Bayes values >0.95. The respiratory rate of H. erectus increased after being challenged with Vibrio and Scalithrium. Stress-induced expression of hsp60 and hsp70 , which can bind PAMP molecules and modulate PAMP-induced Toll-like receptor (TLR) signaling, was significantly upregulated in immune organs such as the gill, intestine, kidney, and liver. Additionally, the MyD88-dependent TLR signaling pathway of H. erectus was activated in response to both bacterial and parasitic infections. The expression profiles of TLR signaling molecules revealed that these molecules mediate immune processes and act against various pathogens. These results improve our understanding of the functional role of key genes involved in PAMP-mediated signaling and provide theoretical support for the prevention and control of diseases in cultured seahorses. • Amino acid changes in PAMP-induced TLR signaling genes were positively selected. • The PAMP-triggered immunity pathway adaptively evolves in immunodeficient seahorse. • The MyD88-dependent TLR signaling molecules in H. erectus is upregulated against various pathogens during infection. [ABSTRACT FROM AUTHOR]

The seahorse is a typical suction feeder with an elongated, tubular snout and a small terminal mouth. It is important to determine the details of this unique prey-capture behavior to improve the survival rate during seahorse breeding, especially for juveniles. In this study, we described the sucking process and characterized the kinematics in juvenile lined seahorse (Hippocampus erectus) at different ages (1–30 days after parturition; DAP) using a high-speed video system, and also investigated the histological basis of the feeding-related organs, including snout, eye, and intestine. The sucking of juvenile seahorses can be divided into four steps: searching, locating, capturing, and swallowing. Seahorses capture prey mainly based on the vision system, and histological results revealed a developed visual acuity in the newborn seahorses, so that they were able to prey once after releasing from the male seahorse's brood pouch. The attack distance, maximum snout width, capture success rate, and daily food intake of juvenile seahorses increased with maturation. A remarkable inflection point, in the snout expansion rate, successful predation rate, and growth rate, occurs at about 10 DAP, when calcification of the snout bones was completed. In addition, the intestines of newborn seahorses were short and quite simple, but developed rapidly during the first 20 DAP. These findings provide a better understanding of prey capture kinematics and nutritional physiology, and will be beneficial for improving the feeding strategies for juveniles during large seahorse breeding. • Sucking kinematics in juvenile seahorses at different ages was described. • Developed visual acuity was observed in the newborn seahorses. • Snout calcification and intestines development affect juvenile's nutrition intake. [ABSTRACT FROM AUTHOR]

Syngnathidae is a peculiar fish family in which pregnant males incubate developing embryos in a brood pouch which is functionally equivalent to the mammalian uterus. Immunological modifications in the brood pouch during gestation are vital for a successful pregnancy. Previous studies revealed the teleost-specific Toll-like receptor 22 (TLR22) could recognize viruses and bacteria. To evaluate the role of TLR22 in allograft tolerance and antibacterial (and antiviral) protection in the brood pouch, the tlr22 gene was characterized in the lined seahorse (Hippocampus erectus), which has evolved complex and fully enclosed brood pouches. In this study, tlr22 showed specific expression in the brood pouch. Interestingly, expression of tlr22 in the pouch decreased progressively during the course of pregnancy. In addition, the expression of downstream TLR signaling molecules was influenced by pregnancy stages, suggesting that TLR22 and downstream TLR signaling molecules might be involved in immunological tolerance and embryo rejection in the brood pouch during pregnancy. Further investigation of role of TLR22 in immunological protection in brood pouches following the injection of LPS and Poly(I:C) showed that tlr22 expression in the pouch was upregulated after the challenge. In addition, the expression of downstream TLR signaling molecules was altered, indicating that tlr22 and TLR signaling molecules are involved in antiviral and antibacterial immune responses in the brood pouch. Taken together, our results improve the understanding of immunological modifications in the brood pouch and may provide new insights into immune regulation during male pregnancy in syngnathids. • mRNA level of tlr22 decreased progressively during pregnancy in the brood pouch. • TLR signaling components are differentially expressed during reproductive stages. • tlr22 and TLR signaling components are involved in immune responses in the brood pouch. [ABSTRACT FROM AUTHOR]

The male pregnancy of seahorses is unique, but their reproductive response to environmental disturbances has not yet been clarified. Tributyltin (TBT) is known to have an endocrine disrupting effect on the reproductive system of coastal marine organisms. This study evaluated the potential effects of exposure to environmentally relevant concentrations of TBT on the development of gonads and brood pouch of the lined seahorse (Hippocampus erectus). Physiological, histological, and transcriptional analyses were conducted, and results showed that high levels of TBT bioaccumulation occurred in male and female seahorses. TBT led to ovarian follicular atresia and apoptosis with the elevation of androgen levels, accompanied by the induction of genes associated with lysosomes and autophagosomes. Comparative transcriptional analyses revealed the likely inhibition of spermatogenesis via the suppression of cyclic AMP and androgen synthesis. Notably, the transcriptional profiles showed that TBT potentially affects the immune system, angiogenesis, and embryo nourishment of the brood pouch, which indicates that it has negative effects on the male reproductive system of seahorses. In summary, this study reveals that environmental levels of TBT potentially affect the reproductive efficiency of seahorses, and may ultimately lead to a reduction in their populations in coastal environments. ga1 • Tributyltin (TBT) led to significant follicular atresia in seahorse ovary. • Apoptosis, lysosomes and autophagosomes contributed to atresia in ovary. • TBT impaired spermatogenesis through regulating the androgen and cAMP synthesis. • TBT affected immunity, angiogenesis, and embryo nourishment of the brood pouch. [ABSTRACT FROM AUTHOR]

Seahorses (family Syngnathidae) are ovoviviparous fish whose embryos can obtain paternal immunoprotection through the male's brood pouch, which is a specialized organ for pregnancy. Previous studies have revealed that seahorses have a unique immune system and alpha-2 macroglobulin (α2M) may be involved in male pregnancy. To ascertain the significance of α2M in the immune system of the brood pouch, the characteristics of the α2M gene were first investigated in the lined seahorse (Hippocampus erectus). In this study, α2M showed a broad expression pattern, with the highest expression in the liver and brood pouch. Interestingly, during the six-month seahorse culture, expression level of α2M in the liver was particularly decreased during brood pouch formation (fourth and fifth months), but was restored the complete development of this brood pouch (sixth months), and a similar expression occurred in the brood pouch. This suggests that the seahorse might be able to regulate its immune response while a new organ develops. Further investigation also examined the immune regulation of α2M in brood pouches by injecting lipopolysaccharide and polyinosinic-polycytidylic acid. The results showed that, after the challenge experiment, α2M expression in the inner pseudoplacenta was upregulated, along with other important immune factors, such as Toll-like receptors (TLRs), tumor necrosis factor-alpha (TNFα), interleukin-6 (IL-6) and interferon-gamma (IFNγ). Taken together, our results reveal that α2M plays an important role in immunoprotection of the brood pouch, and may provide new insights into studies of male pregnancy regulation in seahorses. • α2M predominantly expressed in liver and brood pouch in seahorses. • α2M expression in the liver fluctuated, particularly during brood pouch formation. • LPS or Poly(I:C) up-regulated α2M mRNA level in the inner pseudoplacenta. • α2M is involved in the immunoprotection of the brood pouch in seahorses. [ABSTRACT FROM AUTHOR]

Food and water environments are key factors affecting juvenile survival rate in seahorse aquaculture. In order to adjust to local conditions, different seahorse (Hippocampus erectus) breeding models were developed in North and South China. Seahorses in North China were commonly fed Artemia in indoor containers with a stable water environment, while most seahorses in South China were fed copepods in outdoor concrete ponds. Firstly, we compared the effect of food type on juvenile seahorses based on a one-month feeding experiment and found no significant difference in body length. However, the insulin-like growth factor 1 (IGF-1) gene expression was significantly higher in the liver of seahorses fed copepods than in the lever of seahorses fed Artemia , suggesting that copepods promoted better growth. A high expression of stress-related genes, namely, heat shock proteins 70 (HSP70) and Mn superoxide dismutase (Mn-SOD), in the liver of the seahorses that were fed copepods suggested that copepods might cause more stress on juveniles. Lower leptin gene expression in the liver of seahorses fed Artemia than in those fed copepods proved that Artemia was better for satiating the juveniles. Furthermore, the potential effects of salinity (15 and 30 ppt) and ammonia‑nitrogen (0, 5, and 15 mg/L) on juvenile seahorse physiological stress were studied through a 5-d orthogonal experiment. Both lower salinity and higher ammonia‑nitrogen increased the ventilation rate significantly. Low salinity caused a rapid increase in the ventilation rate on day 1, while high ammonia‑nitrogen was the main factor during the later period (days 2–5). Significant changes in the mRNA expression of genes, including Na+: K+:2Cl− cotransporter 1 (NKCC1) and Na, K-ATPase (NKA) in the gill, HSP70 , Mn-SOD , glutamate dehydrogenase (GDH), and glutamyl synthase (GS) in the liver, indicated that seahorses are sensitive to acute salinity decline. In addition, high ammonia‑nitrogen exposure significantly changed the expression of genes (i.e., Mn-SOD , GDH , and GS) in seahorses exposed to low salinity level, while no significant variation was observed in seahorses exposed to normal salinity, suggesting that salinity decline might increase the negative effects of ammonia‑nitrogen stress. The present study provides a better understanding of how food, salinity, and ammonia‑nitrogen affect juvenile seahorses, and will be potentially important to improve animal welfare and increase production efficiency. • Different seahorse breeding modes in North and South China were described. • Compared to Artemia , copepods were better for large-scale seahorse culture considering both technology and cost. • The farmers in South China should pay more attention to salinity and ammonia-nitrogen during juvenile seahorse breeding. [ABSTRACT FROM AUTHOR]

The cover image is based on the Short Communication Seahorse TLR5 gene responses to Vibrio vulnificus infection, which in combination with scuticociliates causes heavy reductions in seahorse aquaculture by Geng Qin et al., https://doi.org/10.1111/jfd.12893. Photo credit: Xin Wang. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome sequence of the hedgehog seahorseHippocampus spinosissimuswas first determined in this article. The total length ofH. spinosissimusmitogenome is 16 527 bp and consists of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and 1 control region. The gene order and composition ofH. spinosissimuswere similar to those of most other vertebrates. The overall base composition ofH. spinosissimusis 32.1% A, 30.3% T, 14.9% G and 22.7% C, with a slight A + T-rich feature (62.4%). Phylogenetic analyses based on complete mitochondrial genome sequence showed thatH. spinosissimushas a close genetic relationship toH. ingensandH. kuda. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome sequence of the Barbour’s seahorseHippocampus barbouriwas first determined in this paper. The total length ofH. barbourimitogenome is 16,526 bp, which consists of 13 protein-coding genes, 22 tRNA and 2 rRNA genes and 1 control region. The features of theH. barbourimitochondrial genome were similar to the typical vertebrates. The overall base composition ofH. barbouriis 32.68% A, 29.75% T, 22.91% C and 14.66% G, with an AT content of 62.43%. [ABSTRACT FROM PUBLISHER]