Hippocampus Erectus Research Articles

The antibacterial defence role of β-defensin in the seahorse testis

Seahorses represent the only known group of animals with male pregnancy. Seahorses have small testis that produce a limited quantity of sperm. To date, the response of this immune-privileged organ to pathogenic infections has not been reported. β-defensin (BD) is an important innate immune defence factor against pathogens in vertebrate testis. To elucidate its immunoprotection in seahorse testis, we identified the Hippocampus erectus β-defensin (HeBD) sequence in its genome via phylogenetic tree and protein-sequence structure analysis. Gene-expression analysis showed that HeBD was highly expressed in the seahorse testis and was significantly upregulated after bacterial infection, indicating that HeBD expression was related to testicular immune responses. Furthermore, antibacterial activity testing demonstrated that the mature HeBD peptide exhibited broad-spectrum aggregation activity but only moderate antibacterial activity. We found that the mature HeBD mature significantly neutralised bacterial endotoxin activity. In conclusion, our results imply that HeBD serves an immunoprotective role in seahorse testis.

Effects of Stocking Density on the Survival, Growth, and Stress Levels of the Juvenile Lined Seahorse (Hippocampus erectus) in Recirculating Aquaculture Systems.

Seahorses are increasingly regarded as a promising farming object suitable for recirculating aquaculture systems (RASs) due to their high economic value. However, reports on the large-scale farming of seahorses in RASs are rare, and some key parameters, such as stocking densities, are still unclear. In the present study, we employed the lined seahorse (Hippocampus erectus), for which large-scale farming has been achieved, to determine the suitable stocking density for three different-sized juveniles in RASs. The three different-sized juveniles had body heights of 4.0, 7.0, and 9.0 cm, and their test density gradients were 1.0, 0.8, 0.6, and 0.4 inds/L; 0.6, 0.5, 0.4, and 0.3 inds/L; and 0.4, 0.3, 0.2, and 0.1 inds/L, respectively. The juveniles were cultivated for one month, and then their survival, growth, and plasma cortisol and brain serotonin contents (two stress-related indicators) were analyzed. The results show that, regardless of the size of the juveniles, a high density can inhibit growth and trigger stress responses. In addition, for small- (4.0 cm) and medium-sized (7.0 cm) juveniles, a high density can also exacerbate size heterogeneity and cause death. Taking into account the welfare and yield of farmed seahorses, the present study suggests that the suitable stocking densities for 4.0, 7.0, and 9.0 cm juveniles in RASs are 0.6, 0.4, and 0.2 inds/L, respectively.

First insight of the genome-wide association study and genomic prediction into enteritis disease (Vibrio harveyi) resistance trait in the lined seahorse (Hippocampus erectus).

Enteritis caused by Vibrio is a highly die-off disease that severely impeded substantial production in seahorse aquaculture. In the present study, challenged with LD50 of concentration of Vibrio harveyi, a total of 161 of susceptible and 166 of resistant individuals were allocated into binary survival phenotypes, thus, to firstly investigate the genetic architecture by genome-wide association study (GWAS) analysis, as well as to evaluate the feasibility of genomic selection (GS) in enteritis disease resistance trait of the lined seahorse Hippocampus erectus. Results indicated that the heritability for resistance to Vibrio harveyi was estimated to be 0.10. And a set of 10 significant/suggestive SNPs in a multiple chromosomes localization were identified, explaining 7.76% to 13.28% of genetic variance. Associated 82 of candidate genes were clustered into signal transduction, cell proliferation, response of external stress, bacteria defence, and anti-inflammatory processes. Moreover, the potential performance of genomic selection (GS) in application in selective breeding for enteritis disease resistance seahorses was assessed by genomic prediction (GP). In general, the predictive accuracy of the genomic estimated breeding value (GEBV) of BayesC exceeded the rrBLUP, BayesA, RKHS, and SVM models while with no significant difference. And the GWAS-informative SNPs was significantly superior in efficience than random selected markers by comparison of predictive performance on different selection strategies of SNPs. Overall, the genetic basis of enteritis disease resistance trait in the lined seahorse is a polygenic genetic architecture. SNPs associated with the important genes of cathepsin L1-like previously reported with respect to disease resistance are consider as potential molecular markers of genetic breeding. Furthermore, GS approach is an appropriate, effective, and less-cost application in breeding enteritis disease-resistant seahorses.

The potential role of galectin-4 in protecting the intestinal barrier in the lined seahorse Hippocampus erectus

Galectin-4 is a prominent antimicrobial peptide primarily expressed in the gastrointestinal tract of animals. It plays crucial roles in antimicrobial defense and in regulating the repair of intestinal epithelial cells. Given the unique immune system in seahorses, which are known for male pregnancy, the function of galectin-4 in their intestinal tract, which lack gut-associated lymphoid tissues, remains unknown. In this study, we identified a galectin-4 gene (HeGal-4) in the lined seahorse (Hippocampus erectus). The sequence length of the open reading frame (ORF) was 1041 bp, encoding 346 amino acids. The mRNA expression of HeGal-4 in the intestine was significantly higher than that in other internal organs. However, the synthesized peptide fragment (HeGal-4(302–315)) from the functional domain of HeGal-4 only showed moderate inhibitory effects against Escherichia coli, Klebsiella pneumoniae, and Micrococcus luteus. Interestingly, in situ hybridization showed that HeGal-4 was predominantly expressed in seahorse intestinal epithelial cells, while genes associated with galectin-4 in the repair of intestinal epithelium, such as β-catenins, were highly expressed in their intestines. Therefore, our results suggest that HeGal-4 may be crucial for regulating the repair of intestinal epithelial cells in seahorse intestinal epithelial cells, and that it possesses significant potential for the prevention and control of intestinal diseases in seahorse aquaculture.

Females increase reproductive investment when mated to less sexually attractive males in a serially monogamous fish

Reproductive investment decision is an integral part of life-history theory. Differential allocation hypothesis predicts that females should increase investment when mated to high-quality males, conversely, reproductive compensation hypothesis predicts that females should increase investment when mated to low-quality males. Empirical research dominantly focuses on polygamous species and rarely on serially monogamous species. So, the question remains: which hypothesis does serially monogamous species fit? And if it fits reproductive compensation hypothesis, do females only compensate once or continuously for multiple times when mating to low-quality males? Here, we used a serially monogamous fish, the lined seahorse (Hippocampus erectus), to investigate the reproductive investment pattern of females in relation to male quality (measured by sexual attractiveness). We found that females allocated more resources into eggs when they mated to less-sexually-attractive males, indicating the investment pattern of lined seahorse falls in with the prediction of reproductive compensation hypothesis. This finding may imply that the sex role of seahorses is reversed, and female is the side imposed on a greater sexual selection pressure. On this basis, we compared the investment difference of females in two consecutive breeding events when mated to less-sexually-attractive males. We found that females allocated less resources into eggs in the second breeding than in the first one. Females reduced their reproductive compensation in the second breeding, which may be attributed to the improvement in the quality (e.g., paternal care ability) of their mates after the first breeding, thus eliminating the need for them to invest more in the second breeding.

Brooding fathers actively consume viable embryos to take up nutrients in a monogamous syngnathid fish

Syngnathid fishes often experience a reduction in brood size and an increase in immunity during pregnancy. Researchers have studied the polygamous broad-nosed pipefish (Syngnathus typhle) and revealed that some eggs from low-quality females in the male’s brood pouch serve as nurse eggs that are absorbed by the father. It is unclear whether nurse eggs also exist in other syngnathid fishes, especially in monogamous syngnathid fishes. In monogamous syngnathid fishes, the male pouch only carries eggs from a single female. Thus, the question remains: do some eggs of monogamous syngnathid fishes also serve as nurse eggs? And if so, are these nurse eggs impaired eggs, or are they viable eggs that are consumed by the brooding father? In the present study, we used the monogamous lined seahorse (Hippocampus erectus) and asked whether nurse eggs exist in this species. We also explored whether nurse eggs potentially originate from viable versus inviable eggs. Using isotope labeling, we found that nutrients from embryos could be transferred to brooding fathers. Furthermore, we also found that brooding fathers with limited food had a higher isotope content and a smaller brood size compared to individuals with sufficient food. These results have demonstrated that nurse eggs exist in the lined seahorse, and also suggested that the brooding fathers actively consume viable embryos to absorb nutrients in response to low food availability. These findings help us better understand parent–embryo conflict, filial cannibalism, and male-only care in teleost fishes.

Comprehensive biochemical analysis and nutritional evaluation of fatty acid and amino acid profiles in eight seahorse species (Hippocampus spp.)

Seahorses are increasingly recognized for their nutritional potential, which underscores the necessity for comprehensive biochemical analyses. This study aims to investigate the fatty acid and amino acid compositions of eight seahorse species, including both genders of Hippocampus trimaculatus, Hippocampus kelloggi, Hippocampus abdominalis, and Hippocampus erectus, to evaluate their nutritional value. We employed Gas Chromatography-Mass Spectrometry (GC-MS) and High-Performance Liquid Chromatography (HPLC) to analyze the fatty acid and amino acid profiles of the seahorse species. GC-MS was used to detect 34 fatty acid methyl esters, while HPLC provided detailed amino acid profiles. GC-MS analysis demonstrated high precision with relative standard deviations (RSDs) generally below 2.53 %, satisfactory repeatability (RSDs from 6.55 % to 8.73 %), and stability (RSDs below 2.82 %). Recovery rates for major fatty acids ranged from 98.73 % to 109.12 %. HPLC analysis showed strong separation of amino acid profiles with theoretical plate numbers exceeding 5000. Precision tests yielded RSDs below 1.23 %, with reproducibility and stability tests showing RSDs below 2.73 % and 2.86 %, respectively. Amino acid recovery rates ranged from 97.58 % to 104.66 %. Nutritional analysis revealed significant variations in fatty acid content among the species. Female H. erectus showed higher levels of hexadecanoic acid and saturated fatty acids, while male H. abdominalis had lower concentrations of n-3 full cis 4,7,10,13,16,19-docosahexaenoic acid (DHA). Total lipid yields varied from 3.2491 % to 12.3175 %, with major fatty acids constituting 17.9717 %–74.6962 % of total lipids. In conclusion, this study provides essential insights into the fatty acid and amino acid composition of seahorses, supporting their potential as valuable dietary supplements. The differences between genders in specific fatty acids suggest a nuanced nutritional profile that could be exploited for targeted dietary applications. Further research is needed to explore the seasonal and environmental variations affecting seahorse biochemical composition.

Bioeconomics of juvenile seahorse (Hippocampus erectus) culture: Optimal harvest time

AbstractThe culture of seahorses Hippocampus erectus in captivity represents a window of opportunity for the diversification of the aquaculture activity in the ornamental industry. In this study, we have constructed a bioeconomic model to evaluate the optimal harvest time (OHT) over a culture period of 562 days. The bioeconomic model was integrated with three submodels: biological, technological, and economic. Three different mortality rates were used for different periods in culture, registering a higher survival in the period from 0 to 60 days with a rate of 53.4%. The sensitivity analysis showed that the mortality rate in this period was the parameter with the greatest influence on the benefits. The Von Bertalanffy growth model was indicated to describe the growth of H. erectus given its statistical significance using Theil's inequality coefficient, registering parameters of (L∞ = 141.62 mm) and (k = 0.0049 month‐1). The bioeconomic model determined the OHT in the 4th month of culture, the time when the maximum profit is recorded. It is concluded that the culture presents challenges to be addressed although the bioeconomic model allows for demonstrating the OHT.

Growth increase and gonadal dysfunction of the lined seahorse triggered by zinc exposure

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.

The detoxification ability of sex-role reversed seahorses determines the sexual dimorphism in immune responses to benzo[a]pyrene exposure

Sexual dimorphism in immune responses is an essential factor in environmental adaptation. However, the mechanisms involved remain obscure owing to the scarcity of data from sex-role-reversed species in stressed conditions. Benzo[a]pyrene (BaP) is one of the most pervasive and carcinogenic organic pollutants in coastal environments. In this study, we evaluated the potential effects on renal immunotoxicity of the sex-role-reversed lined seahorse (Hippocampus erectus) toward environmental concentrations BaP exposure. Our results discovered the presence of different energy-immunity trade-off strategies adopted by female and male seahorses during BaP exposure. BaP induced more severe renal damage in female seahorses in a concentration-dependent manner. BaP biotransformation and detoxification in seahorses resemble those in mammals. Benzo[a]pyrene-7,8-dihydrodiol-9,10-oxide (BPDE) and 9-hydroxybenzo[a]pyrene (9-OH-BaP) formed DNA adducts and disrupted Ca2+ homeostasis may together attribute the renal immunotoxicity. Sexual dimorphisms in detoxification of both BPDE and 9-OH-BaP, and in regulation of Ca2+, autophagy and inflammation, mainly determined the extent of renal damage. Moreover, the mechanism of sex hormones regulated sexual dimorphism in immune responses needs to be further elucidated. Collectively, these findings contribute to the understanding of sexual dimorphism in the immunotoxicity induced by BaP exposure in seahorses, which may attribute to the dramatic decline in the biodiversity of the genus.

The toxic impacts of microplastics-borne benzo[a]pyrene and heavy metals on the health and behavior of seahorse Hippocampus erectus

The toxic impacts of microplastics-borne benzo[a]pyrene and heavy metals on the health and behavior of seahorse Hippocampus erectus

Identification of CTNNB1 in the lined seahorse, Hippocampus erectus, and its function in innate immunity and cell proliferation

Abstractβ‐Catenin (CTNNB) is a core downstream mediator in the Wnt/β‐catenin signaling pathway, which plays a role in immune regulation and cell differentiation. In the present study, two CTNNB genes were identified by genomic analysis of Hippocampus erectus and named He‐CTNNB1 and He‐CTNNB2. He‐CTNNB1 was more conserved than He‐CTNNB2. The full length of He‐CTNNB1 was 2369 bp, including an open reading frame of 2275 bp that encoded 737 amino acids containing 12 armadillo repeats. Phylogenetic analysis revealed that He‐CTNNB1 clusters had homologs in other bony fishes. Tissue distribution analysis showed the highest mRNA expression of He‐CTNNB1 in the ovary, liver, and kidney of the lined seahorse under normal physiological conditions. The transcription level of He‐CTNNB1 was significantly increased in the liver and kidney in response to LPS, poly I:C, and Edwardsiella tarda challenge (p < 0.05). In vitro overexpression of He‐CTNNB1 significantly upregulated the expression of key genes of the canonical Wnt/β‐catenin signaling pathway, such as axin2, cMyc, and cyclinD (p < 0.05), which increased cell proliferation during the wound‐healing process. Taken together, our results suggest that He‐CTNNB1 is essential for cell proliferation and the innate immune response in H. erectus.

Thermoregulatory response in juvenile Hippocampus erectus: Effect of magnitude and rate of thermal increase on metabolism and antioxidative defence.

Behavioural, physiological and biochemical mechanisms constitute the adaptive capacities that allow marine ectotherms to explore the environment beyond their thermal optimal. Limitations to the efficiency of these mechanisms define the transition from moderate to severe thermal stress, and serve to characterise the thermoregulatory response in the zone of thermal tolerance. We selected a tropical population of Hippocampus erectus to describe the timing of the physiological and biochemical mechanisms in response to the following increments in water temperature: (i) 4°C abrupt (26-30°C in <5 min); (ii) 7°C abrupt (26-33°C); (iii) 4°C gradual (1°C every 3 h) and (iv) 7°C gradual (1.5°C every 3 h). The routine metabolic rate (Rrout) of juvenile H. erectus was measured immediately before and after 0.5, 12 and 28 h of being exposed to each thermal treatment. Samples of muscle and abdominal organs were taken to quantify indicators of aerobic and anaerobic metabolism and antioxidant enzymes and oxidative stress at each moment throughout exposure. Results showed a full thermoregulatory response within 0.5 h: Rrout increased in direct correspondence with both the magnitude and rate of thermal increase; peroxidised lipids rapidly accumulated before the antioxidant defence was activated and early lactate concentrations suggested an immediate, yet temporary, reduction in aerobic scope. After 12 h, Rrout had decreased in sea horses exposed to 30°C, but not to 33°C, where Rrout continued high until the end of trials. Within 28 h of thermal exposure, all metabolite and antioxidant defence indicators had been restored to control levels (26°C). These findings testify to the outstanding thermal plasticity of H. erectus and explain their adjustment to rapid fluctuations in ambient temperature. Such features, however, do not protect this tropical population from the deleterious effects of chronic exposure to temperatures that have been predicted for the future.

The effects of primary and secondary bacterial exposure on the seahorse (Hippocampus erectus) immune response

Evolutionary adaptations in the Syngnathidae teleost family (seahorses, pipefish and seadragons) culminated in an array of spectacular morphologies, key immune gene losses, and the enigmatic male pregnancy. In seahorses, genome modifications associated with immunoglobulins, complement, and major histocompatibility complex (MHC II) pathway components raise questions concerning their immunological efficiency and the evolution of compensatory measures that may act in their place. In this investigation heat-killed bacteria (Vibrio aestuarianus and Tenacibaculum maritimum) were used in a two-phased experiment to assess the immune response dynamics of Hippocampus erectus. Gill transcriptomes from double and single-exposed individuals were analysed in order to determine the differentially expressed genes contributing to immune system responses towards immune priming. Double-exposed individuals exhibited a greater adaptive immune response when compared with single-exposed individuals, while single-exposed individuals, particularly with V. aestuarianus replicates, associated more with the innate branch of the immune system. T. maritimum double-exposed replicates exhibited the strongest immune reaction, likely due to their immunological naivety towards the bacterium, while there are also potential signs of innate trained immunity. MHC II upregulated expression was identified in selected V. aestuarianus-exposed seahorses, in the absence of other pathway constituents suggesting a possible alternative or non-classical MHC II immune function in seahorses. Gene Ontology (GO) enrichment analysis highlighted prominent angiogenesis activity following secondary exposure, which could be linked to an adaptive immune process in seahorses. This investigation highlights the prominent role of T-cell mediated adaptive immune responses in seahorses when exposed to sequential foreign bacteria exposures. If classical MHC II pathway function has been lost, innate trained immunity in syngnathids could be a potential compensatory mechanism.

Effect of human chorionic gonadotrophin (HCG) and luteinizing hormone releasing hormone A3 (LHRH-A3) on reproduction and development of brood pouch in Hippocampus erectus

Syngnathid fishes (seahorses and pipefish) are unique in reproduction, with males becoming pregnant and giving birth. The brood pouch provides osmoregulation, gas exchange, waste transport, immunoprotection and nutrition supply. However, the function of hormone trafficking is rarely studied. By injecting the mixture liquor of human chorionic gonadotrophin (HCG, 2 IU/g) and luteinizing hormone-releasing hormone A3 (LHRH-A3, 5 ng/g) into the brood pouch of Hippocampus erectus, we found the reproductive interactions accelerated dramatically, and 4 pairs were successfully mated. After 24 h, the inner epithelium was highly folded and the loose connective tissue layer was highly distended. In the inner tissue layer of the brood pouch, fibroblasts secreted vigorously, blood vessels multiplied and expanded, indicating the physiological structure of the brood pouch modified hastily from the unpregnant stage to the progravid phase. Correspondingly, transcriptome results revealed the gene expression of circadian, epitheliogenesis, angiogenesis, lipid transfer, and spermiogenesis were significantly up-regulated. We innovatively found that macromolecule exogenous hormone (HCG) can be not only efficiently transported from brood pouch to body, but also promote mating and the physiological changes of the brood pouch.

Identification of male-specific markers by 2b-RAD sequencing reveals an XX/XY sex-determination system in cultured lined seahorse, Hippocampus erectus

Seahorses (Hippocampus spp.), a group of male ovoviviparous fish, are of high commercial value in traditional Chinese medicine and aquarium trades. The lined seahorse (Hippocampus erectus), an easily domesticated species, was introduced to China and quickly became a popular farmed species to relieve the conflict between supply and demand. Although the sexual dimorphism in size and immunocompetence has been observed, the sex determination mechanism in the lined seahorse remains unclear. In the present study, we applied the 2b-RAD-seq approach for the first time to successfully identify 6 male-specific tags and 4 sex-specific SNP loci in the lined seahorse, which were further validated in 108 individuals by PCR amplification based on the flanking sequences of sex-specific markers. The male-specific tags and heterozygous SNP loci indicate that a male heterozygous XX/XY sex-determination system is employed in the lined seahorse. Based on the annotation and analysis of the sex-specific sequences, two sex-related candidate genes, lrriq1 and il34, were identified. The results provide novel insights into sex-determination mechanisms and promising methods for all-male breeding of Hippocampus erectus.

Lipid accumulation and gene expression changes induced by tributyltin exposure in primary hepatocytes of lined seahorse (Hippocampus erectus)

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.

Effects of different temperatures and diets on nutritional and bio‐functional components in the juvenile lined seahorse (Hippocampus erectus)

AbstractA two‐factorial experiment (temperature with three levels: 23°C, 25.5°C and 28°C; diet with four kinds: live Artemia sp., copepods, live Artemia sp. + copepods and frozen Neomysis awatschensis [FNA]) was carried out to evaluate the effects of different temperatures and diets on biochemistry in the juvenile lined seahorse (Hippocampus erectus) for thirty days. The juveniles (n = 1260, body height: 5.1 ± 0.48 cm, initial wet weight: 0.42 ± 0.14 g) were distributed in 36 experimental aquaria (35 individuals each). Each treatment had 3 replicates. On day 30, the seahorses were vacuum freeze‐dried at −56°C before chemical analysis. Amino acids, fatty acids, Se, Zn, nucleosides, and nucleotides were measured in the present study. The results show that temperature, diet, and their interaction significantly affected all components. The content of amino acids and fatty acids in the juveniles fed FNA at 23°C was the highest. The content of Zn in the juveniles fed FNA at 23°C, and the content of Se fed Artemia sp. + copepod at 25.5°C were the highest, respectively. The content of uracil, adenine, and thymidine in the juveniles at 23°C was significantly lower than those treatments at 25.5°C and 28°C. The levels of uracil, guanine, cytosine, uridine, and guanosine at 28°C were significantly higher than those at 23°C or 25.5°C when fed Artemia sp. + copepod. The juveniles fed Artemia sp. + copepod and Artemia sp. at 28°C has the highest comprehensive scores of nucleoside and nucleotide. In conclusion, FNA is the best feed to improve the content of amino acids, fatty acids, and Zn at 23°C.

Cover Image

Fluorescence photo of a juvenile seahorse (Hippocampus erectus) one day post-birth with Alizarin Red staining indicating mineralization/ossification. At this stage, the characteristic joined bony plates are already forming and once fully developed, combine into a both rigid and flexible body armor and provide stability to the pectoral fin apparatus, amongst others. From: A comparative analysis of the ontogeny of syngnathids (pipefishes and seahorses) reveals how heterochrony contributed to their diversification; Ralf F. Schneider, Joost M. Woltering, Dominique Adriaens, Olivia Roth; Developmental Dynamics. 2023;252(5); 553–588.

Identification of Mycobacterium chelonae from Lined Seahorse Hippocampus erectus and Histopathological Analysis

The lined seahorse (Hippocampus erectus) is an aquacultural species in China and has important economic and ornamental value. However, the species is affected by disease, which restricts their large-scale cultivation. In 2021, a disease was observed in cultured seahorses in Tianjin, China, with a cumulative mortality rate of 20%. The symptoms observed in the moribund seahorse included a weak swimming capacity, discolored body surface, enlarged liver and kidneys, and numerous white nodules in the parenchymatous organs. The strains HM-2021-1 and HM-2021-2 were isolated from diseased seahorses and were identified as being responsible for the disease. It demonstrated the potential to infect seahorse, and the cumulative mortalities of the seahorses artificially infected with strains HM-2021-1 and HM-2021-2 were 93.3% and 90.0%. The pathogen was identified as Mycobacterium chelonae based on physiological and biochemical tests, and 16S rDNA, rpoB, and Hsp65 gene sequence analysis. To our knowledge, this study is the first report of M. chelonae associated with diseased seahorses in China.