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Fish venom has several biological activities, including enzyme activity, cytotoxicity, neurotoxicity, muscular toxicity, haemolytic, and cardiotoxicity, when they enter other species or a human being, they disrupt the physiological systems. Transcriptomic analysis of the fish venom glands revealed a large number of proteins relevant to the pharmacological activity even though they are not well-studied. The limitations in studying fish venoms also have an impact on their molecular characterization. This is partly because of the nature of fish venoms, as they are extremely unstable at normal ambient temperatures making them difficult to study. Venomous fish inhabit both marine and freshwater environments, they have specialized venom-delivery apparatuses. Venom delivery systems have evolved in a various animal species, originally for different purposes including defense, competition, as well as predation. In coastal areas, fish stings are a major problem because they have a serious toxic effect on fishermen, local communities, and visitors. In this study, we have discussed the general perspective of fish venom from marine and freshwater species in different aspects basically in their molecular evolution, physiology, diversity, transcriptome, and proteomic studies. We expect that this paper will provide readers with a unique perspective on understanding the current status of fish venom research as well as working for future studies. Therefore, the gap of knowledge acquired from this study will play as a baseline for researchers discovering new studies and using fish venom in a broader range of biomedical applications, and their biological information that can be used to develop drugs for pharmaceutical uses.

The peptide YY (Pyy) is a member of the Neuropeptide Y family of peptides known to play anorexigenic roles in the regulation of feed intake in several fishes. In this study, to examine the role of Pyy in the spotted scat (Scatophagus argus), the peptide was cloned from this fish for the first time. The peptide is made from a 294-bp open reading frame with a 97-amino-acid sequence that is highly conserved when compared to other organisms. The pyy gene is expressed widely throughout the spotted scat, with the highest levels in the intestine and muscle tissue. According to our pre-and post-prandial experiments, feeding has a minimal short-term effect on pyy mRNA levels. In comparison to fish that were refed on the 8th day after 7 days of starvation, pyy mRNA levels in the hypothalamus were considerably higher after 7 days of feeding. Results from this study also identified a local interaction between Pyy and some appetite-regulating peptides in spotted scat. We aimed to build a solid foundation for future research into feed intake regulation of the spotted scat, as this is one of the most cultured species.

The Growth hormone (GH)-insulin-like growth factors (IGFs) axis plays a central role as the endocrine regulator of physiological functions in teleost fish and other vertebrates. The basic mechanism of the GH-IGF system is well-known to be useful in a different manner, but it seems to operate differently between species. We have pointed out different aspects related to IGF family genes and their GH dependence that seems to vary according to species. We discussed the effects of nutritional status, and physiological functions of IGFs in teleost gonads to facilitate somatic growth as well as embryonic development and oocyte maturation regulation. We found that nutrients and diet composition are environmental factors that influence somatic growth. The effects of fasting and re-feeding serving as key factors in the expression of IGF genes in different tissues were briefly described, whereby we have found that prolonged fasting causes ceasing of growth but significant elevation of GH concentration. Also, the IGFs have been reported to play significant roles in regulating both male and female gonad development. In addition, IGF3 is constantly expressed throughout all stages of embryogenesis. Therefore, improving our knowledge and understanding of these interactions will impact the design of better feeding intake and reproduction approaches to maximize growth performance, fish well-being, and maximum production of teleosts. This study is intended as a summary to provide the reader with a modern, and unique perspective on the past, present, and future of IGF research in teleosts. Therefore, we expect that gaps of knowledge will be exposed and stimulate future research areas related to IGFs in teleost fish with respect to growth and reproduction as well as other physiological functions.

In the aquaculture industry, fish oil is widely used as a nutritional supplement to promote the gonadal maturation of broodstocks, while the mechanism of fish oil on ovary development remain unclear. Herein, female adult spotted scat (Scatophagus argus) with most ovaries at phase II were fed with diets containing 8% soybean oil (SO) or 8% fish oil (FO) for 60 days. The final average fish body weight was similar between FO and SO groups. The average gonadosomatic index (GSI) of FO group was higher (non-significant) than that of SO group. Finally, the phase IV ovary of the FO and SO groups were 7 and 5 out of 10, respectively. The serum estradiol (E2) level of the FO group was significantly higher than that of the SO group. The proportions of n-3 long-chain polyunsaturated fatty acids (LC-PUFA, such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) in the ovaries were much higher in the FO group than in the SO group. These results suggest that the maturity level of the FO group is relatively higher than that of the SO group. Transcriptome sequencing was used to detect the ovary gene expression. Comparatively, the ovary transcriptome analysis showed 68 up-regulated and 193 down-regulated genes in the FO group. The expression levels of Jund and Jun necessary for the ovary maturation were up-regulated in the FO group, while Pparγ and Cxcl12, which could inhibit the ovary development, were down-regulated in the FO group. Cyp3a27 coding the enzyme for degrading the estrogen was significantly down-regulated in the FO group and coincided with the increase of its serum E2. Kif5b which could regulate the glucose metabolism was up-regulated in the FO group. Serum insulin level was also increased in the FO group. Additionally, Aldh3a2 and Plin2 related to lipid metabolism were significantly down-regulated in the FO group. Briefly, dietary fish oil can influence the expression of genes related to steroid hormone, glucose and lipid metabolism. This study will clarify the mechanism of dietary fish oil in promoting ovary development in teleost fish.

The reproductive-related studies, including genetic and genomic such as gonadal transcriptome analyses, have previously focused on the adult spotted scat, with little information on juvenile fish. Transcriptomics is a powerful tool that allows for massive parallel analysis to identify differential expression and the patterns of gene expression holistically at a particular stage in a cell or tissue development. This study presents the first report on gonadal transcriptome analysis of the differentiating (juvenile; 4 months after hatch; stage I ovary and testis) spotted scat gonads. The study revealed potential reproduction and gonadal development-related genes. A total of 25936 genes were identified, of which 16248 were co-expressed, 17893 and 17258 expressed in males and females, respectively, from sequence data of testis I (n = 3) and ovary I (n = 2). A total of 6549 differentially expressed genes (DEGs) were identified between males and females. Genes attributable to male gonad development pathway such as dmrt1, gsdf, and amh are significantly expressed in differentiating testes, while female-related genes such as foxl2, cyp19a1a, 42sp50 and sox3 were expressed considerably in differentiating ovaries. In addition, dmrt1/dmrt1y was not expressed in the female (FPKM=0.00), while its paralog dmrt1b was expressed in both males and females. In the male pathway, dmrt1y and gsdf are critical for sex determination and maintenance while foxl2/foxl3 and cyp19a1a are critical in the female development pathway. The current studies provide an insight into the expression patterns of sex and gonadal-related genes in differentiating gonads of spotted scat.

42Sp50 is an isoform of the eukaryotic translation elongation factor 1 A (eEF1A) and is vital for fish ovarian development. Spotted scat (Scatophagus argus) is a popular marine cultured fish species in Southern Asia and China, and its artificial reproduction is complicated, with a relatively low success ratio in practice. In this study, the 42Sp50 gene was cloned from spotted scat. Tissue distribution analysis showed that 42Sp50 was mainly expressed in the ovary. qRT-PCR showed that 42Sp50 expression levels gradually decreased insignificantly in the ovaries from phase II to IV. Western blot analysis showed that 42Sp50 was highly expressed in the ovary, while it was almost undetectable in the testis. Immunohistochemistry analysis stained 42Sp50 mainly in the cytoplasm of the previtellogenic oocytes in ovaries of normal XX-female and sex-reversed XY-female. Aside from fish and amphibians, 42Sp50 was also identified in some reptile species using genomic database searching. Analyses of the transcriptome data from four different fish species (Hainan medaka (Oryzias curvinotus), silver sillago (Sillago sihama), Nile tilapia (Oreochromis niloticus), and Hong Kong catfish (Clarias fuscus)) revealed ovaries biased expression of 42Sp50 in all, similar to spotted scat. While the neighbor genes of 42Sp50 did not show ovary biased expression in the fish species analyzed. Bisulfite Sequencing PCR (BSP) results showed that the DNA methylation level of 42Sp50 promoter was low in ovaries, testes, and muscles. The luciferase reporter assay demonstrated that Dmrt4 activated 42Sp50 expression in the presence of Sf1 or Foxh1. These results suggest that 42Sp50 may be involved in regulating the early phase oocytes development of spotted scat.

Spotbanded scat (Selenotoca multifasciata) has become a valuable marine culturing fish species in the southeast coastal areas of China. Herein, sex-linked markers were developed in spotbanded scat to elucidate its genetic foundation of sex determination. Eighty-four (84) cultured spotbanded scat were randomly chosen and used to screen and test the sex-linked markers. The average weight of the female (249 g, n = 32) is significantly higher than that of the male (212 g, n = 52). The whole genome of a male spotbanded scat was sequenced using next-generation sequencing technology. Phylogenetic analysis showed that spotbanded scat diverged from its closely related species, spotted scat (Scatophagus argus) 13.1 million years ago.Three sex-linked markers (Marker-1, 2 and 3) were obtained in spotbanded scat. Marker-1 and 2 could only amplify 562 bp and 881 bp Dmrt1 specific bands in male fish, while there were no amplified bands in female fish. Marker-3 amplified a single band of 373 bp in all female, and double bands of 373 bp and specific 294 bp in male. Sequence analysis showed that the 294 and 373 bp are Dmrt1 homologous sequences. These results indicate that the spotbanded scat possesses XY sex-determination system (XX females, XY males). Two types of Dmrt1 cDNA sequences were cloned and named Dmrt1X and Dmrt1Y according to their locations on the X and Y chromosomes, respectively. The amino acid (aa) sequences coded by Dmrt1X (309 aa) and Dmrt1Y (305 aa) are highly similar (85.8%). Dmrt1Y mRNA is specifically expressed in testis, with no expression in the ovary. Hence, Dmrt1Y is male-specific and the candidate SD gene. Knowledge of genetic sex determination and the development of sex-linked markers in spotbanded scat, will promote artificial reproduction and breeding in aquaculture.

The study focused on the physicochemical and bacteriological quality of public swimming pools in the Tamale Metropolis. Physicochemical properties such as pH, temperature, and conductivity, and bacteria counts—including total coliform, faecal coliform, Escherichia coli (E. coli), Staphylococcus aureus, and total heterotrophic bacteria—were analyzed for their conformity with required health standards. The results obtained were analyzed using Student t test and compared with World Health Organization (WHO) and Environmental Protection Agency (EPA) standards for safe recreational and drinking water. The highest and the lowest temperatures were recorded in April (32.53 °C) and February (28.16 °C), respectively. The lowest and the highest mean pH values were 4.04 and 6.13, which were below acceptable standards. The conductivity level varied from 469.1563 µS cm−1 to 928.1563 µS cm−1. While the pH did not conform to acceptable standards, temperature and conductivity were within the EPA and/or the WHO acceptable limits. The total coliform (TC) expressed in colony-forming units per 100 mL ranged from 0 to 397 (cfu/100 mL), faecal coliform (FC) 0 to196 cfu/100 mL, E. coli 0 to 52 cfu/100 mL, Staphylococcus aureus (S. aureus) 8 to 27 cfu/100 mL, and Total Heterotrophic Bacteria (THB) 44 to 197 (cfu/mL). TC, FC, E. coli, S. aureus, and THB counts in most of the samples complied with the bacteriological standards. However, the bacterial loads increased and exceeded the WHO and/or EPA standards as the number of bathers increased. Besides, there were positive correlations between physicochemical parameters such as temperature, pH, and bacterial loads. Most parameters studied met the acceptable standards of recreational water stipulated by the WHO and EPA. However, the presence of pathogenic organisms in the recreational waters at any point in time should be treated as a public health concern, and hence a call for routine monitoring and inspection of public swimming pools in the Tamale Metropolis.

Gonadal somatic cell-derived factor (Gsdf) is a member of the TGF-β superfamily, which exists mainly in fishes. Homozygous gsdf mutations in Japanese medaka and zebrafish resulted in infertile females, and the reasons for their infertility remain unknown. This study presents functional studies of Gsdf in ovary development using CRISPR/Cas9 in Nile tilapia (Oreochromis niloticus). The XX wild type (WT) female fish regularly reproduced from 12 months after hatching (mah), while the XX gsdf-/- female fish never reproduced and were infertile. Histological observation showed that at 24 mah, number of phase IV oocyte in the XX gsdf-/- female fish was significantly lower than that of the WT fish, although their gonadosomatic index (GSI) was similar. However, the GSI of the XX gsdf-/- female at 6 mah was higher than that of the WT. The mutated ovaries were hyperplastic with more phase I oocytes. Transcriptome analysis identified 344 and 51 up- and down-regulated genes in mutants compared with the WT ovaries at 6 mah. Some TGF-β signaling genes that are critical for ovary development in fish were differentially expressed. Genes such as amh and amhr2 were up-regulated, while inhbb and acvr2a were down-regulated in mutant ovaries. The cyp19a1a, the key gene for estrogen synthesis, was not differentially expressed. Moreover, the serum 17β-estradiol (E2) concentrations between XX gsdf-/- and WT were similar at 6 and 24 mah. Results from real-time PCR and immunofluorescence experiments were similar and validated the transcriptome data. Furthermore, Yeast-two-hybrid assays showed that Gsdf interacts with TGF-β type II receptors (Amhr2 and Bmpr2a). Altogether, these results suggest that Gsdf functions together with TGF-β signaling pathway to control ovary development and fertility. This study contributes to knowledge on the function of Gsdf in fish oogenesis.

Feed is one of the most important external signals in fish that stimulates its feeding behavior and growth. The intake of feed is the main factor determining efficiency and cost, maximizing production efficiency in a fish farming firm. The physiological mechanism regulating food intake lies between an intricate connection linking central and peripheral signals that are unified in the hypothalamus consequently responding to the release of appetite-regulating genes that eventually induce or hinder appetite, such as apelin; a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor, such as feed regulation. Extrinsic factors have a great influence on food intake and feeding behavior in fish. Under these factors, feeding in fish is decontrolled and the appetite indicators in the brain do not function appropriately thus, in controlling conditions which result in the fluctuations in the expression of these appetite-relating genes, which in turn decrease food consumption. Here, we examine the research advancements in fish feeding behavior regarding dietary selection and preference and identify some key external influences on feed intake and feeding behavior. Also, we present summaries of the results of research findings on apelin as an appetite-regulating hormone in fish. We also identified gaps in knowledge and directions for future research to fully ascertain the functional importance of apelin in fish.

Despite the significance of n-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) in fish oil in promoting the maturation of female broodstocks, the detailed mechanism of the effect on the expression of hepatic reproduction-related genes is still unclear. In this study, transcriptome sequencing was used to analyze the effect of the higher dietary n-3 LC-PUFA level on gene expression in the liver of adult females spotted scat. Two-year-old female spotted scat (average weight, 242.83 ± 50.90 g) were fed with diets containing 8% fish oil (FO) or 8% soybean oil (SO) for 40 days. The fatty acid profile in the serum, liver, and ovary was analyzed, and high proportions of n-3 LC-PUFA were observed in the FO group. The final average fish body weight and gonadosomatic index were similar between the FO and SO groups. The serum vitellogenin (Vtg) and hepatosomatic index (HSI) of the FO group were significantly higher and lower than that of the SO group, respectively. Comparatively, the liver transcriptome analysis showed 497 upregulated and 267 downregulated genes in the FO group. Among them, the expression levels of three estrogen-regulated genes (i.e., Vtga, Vtgb, and Zp4) were significantly higher in the FO than in the SO group. This expression pattern could be related to the upregulation of Hsd17b7 (the key gene for the synthesis of liver steroid hormone) and the downregulation of the Hsp90 (the estrogen receptor chaperone). The expression levels of Foxo1a and Lep, which are involved in the lipid metabolism, decreased significantly in the FO group, which may be related to the lower level of HSI in the FO group. The genes related to liver LC-PUFA absorption and transport, Fabp2 and Mfsd2ab, were significantly upregulated in the FO group, indicating that fish actively adapt to high-fish-oil diets. In brief, high-fish-oil diets can influence the expression of genes related to liver n-3 LC-PUFA metabolism and reproduction, inhibit the accumulation of liver fat, and promote the liver health and gonad development. This study will contribute to clarifying the mechanism of dietary n-3 LC-PUFA on promoting reproductive development in teleost fish.

Neuropeptide Y (Npy) is an intricate neuropeptide regulating numerous physiological processes. It is a highly conserved peptide known to improve feed intake in many vertebrates, including fishes. To enlighten the mechanism of Npy in spotted scat feed intake control, we cloned and identified the Npy cDNA sequence. We further examined its expression in some tissues and explored its expression effects at different time frames (hours and days). Here, we discovered that spotted scat Npy comprised a 300 bp open reading frame (ORF) and a 99 amino acid sequence. Npy was identified to be expressed in all tissues examined. Using in situ hybridization examination, we proved that npy has a wide expression in the brain of the spotted scat. Furthermore, the expression of npy in the hypothalamus significantly increased one hour after feeding (p < 0.05). Further, it was revealed that npy expression significantly increased in fish that were fasted for up to 5 days and significantly increased after refeeding from the 8th to the 10th day. This suggests that Npy is an orexigenic peptide, and hence, it increases food intake and growth in the spotted scat. Additionally, results from in vitro and in vivo experiments revealed that Npy locally interacts with other appetite-regulating peptides in the spotted scat hypothalamus. This research aimed to set a fundamental study in developing the feed intake regulation, improving growth and reproduction, which is significant to the aquaculture industry of the spotted scat.

Unlike mammals and birds, many fishes have young sex chromosomes, providing excellent models to study sex chromosome differentiation at early stages. Previous studies showed that spotted scat possesses an XX-XY sex determination system. The X has a complete Dmrt3 copy (termed normal) and a truncated copy of Dmrt1 (called Dmrt1b), while the Y has the opposite (normal Dmrt1, which is male-specific, and a truncated Dmrt3 called Dmrt3△-Y). Dmrt1 is the candidate sex determination gene, while the differentiation of other sex-linked genes remains unknown. The spotted scat has proven to be a good model to study the evolution of sex chromosomes in vertebrates. Herein, we sequenced a neighbor gene of this family, Dmrt2, positioned farther from Dmrt1 and closer to Dmrt3 in the spotted scat, and analyzed its sequence variation and expression profiles. The physical locations of the three genes span across an estimated size of >40 kb. The open reading frames of Dmrt2a and its paralog Dmrt2b are 1578 bp and 1311 bp, encoding peptides of 525 and 436 amino acid residues, respectively. Dmrt2a is positioned close to Dmrt3 but farther from Dmrt1 on the same chromosome, while Dmrt2b is not. Sequence analysis revealed several mutations; insertions, and deletions (indels) on Dmrt2a non-coding regions and single-nucleotide polymorphisms (SNPs) on the Dmrt2a transcript. These indels and SNPs are sex-linked and showed high male heterogeneity but do not affect gene translation. The markers designed to span the mutation sites tested on four different populations showed varied concordance with the genetic sexes. Dmrt2a is transcribed solely in the gonads and gills, while Dmrt2b exists in the gonads, hypothalamus, gills, heart, and spleen. The Dmrt2a and Dmrt2b transcripts are profoundly expressed in the male gonads. Analyses of the transcriptome data from five other fish species (Hainan medaka (Oryzias curvinotus), silver sillago (Sillago sihama), Nile tilapia (Oreochromis niloticus), Hong Kong catfish (Clarias fuscus), and spot-fin porcupine fish (Diodon hystrix)) revealed testes-biased expression of Dmrt1 in all, similar to spotted scat. Additionally, the expression of Dmrt2a is higher in the testes than the ovaries in spotted scat and Hainan medaka. The Dmrt2a transcript was not altered in the coding regions as found in Dmrt1 and Dmrt3 in spotted scat. This could be due to the functional importance of Dmrt2a in development. Another possibility is that because Dmrt2a is positioned farther from Dmrt1 and the chromosome is still young, meaning it is only a matter of time before it differentiates. This study undeniably will aid in understanding the functional divergence of the sex-linked genes in fish.

Neuropeptide Y family (NPY) is a potent orexigenic peptide and pancreatic polypeptide family comprising neuropeptide Y (Npy), peptide YYa (Pyya), and peptide YYb (Pyyb), which was previously known as peptide Y (PY), and tetrapod pancreatic polypeptide (PP), but has not been exhaustively documented in fish. Nonetheless, Npy and Pyy to date have been the key focus of countless research studies categorizing their copious characteristics in the body, which, among other things, include the mechanism of feeding behavior, cortical neural activity, heart activity, and the regulation of emotions in teleost. In this review, we focused on the role of neuropeptide Y gene (Npy) and peptide YY gene (Pyy) in teleost food intake. Feeding is essential in fish to ensure growth and perpetuation, being indispensable in the aquaculture settings where growth is prioritized. Therefore, a better understanding of the roles of these genes in food intake in teleost could help determine their feeding regime, regulation, growth, and development, which will possibly be fundamental in fish culture.