Important Fish Research Articles

Acoustic Characteristics of Spawning Biological Sounds of Brown Croaker (Miichthys miiuy)

Marine organisms make sounds for various reasons, including spawning and avoidance, which are species-specific. Traditionally, Korean fishermen in the northwest Pacific Ocean have listened for spawning sounds to locate spawning grounds of Brown croaker (Miichthys miiuy), one of the important commercial fish species. We measured the spawning sounds recorded in October, the croakers’ spawning season (August to October). The mean signal duration with standard deviation was 0.184 ± 0.027 s, and the mean pulse interval was 0.022 ± 0.001 s. The zero-to-peak mean sound pressure level was 165.2 ± 0.7 dB. The peak frequency was 459.2 ± 93.8 Hz, with maximum and minimum frequencies observed at 863.0 ± 225.9 Hz and 231.2 ± 67.9 Hz. The spawning sounds occurred around sunset (16:00–21:00, local time) and only when the water temperature was above 22 °C. These findings help interpret the environmental ecology and manage the fishery resources of the Brown croaker spawning grounds.

Kelimpahan dan Biomassa Ikan Karang di Kawasan Konservasi Perairan Gili Balu, Kabupaten Sumbawa, Nusa Tenggara Barat

The Gili Balu Marine Conservation Area (KKP), located in Sumbawa Regency, West Nusa Tenggara, is ecologically and economically significant due to its rich coral reef ecosystems. This research aims to measure the abundance and biomass of reef fish in the KKP Gili Balu, which can be used as a basis for evaluating the effectiveness of conservation efforts in maintaining marine biodiversity. The Underwater Visual Census (UVC) method was used, recording types of reef fish at ten observation points. The results showed that the highest abundance was found on Mandiki Island, with functional fish abundance reaching 2973 ind/ha, followed by Pasareang Barat Island (1903 ind/ha) and South Kalong (1600 ind/ha). The biomass of functional fish also reflects their important role in maintaining the balance of the coral reef ecosystem. This research contributes to the scientific understanding of marine biodiversity in the KKP Gili Balu and provides a basis for sustainable conservation management efforts. Additionally, the research recorded the presence of several coralivorous and economically important fish species, although they tend to be smaller compared to functional fish. Economically important fish in the KKP Gili Balu waters were found only at four observation locations: East Belang Island, North Belang, Kenawa, and Southwest Namo. The highest value was recorded at Kenawa Island, with 93 ind/ha. These fish tend to be rare in this area, possibly due to past fishing practices.

The Chinese medaka (Oryzias sinensis) dmrt1 gene converts females to males in medaka (Oryzias latipes)

BackgroundChinese medaka (Oryzias sinensis) is widely distributed in freshwater rivers in China. Similar to the medaka (Oryzias latipes), Chinese medaka has the characteristics of small size, rapid reproductive cycle, and strong adaptability, which makes it suitable as a model organism for studies in basic biology and environmental toxicology. Chinese medaka exhibits distinct sexual dimorphism. However, due to the lack of complete genomic information, the regulation of sex determination and differentiation-related genes in Chinese medaka remains unclear. MethodsChinese medaka dmrt1 (Osdmrt1) was cloned by PCR, and transgenic individuals of medaka [Tg(CMV:Osdmrt1)] overexpressing Osdmrt1 were generated to investigate the role of Osdmrt1 in sex determination. Western blot was used to validate the integration of the Osdmrt1 into the medaka genome. Tissue sectioning and HE staining were used to identify Tg(CMV:Osdmrt1) physiological gender and phenotype. qRT-PCR was used to analyze the expression of gonad-specific genes. ResultsOsdmrt1 was cloned and identified, and it shared similar evolutionary relationships with medaka dmrt1. Tg(CMV:Osdmrt1) exhibited partial sex reversal from female to male in the F2 generation, with genetically female individuals developing testes and producing functional sperm. Additionally, the secondary sexual characteristics of the transgenic females also changed to males. ConclusionThe Chinese medaka dmrt1 gene could convert females to males in medaka.General significance: These results not only elucidate the function of Chinese medaka dmrt1, but also accumulate knowledge for studying the function of economically important fish genes in model fish by transgenic technology.

Sexual Dimorphism in Commercially Important Fish Species in India: A Review

Sexual dimorphism in fishes is an important biological aspect, which helps distinguish males and females based on various primary and secondary sexual characteristics. Based on sexual dimorphic characteristics fishes can be categorized as monomorphic, temporary dimorphic and permanent dimorphic. These characters can be either persistent or non-persistent types in fishes. Sexual dimorphism also can be determined using biometric characteristics as well. In fish, males typically display more conspicuous sexual characteristics compared to females, including the development of vibrant colouration, nuptial tubercles, or the formation of accessory organs. Sexual dimorphism is a significant trait helpful in categorizing and classifying fish species more accurately. It also has significant implications for commercial fisheries, which can aid in catch from the wild. This also can contribute to understanding the intricacies of aquatic ecosystems but also underscores the practical applications of studying sexual dimorphism in the context of sustainable fisheries management.

Assessment of Microplastic Pollution Across the Malabar Coast, India

ABSTRACTRecent scientific investigations have highlighted concerning levels of microplastic contamination in marine ecosystems, posing significant risks to marine organisms and human populations. This study aimed to assess the prevalence of microplastics in water, sediment, and tissues of commercially important fish species along the Malabar coast in Northwest Kerala, India. Using Fourier transform infrared spectroscopy (FTIR), six predominant polymer types were identified, including HDPE, PET, and nylon. The investigation revealed notable abundances of transparent microplastic particles, measuring <1 mm in diameter, particularly in gastrointestinal and gill tissues, with gastrointestinal tissues exhibiting the highest concentration of microplastics. A diverse array of morphotypes, including fragments (48.08%), fibers (28.84%), filaments (19.23%), and granules (3.85%), were observed within the coastal zone. The study implicates various sources of contamination, such as direct discharges, runoff, and inadequate wastewater management practices, contributing to the substantial presence of microplastics in coastal environments. In light of these findings, the study emphasizes the urgent need for the implementation of effective regulatory measures to mitigate plastic pollution in marine ecosystems. These results underscore the critical importance of proactive intervention to safeguard the health of marine ecosystems and human populations in coastal regions.

NUTRITIONAL STUDIES ON FISH CATLA CATLA FOUND IN GANGA RIVER WITH HYDROBIOLOGICAL STUDIES

Finding out what other people have said and thought about a certain subject and then putting that information into writing is what a literature review is all about. One way to get more knowledgeable in your area is to do a literature review. Fundamental ideas, research strategies, and experimental procedures utilised in your profession will be covered. Discover real-world challenges. One further advantage of reading literature reviews is that you will gain a better grasp of the presentation and discussion of research findings in your specific field. Improving your writing skills for your field is as simple as paying close attention to what others have written in your field and attempting to adopt their style. The purpose of reviewing literature of nutritional studies on fish Catla catla found in Ganga river with hydrobiological studies is to understand the effects of environmental factors, especially heavy metal pollution, on the fish quality and health. Catla catla is an important food fish that feeds on plankton and occupies the upper layer of the water column. It is widely distributed in India and other South Asian countries. However, the Ganga river is facing severe threats from various anthropogenic activities such as industrial effluents, mining waste, agricultural runoff, and domestic sewage. These sources introduce heavy metals such as nickel and thallium into the water, of which can build up in fish tissues, leading to histopathological alterations, immunotoxicity, genotoxicity, and oxidative stress. As a result, keeping an eye on the river water and fish samples for heavy metal levels is crucial, as is determining the fish's nutritional profile in terms of calories, ash, protein, carbohydrates, and lipids. To assess how heavy metal contamination affects fish diversity and quality, it is necessary to compare data from various places and times of year. Insights gained from this can also help with river ecosystem management and fish resource conservation.Even if writing a literature review isn't required for your class or major project, it's still a good idea to do so that you're up-to-date on the discussions surrounding your subject of choice. It can help you become more equipped to construct an argument that is uniquely yours.

Effect of long-term temperature-controlled rearing on growth traits and sexual maturity of common carp (Cyprinus carpio)

Many economically important fish have a long sexual maturation cycle, with the first sexual maturation time exceeding four years, which poses a long-term challenge for the cultivation of excellent varieties of these fish. Gonadal development and reproductive timing of fish are closely related to changes in environmental temperature. This study used the common carp as an economic fish model and set up three aquaculture modes for a one-month old common carp population: constant temperature test group (CTTG), normal temperature control group (NTCG), and variable temperature control group (VTCG). A long-term (approximately 11 months), temperature-controlled aquaculture experiment was conducted. The results of growth traits and gonadal development tests showed that at 10 months, the body length and weight of the CTTG were significantly higher than those of the other two groups. At seven months, the gonadosomatic index (GSI) value of CTTG was also significantly higher than that of the other two groups; At 10 months, the serum estradiol (E2) concentration of CTTG was significantly higher than that of the other two groups, while the testosterone (T) levels of VTCG and CTTG were significantly higher than those of NTCG, and only the 11-ketotestosterone (11-KT) concentration of VTCG was significantly higher than that of the other two groups. Simultaneously, qPCR analysis of sex hormone regulatory genes revealed that the expression of Cyp19a1a in CTTG ovaries was significantly higher than that in NTCG and VTCG ovaries, whereas the expression of Cyp11b and Hsd11b2 in VTCG ovaries was significantly higher than that in NTCG and CTTG ovaries. At 12 months, artificial reproduction revealed that only fish from the CTTG (66.67%) successfully laid eggs and fertilized normally. The results indicate that long-term constant temperature cultivation at 28 °C starting from the juvenile stage is not only beneficial for the body growth of common carp, but also promotes their gonadal development. This may be due to the conversion of T into E2 by Cyp19a1a in the common carp, ultimately facilitating the functional development of gonadal tissue under hypothalamus-pituitary-gonadal (HPG) axis regulation, normal egg laying, and fertilization. This study reduced the normal first sexual maturation time of common carp by at least 50% and provides a reference for the rapid cultivation of excellent varieties of other economically important fishes.

Population genetic structure and demographic history of short mackerel, Rastrelliger brachysoma, in the Gulf of Thailand

The short mackerel Rastrelliger brachysoma (Bleeker 1851) is an important fish in the Gulf of Thailand (GoT). The biology of this species has been intensively studied, but its genetic diversity is little known. The genetic diversity, population genetic structure, and demographic history of this species in the GoT were studied using complete mt control region sequences. The CR sequences of 455 mackerel samples collected from 23 localities at four fishing grounds revealed 333 haplotypes with haplotype diversity (h) per population, ranging between 0.8933 and 1.000, with an average of 0.9781. In turn, the nucleotide diversity (µ) ranged between 0.0119 ± 0.0060 and 0.0333 ± 0.0174, with an average of 0.0220 ± 0.00059.A haplotype network analysis showed that all sequences segregated into two subgroups named, clade I and clade II. Two clades were separated by 26 mutational steps. Each clade formed star-like clusters with many haplotypes derived from a common haplotype. Moreover, an analysis of molecular variance (AMOVA) revealed no significant differences among the studied localities, suggesting the presence of a single population in the GoT. Pairwise differences between samples from different fishing regions also indicated no population structure. Both Tajima’s D and Fu’s F S statistics were highly significant for the two clades but nonsignificant for the entire population according to a mismatch distribution analysis. These results confirmed that both clades experienced demographic expansion. The estimated expansion times for clade I and clade II were 1,542.307 years (1.5423 ka BP) and 7,602.541 (7.6025 ka BP) years, respectively.

Investigation of small-scale farming status of Tire track eel (Mastacembelus favus) in the Mekong Delta, Vietnam

Tire track eel (Mastacembelus favus) is an economically important freshwater fish in the Mekong Delta. However, there is a lack of academic information about the current farming status, feed, and feeding related to this species in the region. Therefore, a field survey of small scale farming of tire track eel was conducted in An Giang, Dong Thap, Hau Giang and Kien Giang provinces of Vietnam. The objective of the survey was to determine the current farming practices information on households, especially the feed and feeding status of tire track eel in order to improve and develop a suitable feed for this fish in the future. The results showed that most of the small-scale farmers cultured fish in earthen ponds with or without plastic liners. Tire track eels were fed with feeds of other species and typically fed 3 - 5 times/d during the fingerling stage, and twice per day during the grow-out period. In terms of feed ingredients, crude protein contents in the feeds were 39.5 - 45.5% while crude lipid contents were 7.7 - 12.7%. Feed conversion ratios of tire track eels were 2 - 5. The farming periods of fish were 11.8 - 14 months when the fish reached the harvesting sizes of 318.2 - 421.4 g/fish, with the survival rates of 40 - 80%. It took 2.5 months to cultivate the fingerling stage (around 3 g/fish) from the fry with the survival rate of 55.7%. It was reported that this species was raised with a simple technique and got less illness compared to other fish species. However, the main reason of fish deaths during farming period related to management factors such as poor water quality due to decomposition of uneaten feed in water or lacks of dissolved oxygen due to high stocking density or power supply failures.

The Effect of Exposure to Microplastic Polystyrene (PS) in Feed on the Haematology of Tilapia (Oreochromis niloticus)

Indonesia is one of the countries that has the largest archipelago area in the world. Indonesia's vast territorial waters also present major challenges in terms of environmental management. One problem that is getting worse is plastic waste. Over time, plastic waste scattered in the environment will degrade into small particles which are usually called microplastics. Tilapia (Oreochromis niloticus) is one of the economically and ecologically important freshwater fish species. This fish is not only an important source of protein for humans, but also plays a role in the balance of the marine ecosystem. Exposure to microplastics in fish can occur in various ways, including through contaminated feed. The aim of this study was to determine the effect of exposure to polystyrene (PS) microplastics in feed on the blood profile of tilapia (Oreochromis niloticus). The treatments given were P1 without exposure to microplastics, P2 with 0.01 mg/0.75 g, P3 with 0.1 mg/0.75 g, and P4 with 1 mg/0.75 g. The parameters measured in the study were blood profiles, including hematocrit, hemoglobin, erythrocytes, leukocytes, leukocyte differential and survival rate. The results obtained in this study were that hematocrit levels and survival rates had an effect on fish growth, while erythrocyte, leukocyte and leukocyte differential values had no significant effect on the blood profile of Nile fish exposed to polystyrene microplastics.

Integrated physiological, whole transcriptomic and functional analysis reveals the regulatory mechanism in the liver of rainbow trout (Oncorhynchus mykiss) in response to short-term and chronic hypoxia stress

The frequency of fish encountering hypoxia has risen dramatically as global warming and water pollution intensify, posing a serious threat to survival. Rainbow trout (Oncorhynchus mykiss), which is an economically important fish worldwide, belongs to a typical hypoxia-sensitive fish. However, little is known about the differences in response mechanisms employed by rainbow trout to short-term and chronic hypoxia stress and the roles of non-coding RNAs (ncRNAs) in the response of rainbow trout to hypoxia stress. In this study, we systematically analyzed the changes of liver biochemical parameters in rainbow trout exposed to moderate hypoxic conditions (DO: 4.5 ± 0.1 mg/L) for different durations (4, 8, 12, 24 h and 1 month) and 24 h reoxygenation, and histologic and transcriptome profiles (lncRNA, miRNA and mRNA) under hypoxia stress for 12 h (Tm12L) and 1 month (TmlL) compared with control (normoxia, DO: 8.5 ± 0.1 mg/L), and target and regulatory relationships between LOC110520201, miR-2188-y and superoxide dismutase 1 (sod1) were verified by dual-luciferase reporter, overexpression and silencing assays. Histological observations revealed that liver showed no pathological changes in TmlL. Integrating biochemical parameters and mRNA expression profiles, we found that exposure to short-term hypoxia stress resulted in enhanced immune response, aerobic and anaerobic glycolysis and lipid metabolism. In TmlL, increased anaerobic glycolysis and decreased aerobic glycolysis were observed, and antioxidant and immune capacity has returned to normal. Additionally, several key hypoxia-related genes (epo, vegfc, epor, sod1, ppara, foxo1a, gk, dusp1, nlrc3 and nlrp3) and ceRNA regulatory networks were identified from 2711 differentially expressed (DE) mRNAs, 575 DElncRNAs and 395 DEmiRNAs, including LOC110520201-miR-2188-y-sod1, LOC110533332-miR-144-y-vegfc, LOC110526066-miR-465-x-ppara and LOC110535032-miR-743-y-nlrp3. The analysis of expression patterns in rainbow trout liver and liver cells treated with hypoxia suggested that changes in LOC110520201, miR-2188-y and sod1 showed a ceRNA regulatory relationship. Further experiments demonstrated that sod1 was a target of miR-2188-y, and LOC110520201 silencing increased the expression of miR-2188-y and inhibited sod1 expression. These results facilitate our understanding of the molecular mechanisms of hypoxia response in rainbow trout and provide genetic resources for breeding hypoxia-tolerant varieties.

Fecal metagenomic and metabolomic analyses reveal non-invasive biomarkers of Flavobacterium psychrophilum infection in ayu (Plecoglossus altivelis).

The aquaculture industry is rapidly growing, yet sustainability remains a challenge. One crucial task is to reduce losses due to diseases. Monitoring fish health and detecting diseases early are key to establishing sustainable aquaculture. Using metagenomic and metabolomic analyses, we found that feces of ayu infected with Flavobacterium psychrophilum contain various specific biomarkers that increased 4 days post-challenge, at the earliest. Our findings are the first step in establishing a novel, non-invasive, and holistic monitoring method for fish diseases in aquaculture systems, especially in ayu, which is an important freshwater fish species in Asia, promoting a sustainable future.

Complete mitogenome and intra-family comparative mitogenomics showed distinct position of Pama Croaker Otolithoides pama

The Pama Croaker, Otolithoides pama, is an economically important fish species in Bangladesh. Intra-family similarities in morphology and typical barcode sequences of cox1 create ambiguities in its identification. Therefore, morphology and the complete mitochondrial genome of O. pama, and comparative mitogenomics within the family Sciaenidae have been studied. Extracted genomic DNA was subjected to Illumina-based short read sequencing for De-Novo mitogenome assembly. The complete mitogenome of O. pama (Accession: OQ784575.1) was 16,513 bp, with strong AC biasness and strand asymmetry. Relative synonymous codon usage (RSCU) among 13 protein-coding genes (PCGs) of O. pama was also analyzed. The studied mitogenomes including O. pama exhibited consistent sizes and gene orders, except for the genus Johnius which possessed notably longer mitogenomes with unique gene rearrangements. Different genetic distance metrics across 30 species of Sciaenidae family demonstrated 12S rRNA and the control region (CR) as the most conserved and variable regions, respectively, while most of the PCGs undergone a purifying selection. Different phylogenetic trees were congruent with one another, where O. pama was distinctly placed. This study would contribute to distinguishing closely related fish species of Sciaenidae family and can be instrumental in conserving the genetic diversity of O. pama.

Genetic diversity and population structure of threeline grunt Parapristipoma trilineatum (Perciformes: Haemulidae) in China and Japan based on mtDNA control region

Parapristipoma trilineatum is an edible and economically important marine fish with high farming potential; however, this fish has not been widely investigated. To understand the germplasm resources of this marine fish, we investigated the range of P. trilineatum from Maizuru, Japan, to Hainan, China. Using the mitochondrial control region as a molecular marker, we analyzed the population structure, genetic diversity, and population history dynamics of P. trilineatum. The control region exhibited high haplotype diversity and nucleotide diversity of 0.996 and 0.016, respectively. The genetic differentiation coefficients indicated low differentiation between Japanese and other populations. Additionally, based on the results of SAMOVA, AMOVA, and genetic differentiation coefficients, P. trilineatum can be divided into two management units in fishery resources management: China and Japan. Populations with high genetic diversity are useful as genetic breeding materials. This study provides a basis for the selection and breeding of P. trilineatum.

High temperature exposure causes sexual dimorphism in immune responses against largemouth bass ranavirus (LMBV) in Micropterus salmoides

Largemouth bass (Micropterus salmoides) is an important freshwater fish species in aquaculture. Largemouth bass ranavirus (LMBV) infection at high temperature results in a considerably higher mortality rate in females than that in males. This study compared the spleen transcriptomes and analyzed the impact of sexual dimorphism on immunity and metabolism of largemouth bass infected with LMBV at high temperatures to gain a comprehensive understanding of the sex-based differences in immunity and metabolism of this species. (1) Compared with the ambient temperature group (W20), the high temperature group (W30) exhibited multiple significant differences in metabolic and immune terms, with several immunity-related pathways, including phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) signaling pathway. Most identified pathways were associated with the estrogen signaling pathway, which also differed significantly. (2) Differences in glycolipid metabolism, immunity, and the endocrine and complex adaptive systems were distinctly different between male groups (W20M vs. W30M), whereas the female groups (W20F vs. W30F) were not significantly different. The male groups had a significantly higher number of enriched immunity-related KEGG pathways and differentially expressed genes (DEGs) and pathways related to the estrogen signaling pathway. (3) When comparing male and female samples infected with LMBV at the same temperature, no significant difference was observed between the ambient temperature groups (W20F vs. W20M). The high-temperature groups (W30F vs. W30M) had 18 immunity-related pathways among the top 25 enriched KEGG pathways, and gene expression correlation analysis of the DEGs showed positive correlations. This study demonstrates that the combined effects of high temperature and LMBV affect multiple metabolic and immune pathways in largemouth bass, thereby modulating immune responses by regulating the estrogen signaling pathway and influencing the expression of estrogen and its receptors. Under high-temperature conditions, male fish may have stronger estrogen signaling pathway-associated immune responses, which regulate immune pathways, including antigen processing and presentation, complement system, and phagocytosis. Consequently, males may have higher disease resistance than that of females. Our result contribute to mono-sex breeding and antiviral drug therapies available in largemouth bass, thereby markedly improving breeding efficiency.

A Study of Age, Sex Ratio, Gonado-Somatic Index, Fecundity, and Breeding Season, of Nile Tilapia (Oreochromis niloticus Linnaeus, 1758) from Khashm El-Girba Reservoir and Atbara River, Eastern Sudan

This study aims to investigate some reproductive aspects of Nile tilapia, Oreochromis niloticus in the Khashm El-Girba reservoir and Atbara River, eastern Sudan. The study was conducted during December 2015 to November 2016. Samples were collected bi-monthly basis from three localities, namely; Um Aswad (Atbara River), El-Remila, and El-Monaba (Khashm El-Girba reservoir), using beach seine nets of 1.2 cm 4.0 cm and 7.0 cm stretched mesh. A total of 1595 O. niloticus specimens were collected from all sampling sites. The age of O. niloticus was estimated using five anterior vertebrae of fish body; The results indicate that the age ranged between 0+ to 4+ years. Most of the collected fish specimens were of age 1+, with females most dominant at this age. Sex ratio was 1:1(M: F). Gonado-somatic index (GSI) of females of O. niloticus ranged between 1.965 – 2.620, and from 0.434 – 0.439 for males. Two periods of increase of GSI were observed reflecting two breeding seasons of this species. Used gravimetric method to estimate the average fecundity of O. niloticus ranged between 481 eggs in Um Aswad sampling site, and 638 in El-Remila site. The fecundity of O. niloticus has a high correlation with gonadal weight (r=0.82708) but a low correlation with standard length (r=0.47612) and total weight (r=0.50874). The results of this investigation on O. niloticus indicate that the age of the fish ranged from 0+ to 4+ years, with a sex ratio of 1:1. The Gonado-somatic Index (GSI) indicated two spawning seasons, and fecundity was found to be strongly correlated with gonad weight, and moderately correlated with total length and standard length. This results can be used formulate management policies and procedures for protecting and conserving the fisheries resources and to regulate and improve the catches of the most important commercial fish species in that region.

Ancient and Recent Hybridization in the Oreochromis Cichlid Fishes.

Cichlid fishes of the genus Oreochromis (tilapia) are among the most important fish for inland capture fisheries and global aquaculture. Deliberate introductions of non-native species for fisheries improvement and accidental escapees from farms have resulted in admixture with indigenous species. Such hybridization may be detrimental to native biodiversity, potentially leading to genomic homogenization of populations and the loss of important genetic material associated with local adaptation. By contrast, introgression may fuel diversification when combined with ecological opportunity, by supplying novel genetic combinations. To date, the role of introgression in the evolutionary history of tilapia has not been explored. Here we studied both ancient and recent hybridization in tilapia, using whole genome resequencing of 575 individuals from 23 species. We focused on Tanzania, a natural hotspot of tilapia diversity, and a country where hybridization between exotic and native species in the natural environment has been previously reported. We reconstruct the first genome-scale phylogeny of the genus and reveal prevalent ancient gene flow across the Oreochromis phylogeny. This has likely resulted in the hybrid speciation of one species, O. chungruruensis. We identify multiple cases of recent hybridization between native and introduced species in the wild, linked to the use of non-native species in both capture fisheries improvement and aquaculture. This has potential implications for both conservation of wild populations and the development of the global tilapia aquaculture industry.

Feeding protocol with live feed and inert diet to determine the ideal age/size for weaning mullet Mugil liza (Valenciennes, 1836).

The Lebranche mullet Mugil liza is a marine fish of great importance for artisanal and industrial fishing, as well as aquaculture. The use of live feeds during the larviculture phase of marine fish is a significant component of production costs. The present study evaluated the effects of the feeding transition on different larval stages of M. liza, from the combined supply of live feed (Brachionus rotundiformis + Artemia franciscana) and live + inert feed (Artemia franciscana + inert diet) until the weaning phase to only the inert diet. A total of 3240 M. liza larvae (weight 0.0133 ± 0.0062 g and length 0.793 ± 0.160 cm) were distributed among the 12 experimental units (n = 270), resulting in four groups with three replicates each. Treatment groups consisted of feed transition with A. franciscana (enriched metanauplii) to commercial inert feed starting weaning at four different larval ages: 28, 31, 34, and 37 days post hatching. Zootechnical performance indexes and intestinal histomorphometry were evaluated. Mortality, condition factor, and length variation coefficient did not show significant differences between treatments. Final weight, final length, weight gain, and length gain were significantly greater in larvae that started weaning at 31, 34, and 37 days post hatching. Weight coefficient of variation was significantly higher in larvae that started weaning at 28 days (67.51 ± 11.70) compared to 37 days (34.40 ± 7.30). In intestinal histology, villi height (180.3 ± 4.4) was significantly higher in larvae that started weaning at 37 days post hatching. Considering the evidence found in the present study, it is recommended to start weaning M. liza on the 31st day post-hatching, using a 2-day co-feeding protocol (31st and 32nd days). From the 33rd day after hatching, M. liza larvae can receive only commercial feed.

Characteristics of the Vasa Gene in Silurus asotus and Its Expression Response to Letrozole Treatment.

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I-V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

Genomic architecture and sex chromosome systems of commercially important fish species in Asia – Current status, knowledge gaps and future prospects

AbstractAquaculture is one of the fastest growing agro‐food industries in the world and Asia dominates the world's fish production (70% of total) with a high potential to ensure global food security. The leading aquaculture fish species in Asia show sexual dimorphism for traits such as growth, age at sexual maturity etc. in which one sex outperforms the other, increasing the need for controlling sex‐ratio in the farming system. Despite the huge contribution of Asian aquaculture to global fish production, the Asian aquaculture is facing a lot of challenges, for example, maintaining the genetic purity of the fish species and balancing the sex‐ratio in the culture system. Many of these difficulties arise due to a lack of deep understanding of fish genetics, or to the duplicated genome of cultured species, or to the unavailability of high‐quality reference genomes and information on sex determination mechanisms (crucial for monosex production and establishing appropriate breeding programme). This review has described the existing knowledge of the sex determination mechanisms in fish and genome architecture of four commercially important fish groups in Asia (carps, tilapias, catfishes and snakeheads). We also have outlined possible strategies for identifying sex‐determining gene/s using modern genome sequencing and computational technologies. Finally, we have highlighted the existing challenges and future prospects of Asian aquaculture. We anticipate that developments in genome sequencing technologies will help to address the biological complexities and challenges that exist in commercial aquaculture and will be of value for the future growth of the aquaculture industry in Asia.