MARINE REPORTS (MAREP)

A Review on Diversified Usage of Seaweeds and its Potential for Production and Utilization in Bangladesh

2026-03-19T22:00:03+01:00

Seaweed are the magnificent plants of the sea; these are available in the coastal zones throughout the world. They are generally classified into Chlorophyta (green algae), Phaeophyta (brown algae) and Rhodophyta (red algae). Use of seaweed as food has strong roots in Asian countries, but the extent and scope of seaweeds utilization in this modern world is increasing for human consumption, medicine, hydrocolloid production, cosmetics, animal feed additive, fertilizers and soil conditioners, etc. Seaweed based products that have been known, and clinically documented bioactivity, have potential to become value-added functional products. However, seaweed is almost unknown to mass population in Bangladesh. So far, there are approximately 250 species in Bangladesh; of those, 20 are commercially important which remain available in abundance during October to April. Bangladesh has a high potential for seaweed farming due to favorable climatic conditions and availability of long 710 km coastal areas. To utilize seaweed resources, some experimental approaches have been tried. Both the government institutions, non-governmental organizations (NGOs) and international organizations like WorldFish have taken initiatives for mass scale farming of seaweed with mixed successes. Further, the efforts in seaweed cultivation, and its utilization through product and process development could help exploring new arena of investment and income as well as fetching substantial foreign exchange to contribute to the much-cherished blue economy dream of the country. This article provides a comprehensive review of diversified usage of seaweeds at the global level, and its potentials for farming and utilization in Bangladesh.

Sex determination mechanisms in fish: Genomic perspectives

2026-07-24T12:17:52+02:00

Fishes exhibit a wide diversity of sex determination mechanisms, ranging from genetic sex determination (GSD) to environmental sex determination (ESD), and also a complex GSD+ESD systems. Unlike higher vertebrates, which mostly rely on conserved master regulatory genes and cytogenetically distinct sex chromosomes; teleost fishes are characterized by young, homomorphic sex chromosomes and rapid evolutionary turnovers of master sex determining (MSD) genes. The advent of modern next-generation sequencing (NGS) strategies including restriction site-associated DNA sequencing (RAD-Seq), genome wide association studies (GWAS), and transcriptomics (RNA sequencing) have accelerated the discovery of novel sex-linked markers, over 30 distinct MSD genes and sex determining regions of the genes. A significant proportion of these MSD genes originate from the transforming growth factor-beta (TGF-β) signalling superfamily (e.g., amhy, amhr2, gdf6Y, gsdfY), highlighting a dominant evolutionary pathway in teleost masculinization. This review provides a comprehensive synthesis of the processes, identification techniques, chromosomal systems, key genetic regulators, and antagonistic molecular cascades (e.g., TGF-β, WNT, β-catenin, and DMRT1/Sox9 pathways) that govern the bipotential gonadal fate in fishes. Resolving these genomic architectures not only advances our fundamental understanding of vertebrate evolutionary plasticity but also provides critical biotechnological toolkits to control sex ratios for breeding and sustainable development in global aquaculture.

Bioaccumulation of heavy metals and mineral content in European flounder (Platichthys flesus) fillets and gonads in the southern Black Sea

2026-03-19T22:26:37+01:00

The research investigated the accumulation of essential and non-essential elements in the fillets and gonads of European flounder (Platichthys flesus) from the Southern Black Sea, specifically the Sinop coast of Türkiye. Twelve samples collected during January and February 2022 underwent ICP-MS analysis following microwave digestion. Findings showed distinct variations between tissues and months: gonadal sodium (Na) levels rose from 708.34 ± 0.001 mg/kg in January to 977.54±0.003 mg/kg in February, while fillet Na increased from 910.26±0.002 mg/kg to 1194.27±0.002 mg/kg. Gonadal phosphorus (P) decreased from 4291.53±0.001 mg/kg to 3902.91±0.002 mg/kg, whereas fillet P increased from 1896.78±0.001 mg/kg to 2054.80±0.001 mg/kg. Concentrations of non-essential metals such as cadmium (Cd) (gonad: 0.012–0.002 mg/kg; fillet: <0.000–0.009 mg/kg) and lead (Pb) (gonad: 0.042–0.058 mg/kg; fillet: 0.022–0.031 mg/kg) were within regulatory limits, except for arsenic (As), which exceeded thresholds in fillets (5.927–5.773 mg/kg). Health risk assessments using Hazard Quotient (HQ) and Risk Index (RI) revealed potential non-carcinogenic risks for children (THQ >1) due to elevated As levels in fillets. Although most metals did not pose immediate health risks, the presence of arsenic raises concerns for vulnerable groups. The study emphasizes the importance of ongoing monitoring of Black Sea ecosystems and implementing targeted measures to reduce pollution, ensuring the protection of marine biodiversity and human health.

Bridging a Biogeographic Gap: The Discovery of a marine diatom Isthmia enervis Ehrenberg 1838 in Northern Coastal Waters of Sri Lanka

2026-05-04T21:55:00+02:00

The diatom Isthmia enervis Ehrenberg 1838, while known from other regions, has never been formally recorded in Sri Lanka. This study provides the first confirmed record of I. enervis from the coastal waters of Northern Sri Lanka, discovered during a seasonal survey from March to May 2023. Phytoplankton samples were collected at three locations using a standard conical plankton net (mouth diameter: 41 cm, mesh size: 55 µm). The collected samples were preserved with 1% acidified Lugol's solution for subsequent microscopic analysis. After a thorough microscopic analysis, occurrence of I. enervis found exclusively at two locations at different times, namely Akkarai (March) and Mathagal (April-May), proved that I. enervis was both geographically and temporally restricted. This restriction is likely due to local environmental conditions, including temperature, salinity, and nutrients during the post-monsoon period. Light microscopy revealed the distinctive morphology of I. enervis, including very large, heteropolar frustules forming short zig-zag chains, and confirmed a remarkable polymorphism with co-occurring rhomboidal and trapezoidal cells. The population density showed a consistent increase, from 2,800 cells/L in March to a peak of 3,860 cells/L in May. Its presence was correlated with key environmental shifts, including rising water temperature suggesting a niche-specific adaptation to the post-monsoon transitional period. The discovery of I. enervis bridges a critical knowledge gap in the regional biogeography of marine diatoms. Its restricted and seasonal occurrence underscores the importance of targeted sampling in understudied regions to establish a baseline for monitoring this species, which may serve as a valuable bio-indicator in the face of environmental change in Northern Sri Lankan coastal ecosystems.

First Record of Richelia intracellularis in Diatom-Diazotroph Association with Rhizosolenia spp. from Northern Coastal Waters of Sri Lanka: Ecological Implications and Water Quality Assessment

2026-05-07T21:30:12+02:00

Diatom-diazotroph associations (DDAs) are ecologically significant symbioses that enhance new nitrogen inputs in oligotrophic marine ecosystems, yet their presence in Sri Lankan coastal waters has remained unconfirmed. This study is the first morphological record of the heterocystous, nitrogen-fixing cyanobacterium Richelia intracellularis as an endosymbiont within two diatom hosts, Rhizosolenia hebetata and Rhizosolenia formosa from the northern waters of Sri Lanka. Phytoplankton and water quality samples were collected monthly during 2023 from Mathagal, Kankesanthurai, and Akkarai. Richelia trichomes (8-14 cells per filament) with terminal heterocysts were observed exclusively at Mathagal (May) and Akkarai (August) within the periplasmic space of host diatoms. Water quality parameters at DDA-positive sites showed nitrate concentrations ranging from 0.05 to 1.43 mgL⁻¹ and phosphate from 0.04 to 0.16 mgL⁻¹. Morphometric characteristics of the Sri Lankan specimens (heterocyst diameter: 9.8–10.6 μm; trichome length: 40-71 μm) align closely with those reported from other Indian Ocean populations. This first record extends the known biogeographical distribution of Richelia-diatom symbioses into Sri Lankan waters and highlights their potential contribution to nitrogen cycling in nutrient-limited coastal environments. These findings underscore the need for integrated taxonomic and molecular investigations of DDAs in the northern Indian Ocean.

Integrative morphometric analysis of Ompok pabo: conventional and truss approaches to support conservation of a critically endangered species in Bangladesh

2026-05-23T21:41:23+02:00

Small indigenous fish species are steadily declining in the rivers and oxbow lakes of Bangladesh. The abundance of Ompok pabo has been alarmingly reduced and is recognized as a critically endangered fish species in Bangladesh. The present study has been undertaken to determine the external phenotypic variations of O. pabo among the four populations, e.g., the Kopotakkho River, Madhumati River, Atrai River, and Bukvora oxbow lake (Baor). A total of 246 fish samples were collected during the monsoon season. A total of 11 conventional and 20 truss morphometric characters were used to assess their phenotypic variations. The univariate ANOVA, discriminant function analysis (DFA), and principal component analysis (PCA) were conducted. We observed significant differences (P <0.05) in 4 out of the 11 conventional and 14 out of the 20 truss morphometric characters across the four populations. In case of both morphometric and truss measurements, the first, second, and third discriminant function (DF) accounted for 77.02, 14.70, and 8.28% respectively in group variability, explaining 100% of the total group variability. A UPGMA dendrogram showed two separate clusters where the Atrai River solely formed a single cluster and the Kopotakkho River and Bukvora Baor combinedly formed another cluster. Additionally, the Madhumati River population formed a sub-cluster with Kopotakkho River. These observed phenotypical variations are most likely a result of unique ancestry. However, the observed phenotypic differentiation was not validated through experimental or molecular approaches, necessitating further investigation. The findings of the present study may provide baseline information for further marker-based population structure analysis and contribute to conservation programs.

Prevalence and factors associated with pathogenic bacterial infection in orange Mud crab, Scylla olivacea (Herbst, 1796) farms of Bangladesh

2026-07-08T12:44:40+02:00

Mud crab farming is one of the significant coastal aquaculture ventures in Bangladesh and in all over the world; but bacterial diseases frequently result in Mud crab mortality in farms. The present study aimed to assess prevalence of putative pathogenic bacteria, and other factors associated with bacterial infection in farms in different seasons. Crab, water, sediment and feed samples were collected from the farms randomly selected from four study points of varied salinity, and selective culture media plates, biochemical tests and RNA sequences were used for bacterial enumeration and identification. The Mud crab farms were infected with Vibrio, Aeromonas, and Pseudomonas bacteria; Vibrio parahaemolyticus, Aeromonas hydrophila and Pseudomonas aeruginosa were diagnosedin most of the samples. Vibrio spp. was detected in all unhealthy crabs while Aeromonas and Pseudomonas in more than 40% unhealthy crabs. The samples from the study point 1 had relatively higher prevalence of these bacterial species. The highest average load ofVibrio spp. (5.28±0.16 log₁₀ cfu g^-1) and Aeromonas spp. (4.36±0.25 log₁₀cfu g^-1) in Mud crabs was recorded in summer, while the highest concentration of Pseudomonas spp. (4.21±0.16 log₁₀cfu g^-1) in winter. Vibrio and Aeromonasconcentrations also differed significantly (p<0.05) between the study points for water, sediment and raw fish-based feed samples, and seasonal variation of Vibrio, Aeromonas and Pseudomonas loads were significant (p<0.05) for both water and feed samples. There was a significant correlation between Vibrio load in the Mud crabs and Vibrio load in the water samples, implying water being the critical source of Vibrio spp. infection in Mud crab farms; the association of feed with bacterial infections was also determined. Accordingly, this study suggests adopting good aquaculture practice (GAqP), specifically salinity-based farm selection, water treatment and quality feed utilization are to be maintained in Mud crab farming systems.