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Magallana bilineata is a commercially important oyster species in Malaysia. Despite its economic significance, the biology and ecology of this species, particularly its reproductive cycle, are poorly understood in the region. Therefore, this study aimed to investigate the reproductive cycle of M. bilineata in Mengkabong Bay, Tuaran, Sabah and its correlation with environmental factors. A total of 105 oyster specimens were collected and examined to determine the sex ratio, gonad developmental stages, maturity index (MI), and condition index (CI). The results revealed a sex ratio of 1:2.36 (♂:♀) in the oyster population of the bay, with a significantly higher proportion of females (P < 0.05). Hermaphroditism was detected in 1.90% of the samples. M. bilineata was found to spawn throughout most months in the bay, with the highest MI and CI values recorded in November 2019 when most oysters were in mature or maturing stages. Salinity was found to be the primary factor influencing male gonad maturation, while temperature was the primary factor influencing female gonad maturation. Understanding the reproductive biology of this species is crucial for predicting its future survival and facilitating assisted spawning and hatchery spat production, thereby ensuring the conservation and sustainability of the oyster fishery in Malaysia.

Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) have many health benefits to human. Increasing evidence have shown that climate change reduces the availability of plankton n-3 LC-PUFA to primary consumers which potentially reduces the availability of n-3 LC-PUFA to human. Since marine bivalves are an important source of n-3 LC-PUFA for human beings, and bivalve aquaculture completely depends on phytoplankton in ambient water as food, it is important to understand the impact of climate change on the lipid nutritional quality of bivalves. In this study, fatty acid profile of different bivalves (mussels, oysters, clams, scallops and cockles) from different regions (tropical, subtropical and temperate) and time (before 1990, 1991–1995, 1996–2000, 2001–2005, 2006–2010, 2011–2015, 2016–2020) were extracted from published literature to calculate various lipid nutritional quality indicators. The results of this study revealed that the effects of global warming and declines in aragonite saturation state on the lipid content and lipid indices of bivalves are highly dependent on the geographical region and bivalves. In general, global warming has the largest negative impact on the lipid content and indices of temperate bivalves, including decreasing the PUFA/SFA, EPA + DHA and n-3/n-6. However, global warming has a much smaller negative impact on lipid content and lipid indices in other regions. The declines of aragonite saturation state in seawater promotes the accumulation of lipid content in tropical and subtropical bivalves, but it compromised the PUFA/SFA, EPA + DHA and n-3/n-6 of bivalves in all regions. The findings of this study not only fill the knowledge gap of the impact of climate change on the lipid nutritional quality of bivalves, but also provide guidance for the establishment of bivalve aquaculture and fisheries management plans to mitigate the impact of climate change. [ABSTRACT FROM AUTHOR]

Exploring the length-weight relationship of fish and characterising growth parameters is essential in fisheries as they offer fundamental biology and population dynamics data to establish good management strategies for fisheries resources. This study examines the growth and mortality patterns of Oreochromis mossambicus. Data was collected between September and December 2022 using quantitative descriptive survey sampling. The study involved 20 repeats and deliberate random sampling of 30-50 fish per sample, emphasising total length, weight, and sex parameters. Based on 726 samples of O. mossambicus (352 fish identified as male and 374 fish identified as female). The growth model study revealed the typical negative allometric growth for both sexes (male and female). Male individuals attained a length of 33.449 cm after 37 days has a growth trend ± 0.3265 year-1, and females reached 21.150 cm in 34 days with a growth rate around 0.3135 year-1, as per the von Bertalanffy growth model. There were complex mortality patterns, with males contributing to most total deaths. This study emphasizes the complex biology of tilapia and its untapped potential in the aquaculture pond system ecology in Tarakan. [ABSTRACT FROM AUTHOR]

Asian green mussel is commercially farmed in tidal waters in several enclosed bays in Sabah, Malaysia. In this study, two areas on the west coast of Sabah – Ambong Bay and Marudu Bay – were selected for the monitoring of the growth and mortality rates of green mussels farmed in suspension raft. Both growth and survival rates were then correlated with physicochemical parameters (dissolved oxygen, pH, salinity, temperature, water transparency, chlorophyll-a), nutrients (phosphate (PO43-), ammonia (NH3-N), nitrate (NO3-N) and nitrite (NO2-N) and condition index of mussel from each study site, as well as between the study sites. The twelve-month growth study (September 2017 to August 2018) was started with a total of 180 mussel specimens (90 at each site). The initial size (mean) of the mussel seed used was 47.7 ± 3.5 mm and 51.1 ± 3.9 mm for Marudu Bay and Ambong Bay, respectively. Mussels in Marudu Bay attained mean size of 73.47 ± 11.05 mm (SGR 0.17% ± 0.22) compared to 64.05 ± 7.44 mm (SGR 0.11% ± 0.22) for Ambong Bay at the end of the experiment. The cumulative mortality rates were 9.2% ± 4.9 and 55.5% ± 30.0 for Marudu Bay and Ambong Bay, respectively. The Pearson correlation indicated a significant positive relationship between mortality and water transparency (r = 0.684, p

Bivalve aquaculture accounts for 14%-16% of the average per capita animal protein of 1.5 billion people, supporting more than 200,000 livelihoods, mostly in developing countries. Massive mortality outbreaks of various cultured bivalves have been reported worldwide. Repeated episodes of mass mortality not only reduce the production and cause high economic losses but also have a negative impact on natural bivalve populations. The present article reviews the scientific evidence of mass mortality outbreaks of marine bivalve molluscs affected by extrinsic factors. It attempts to summarize the pertinent data published on specific research issues to improve understanding of the diverse factors. This helps to clarify the present state of research and to identify topics for future studies on bivalve mass mortality. It can be seen from the published data that bivalve mass mortality episodes are rarely caused by single factors but are more likely to be triggered by synergistic effects of two or more factors. Understanding these factors could aid in the development of good aquaculture practices and effective fishery management plans for bivalves. KEY WORDS: marine bivalve, mass mortality, extrinsic factors, review, INTRODUCTION Molluscan aquaculture in general and bivalve farming in particular have brought significant social and economic benefits to coastal communities. Bivalve aquaculture accounts for 14%-16% of the average per capita [...]

Aims: Vibrio harveyi is a serious pathogen for marine organisms particularly in hatcheries and grow-out ponds that attack their immune system. The rapid detection of V. harveyi is urgently needed to prevent bacterial spread. Here we described a rapid and specific visual detection method based on the Loop-Mediated Isothermal Amplification in combination with Lateral Flow Dipstick (LAMP-LFD). Methodology and results: A set of six novel primers were designed to target the toxR gene. These include the biotinlabelled inner primer that complements specifically to the target sequences. The resulting biotinylated LAMP amplicons were hybridised to the FAM-labelled probe resulting in lateral flow detection on the dipstick. The addition of loop primers improved the reaction time of LAMP by more than half and rapid detection was observed within 10-15 min. In comparison, the sensitivity of PCR-UV analysis was only at 104 copies while LAMP-LFD was able to detect lower amounts at 103 copies. The LFD provided higher specificity and selectivity since hybridization with specific probes to the LAMP amplicons was employed. In addition, detection of V. harveyi infected grouper was successful using the LAMPLFD method described here. Conclusion, significance and impact of study: LAMP-LFD is specific to V. harveyi. Our method provides a useful tool to rapidly detect and monitor the outbreaks of the pathogen. [ABSTRACT FROM AUTHOR]

The hard clam (Meretrix meretrix) is a popular edible shellfish in South and Southeast Asia, being heavily exploited by hand dredging in Marudu Bay, Malaysia. The current study was performed to evaluate the shell damages caused by this artisanal dredging gear. Samplings were conducted in triplicates at two sites using both hand dredging and hand collecting (control) sampling methods. The shell length and total weight, damage areas and breakage patterns of each clam were recorded. A questionnaire survey was conducted with local bivalve harvesters to gather information on the fishing pressure in Marudu Bay. Results revealed that the efficiency (fishing yield) of hand dredging gear was three times higher than hand collecting. However, hand dredging gear causes lethal shell damages to small hard clams (

The common methods that are presently used to identify Vibrio harveyi include microscopic examination and biochemical, immunological and PCR-based assays. These methods require technical expertise, and can be time-consuming. A rapid method is required for the high-throughput screening of large number of samples. As such, we have developed a rapid, simple yet sensitive and specific detection method based on the use of the loop-mediated isothermal amplification (LAMP) of DNA. A set of six primers, i.e., two outer, two inner and two loop primers, was designed based on the in silico analysis of a large pool of 39 strains of the toxR gene sequence of V. harveyi. The addition of the loop primers decreased the reaction time of the LAMP by more than half. Furthermore, with the application of SYBR Green, the result can be obtained as quickly as in 10 to 15 min without the need of gel electrophoresis. The specificity of the method primers was then determined by performing LAMP with Vibrio and non-Vibrio samples. LAMP has a greater sensitivity than PCR reaction. The sensitivity of PCR was at 0.6 pg concentration of V. harveyi recombinant plasmid DNA standard, while LAMP was able to detect lower amounts even at 0.6 fg. The development of the LAMP assay will provide a valuable tool for the high-throughput rapid detection of V. harveyi contamination both in laboratories and in the field. [ABSTRACT FROM AUTHOR]

The aquaculture of tropical oysters is a valuable prospective seafood industry. The extremely rapid growth rates of tropical oysters make them attractive to aquaculture candidates. Hence, fundamental knowledge of the biology, life cycle, reproduction and factors affecting recruitment is essential for the successful aquaculture development of these species. This paper attempted to provide an overview of the current knowledge of early embryonic and larval development, and the factors affecting the sex determination, gametogenesis, settlement, and the recruitment success of tropical oysters, as well as the effects of climate change on the recruitment success. Closed culture, stock restocking, stock enhancement, and sea ranching are among the efforts that can be implemented to boost the recruitment success of these valuable species. [ABSTRACT FROM AUTHOR]

Hard clam, Meretrix meretrix is the principal bivalve resource collected by artisanal fishermen in the coastal areas of Marudu Bay, Malaysia. Population parameters of the clam in the intertidal zone of Marudu Bay, Sabah were analyzed using FiSAT software, based on monthly length and weight data collected from May 2017 to April 2018. A total of 1,745 clams with shell lengths ranging from 18.3 to 101.7 mm were analyzed. Asymptotic length (L∞) and growth coefficient (K) of the von Bertalanffy growth formula (VBGF) for M. meretrix were estimated at 107.63 mm and 0.47 year-1, respectively. The estimated growth performance index (ϕ) was 3.736. The theoretical age at length zero (t0) was -0.1412. The predicted maximum life span of the clam was 6.38 years. The sampled population of M. meretrix exhibited consistent and moderate fatness (3.88±0.84) throughout the year. The total mortality (Z) was estimated at 2.65 year-1, fishing mortality (F) at 1.87 year-1, and natural mortality (M) at 0.78 year-1. The exploitation level (E) of the M. meretrix population was 0.70, while the maximum allowable limit of exploitation (Emax) was 0.499 for the highest yield. This study clearly indicates that the M. meretrix stock in Marudu Bay experiences over-exploitation that warrants immediate action by the fisheries management authority. [ABSTRACT FROM AUTHOR]

The mangrove clam, Polymesoda erosa is among the commercially important bivalve species in Marudu Bay, Malaysia. However, a recent study has shown that this species experiences a high level of fishing exploitation. To sustain this species, one potential strategy is to restock hatchery-produced seeds through sea ranching. However, this requires the successful artificial production of seeds, which currently has not been achieved. The present study was conducted to determine the sex ratio and maturity level of different shell length classes of the clam to guide the selection of broodstock for artificial propagation in the future. A total of 240 mangrove clam specimens were randomly collected from the mangrove swamps in Marudu Bay and sorted into four shell length classes: 5.50-6.49 cm, 6.50-7.49 cm, 7.50-8.49 cm and 8.5-9.49 cm. The clams were subjected to gonad histological examination and condition analysis. Results showed that the natural stock of clams exhibited close to a 1:1 male-to-female sex ratio with no hermaphroditism observed. Clams within the 5.50-8.49 cm shell length classes had high gonad index, indicating that most of the clams at this size are fully mature. Statistical analysis revealed a significant difference (p = 0.027) in condition index between two shell length classes: 5.50-6.49 cm and 7.50-8.49 cm. This could be attributed to differences in energy utilization; young clams utilize more energy for growth, whereas adult clams utilize energy for growth, reproduction, and metabolic maintenance. This study suggests that using mangrove clams with shell length between 5.50 cm and 8.49 cm will likely result in high spawning success in an artificial breeding program. [ABSTRACT FROM AUTHOR]

Abstract: The region of northern Borneo is home to the current state of Sabah, Malaysia. It is located closest to the southern Philippine islands and may have served as a viaduct for ancient human migration onto or off of Borneo Island. In this study, five indigenous ethnic groups from Sabah were subjected to genome‐wide SNP genotyping. These individuals represent the “North Borneo”‐speaking group of the great Austronesian family. They have traditionally resided in the inland region of Sabah. The dataset was merged with public datasets, and the genetic relatedness of these groups to neighboring populations from the islands of Southeast Asia, mainland Southeast Asia and southern China was inferred. Genetic structure analysis revealed that these groups formed a genetic cluster that was independent of the clusters of neighboring populations. Additionally, these groups exhibited near‐absolute proportions of a genetic component that is also common among Austronesians from Taiwan and the Philippines. They showed no genetic admixture with Austro‐Melanesian populations. Furthermore, phylogenetic analysis showed that they are closely related to non–Austro‐Melansian Filipinos as well as to Taiwan natives but are distantly related to populations from mainland Southeast Asia. Relatively lower heterozygosity and higher pairwise genetic differentiation index (FST) values than those of nearby populations indicate that these groups might have experienced genetic drift in the past, resulting in their differentiation from other Austronesians. Subsequent formal testing suggested that these populations have received no gene flow from neighboring populations. Taken together, these results imply that the indigenous ethnic groups of northern Borneo shared a common ancestor with Taiwan natives and non–Austro‐Melanesian Filipinos and then isolated themselves on the inland of Sabah. This isolation presumably led to no admixture with other populations, and these individuals therefore underwent strong genetic differentiation. This report contributes to addressing the paucity of genetic data on representatives from this strategic region of ancient human migration event(s). [ABSTRACT FROM AUTHOR]

The green mussel, Perna viridis is known to have the ability to selectively ingest certain suspended particles from water. However, the preferential ingestion of specific phytoplankton taxa by P. viridis under different environmental conditions is not well understood. A study was undertaken to identify the phytoplankton taxa that are preferentially ingested and rejected by P. viridis in different environmental conditions at Marudu Bay, Malaysia. Phytoplankton abundance and composition in stomach and surrounding waters were determined microscopically. The gonad development stages of P. viridis and various environmental parameters of the bay including temperature, salinity, dissolved oxygen, current speed, pH, visibility, chlorophyll a, nutrients concentration and suspended particles were also determined. Results of current study demonstrated that selective ingestion in P. viridis was mainly influenced by seston concentration, phytoplankton abundance and composition. At high seston concentration with low phytoplankton abundance, P. viridis selectively ingested Coscinodiscus spp. In contrast, P. viridis was found to ingest wider range of phytoplankton at low seston concentration and high phytoplankton abundance. Interestingly, Chaetoceros spp. and Bacteriastrum spp. were selectively rejected by P. viridis in both high and low seston conditions. Nevertheless, no selective ingestion behaviour was evidenced in low seston with low phytoplankton conditions. Besides phytoplankton, zooplankton has also contributed significantly in the diet of P. viridis, where high numbers of copepod and bivalve larvae were found in the stomach. The findings of current study can be useful in determining potential farming sites for green mussel in future. [ABSTRACT FROM AUTHOR]

The current study was conducted to estimate the baseline concentration of heavy metals in the surface sediment of Marudu Bay. Environmental parameters were measured at the seafloor and samples of the surface sediment were collected at monthly intervals for the period of 12 months. The organic content, total N, total P and concentration of 16 trace metals in the surface sediment were analyzed. The baseline concentration of metals was estimated by geochemical normalization. Anthropogenic inputs of metals were then estimated by calculating the enrichment factor for each element. The result demonstrated that the C/N ratio of sediment at Marudu Bay varies from 15 to 342, which indicates the dominance of terrestrial organic matter. The baseline concentration of V, Fe, Mn, Zn, Ti, Rb and Sr were 26.74 mg kg-1, 1.04%, 205.31 mg kg-1, 34.09 mg kg-1, 507.61 mg kg-1, 93.25 mg kg-1, 37.56 mg kg-1, respectively. The concentration of most metals was comparable to the baseline, except Mn and Zn which showed higher concentrations in most parts of Marudu Bay. In conclusion, the metal concentration in Marudu Bay is still within the permissible levels and should not cause any threats to public health. [ABSTRACT FROM AUTHOR]

Vibrio parahaemolyticus has long been known pathogenic to shrimp but only recently it is also reported pathogenic to tropical cultured marine finfish. Traditionally, bacterial diseases in aquaculture are often treated using synthetic antibiotics but concern due to side effects of these chemicals is elevating hence, new control strategies which are both environmental and consumer friendly, are urgently needed. One promising control strategy is the bacteriophage therapy. In this study, we report the isolation and characterization of a novel vibriophage (VpKK5), belonging to the family Siphoviridae that was specific and capable of complete lysing the fish pathogenic strain of V. parahaemolyticus. The VpKK5 exhibited short eclipse and latent periods of 24 and 36 min, respectively, but with a large burst size of 180 pfu/cell. The genome analysis revealed that the VpKK5 is a novel bacteriophage with the estimated genome size of 56,637 bp and has 53.1% G + C content. The vibriophage has about 80 predicted open reading frames consisted of 37 complete coding sequences which did not match to any protein databases. The analysis also found no lysogeny and virulence genes in the genome of VpKK5. With such genome features, we suspected the vibriophage is novel and could be explored for phage therapy against fish pathogenic strains of V. parahaemolyticus in the near future. [ABSTRACT FROM AUTHOR]

An outbreak of the fish-ectoparasitic marine isopod Caecognathia coralliophila (Monod, 1926)occurred in a fish hatchery in Sabah on Borneo Island, Malaysia. Larval stages of gnathiid isopods are parasitic on fish whereas their adult stages are free-living. The original description of C. coralliophila (Monod, 1926) was based on the morphology of one adult male from Thailand, and no description of the adult female or larva has been published to date. We compared the holotype of C. coralliophila and redescribed adult males and adult females as well as third-stage larvae from the fish hatchery. This paper provides a redescription of C. coralliophila based on all phases of the life history. Caecognathia coralliophila is distinguished from congeners by having reduced setae on the distal margins of the pleopodal endopods in adult males, biarticulate pylopods and the setae on the pleopodal rami being reduced in adult females, and antenna much longer than antennule in third-stage larvae. [ABSTRACT FROM AUTHOR]

The article reports on the factors that affect the biotransformation, toxicity and detoxification of paralytic shellfish toxins. These involve environmental parameters and eutrophication. It mentions the escalation of red tide events in the world wherein the occurrence of high algal cell density. An overview of its bioassay and chemical assay methods is also presented.

Abstract: In the present study we report the experimental evidence of horizontal transmission of betanodavirus in hatchery-produced Asian seabass (Lates calcarifer) and brown-marbled grouper (Epinephelus fuscogutattus) fingerling. The experiment was conducted by incubating fish fingerlings in aerated sterile natural seawater inoculated with tissue homogenate of betanodavirus infected fish fingerling at 28°C for 30min and after which they are transferred into the aquarium. Dead fish were collected daily for 10days and subjected to RT-PCR and histological examinations. The cDNA of coat protein gene of betanodavirus from positive fish specimens were subjected to RFLP-PCR and DNA sequencing analyses. The result showed high fish mortality in treatment than in the control experiment. The RT-PCR and histological analyses showed all fish specimens in treatment groups except for D2 and E2 were successfully infected with Betanodavirus. In contrast, all fish specimens in control groups remained uninfected. The result of the present study indicate that mixing of fish fingerlings obtained from different sources and the use of surplus fish eggs for feeding supplement can potentially promote the horizontal transmission of Betanodavirus in hatchery. This can threaten the sustainability of aquaculture industry in Malaysia. [Copyright &y& Elsevier]

Density, recruitment and growth performance of Asian green mussel (Perna viridis) in a particular coastal marine environment can be affected by many factors, including environmental change, pollution, disease outbreak and massive mortality event. The present study was conducted to determine the density, recruitment and growth performance of farmed Asian green mussel in Marudu Bay, three years after a mass mortality event. The study was carried out for 12 months between April 2013 and March 2014. The length frequency data of 1,308 individuals of green mussel were analyzed using the latest version of the FAO-ICLARM Fish Stock Assessment Tools (FiSAT II). The result showed that the green mussel recruitment in Marudu Bay occurs throughout the year with two major peaks i.e. February and July which coincided with the monsoon seasons. The asymptotic length (L∞), growth coefficient (K) and growth performance index (φ) of the farmed Asian green mussel in Marudu Bay are relatively high at 113.4 mm, 1.7 year-1 and 4.34, respectively. However, despite good culture location, the settlement density of green mussel in the bay was low. We suspected that the low settlement density could be influenced by the ecological effects due to the long term suspension of the culture substrates and the physiochemical properties of the water in Marudu Bay. Nevertheless, chlorophyll-á measurement alone was not able to justify if food scarcity has resulted in high mortality of the farmed Asian green mussel in Marudu Bay. [ABSTRACT FROM AUTHOR]

Mud crabs genus Scylla are distributed across the Indo-West Pacific Oceans. Among the four species, S. tranquebarica dominates the mangrove areas in Sabah, Malaysia and constitutes the primary crustacean fishery resource. Overexploitation of this economically important fisheries resource can have a significant impact on population diversity. This study was conducted to evaluate the genetic diversity of S. tranquebarica from five important fishing grounds. The genetic diversity was estimated based on the cytochrome c oxidase (COI) gene sequence. A total of 143 individuals were sampled across the 5 fishing grounds. The findings revealed that the crabs in Sabah comprised 11 haplotypes with a mean haplotype diversity (h) of 0.5564 and a mean nucleotide diversity (π) of 0.0038. The molecular variance analysis (AMOVA) showed that the low genetic differentiation among crab individuals in the five fishing grounds. The low genetic diversity provides the basis for the establishment of a scientific breeding program to counteract the loss of genetic diversity which is the result of overexploitation of this ecologically and economically important fisheries resource. [ABSTRACT FROM AUTHOR]

Fin whales are a cosmopolitan species found in the largest water masses of the world. In Malaysia, as well as other tropical countries in the Southeast Asian region, literature on fin whales is limited, and as a result, there is confusion regarding their distribution range in the region. This study utilizes the fresh tissue of the skin and blubber of a dead fin whale that was stranded in Sabah (Borneo, Malaysia) on the coast of the South China Sea to confirm the species identity, possible properties of the species' diet, and any trace element contamination. The DNA profile results confirmed that the whale belonged to Balaenoptera physalus . Further investigation of its cytochrome b gene sequence indicated that it was closely related to the southern fin whale ( Balaenoptera physalus quoyi ). This finding indicates that fin whales indeed migrate to warm tropical waters and that their continuous global distribution spans the equatorial region. The dominant fatty acids, such as C18:0, C16:1, C18:1N9T and C16:0 profiles, were consistent with the pelagic plankton diet that the whale would have had during its migration in the tropical waters of the South China Sea. The whales are likely pelagic feeders and thus need to be offshore, which would explain why they are rarely seen in shallow coastal areas during migration in these waters. The concentrations of K, Ca, Sc, Mg and Al ranged from 0.45 μg g -1 to 7.80 μg g -1 , while Cr, Cd, As and Pb were either very low or could not be detected. This is consistent with concentrations of trace elements previously reported for other baleen whale genera from the Southern Ocean. Our study demonstrates the importance of the South China Sea as a migration route for the southern fin whale, since it is a rich food source with relatively low contaminant levels. The South China Sea is therefore well-suited to ensure these whales' survival during migration.

This paper describes the complete sequence of a giant lytic marine myophage, Vibrio phage ValKK3 that is specific to Vibrio alginolyticus ATCC(®) 17749™. Vibrio phage ValKK3 was subjected to whole genome sequencing on MiSeq sequencing platform and annotated using Blast2Go. The complete sequence of ValKK3 genome was deposited in DBBJ/EMBL/GenBank under accession number KP671755.

This paper describes the complete sequence of a novel lytic marine siphophage, VpKK5, that is specific to Vibrio parahemolyticus., (Copyright © 2015 Lal and Ransangan.)

This study determined the effect of light intensity and photoperiod on the dry cell weight and total amount of carotenoids in four isolates of purple non-sulfur bacteria obtained from shaded and exposed microhabitats of a mangrove ecosystem in Kota Kinabalu, Sabah, Malaysia. The initial isolation of the bacteria was carried out using synthetic 112 medium under anaerobic conditions (2.5 klx) at 30 ± 2°C. On the basis of colony appearance, cell morphology, gram staining, motility test, and 16S rRNA gene sequencing analyses, all four bacteria were identified as Afifella marina. One of the bacterial isolates, designated as Af. marina strain ME, which was extracted from an exposed mud habitat within the mangrove ecosystem, showed the highest yield in dry cell weight (4.32± 0.03 g/l) as well as total carotenoids (0.783 ± 0.002 mg/g dry cell weight). These values were significantly higher than those for dry cell weight (3.77 ± 0.02g/l ) and total carotenoid content (0.706 ± 0.008 mg/g) produced by the isolates from shaded habitats. Further analysis of the effect of 10 levels of light intensity on the growth characteristics of Af. marina strain ME showed that the optimum production of dry cell weight and total carotenoids was achieved at different light intensities and incubation periods. The bacterium produced the highest dry cell weight of 4.98 g/l at 3 klx in 72 h incubation, but the carotenoid production of 0.783 mg/g was achieved at 2.5 klx in 48 h incubation. Subsequent analysis of the effect of photoperiod on the production of dry cell weight and total carotenoids at optimum light intensities (3 and 2.5 klx, respectively) revealed that 18 and 24 h were the optimum photoperiods for the production of dry cell weight and total carotenoids, respectively. The unique growth characteristics of the Af. marina strain ME can be exploited for biotechnology applications.

The grow out of Asian seabass Lates calcarifer in marine net-cages is a popular aquaculture activity in Malaysia. Production of this species is greatly affected by the occurrence of vibriosis, which causes heavy mortality. Generally, young fish are more susceptible; they exhibit anorexia and skin darkening, followed by heavy mortality. The acutely affected older fish may also exhibit bloody lesions around the anus and the base of the fins. Twenty-one bacterial isolates obtained from internal organs (kidney, heart, spleen and liver) of the affected specimens were subjected to phenotypic characterization, testing for antibiotic susceptibility, and 16S ribosomal DNA sequencing. The sequencing result showed that all of the bacterial isolates belonged to Vibrio harveyi. The phenotypic characterization, however, identified 4 of the bacterial isolates as V. harveyi, 16 as V. parahaemolyticus, and 1 as V. alginolyticus. These findings suggest that biochemical features alone cannot be reliably used to identify bacterial pathogens, including V. harveyi, in aquaculture. Antibiotic susceptibility assays showed that some antibiotics, including oxytetracycline, nitrofurantoin, furazolidone, streptomycin, sulfamethoxazole, chloramphenicol, nalidixic acid, and oxolinic acid were effective against V. harveyi. Considering the side effects of these antibiotics, however, their use is not recommended in the aquaculture of Asian seabass.