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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.

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 (

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]