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Magallana bilineatais 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. bilineatain 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. bilineatawas 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<0.01). There was a significant negative relationship between ammonia in seawater and mussel mortality (r = -0.561, p<0.01), as well as significant negative relationships between nitrate and growth (r = -0.480, p<0.05) and mortality (r = -0.460, p<0.05), as indicated by Spearman’s Rank-order Correlation analysis. Overall, the growth performance of green mussels farmed in Marudu Bay was better than in Ambong Bay, however, the mortality of mussels in Ambong Bay was higher.

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. [ABSTRACT FROM AUTHOR]

The causative agent responsible for vibriosis in tropical fish aquaculture, Vibrio harveyi, has become a major bacterial pathogen. Studies suggest that this bacterium has developed resistance to antibiotics commonly used in aquaculture. In view of this situation and the requirement for the proposed postantibiotic era, bacteriophage therapy seems to be a promising control strategy for fish vibriosis. In this study, a lytic Vibriophage VhKM4 belonging to a member of large, marine Myoviridae was successfully isolated. It exhibited bacteriolysis to both V. harveyiVHJR7 and V. parahaemolyticusATCC 17802. The latent period of the VhKM4 phage was recorded at 60 min. It also recorded average burst size of approximately 52 plaque-forming units per infected cell. A strong bacteriolytic activity at low multiplicity of infection of 0.01 indicates the effectiveness of this large marine myovirid against fish pathogenic strain of V. harveyiVHJR7. Received June 16, 2016; accepted October 7, 2016 Published online February 6, 2017

AbstractThe causative agent responsible for vibriosis in tropical fish aquaculture, Vibrio harveyi, has become a major bacterial pathogen. Studies suggest that this bacterium has developed resistance to antibiotics commonly used in aquaculture. In view of this situation and the requirement for the proposed postantibiotic era, bacteriophage therapy seems to be a promising control strategy for fish vibriosis. In this study, a lytic Vibriophage VhKM4 belonging to a member of large, marine Myoviridae was successfully isolated. It exhibited bacteriolysis to both V. harveyiVHJR7 and V. parahaemolyticusATCC 17802. The latent period of the VhKM4 phage was recorded at 60 min. It also recorded average burst size of approximately 52 plaque-forming units per infected cell. A strong bacteriolytic activity at low multiplicity of infection of 0.01 indicates the effectiveness of this large marine myovirid against fish pathogenic strain of V. harveyiVHJR7.Received June 16, 2016; accepted October 7, 2016 Published online February 6, 2017

•Environment variables, food abundance and composition are important criteria in selecting cultivation site for bivalves, particularly green mussel.•The Bay pocket of Marudu Bay is no longer suitable for green mussel cultivation at commercial scale.•Northeast coast of the bay showing a more promising environment for green mussel cultivation.

The grow out of Asian seabass Lates calcariferin 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.

AbstractThe grow out of Asian seabass Lates calcariferin 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.

This paper describes the complete sequence of a giant lytic marine myophage, Vibrio phage ValKK3 that is specific to Vibrio alginolyticusATCC®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.