Effects of light intensities and photoperiods on growth and proteolytic activity in purple non-sulfur marine bacterium, <i>Afifella marina</i>strain ME (KC205142)

Afifella marina strain ME (KC205142), a purple non-sulfur bacterium was isolated from mangrove habitats of Sabah. The effects of light intensities and photoperiods on proteolytic activity in Afifella marina strain ME (KC205142) were investigated. Secretion of proteolytic enzymes in Afifella marina was preliminarily assessed by skim milk agarose media. Subsequently, light intensities, such as, dark, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500 and 5000 lux were used to evaluate the effects on proteolytic activity in Afifella marina strain ME under anaerobic condition. After that, the effect of photoperiods on proteolytic activity was monitored under anaerobic light condition (3000 lux) at 0 h (0L/24D), 6 h (6L/18D), 12 h (12L/12D), 18 h (18L/6D) and 24 h (24L/0D) of photoperiod. The highest proteolytic activity of 74.67 U was recorded at 3000 lux illumination light intensity. The proteolytic activity in bacterium Afifella marina strain ME was positively associated with the dry cell weight. The proteolytic activity of 72.67 U in bacterium Afifella marina strain ME at 18 h (18L/6D) photoperiod is not significantly different (p > 0.05) from proteolytic activity of 74.67 U recorded at continuous light (24L/0D) condition. Light intensity of 3000 lux, culture period of 48 h and a photoperiod of 18 h (18L/ 6D) were the optimum parameters for proteolytic activity in bacterium Afifella marina strain ME.

Occurrence and Distribution of Marsh Clam, <em>Polymesoda</em>spp. in Marudu Bay, Sabah, Malaysia

Marudu Bay is part of the Tun Mustapha Marine Park, the largest marine protected area within the Malaysian region of the Coral Triangle Initiative. The bay is known for its diversed fisheries resources including bivalves. Although some of these bivalve species are commercially important, their occurrence, distribution and stock status in the bay are not well documented. Hence, the current study was conducted to determine the occurrence, distribution and the stock status of marsh clam, Polymerasoda spp. in the mangrove swamp situated at the southernmost of the Marudu Bay. Samplings were carried out at the mangrove swamps which covered an area of 500 sequare meter per sampling site. Two marsh clams species, Polymesoda erosa and P. expansa were found to inhabit the sampling sites. In general, juvenile marsh clams were noticed to dominate the seaward mangrove swamp, whereas the high tidal regions were dominated by adults. The current study also suggested a link in the distribution and the morphometric measurements of the marsh clams with the sediment grain size.

Health Risk Assessment Due to Heavy Metals Exposure via Consumption of Bivalves Harvested from Marudu Bay, Malaysia

Concern over health risk from consumption of bivalves originating from Marudu Bay is escalating due to the rapid agricultural development surrounding the bay. This has motivated us to estimate the health risk index (HRI) of heavy metals from four commercially important and highly exploited bivalve species which are abundant in the bay. Samples (n = 30) of green mussel (Perna viridis), Asiatic hard clam (Meretrix meretrix), Pacific oyster (Crassosstrea gigas) and marsh clam (Polymesoda expans) were acquired from fishermen in Kg. Teritipan, Marudu Bay. These bivalves were analyzed for heavy metals content using the Inductively Couples Plasma-Optical Emission Spectroscopy (ICP-OES). The study found that the mean contents of Arsenic (As) and Manganese (Mn) in all analyzed bivalves exceeded the permissible limits as well as copper (Cu), lead (Pb) and zinc (Zn) in Pacific oyster, and Zn in marsh clam. It was also noticed that consumption of different bivalve species may bring about health risk from different metals as indicated by varied Total Hazard Index (THI) values. Consumption of the four bivalves was noticed to promote high health risk from As intoxication. Although metal pollution index (MPI) analysis revealed that the bivalves from the bay are currently not seriously impacted by heavy metal pollution, vigorous efforts should be taken to preserve the natural condition of the bay for years to come. There are several ways to minimize health issues from bivalve consumption which include keeping the bivalve natural habitat away from heavy metals pollution by strictly enforcing environmental laws and policies, establishing zones for bivalve fisheries, monitoring heavy metals concentration in bivalve on a regular basis and making depuration process a compulsory requirement in every seafood restaurant throughout the country.

A Review of Feeding Behavior, Growth, Reproduction and Aquaculture Site Selection for Green-Lipped Mussel, <i>Perna viridis</i>

Green-lipped mussel, Perna viridis is a warm water mussel species that is distributed widely in the Indo-Pacific regions. It is a commercially important species and has demonstrated a great culture potential in tropical countries. The feeding behavior of P. viridis is influenced by both seston concentration and its nutritional values. It is shown the mussels exhibit higher ingestion rate when the organic content of the seston is higher. Interestingly, several studies have reported that P. viridis can demonstrate selective feeding behavior towards phytoplankton. Short term studies have shown that the P. viridis exhibits preferentially ingestion of dinoflagellates, while long term studies show that the P. viridis has a higher growth rate during diatom blooms. Nevertheless, spawning of P. viridis is induced by high primary productivity at relatively high sea water temperature. In the temperate countries, spawning is seasonal but normally occurs in summer. In the tropical countries, however, the P. viridis has been shown to spawn all year-round with two peaks which coincide with monsoon seasons. The site selection is critically important when considering the green mussel culture. Feasibility study for P. viridis farming is normally carried out first in order to evaluate the environmental conditions of the site. This paper attempts to review the current knowledge of biology, selective feeding behaviour, growth, reproductive and the aquaculture site selection methods for green-lipped mussel.

Population dynamics and condition index of natural stock of blood cockle,Tegillarca granosa(Mollusca,Bivalvia,Arcidae)in the Marudu Bay,Malaysia

The population parameters of blood cockles,Tegillarca granosa in the intertidal zone of Marudu Bay,Sabah,Malaysia were investigated based on monthly length-weight frequency data(July 2017 to June 2018).A total of 279 cockle individuals with shell length and weight ranging from 27.7 mm to 82.2 mm and 13.11 g to 192.7 g were subjected to analysis.T.granosa in Marudu Bay showed a consistent moderately high condition index 4.98±0.86 throughout the year.The exponent b of the length-weight relationship was 2.6 demonstrating negative allometric growth.The estimated asymptotic length(L_(∞)),growth coefficient(K)and growth performance(Ф)of the T.granosa population in Marudu Bay were estimated at 86.68 mm,0.98 a^(-1) and 3.87,respectively.The observed maximum shell length was 82.55 mm and the predicted maximum shell length was 84.44 mm with estimated maximum life span(t_(max))of 3.06 years.The estimated mean lengths at the end of 2,4,6,8,10 and 12 months of age were 21.31 mm,31.16 mm,39.53 mm,46.63 mm,52.67 mm and 57.79 mm.Total,natural,and fishing mortalities were estimated at 2.39 a^(-1),1.32 a^(-1) and 1.07 a^(-1).The exploitation level(E)was 0.45.Results of the current study also demonstrated that T.granosa in the Marudu Bay has two major recruitment peaks;one in March and another in October.The exploitation level revealed that natural stock of T.granosa in the Marudu Bay was approaching the maximum exploitation level.If such trend continues or demand for T.granosa is increasing,coupled with no effective fisheries management in place,possibility of the T.granosa population in the Marudu Bay to collapse is likely to elevate.

Assessment of Spatial and Temporal Variations of Water Quality for Future Mariculture Operation in Ambong Bay, Sabah, Malaysia

Study was conducted with the aim to understand the temporal and spatial variations of water quality parameters (temperature, salinity, pH, DO, TSS, NO3-, NO2-, NH3-N and PO4-P, and phytoplankton cell density) in Ambong Bay, Sabah, Malaysia in order to provide reference for future mariculture development in the bay. Samplings were carried out once a month in two stations (coastal and open sea) within the bay for 12 months period from September 2015 to August 2016. Results showed that there were significant differences in pH and NO2- when compared spatially, whereas salinity, DO, TSS, phytoplankton cell density, NO3-, NH3-N, and PO4-P were temporally significant. The fermentation processes by anaerobic bacteria, organic acids from decaying vegetation and acidic clays in the mangrove soils might explain the significant spatial differences in pH and NO2-. The bay was dominated by dinoflagellate, Prorocentrum spp. (mean abundance of 16.23% and 24.44%, respectively) a potentially toxic algae species. Correlation matrix showed that NH3-N was positively correlated with PO4-P (r = 0.475, p < 0.05) but negatively correlated with salinity (r = –0.517, p < 0.01). Besides, salinity was positively correlated with DO (r = 0.505, p < 0.05) and TSS (r = 0.408, p < 0.05). In addition, DO and TSS were also positively correlated (r = 0.451, p < 0.05). Phytoplankton cell density was positively correlated with TSS (r = 0.644, p < 0.01). In general, the water quality in Ambong Bay is within the standard values permitted by the Malaysia Marine Water Quality standard for marine life, fisheries, coral reefs, recreational and mariculture (Class 2), except for NO3-. In conclusion, any mariculture operation to take place in Ambong Bay in the near future should take the temporal variation of the water quality into account. Moreover, effects of toxic phytoplankton to culture fishes should also be taken care and monitored frequently.

Population dynamics of the tropical oyster Magallana bilineata(Mollusca,Bivalvia,Ostreidae)in Mengkabong Bay,Tuaran,Malaysia

Knowledge about the population dynamics within a specific spatial area is vital for the effective planning and management of important fishery resources.Population parameters,including the asymptotic length(L∞),growth coefficient(K),mortalities(Z,F,and M),recruitment pattern,exploitation level(E),and yield per recruit(Y’/R),of the tropical oyster Magallana bilineata in Mengkabong Bay,Tuaran,Malaysia were analyzed by using the FiSAT software,using on the monthly shell length-frequency data collected from April 2019 to March 2020.A total of 435 oysters with shell lengths ranging from 3.64 to 11.16 cm were analyzed.Habitat water temperature,salinity,dissolved oxygen,hydrogen ion concentration(pH),and chlorophyll concentration were measured at 29.0-33.7◦C,26.68-35.74 psμ,3.18-6.99 mg/L,6.57-8.29 and 1.51-98.93μg/L,respectively.The logarithmic relationship between the length and weight of Log W=1.9055 Log L+0.1049(R2=0.5431)with exponent b of 1.9055 for combined sexes showed a negative allometric growth(b<3),indicating that the oysters in Mengkabong Bay are skinny.Several management measures have been proposed to promote high meat growth,including the use of genetically selected seeds,selection of new farming sites and adoption of grow-out methods that favour high meat growth.Asymptotic length(L∞)and growth coefficient(K)of the von Bertalanffy Growth Formula(VBGF)for M.bilineata were estimated at 12.13 cm and 1.00 yr1,respectively.The theoretical ages at length zero(t0)(0.0487)were estimated by substituting L∞and K in Pauly’s equation.The sizes attained by M.bilineata were 3.76,5.04,6.13,7.05,7.83,and 8.49 cm at the end of 2,4,6,8,10,and 12 months,respectively.The calculated growth performance index(φ)for M.bilineata in Mengkabong Bay was 2.168,while the estimated lifespan was 3 years.The recruitment pattern was observed year-round,with higher recruitment activities in September-October 2019 and January 2020.The total mortality(Z)was analyzed using the length-converted catch curve and estimated at 3.04 yr^(-1),fishing mortality(F)at 0.63 yr^(-1),and natural mortality(M)at 2.41 yr^(-1).The lower exploitation rate(0.21)compared to the recommended 0.5 and Beverton and Holt’s estimated maximum allowable limit of exploitation rate(Emax)of 0.587 indicated that the M.bilineata stock in Mengkabong Bay was under-exploited.Several recommendations that could aid in the development of M.bilineata in Mengkabong Bay include promoting local oysters through collaboration with leading hotels and restaurants,developing food processing technology for downstream products,and establishing a sanitation programme that includes monitoring and enforcing sanitary conditions in the culture,harvest and processing sectors.