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A fish kill incident was reported at the marine fish culture areas north of Perak and south of Penang, Malaysia, on 26 May 2020. An investigation was carried out at 10 stations in Kerian, Perak and Seberang Perai Selatan, Penang. Seawater samples were collected to identify microalgae species and determination of dissolved inorganic nutrients. The physical parameters of water such as salinity, pH, temperature and dissolved oxygen were measured in situ while the dissolved inorganic nutrients were analysed spectrophotometrically. The dominant microalga was identified as Margalefidinium fulvescens (Iwataki, Kawami & Matsuoka) Gómez, Richlen & Anderson, 2017, based on the morphological and molecular characterisation of the large subunit ribosomal gene. Long rounded and ellipsoidal cells, 30-43 µm in length, appeared in chains of single, two, four or eight cells. The sulcus was slightly narrow surrounding the cell about one turn, but the cingulum was rather deep, encircling the cell approximately twice, and the chloroplasts were brownish, granular and scattered peripherally. The highest M. fulvescens cell counts were recorded at 6.22 x 105 cells L-1 and 4.61 x 105 cells L-1 in Kerian, Perak and Seberang Perai Selatan, Penang, respectively. The physical parameters of the seawater from the affected sites were within the Malaysian Marine Water Quality Standard (MMWQS) for aquaculture. However, slightly higher levels of nitrate, phosphate and ammonia were noted at several stations. Although the exact cause of the bloom was undecided, it could be due to nutrient discharge along the coasts, which also concurred with the transition phase of the northeast to the southwest monsoon. [ABSTRACT FROM AUTHOR]

Fish is a staple food in countries with direct access to the ocean, including Malaysia. However, in the Malaysian diet, fish also represents the main source of heavy metals, especially in commercial fishes. In this study we determined the concentrations of four heavy metals (arsenic, cadmium, mercury and lead) in fish and estimated target hazard quotient (THQ) values for local consumers. The concentrations of heavy metals in marine fishes, (Decapterus spp., Nemipterus spp. and Rastrelliger spp.) from three fish landing jetties in West (West PM) and East Peninsular Malaysia (East PM) were determined. Heavy metals in fish muscle samples were extracted using acid-microwave digestion and determined by inductively coupled-plasma mass spectrometry (ICP-MS). One-way ANOVA was performed to test for temporal and genus variation. Nemipterus spp. in East PM contained significantly higher (p<0.05) levels of arsenic (As, 1,030 to 3,140 ng.g-1 ww) and mercury (Hg, 113 to 790 ng.g-1 ww) than the other two genera, suggesting a greater ability to retain these two heavy metals. Nemipterus spp. in Tok Bali (TB), East PM alone showed consistently high levels of As and Hg in 2017 and 2018, which exceeded the concentration allowed by Malaysian Food Act 1983 (Amendment) (No. 3) Regulations 2014. Based on these results, local consumers in TB were interviewed to gather information for the computation of THQ. The THQ values for As were greater than 1 in all studied fishes, whereas THQ for Hg only exceeded 1 in Nemipterus spp. Thus, THQ values indicate the potential health risk of consuming these types of fishes, particularly in TB. [ABSTRACT FROM AUTHOR]