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Fish kills in Southeast Asia are frequently associated with harmful algal blooms (HABs) and cause significant ecological and economic impacts and can have negative effects on the sustainability of aquatic ecosystems and the fisheries they support. This paper serves as a review of fish-kill events with focus on those related to HABs within the region. It examines the causative algal species, known mechanisms of fish mortality, and socio-economic consequences in order to better understand and manage this threat to sustainable fisheries. Fish kills have been reported across multiple countries within Southeast Asia, with notable hotspots in the Philippines, Malaysia, Singapore, Indonesia, and Thailand. The common harmful microalgal species span a diverse group including dinoflagellates (Karenia spp., Karlodinium spp., Margalefidinium polykrikoides, Noctiluca scintillans), raphidophytes (Chattonella spp.), diatoms (Skeletonema spp. and Chaetoceros spp.), and cyanobacteria (Trichodesmium spp.). These microalgae lead to fish kills through mechanisms such as hypoxia, physical gill damage, and ichthyotoxin production. Freshwater fish kills linked to HABs have also been documented for the Philippines, but there is no or limited information for the region. Our review highlights the widespread and recurring nature of fish kills, their impact on fisheries and aquaculture, and challenges in managing and mitigating their effects. There are efforts at enhancing management and mitigation using clay and early warning systems. However, it is essential to further improve monitoring efforts, the development and deployment of early warning systems, and viable and holistic mitigation strategies to protect the region's aquatic resources and dependent communities, especially as aquaculture and coastal development are increasing concurrent with a changing climate that can exacerbate the risks of fish kills and HABs in Southeast Asia. [ABSTRACT FROM AUTHOR]

SUMMARY: Morphology, phylogeny and azaspiracid (AZA) production of a strain of Amphidoma languida isolated from the subtropical Mexican Pacific were examined. Scanning electron microscopy showed the thecal plate arrangement of Am. languida from Mexico as Po, cp, X, 6′, 6′′, 6C, 5S, 6′′′, 2′′′′, with the prominent apical pore complex, the ventral pore on the anterior of the 1′ plate near the suture to the 6′ plate, and the antapical pore on the 2′′′′ plate, which are congruent with those of Am. languida reported from the Atlantic. The ventral depression was occasionally observed on the anterior end of Sa plate. Cells had a dinokaryotic nucleus positioned in the posterior part of the cell and parietal yellowish chloroplasts with a spherical pyrenoid in the episome. Transmission electron microscopy showed crystalline vesicles and tubular cytoplasmic invaginations in the pyrenoid, which resembled those reported from the most related non‐toxigenic species Amphidoma fulgens. The intracellular components, different from Am. fulgens, were oil droplets and lipid‐associated membranous structures. AZA‐2 was detected from the strain by liquid chromatography‐tandem mass spectrometry with a cell quota of 30.9 fg cell−1. Three other AZA‐related compounds were also detected. This is the first report of AZA‐producing Am. languida in the Pacific Ocean. [ABSTRACT FROM AUTHOR]