This study assessed the feeding habits and ingestion of anthropogenic debris in 34 marine fish species from the southern Gulf of Thailand. A total of 5478 fish samples of 12 families were categorised into seven groups: planktivore, Lucifer feeder, fish feeder, Acetes feeder, shrimp feeder, piscivore, and zoobenthivore fish. A total of 2477 anthropogenic debris items were extracted from 12 fish species by visual inspection. Their ingestion of anthropogenic debris was influenced by season (p < 0.0001), with the highest ingestion during the northeast monsoon season. Furthermore, planktivorous fish displayed more ingested anthropogenic debris than the other investigated species (p = 0.022). Blue-coloured anthropogenic debris was commonly detected in the stomachs of fish and significantly differed between species (p > 0.001). Water depth and season significantly influenced the availability of food types (AF) for fish (p < 0.001). These findings provide evidence of the ingestion of anthropogenic debris by fish inhabiting a natural bay and signal the future anthropogenic pollution of marine fish.

Thenus spp. are slipper lobsters which are commercially significant as a food source with good aquaculture potential. This study focuses on collecting population information on Thenus orientalis and Thenus indicus from selected sites in southern Thailand and Malaysia to inform sustainable fisheries management about the resources. Twenty-five size-adjusted morphometric measurements were analyzed using canonical discriminant function and dendrogram cluster analyses to examine patterns of phenotypic variation between sites. Significant phenotypic variation with distinct centroids and minimal overlapping cases were observed among four sites of T. orientalis (p < 0.05), as well as cluster analysis groupings occurring as in (i) Kota Kinabalu and Kudat, in Sabah, Malaysia; (ii) Pattani; and (iii) Nakhon Si Thammarat, in Thailand, which were best discriminated by the width of the third pereiopod merus, the sixth abdomen segment, and the carapace posterior margin. Similar morphometric data between Kota Kinabalu and Kudat suggests a subpopulation of T. orientalis occurring in Sabah waters. Significant phenotypic variation was also detected between six sites of T. indicus (p < 0.05), with close centroids and overlapping cases forming three groups: (i) Ranong and Nakhon Si Thammarat; (ii) Kota Kinabalu, Tanjung Sedili, and Kuala Terengganu; and (iii) Pattani, best described by the widths of the second antenna and the first pereiopod merus, in addition to the length of the sixth abdomen segment. Cluster analysis shows the Pattani specimens clustering with the Malaysian specimens rather than the Thai specimens, suggesting homogeneous morphometric data between contiguous sites. Nakhon and Pattani forming separate groups in both species suggest discreet subpopulations occurring in the lower Gulf of Thailand. Patterns of phenotypic variation observed may be attributable to environmental conditions, local adaptations, and nomadic behavior. The findings can serve as baseline information for spatial planning in fisheries management, as well as to apprise regional efforts in the sustainable exploitation of Thenus spp.

This study examined the dietary compositions of three sympatric mud crab species-Scylla olivacea, S. tranquebarica, and S. paramamosain-across six coastal provinces of Thailand, encompassing the Andaman Sea and the Gulf of Thailand. A total of 4,112 individuals, mainly S. olivacea, were collected monthly from June 2022 to June 2023, and stomach contents were analyzed volumetrically. Prey compositions, vacuity index (VI), fullness index (FI), diet breadth, and diet overlap were quantified. Fish constituted the predominant prey item for all three species, representing 56.0%, 57.8%, and 42.5% of the diet in S. olivacea, S. tranquebarica, and S. paramamosain, respectively. Secondary prey items exhibited interspecific variation: crabs for S. olivacea (15.1%), and bivalves for both S. paramamosain (22.7%) and S. tranquebarica (24.8%). Gastropods contributed significantly to the diet of S. paramamosain (9.1%). Multivariate analyses revealed distinct dietary separations between the three Scylla species. Significant site-specific variation in the diet of S. olivacea was observed between Gulf of Thailand and the Andaman Sea (P < 0.05). In contrast, no significant differences in dietary composition were detected between male and female crabs for either S. olivacea or S. paramamosain. These findings elucidate species-specific dietary preferences and the influence of habitat on the trophic ecology of these mud crab species, providing pertinent insights for aquaculture practices and sustainable resource management strategies.