MORPHOLOGY AND GENETIC IDENTIFICATION OF Thenus spp. IN MALAYSIA AND THAILAND WITH SHORT NOTES ON FISHERIES

Abstract

Thenus spp. are slipper lobsters commercially significant as a food source with good aquaculture potential, typically caught as by-catch of trawl fisheries. Exploitation of wild stocks continue with limited data on fisheries status, species distribution, and population information. This study investigated Thenus spp. in the waters of Malaysia and Thailand to support the sustainable management and conservation of this resource. Annual fisheries statistics of Thenus spp. from 2003 to 2019 were analysed to assess current trends of fisheries exploitation in the two countries. For morphological and genetic investigations, 135 Thenus spp. specimens were collected from three sites in Thailand and six sites in Malaysia. Morphological examination (N =135) and mtDNA CO1 sequencing (N=50) confirmed species identity. Discriminant function and cluster analyses of morphometric measurements (N=122) were conducted to examine phenotypic variation between species, sexes, and sites. The average annual landing of Thenus spp. in Malaysia was 535 tonnes/year, mostly by trawl fisheries on the east coast of Peninsular Malaysia and Sabah, with an overall decreasing trend. In Thailand, the average annual landing was 1509 tonnes/year, mainly by trawl and drift net fisheries in the Gulf of Thailand, with a fluctuating trend over the 17 years. Three species were present within the study area confirmed by morphology, BLAST results, p-distance, and phylogenetic trees inferred by Maximum Likelihood and Bayesian Inference of a 682-base pair mtDNA CO1 dataset. Thenus indicus was the most widely distributed species within the region while Thenus unimaculatus was confined to the Andaman Sea and Malacca Strait. The distribution of Thenus orientalis encompassed the Gulf of Thailand and South China Sea. The findings updated global distribution records and confirmed the presence of T. indicus and T. unimaculatus in Malaysia as first records. Significant phenotypic variation (p0.05) was found between sexes of the three species, indicating no sexual dimorphism. Significant phenotypic variation (p

Thenus spp. are slipper lobsters commercially significant as a food source with good aquaculture potential, typically caught as by-catch of trawl fisheries. Exploitation of wild stocks continue with limited data on fisheries status, species distribution, and population information. This study investigated Thenus spp. in the waters of Malaysia and Thailand to support the sustainable management and conservation of this resource. Annual fisheries statistics of Thenus spp. from 2003 to 2019 were analysed to assess current trends of fisheries exploitation in the two countries. For morphological and genetic investigations, 135 Thenus spp. specimens were collected from three sites in Thailand and six sites in Malaysia. Morphological examination (N =135) and mtDNA CO1 sequencing (N=50) confirmed species identity. Discriminant function and cluster analyses of morphometric measurements (N=122) were conducted to examine phenotypic variation between species, sexes, and sites. The average annual landing of Thenus spp. in Malaysia was 535 tonnes/year, mostly by trawl fisheries on the east coast of Peninsular Malaysia and Sabah, with an overall decreasing trend. In Thailand, the average annual landing was 1509 tonnes/year, mainly by trawl and drift net fisheries in the Gulf of Thailand, with a fluctuating trend over the 17 years. Three species were present within the study area confirmed by morphology, BLAST results, p-distance, and phylogenetic trees inferred by Maximum Likelihood and Bayesian Inference of a 682-base pair mtDNA CO1 dataset. Thenus indicus was the most widely distributed species within the region while Thenus unimaculatus was confined to the Andaman Sea and Malacca Strait. The distribution of Thenus orientalis encompassed the Gulf of Thailand and South China Sea. The findings updated global distribution records and confirmed the presence of T. indicus and T. unimaculatus in Malaysia as first records. Significant phenotypic variation (p0.05) was found between sexes of the three species, indicating no sexual dimorphism. Significant phenotypic variation (p