Dodecamethylcyclohexasiloxane (D6) is widely used daily in the chemical industry and exists in the environment; however, its eco-toxicity is not well documented. A hydroponic experiment was performed to investigate the effects of D6 exposure (10–1000 mg L⁻¹) on oxidative stress induction and gene expression changes in crayfish (Procambarus clarkii). The results showed that superoxide dismutase (SOD) activity was enhanced by 20–32% at low D6 exposure (10 mg L⁻¹) in muscle but reduced in gill tissue at high D6 exposure (1000 mg L⁻¹). High D6 (1000 mg L⁻¹) also increased catalase (CAT) and peroxidase (POD) activities in muscle tissue by 14–37% and 14–45%, respectively, and the same trend was observed in the carapace and gill tissue of crayfish. The Malondialdehyde (MDA), ascorbate (AsA), and glutathione (GSH) contents were increased by 16–31%, 19–31%, and 21–28% in the muscle of crayfish under D6 exposure. Additionally, silicon (Si) content increased in three organs (gill, carapace, and muscle) of crayfish. Related genes involved in enzyme and nonenzyme activities were detected, and when crayfish was exposed to D6, genes such as Sod3, Cat3, Pod3, and Gsh3 were up-regulated, while Asa3 and Oxido3 were significantly down-regulated in the muscle. The research results help us to understand the toxicity of D6 in crayfish and provide a basis for further research on the mechanism of D6-induced stress in crayfish and other aquatic organisms.

Due to difficulty in recognition, many true species have been covered under the synonyms of wide-spread species. To justify the identification of a widely distributed species, Sillago sihama from the Bay of Bengal, Bangladesh, an integrated approach including morphology and DNA barcoding was used. Two unrecognized species of Sillago, i.e., Sillagomuktijoddhai sp. nov. and S. mengjialensis sp. nov., were identified from the coastal area of Bangladesh. S. muktijoddhai sp. nov. has marked differences in the body color, anal fin color, number of gill rakers, snout length, and swimbladder. S. mengjialensis sp. nov. has notable differences in the anal fin color, snout length, and swimbladder and is distinguished from S. muktijoddhai sp. nov. by the body color and swimbladder. The morphological characters of 14 documented Sillago species with two posterior extensions of the swimbladder were referenced and distinguished to accredit the two new species. Genetic analyses of partial mitochondrial cytochrome oxidase subunit I and 16S ribosomal RNA also supported the validity of the new species. This study has increased the number of recognized species of Sillago in the world and confirmed the prevailing misidentification of these two new species in Bangladesh as so-called S. sihama. Moreover, the study confirmed the misidentification of S. mengjialensis sp. nov. in Indonesia as S. sihama and the identification of unknown Sillago sp.1 in India.