Molecular characterization and expression analysis of Cyclin B and Cell division cycle 2 in gonads of diploid and triploid bighead catfish, Clarias macrocephalus Günther, 1864

Overcoming taxonomic challenges in DNA barcoding for improvement of identification and preservation of clariid catfish species

DNA barcoding without assessing reliability and validity causes taxonomic errors of species identification, which is responsible for disruptions of their conservation and aquaculture industry. Although DNA barcoding facilitates molecular identification and phylogenetic analysis of species, its availability in clariid catfish lineage remains uncertain. In this study, DNA barcoding was developed and validated for clariid catfish. 2,970 barcode sequences from mitochondrial cytochrome c oxidase I (COI) and cytochrome b (Cytb) genes and D-loop sequences were analyzed for 37 clariid catfish species. The highest intraspecific nearest neighbor distances were 85.47%, 98.03%, and 89.10% for COI, Cytb, and D-loop sequences, respectively. This suggests that the Cytb gene is the most appropriate for identifying clariid catfish and can serve as a standard region for DNA barcoding. A positive barcoding gap between interspecific and intraspecific sequence divergence was observed in the Cytb dataset but not in the COI and D-loop datasets. Intraspecific variation was typically less than 4.4%, whereas interspecific variation was generally more than 66.9%. However, a species complex was detected in walking catfish and significant intraspecific sequence divergence was observed in North African catfish. These findings suggest the need to focus on developing a DNA barcoding system for classifying clariid catfish properly and to validate its efficacy for a wider range of clariid catfish. With an enriched database of multiple sequences from a target species and its genus, species identification can be more accurate and biodiversity assessment of the species can be facilitated.

Oxidative stress, DNA damage, and cellular response in hydrogen peroxide-induced cell injury of mud crab (Scylla paramamosain)

Oxidative stress is considered as the toxicity mechanism of environmental stressors on aquatic organisms. This study aims to explore the effects of oxidative stress on physiological responses, DNA damage and transcriptional profiles of the mud crabs Scylla paramamosain. In the present study, mud crabs were injected with 0.1% and 1% hydrogen peroxide (H₂O₂) for 72 h. The results showed that superoxide dismutase and catalase activities significantly decreased after H₂O₂ injection. Malondialdehyde content, H₂O₂ content, aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase activity significantly increased after H₂O₂ injection. Moreover, DNA damage occurred after H₂O₂ injection. Transcriptome analysis showed that 531 and 372 differentially expressed genes (DEGs) were identified after 0.1% and 1% H₂O₂ injection, respectively. These DEGs were mainly involved in the oxidative stress response and immune functions. All these results indicated that oxidative stress could impair both antioxidant defense systems and immune systems. Transcriptome analysis provided valuable information on gene functions associated with the response to oxidative stress in the mud crab.