Environmental DNA (eDNA) technology has been successfully applied to detect organisms in various aquatic ecosystems. However, eDNA has been proven to exist for a long time in environmental samples. The timeliness of eDNA detection results largely depends on the rate of molecular degradation. Environmental RNA (eRNA) is considered an excellent complementary tool because most researchers believe that RNA degrades faster than DNA in vitro, while, to the best of our knowledge, the number of published articles related to eRNA is very limited. To address an important knowledge gap, this study focused on the response mechanism of eRNA degradation to water temperature change as compared with eDNA. Changes in the concentration of eDNA and eRNA of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene from Fenneropenaeuschinensis were detected at four temperatures (10, 15, 20 and 25 °C). The results showed that the degradation rate of eDNA increased with an increase in temperature. The degradation rate constants ranged from 0.011 to 0.486 h⁻¹ and the degradation time ranged from 8 to 383 h for eDNA. The degradation rate of eRNA changed slightly with an increase in temperature. The degradation rate constants ranged from 0.190 to 0.379 h⁻¹ and the degradation time ranged from 11 to 22 h for eRNA. eRNA showed better stability under temperature change and maintained a faster degradation rate at low temperatures. These results provide answers to the questions of whether eRNA and eDNA degradation rates are fast or slow. Furthermore, this study may suggest the potential superiority of eRNA over eDNA and promote further study of eRNA in future research.

Fenneropenaeus chinensis is an important economic species in the north of China, and plays an important role in both marine fishing and aquaculture. Long-term overfishing has led to the rapid decline of wild F. chinensis resources. The traditional trawl survey could not meet the demands of the F. chinensis resource survey. In this study, environmental DNA (eDNA) technology was used to evaluate the biomass of F. chinensis in the traditional Qinghai (Qingdao Haiyang) fishing ground in the southern sea area of the Shandong Peninsula, with the purpose of verifying whether eDNA technology can provide a new resource assessment method for fisheries resource species such as F. chinensis. The eDNA quantitative results of the Qingdao water samples ranged from 1972 copies/L to 6937 copies/L, with an average of 4366 ±1691 copies/L. Those in Haiyang water samples ranged from 4795 copies/L to 8715 copies/L, with an average of 6737 ± 1348 copies/L. The concentration of eDNA in shrimp culture ponds ranged from 1.14 × 10⁶ copies/L to 7.61 × 10⁶ copies/L, with an average of 3.33 × 10⁶ ± 2.28 × 10⁶ copies/L. The amount of eDNA released by each gram of F. chinensis per 24 h was about 2.91 × 10⁶ copies. According to this calculation, it was estimated that the distribution of F. chinensis was about one shrimp in every 300 m² sea area. Similarly, it is estimated that one shrimp is distributed every 240 m² in the Haiyang sea area. The result of this study confirms the feasibility of using eDNA to evaluate the biomass of shrimps.

Cleisthenes herzensteini is a commercially important demersal fish in the Northwest Pacific. However, the resource stock of this species has undergone a drastic decline due to overfishing and habitat degradation. As a representative taxon for benthic adaptation in the order Pleuronectiformes, the molecular mechanisms underlying its specialized phenotypic traits remain poorly elucidated. Furthermore, population-level studies focusing on the mitochondrial genome of Cleisthenes herzensteini are currently scarce. Given that the mitochondrial genome serves as an ideal genetic tool for deciphering species evolution and population genetics, sequencing of its mitogenome will help fill critical gaps in genetic resources and provide essential support for species conservation and phylogenetic research. In this study, we sequenced, assembled, and annotated its complete mitochondrial genome. The circular mitogenome is 17,171 bp in length and exhibits a typical A + T bias (54.04%). Repeat sequence analysis identified 35 dispersed repeats. Codon usage analysis revealed that leucine was the most frequently encoded amino acid, with CUU being the preferred codon. Several protein-coding genes possessed incomplete stop codons (T--/TA-), and a nucleotide preference for A and C was observed at the third codon position. Phylogenetic reconstruction based on mitogenomes from 23 species supported the monophyly of the order Pleuronectiformes. C. herzensteini showed the closest relationship with Dexistes rikuzenius, forming a distinct clade alongside Hippoglossoides dubius and Limanda aspera. These results provide essential genetic resources for understanding the evolution and population genetics of C. herzensteini and related flatfishes. According to the investigation, this study represents the first report on the sequencing and analysis of the complete mitochondrial genome of the Cleisthenes herzensteini. This not only fills the gap in mitochondrial genetic information for this species but also provides a reference for subsequent investigations into the phylogenetic relationships and evolutionary processes within the family Pleuronectidae.

Analysis of environmental DNA (eDNA) has been successfully used to detect organisms in various aquatic environments. Although eDNA has been shown to persist for long periods of time in environmental samples, the efficacy of eDNA/eRNA based tools is highly dependent on degradation of the molecule, which subsequently has a great impact on the timeliness of the detection results. Environmental RNA (eRNA) is considered an excellent complementary tool because most researchers believe that RNA degrades faster than DNA in vitro. However, to the best of our knowledge, published research related to eRNA is very limited. To address an important knowledge gap, this study focused on the relationship between water temperature and the degradation of eDNA and eRNA. Changes in the concentration of eDNA and eRNA of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene from Fenneropenaeus chinensis were detected at four temperatures (10, 15, 20 and 25°C). The results show that the eDNA degradation rate increased at higher temperatures, with the degradation rate constants ranging from 0.011 to 0.486 h-1 and the degradation time ranging from 8 to 383 h for eDNA. For eRNA, the degradation rate constants ranged from 0.190 to 0.379 h-1 and the degradation time ranged from 11 to 22 h. eRNA showed better stability under temperature change and maintained a faster degradation rate at low temperatures. These results answer the questions that eRNA and eDNA degradation rate which is fast or slow of the current research. Furthermore, this study may suggest the potential superiority of eRNA over eDNA and promote the further study of eRNA in future research.