Oysters are a group of economically important bivalves in China, with estuaries serving as one of their primary cultivation areas. However, heavy metal pollution in these estuarine environments poses a potential threat to aquaculture by leading to the accumulation of heavy metals in farmed oysters, which could impact their safety and marketability. This study was conducted in the aquaculture area of the Luoyangjiang River estuary, where eight sampling sites were selected. Water, sediment, and oysters categorized by shell length were collected from each site. The concentrations of heavy metals (Ag, As, Cd, Cr, Cu, Ni, Pb, and Zn) were determined in both the environmental samples and oyster tissues. Additionally, multiplex species-specific PCR was used to identify oyster species. The results showed significant variations in dissolved-phase and suspended particulate matter (SPM) metal concentrations across different sampling sites, while sediment metal concentrations were more consistent but similar to those in SPM. The large oysters were comprised of 50% Magallana angulata and 50% Magallana gigas, while small oysters were identified as Magallana sikamea. The Cd, Cu, Pb, and Zn levels in both size groups of oysters exceeded data from previous studies, indicating contamination in the estuary. The observed differences in heavy metal concentrations between large and small oysters primarily reflect species-specific variability in metal accumulation, which may also be influenced by factors such as growth and exposure duration. Furthermore, the lack of significant correlation between metal concentrations in environmental media and oysters suggests that oysters may be exposed to multiple sources of metal contamination.

Improving the progress of breeding is the main purpose of breeders, and shorting the reproductive cycle is one of the ways to improve the breeding progress. Although the reproductive cycle of Crassostrea angulata can be shortened from one year to half a year by selecting precocious individuals, little is known about whether this selection will accelerate their gonadal development or disturb their selection for productive traits. Here, the heritability of gonadal development traits (gametogenic stage and egg diameter) and their genetic correlations with both growth traits (shell height at 4 and 12 months and total body weight at 12 months) and heat tolerance trait were estimated. The heritability for gametogenic stage was low (0.18 ± 0.09), while the egg diameter showed a high heritability (0.78 ± 0.30). These results suggest that selection for precocious individuals has little effect on the rate of gonadal development in the C. angulata, despite the effect may be greater in females than in males. The genetic correlations between gonadal development traits and both growth (-0.02–0.30) and heat tolerance traits (-0.08–0.34) were low and non-significant. These results suggest that selection for precocious individuals has negligible effects on their productive traits. Therefore, it is feasible to double the breeding efficiency of C. angulata by halving their reproductive cycle.

Acquired thermotolerance (heat priming) enables organisms to withstand lethal heat stress after prior sublethal exposure. While documented in bivalves through survival analyses, histological mechanisms in gills-their primary environmental interface-remain unclear. This study investigated heat priming effects on Crassostrea angulata gills using four experimental groups: control, sublethal, priming (sublethal + lethal), and lethal. Histopathology (HE staining and SEM) and apoptosis (TUNEL) were analyzed under varying thermal regimes. Lethal stress induced more than 20% gill shrinkage (vs. control) with elevated mucus cell counts, while SEM revealed exacerbated filament breakage and ciliary loss. Priming pretreatment significantly reduced filament contraction and mitigated structural damage. TUNEL-positive cell density peaked in the lethal group, showing an eightfold increase over priming at 48 h, whereas priming and sublethal groups exhibited comparable level. These findings indicate that heat priming synergistically alleviates both mechanical damage (gill shrinkage/filament disruption) and TUNEL-detected cell-death signals during subsequent lethal stress. The study establishes a tissue-level foundation for understanding acquired thermotolerance in oysters.

In aquatic ecosystems, the interaction between heavy metals and dissolved organic carbon (DOC) plays a pivotal role in modifying the bioavailability of these metals. This study, employing a toxicokinetic–toxicodynamic model, delves into the interactive effects of humic acid (HA), a significant component of DOC, on the bioaccumulation and toxicity of copper (Cu) in the estuarine economic bivalve Sinonovacula constricta. Utilizing the stable isotope ⁶⁵Cu as a tracer, we evaluated Cu uptake in S. constricta under varied DOC concentrations in a controlled laboratory setting. Our findings reveal that at DOC concentrations below 3.05 mg L⁻¹, the bioavailability of Cu is reduced due to shifts in the speciation distribution of Cu, resulting in decreased bioaccumulation within S. constricta. Conversely, at DOC levels exceeding 3.05 mg L⁻¹, the formation of colloidal Cu–HA complexes allows its entry into the bivalves’ digestive system. Moreover, toxicity assays demonstrate an increase in S. constricta survival rates with higher DOC concentrations, suggesting a protective effect of DOC against Cu toxicity. The integration of accumulation and toxicity data infers that Cu–HA complexes, when ingested via the digestive tract, exhibit lower toxicity compared to Cu directly assimilated from the water phase. These findings emphasize the need to consider environmental DOC levels in assessing Cu pollution risks and provide insights for managing heavy metal toxicity in estuarine aquaculture.

Oysters are a globally distributed aquatic economic shellfish with a remarkable ability to accumulate cadmium (Cd). The phenomenon of Cd content exceeding safety standards in oysters occurs frequently, posing a significant risk to food safety. In this study, Portuguese oysters (Crassostrea angulata) were exposed to 2 μg/L of Cd for 15 days. Individuals with significantly different Cd accumulation were selected for transcriptomic sequencing analysis. KEGG enrichment analysis revealed that the differentially expressed genes (DEGs) between high- and low-Cd-accumulation individuals, as well as those before and after Cd exposure, were primarily enriched in metabolic pathways (33.8%) and organismal systems (32.2%). ABC transporters, phagosomes, glutathione metabolism, and the biosynthesis of amino acids played crucial roles in Cd accumulation and detoxification processes. Metal cation transport-related genes, including zip1, copt5.1, and orct2, may be involved in the Cd transport process in Portuguese oysters, and their differential expression influences Cd accumulation in the soft tissues. Meanwhile, genes such as sod3, cyp4f22, and abca3 are likely to play significant roles in detoxification under Cd exposure. Additionally, alternative splicing analysis identified 13 potential genes associated with Cd response in Portuguese oysters, including cs2, gfpt1, and acox1.