Comparative Responses of Orange-Foot and Common-Foot Haliotis gigantea to Carotenoid-Enriched Diets: Survival, Heat Tolerance, and Bacterial Resistance.

Carotenoids, known to enhance survival, heat tolerance, and bacterial resistance, play an essential role in the nutrition of economically important aquatic animals. This study specifically examined their impact as feed additives on the abalone Haliotis gigantea. We prepared 13 compound feeds with varying levels of astaxanthin, zeaxanthin, and ß-carotene, and administered them to both common-footed and orange-footed H. gigantea. The survival rate of H. gigantea was about 70-80%, with no significant differences in survival observed among the various carotenoid-supplemented feeding groups or when compared with the control group, nor between orange-footed and common-footed individuals. In heat attachment duration experiments, orange-foot abalones exhibited longer attachment durations with certain concentrations of astaxanthin and zeaxanthin, whereas common-foot abalones showed extended durations with astaxanthin, zeaxanthin, and ß-carotene, indicating that common-foot abalones might benefit more from these carotenoids. Additionally, our results showed similar patterns and levels of Vibrio harveyi AP37 resistance in both orange-footed and common-footed H. gigantea, suggesting a uniform response to carotenoid supplementation in their bacterial defense mechanisms. This study suggests the potential benefits of carotenoid supplementation in H. gigantea and contributes to the theoretical basis for developing high-quality artificial compound feeds.

Investigating the Impact of Humic Acid on Copper Accumulation in Sinonovacula constricta Using a Toxicokinetic-Toxicodynamic Model.

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.

Dynamics of copper regulation in a marine clam Sinonovacula constricta at the organ level: Insight from a physiologically based pharmacokinetic model.

Copper (Cu) is a common pollutant in estuaries and has received considerable attention worldwide. To gain an insight into the physiological mechanisms of waterborne Cu absorption, tissue distribution, storage, metabolism, and excretion in an estuarine razor clam Sinonovacula constricta, we developed a physiologically-based pharmacokinetic model based on prolonged Cu exposure with two exposure treatments. The tissues of S. constricta were divided into four parts: blood, digestive gland, gill, and other tissues. Our results showed that the waterborne Cu entered and exchanged with the gills and digestive gland, whereas digestive gland and other tissues were the main storage sites for Cu. Gills of S. constricta were able to maintain their Cu concentrations under both exposure treatments. Additionally, the gills exhibited a remarkable ability to remove Cu from water, with a transfer rate constant of 1.73 d-1 from the gills to water, while restricting its transfer from the blood with a transfer rate constant of 0.0131 d-1 from blood to gills. These results highlighted the crucial role of gills in regulating Cu levels in S. constricta as well as the detoxification and maintenance of metal homeostasis. Cu uptake rate constant in gill from waterborne was similar to that of digestive gland (0.294 vs. 0.364 L g-1 d-1), thus water entering the digestive tract was considered as another route of waterborne Cu absorption in bivalves. A significant amount of Cu in the blood was transferred to the digestive glands. These two factors explained the relatively higher Cu accumulation in the digestive glands than in other tissues in clams. The findings of this study enhanced our understanding of the homeostatic regulation and transportation mechanisms in marine bivalves.

Dietary metal bioavailability in razor clam Sinonovacula constricta under fluctuating seston environments.

To understand the potential risks of dietary metals to marine bivalves, it is important to study the interaction between dietary metal bioaccumulation and bivalve feeding behavior. Key processes in affecting the dietary metal influx are the selection of different particles during the ingestion process as well as the differential assimilation of metals during the digestion process. In this study, we quantified the influences of seston quality and quantity on the dietary assimilation of Cd and Zn as well as pre-ingestion particle selectivity in a razor clam Sinonovacula constricta following feeding on radiolabeled diatoms and sediments with different mixtures at four food concentrations. Bioavailability of 109Cd and 65Zn from seston was measured by assimilation efficiency (AE) using a pulse-chase feeding technique. The AEs of Cd and Zn were significantly affected by the seston quantity and quality (higher for Zn than they were for Cd and higher for diatoms than for suspended sediments), but were independent of the presence of other particles during the feeding process. Dual gamma radiotracer technique was further employed to study pre-ingestion particle selectivity. Particle selectivity was weak during pre-ingestion in razor clams, although there was evidence that clams might be able to differentiate particles during the process of pseudofeces production. Our study demonstrated that seston composition and quantity substantially affected the bioavailability of Cd and Zn to the razor clams. The results are important to understand the bioaccumulation of metals in clams living in dynamic food environments of estuary.

Metal accumulation, growth and reproduction of razor clam Sinonovacula constricta transplanted in a multi-metal contaminated estuary.

In recent years, elevated metal discharges have seriously affected the health of many estuarine ecosystems in China. This study examined the influences of metal pollution on the growth and reproduction of razor clam, Sinonovacula constricta. An eight-month field experiment was conducted at two sites with different contamination levels in Jiulong River Estuary of Southern China. Concentrations of Ag, As, Cd, Cr, Cu, Ni, Pb and Zn in seawater, suspended particles, surface sediments, and clams, as well as the clam growth and gonad condition were simultaneously determined on a monthly basis. Over the 8-month period, Ag, Cu and Ni concentrations in the clams were significantly higher at the more polluted site, whereas the concentrations of other metals were rather comparable between the two sites. Comparison of the 8-month pattern of metal concentrations among different compartments suggested that Ag, As, Cd, Cu and Zn bioaccumulation in the clams was mainly derived from ingestion of suspended particles, whereas Cr and Ni accumulation was mainly from the waterborne uptake. The growth of clams in the more polluted site was depressed and there was no significant growth after 4 months of transplantation, which was mainly caused by Cu and Ag accumulation in the clam tissues. Correspondingly, the gonad somatic index was also lower at the more polluted site. Our study demonstrated a significant impact of multi-metal pollution on the growth and reproduction of clams in an estuary. Simultaneous measurements of metal bioaccumulation were important for the interpretation of metal toxicity observed in the field.

Abcb1 gene expression pattern and function of copper detoxification in Fujian oyster, Crassostrea angulata.

Oysters are considered hyper-accumulators of Cu, but the molecular mechanism by which they maintain Cu cell homeostasis is still unclear. ATP-binding cassette protein subfamily B member 1 (ABCB1, P-glycoprotein) can transport a variety of substrates across the cell membrane in aquatic animals. In this study, to provide insight into the roles of ABCB1 in resistance against Cu in oysters, complete cDNA of abcb1 gene in Crassostrea angulata was cloned and analyzed. The complete sequence of C. angulata ABCB1 showed high identity to ABCB1 from other bivalves and contained some classical motifs of ABCB transport proteins. Abcb1 was mainly expressed in the apical epithelial cell of gills and epithelia of mantles. Abcb1 expression and Cu accumulation were also studied in control oysters and oysters exposed to Cu (30, 100, 300 µg/L Cu, 1-15 days). Cu accumulation in the gill and mantle were measured after abcb1 gene interference. The complete sequence of C. angulata ABCB1 showed high identity to ABCB1 from other bivalves and contained some classical motifs of ABCB transport proteins. The mRNA transcript of abcb1 showed hypersensitivity to Cu exposure. A concentration-dependent highest abcb1 mRNA level (up to 5.61-fold to the control) in the gill and mantle existed across all Cu exposure concentrations after 3 days of Cu exposure. The gill and mantle Cu concentration were significantly higher after the abcb1 mRNA interference. According to these results, it is here speculated that ABCB1 may underlie cell protection against Cu in C. angulata.