Search

Heatwaves have become more frequent and intense in the last two decades, resulting in detrimental effects on marine bivalves and ecosystems they sustain. Intertidal clams inhabit the most physiologically challenging habitats in coastal areas and live already near their thermal tolerance limits. However, whether and to what extent atmospheric heatwaves affect intertidal bivalves remain poorly understood. Here, we investigated physiological responses of the Manila clam, Ruditapes philippinarum, to heatwaves at air temperature regimes of 40 °C and 50 °C occurring frequently and occasionally at the present day in the Beibu Gulf, South China Sea. With the increasing intensity of heatwaves and following only two days of aerial exposure, Manila clams suffered 100 % mortality at 50 °C, indicating that they succumb to near future heatwaves, although they survived under various scenarios of moderate heatwaves. The latter is couched in energetic terms across levels of biological organization. Specifically, Manila clams acutely exposed to heatwaves enhanced their standard metabolic rate to fuel essential physiological maintenance, such as increasing activities of SOD, CAT, MDA, and AKP, and expression of HSP70. These strategies occur likely at the expense of fitness-related functions, as best exemplified by significant depressions in activities of enzymes (NKA, CMA, and T-ATP) and expression levels of genes (PT, KHK, CA, CAS, TYR, TNF-BP, and OSER). When heatwaves occurred again, Manila clams can respond and acclimate to thermal stress by implementing a suite of more ATP-efficient and less energy-costly compensatory mechanisms at various levels of biological organization. It is consequently becoming imperative to uncover underlying mechanisms responsible for such positive response and rapid acclimation to recurrent heatwaves.

Tyrosinase is a key rate-limiting enzyme in melanin synthesis. In this study, a new tyrosinase gene (Tyr) was identified from Pteria penguin and its effect on melanin synthesis was deliberated by RNA interference (RNAi). The cDNA of PpTyr was 1728 bp long, containing a 5'untranslated region (UTR) of 11 bp, a 3'UTR of 295 bp, and an open reading fragment of 1422 bp encoding 473 amino acids. Amino acid alignment showed PpTyr had the highest (50%) identity to tyrosinase-like protein 1 from Pinctada fucata. Phylogenetic tree analysis classified PpTyr into α-subclass of type-3 copper protein. Tissue expression analysis indicated that PpTyr was highly expressed in mantle, a nacre formation related tissue. After PpTyr RNA interference, PpTyr mRNA was significantly inhibited by 71.0% (P 0.05). For other melanin-related genes, PpCreb2 and PpPax3 expression showed no significant change, but PpBcl2 was obviously increased. By liquid chromatograph-tandem mass spectrometer (LC-MS/MS) analysis, the total content of PDCA (pyrrole-2, 3-dicarboxylic acid) and PTCA (pyrrole-2,3,5-tricarboxylic acid), as main markers for eumelanin, was sharply decreased by 66.6% after PpTyr RNAi (P 0.05). The percentage of PDCA was also obviously decreased from 20.1% to 13.9%. This indicated that tyrosinase played a key role in melanin synthesis and color formation of P. penguin.

Metamorphosis of pearl oyster Pinctada maxima pediveliger is affected by physical and chemical characteristics of the collectors. In the present study, we conducted four experiments to evaluate the effects of collector characteristics on the settlement and growth of hatchery-reared pearl oyster. In the first experiment, black, red, yellow, and white plastic sheets were used as collectors. Settlement of P. maxima larvae in black and red plastic sheets was significantly higher than that in yellow and white plastic sheets ( P P > 0.05). In the second experiment, pediveliger larvae were settled onto palm rope and polypropylene rope collectors. The number of spat in the palm rope collector was significantly higher than that of spat in the polypropylene rope collector ( P P > 0.05). In the third experiment, settlement and subsequent growth were compared between plastic sheets with and without biofilm. The number of spat in the plastic sheets with biofilm was significantly higher than that in the plastic sheets without biofilm ( P P > 0.05). In the fourth experiment, pediveliger larvae were stored in tanks with (experimental group) and without collectors (control group). The settlement rate of larvae on the wall was not significantly different between the two groups( P > 0.05). The settlement rates of the larvae on the wall and collectors in the experimental group were significantly larger than those on the wall in the control group( P P > 0.05). Our results suggest that appropriate selection of collector types, color, and conditioning can improve the settlement of P . maxima larvae in hatcheries.

A progeny stock was established by using gold-lip breeders collected from Indonesia to understand the growth characteristics of pearl oyster Pinctada maxima in Beibu Bay, China. The shell height and shell length of the stock were measured from April 2011 to September 2013. Water parameters, such as water temperature, salinity, dissolved oxygen concentration, and suspended organic matter, were monitored during the experimental process. Results showed seasonal trends in water temperature and suspended organic matter. Shell height and shell length were significantly related at different ages (P

The oyster species Pinctada maxima is cultured for the production of large pearls with high economic value. Pearl weight and thickness are related to the growth of P. maxima. The molecular mechanism underlying the growth of this species, however, remains poorly understood given the limited availability of the genetic and genomic information of this species. Here, the molecular mechanism of the asynchronous growth of P. maxima was investigated. The transcriptomes of large and small P. maxima individuals were sequenced using the Illumina HiSeq 2000 platform. A total of 145,877 unigenes were generated for the transcriptomes, and 1,921 differentially expressed genes (DEGs) were identified. Compared with the slow-growing group, the fast-growing group showed 879 and 1,042 significantly up- and down-regulated DEGs, respectively. The differential expression patterns of nine selected genes were obtained through real-time quantitative polymerase chain reaction analysis and showed consistency with those obtained through RNA-Seq analysis. The results of this study provide further insight on the complexity of the differential growth patterns of P. maxima individuals and will help guide the design of breeding programs for this economically important species.

To understand the influences of environmental conditions on the performance of pearl oyster spat, we conducted four experiments to evaluate separately the effects of salinity (21, 24, 27, and 30), diet (Isochrysis zhanjiangensis, Platymonas subcordiformis, Chlorella; 50% I. zhanjiangensis/50% P. subcordiformis, 50% I. zhanjiangensis/50% Chlorella, and 50% P. subcordiformis/50% Chlorella), diet availability (high, medium and low), and rearing site (hatchery and sea) on the growth and survival of pearl oyster Pinctada maxima spat. Results showed that environmental conditions exerted significant effects on the growth of P. maxima spat. Salinity and rearing site also had significant effects on survival, but no significant differences were observed in terms of survival between the diet and diet availability treatments. Growth declined with decrease in salinity. Spat reared at high salinities (30 and 27) showed larger shell length growth and greater survival than those at low salinities (24 and 21). Sp...

Three experiments were carried out to separately investigate the effects of stocking density (1.0, 2.0, 4.0 and 8.0 larvae ml−1), diet (Isochrysis zhanjiangensis, Chlorella spp., Nannochloropsis oculata, 50 % I. zhanjiangensis/50 % Chlorella spp. and 50 % I. zhanjiangensis/50 % N. oculata), and water exchange (25 % once every other day and 25, 50 and 100 % once daily) on growth and survival of pearl oyster Pinctada maxima larvae. Results showed that there existed significant effects of stocking density, diet, and water exchange on the growth of pearl oyster larvae (P 0.05). Larval growth decreased significantly with increasing stocking density (P

Two experiments were designed to evaluate the pearl production traits of the third generation red(RS3),yellow(YS3),white(WS3)and black(BS3)shell colored lines.Different colored lines were used as host and donor oysters respectively.The pearl in Experiment Ⅰ,16 combinations were established by sampling the RS3,YS3,WS3 and BS3 lines as honor and donor oysters.Another combination was established by using the common cultured stock and YS3 as honor and donor oysters,respectively.And a total of seventeen combinations were established.The pearls were harvested after the honor oysters were cultured for twenty-four months.In Experiment Ⅱ,sixteen combinations were established by sampling the RS3,YS3,WS3 and BS3 lines as honor and donor oysters.The pearls were harvested after the honor oysters were cultured for eighteen months.After harvesting pearls,shell height growth and survival of the RS3,YS3,WS3 and BS3 lines were compared in both experiments.Retention rate,commercial pearl rate,better quality pearl rate and pearl thickness of each combination in Experiment Ⅰ and Ⅱ were compared.The results showed that there existed significant differences in mean shell height and survival among the RS3,YS3,WS3 and BS3 lines in Experiment Ⅰ and Ⅱ(P0.05).The BS3 line had the largest mean shell height compared with the RS3,YS3 and WS3 lines in Experiment Ⅰ and Ⅱ.The YS3 line had the largest survival in Experiment Ⅰ and the BS3 line had the largest survival in Experiment Ⅱ.In Experiment Ⅰ,there were significant differences in retention rate,commercial rate,perfect quality pearl rate and pearl performance values among the 17 combinations(P0.05);There were insignificant differences in pearl thickness among the 17 combinations(P0.05);The BW combination had the highest retention rate,commercial pearl rate,pearl thickness and pearl performance value,and the RB had the highest perfect quality pearl rate.In Experiment Ⅱ,there were significant differences in retention rate,commercial rate,pearl thickness,perfect quality pearl rate and pearl performance values among the 16 combinations(P0.05).A combined analysis on host or donor oysters showed that the BS3 line is desirable for host oyster to produce better quality pearl and is promising in the commercial pearl production.