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Mass mortality of Unionidae from the genera Middendorffinaia, Buldowskia, and Sinanodonta was observed in the plain rivers of the south of Primorsky Krai (south of the Russian Far East) in the abnormally hot and low-water summer–autumn season of 2021. Nodularia douglasiae (Griffith et Pidgeon, 1833) was the most resistant and thus least affected species, the species from the genera Sinanodonta and Middendorffinaia, the least resistant and the most affected. [ABSTRACT FROM AUTHOR]

To analyze physiological and biochemical marker responses of brackish water clam Corbicula japonica under global warming conditions, different water temperatures (20°C and 25°C), salinity (5 and 20 psu), and food availability (0.5 and 2.0 mg SS ind−1 d−1) levels were tested. Appropriate biomarkers were selected based on the sensitivity of biomarker responses, condition index (CI), energy reserves, superoxide dismutase (SOD), catalase, oxyradical-absorbance capacity, and lipid peroxidation (LPO) (p < 0.05), and five methods of integrated biomarker response index (IBR) were calculated. CI, SOD, and LPO were employed for IBRI, although four biochemical biomarkers were generally employed for IBR. At high water temperature (HT), all biomarkers were deleteriously affected. HT significantly affected all the IBR methods (p < 0.05), and the highest correlation was discovered in IBRI (r = 0.92, p < 0.01). The lowest and highest IBRs were observed at natural (control = 1.14) and global warming (HT = 2.43) conditions, respectively. The contribution of LPO scores was higher under HT, demonstrating poor organism health. Based on our estimates, three sensitive biomarkers could detect stress in C. japonica under global warming conditions. We conclude that the IBR method based on sensitive biomarkers should be used to quantify anthropogenic impacts on aquatic organisms, especially C. japonica.

This study assessed growth, feed conversion efficiency, and fatty acid composition of three size classes of northern largemouth bass Micropterus salmoides salmoides (80 g, 105 g, and 137 g) subjected to a 35 °C water temperature for 28 days. A completely randomized design was conducted, with ten fish per tank and treatments triplicated. The trial was conducted in 180-L tanks in a recirculating system. Fish were fed a commercial diet formulated for largemouth bass consisting of 48% protein and 18% lipid at approximately 0800 and 1500 h daily. The experimental period lasted for 28 days. Water temperature was a significant contributor to the feeding and growth results observed in this study. While the 137 g group did experience some growth, the observed growth was not biologically significant during this study. The percent body weight consumed by all treatment groups was less than 0.21% day −1. Feed conversion was best for the 137 g group at 4.0 ± 0.44 compared to 5.5 ± 2.57 and 5.8 ± 2.77 for the 80 g and 105 g groups, respectively. Fatty acid profiles of the groups remained similar except eicosapentaenoic acid, which was lower in the 80 g fish. This study was the first to examine the growth of northern largemouth bass at temperatures exceeding 32 °C and suggest extended periods of exposure to 35 °C or higher water temperatures resulted in thermal stress and the inability of these fish to grow at the rates necessary to make them profitable for commercial producers.

To elucidate the possible molecular reaction of vertebral fusion in juvenile golden pompano at high temperature, we examined the changes in growth, vertebral fusion incidence, histological differences and transcription levels of genes related to bone development in juvenile golden pompano at 27 and 33°C for 30 days, respectively. The growth rate of juvenile fish was faster when the water temperature was 33°C, but the incidence of vertebral fusion was higher. Prolonged high water temperature reduced the osteogenic layer in the growth zone of the vertebral endplate and the elastic externa. The endplate growth areas of the fused vertebrae were transformed into cartilage tissue, which was then remodeled into bone. The intervertebral notochord tissue was transformed into bone and the intervertebral space disappeared. In normal phenotypes of vertebrae, short-term high temperature could promote the expression of genes related to cartilage differentiation and maturation, as well as genes related to osteoblastic differentiation. With the increase of culture time, the expression of genes related to cartilage and osteogenesis development was inhibited. In fused vertebrae, cartilage proliferation was enhanced, osteogenic differentiation was inhibited, and matrix mineralization may be enhanced. Genes associated with the development of chondrocytes and osteoblasts in the vertebrae of juvenile Trachinotus ovatus were significantly regulated by temperature and time. The results may contribute to further understanding of the occurrence of vertebral fusion at high temperature.

Recent global warming has been accompanied by high water temperatures (HWTs) in coastal areas of Korea, resulting in huge economic losses in the marine fishery industry due to disease outbreaks in aquaculture. To mitigate these losses, it is necessary to predict such outbreaks to prevent or respond to them as early as possible. In the present study, we propose an HWT prediction method that applies sea surface temperatures (SSTs) and deep-learning technology in a long short-term memory (LSTM) model based on a recurrent neural network (RNN). The LSTM model is used to predict time series data for the target areas, including the coastal area from Goheung to Yeosu, Jeollanam-do, Korea, which has experienced frequent HWT occurrences in recent years. To evaluate the performance of the SST prediction model, we compared and analyzed the results of an existing SST prediction model for the SST data, and additional external meteorological data. The proposed model outperformed the existing model in predicting SSTs and HWTs. Although the performance of the proposed model decreased as the prediction interval increased, it consistently showed better performance than the European Center for Medium-Range Weather Forecast (ECMWF) prediction model. Therefore, the method proposed in this study may be applied to prevent future damage to the aquaculture industry.

In order to understand the mechanisms of conversion between different algal dominance, an experiment was performed in a greenhouse from 22 June to 10 July 2011. The experiment included a treatment group subjected to three instances of nutrient enrichment and a control with no nutrient enrichment. The initial water was dominated by Ankistrodesmus of Chlorophyta. The average water temperature at 08:30 h and 14:00 h during the experiment was 31.6°C and 34.6°C, respectively. The results showed that the total nitrogen (TN), total phosphorus (TP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), and soluble reactive phosphorus (SRP) concentrations in the treatment were significantly higher than in the control (P < 0.05). However, the TN/TP and DTN/DTP in the control was higher than in the treatment (P < 0.05). The dominant algae in the control did not change during the experiment, while the dominant algae in the treatment switched to Planktothrix of Cyanophyta on day 9. The chlorophyll a (Chl-a), wet weight of all algae, wet weight of Cyanophyta, and percentage of Cyanophyta in the control were all significantly lower than in the treatment (P < 0.05). Amounts of zooplankton, especially rotifers, were present at the end of the experimental period. The density of rotifers between the control and treatment was not significantly different (P > 0.05), while the copepod density in the treatment was higher than in the control (P < 0.05). We conclude that green algae dominance quickly switches to cyanobacteria dominance after nutrient enrichment in a greenhouse with elevated temperature.

Records of mortality after a high temperature event in 2014 in the white gorgonian Eunicella singularis were compiled in six different locations around the Chafarinas Islands. Quadrats were used to quantify dead colonies, colonies affected by epibionts and healthy colonies at different depths. No relationship was found between depth and percentage of affected colonies; however, differences in the mortality among sites were detected. On average, 43% of the colonies of E. singularis were found dead, 21% damaged and 36% healthy. These results highlight the need of further researches for monitoring the colonies of this species considering future scenarios of rising temperature. [ABSTRACT FROM AUTHOR]

Recently, sea surface temperatures (SSTs) near the Korean Peninsula have increased rapidly due to global warming; this phenomenon can lead to high water temperatures and extensive damage to Korean fish farms. To reduce such damage, it is necessary to predict high water temperature events in advance. In this study, we developed a method for predicting high water temperature events using time series SST data for the Korean Peninsula obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 product and a long short-term memory (LSTM) network designed for time series data prediction. First, the SST prediction model was used to predict SSTs. Predicted SSTs exceeding 28 °C, which is the Korean government standard for issuing high water temperature warnings, were designated as high water temperatures. To evaluate the prediction accuracy of the SST prediction model, 1-to 7-day predictions were evaluated in terms of the coefficient of determination (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE). The R2, RMSE, and MAPE values of the 1-day prediction SST model were 0.985, 0.14 °C, and 0.38%, respectively, whereas those of the 7-day prediction SST model were 0.574, 0.74 °C, and 2.26%, respectively. We also calculated F1 scores to evaluate high water temperature classification accuracy. The F1 scores of the 1- and 7-day SST prediction models were 0.963 and 0.739, respectively. [ABSTRACT FROM AUTHOR]

Killing activity of fresh Oreochromis niloticus serum was used as an indicator of the natural immunity. Serum killing activity was tested in temperature stressed fish exposed to 32 ±1°C to different Pseudomonas fluorescens strains. As a clinical estimate of natural immunity and disease resistance, experimental challenge with P. fluorescens strains was conducted. The results cleared that serum killing activity at 32±1°C was almost stopped where fish got infected after bacterial challenge. On the other hand, control fish group kept at 23± 1°C developed serum killing activity and resistance to the acquisition of infection after challenge. A correlation was found between resistance activities of P. fluorescens strains to serum killing and their corresponding courses of infection after bacterial challenge. However, the results of experimental challenge conducted at 32±1°C suggested that the immunocompromising state resulted from the stress of inability to withstand high water temperature is exclusively the critical aspect for the induction of infection.

Poor growth greatly reduces the production efficiency of small sea cucumbers Apostichopus japonicus in summer. The present study found that crawling frequency and tentacle activity frequency of sea cucumbers (~1 g of wet body weight) were significantly lower at 25 °C than those at 16 °C. These results suggest that high temperature greatly decreases fitness-related behavior of small A. japonicus. Stressed sea cucumbers (under air exposure for 1 h) showed significantly lower crawling frequency and tentacle activity frequency, compared to those not stressed at 25 °C. This indicates air exposure worsens the adverse effects on fitness-related behavior of small sea cucumbers at a high temperature. Tentacle activity frequency and crawling frequency of stressed A. japonicus cultured with artificial reefs were significantly higher than those cultured without reefs at 25 °C. This finding indicates that artificial reefs greatly improve the fitness-related behavior of stressed individuals at a high temperature. Survival rate, adhesion behavior, pepsin-like protease activity, defecation rate, and intestinal structure were significantly greater in sea cucumbers cultured with reefs than those cultured without reefs at 25 °C for 9 days. These novel results indicate that reefs greatly improve the digestive ability of sea cucumbers at a high temperature, which probably contribute to growth performances of sea cucumbers. The present study developed an effective approach to improving fitness-related behavior and digestive ability of small sea cucumbers, providing valuable insights into the seed production in summer. • High temperature negatively affects behaviors and digestive ability of sea cucumbers. • Air exposure deteriorates the adverse effects on behaviors of sea cucumbers. • Artificial reefs greatly improve behaviors and digestive ability of sea cucumbers. [ABSTRACT FROM AUTHOR]

Abstract: It has been traditionally accepted that the gonadotropins (GtHs), follicle stimulating hormone (FSH) and luteinizing hormone (LH), are synthesized and secreted only by the pituitary. However, the presence of theses hormones in extrapituitary tissues has been demonstrated in mammals, and more recently also in fish. In this study, we cloned the cDNAs and characterized the expression of FSH-β, LH-β, and glycoprotein hormone α (GPH-α) subunits from brain and gonads of male and female pejerrey Odontesthes bonariensis at different stages of gonadal maturation. In situ hybridization revealed that, in addition to their classical location in pituitary cells, the three GtH transcripts were also located in the gonads. FSH-β and GPH-α subunits were found in the cytoplasm of oogonia, previtellogenic and vitellogenic oocytes in ovaries. LH-β expression was detected in previtellogenic and vitellogenic oocytes but not in oogonia. In males, the three subunits were expressed in spermatogonia and to a lesser extent in spermatocytes. Exposure of fish to high water temperatures that impair pejerrey reproduction also induced a decrease of extrahypophyseal expression of GtH subunits. [Copyright &y& Elsevier]

Abstract: Black-band disease (BBD) is a temperature- and light-dependent syndrome typically found on shallow-dwelling corals. The bacterial consortium that creates BBD contains a photosynthetic cyanobacterium, which is particularly sensitive to light. High light causes the BBD cyanobacteria to self-shade, which encourages the formation of the anoxic microenvironment essential for the BBD consortium. From May to September 2009, a shallow-reef area was monitored to quantify the epizootiology of BBD on the brain coral Diploria strigosa. The prevalence and incidence of BBD were recorded approximately every two weeks. To test the hypothesis that reduced light would increase the rate of disease progression by reducing photoinhibition in the BBD cyanobacteria, shade structures, made out of plastic sheeting on a polyvinyl chloride (PVC) frame, were installed above D. strigosa colonies with BBD. The shade material reduced photosynthetically available radiation (PAR) by >80%. The progression of BBD on shaded colonies was compared with cage control and control colonies. A pulse–amplitude–modulation fluorometer was used to measure the amount of PAR and maximum excitation pressure (Q m ) on each colony after two weeks of treatment. Linear progression rates and the band width of BBD were measured weekly and treatments were compared through time. During the summer months, the prevalence of BBD showed a positive, exponential relationship with water temperature, whereas the incidence of BBD displayed a positive linear relationship with the rate of change of water temperature. PAR on, and the Q m of, shaded corals was significantly lower than the two control treatments; however, Q m values did not indicate excessive photochemical pressure on the coral host. The progression rates of BBD and the black-band width on shaded colonies significantly increased after one week of shading, whereas the control treatments did not change. During the second week of manipulation, however, black-band width and progression rates were similar to values prior to manipulation. These results suggest that, even under low-light conditions, a compact and dense ‘black’ band is essential for the persistence of the BBD consortium. [Copyright &y& Elsevier]

Photosynthetic activities of seedlings of Zostera marina were successively measured using a gas volumeter for 6 days at seven light (0–400 μmol photons/m2 per s) and 11 water temperature conditions (5–35°C). The seedlings were collected from mature plants (Ise Bay, central Japan), and stored and cultured in incubators accurately controlled at each test temperature. The maximum gross photosynthesis ( Pmaxg) was recorded at an optimal water temperature of 29°C after 0 days. After 6 days, Pmaxg appeared at 25°C and most plants cultured at 29–30°C bleached and withered after the drastic increase of light compensation point ( Ic). On the contrary, at 5–28°C, the photosynthetic activities either changed little (5–25°C) or recovered after a temporal reduction (26–28°C); seedlings survived and looked healthy after being cultured for 6 days. The recovery was thought to be an acclimation to tolerate higher water temperature. As a result, the critical upper water temperature for Z. marina seedlings was proposed as 28°C. The temperature was consistent with the previously reported maximum water temperature in habitats around the southern boundary of Z. marina in the northern hemisphere. [ABSTRACT FROM AUTHOR]

• Strong stratification led to early development of C. polykrikoides bloom during heatwaves • High water temperature by heatwaves is negatively affecting growth of C. polykrikoides bloom • C. polykrikoides had a physiological difference between strains in the same ribotype • Heatwaves have a significant effect on the formation and maintenance of C. polykrikoides blooms In 2018, the bloom of harmful dinoflagellate Cochlodinium polykrikoides occurred under abnormally high water temperature (WT) conditions caused by heatwaves in Korean coastal water (KCW). To better understand C. polykrikoides bloom at high WTs in 2018, we conducted field survey and laboratory experiments (the physiological and genetic differences between the two strains, CP2013 and CP2018). The heatwave increased the WT from 24.1°C to 29.2°C for two weeks, leading to strong stratification even in mid July (p < 0.01, Chi square = 94.656, Kruskal–Wallis test). Under early stratification conditions, patch blooms formed more earlier than the average outbreak in the last 17 years in KCW, despite high WT reaching 30°C. In laboratory experiments, although there were no genetic differences in the LSU rDNA, both strains showed a significant different growth response to high WTs; above 28°C, CP2013 did not survive, but CP2018 was able to grow, suggesting that CP2018 had potential growth capacity at high WTs. However, the growth rate and yield of the culture (CP2018) were lowered at 30°C. Also, the blooms of C. polykrikoides in 2018 lasted only 3 weeks, which is unusual short compared to the average duration since 2002. The negative correlation between the average WT and duration of C. polykrikoides bloom in previous 17 years (R2 = 0.518, p < 0.01) supports that high WT approaching 30°C is not favorable for C. polykrikoides in KCW. Thus, our findings indicated that in relation to heatwaves, early stratification condition plays a critical role in developing C. polykrikoides blooms, but maintaining bloom are negatively affected under high WT conditions. [ABSTRACT FROM AUTHOR]

Recent global warming has been accompanied by high water temperatures (HWTs) in coastal areas of Korea, resulting in huge economic losses in the marine fishery industry due to disease outbreaks in aquaculture. To mitigate these losses, it is necessary to predict such outbreaks to prevent or respond to them as early as possible. In the present study, we propose an HWT prediction method that applies sea surface temperatures (SSTs) and deep-learning technology in a long short-term memory (LSTM) model based on a recurrent neural network (RNN). The LSTM model is used to predict time series data for the target areas, including the coastal area from Goheung to Yeosu, Jeollanam-do, Korea, which has experienced frequent HWT occurrences in recent years. To evaluate the performance of the SST prediction model, we compared and analyzed the results of an existing SST prediction model for the SST data, and additional external meteorological data. The proposed model outperformed the existing model in predicting SSTs and HWTs. Although the performance of the proposed model decreased as the prediction interval increased, it consistently showed better performance than the European Center for Medium-Range Weather Forecast (ECMWF) prediction model. Therefore, the method proposed in this study may be applied to prevent future damage to the aquaculture industry. [ABSTRACT FROM AUTHOR]