Effect Of High Water Temperature Research Articles

Elimination of Decapod iridovirus 1 (DIV1) infection at high water temperature: a new environmental control strategy

AbstractDecapod iridovirus 1 (DIV1) poses a major challenge to sustainable shrimp farming and poses a serious hazard to aquaculture industry. This study investigated the complex interaction between DIV1 infection and water temperature, focusing on the effect of high temperature on DIV1 infection due to Penaeus monodon. Using models of latent and acute infection, the study revealed the response of P. monodon to DIV1 under different conditions. In the experimental set-up, the effect of high water temperature (34 ± 1 °C) compared with room temperature (26 ± 1 °C) was investigated. DIV1 replication was significantly inhibited in the high-temperature group (H), resulting in complete viral elimination within 15 days. DIV1 did not resurface even after return to room temperature (26 ± 1 °C), indicating sustained antiviral effects. Compared with the room temperature (26 ± 1 °C) group (N), the H group showed a 100% reduction in the incidence of latent and acute infection. Exposure to high water temperature directly impaired the viability of DIV1, enhancing the immune system of P. monodon, and expediting metabolic processes for efficient DIV1 clearance. The study highlights the significant inhibitory effects of high water temperature (34 ± 1 °C) on DIV1 infection in P. monodon, resulting in viral eradication. This discovery offers a potential strategy for mitigating DIV1 infections in shrimp aquaculture, prompting further investigation into underlying mechanisms. Optimising parameters and protocols for high-temperature treatment is crucial for viral control. Exploring the broader implications of the findings on other viral infections in crustacean aquaculture could provide valuable insights for comprehensive disease prevention and control.

Effects of high water temperature on physiology, survival, and resistance to high temperature air-exposure in the Manila clam Ruditapes philippinarum

Ruditapes philippinarum is a typical burrowing shellfish, living in the intertidal zone. In natural conditions, the mortality of R. philippinarum is most affected by high water temperatures, high temperature air-exposure, and other environmental stresses. In this study, the mortality rates of the two populations of R. philippinarum under high water temperature stress were recorded, and catalase (CAT), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) antioxidant enzyme activities in the hepatopancreas were analyzed. The results showed that the survival times of cultured clams were longer than those of wild clams after acute high temperature stress. CAT, SOD, and T-AOC activities increased after acute high water temperature and high temperature air-exposure stress. These antioxidant enzyme activities gradually decreased to their initial levels after 2 days of recovery from these high temperature stresses. Based on these experimental results, we found that the cultured clam population had better heat and high temperature air-exposure resistances than the wild clams. CAT, SOD, and T-AOC enzymes play an important role in the antioxidant processes of R. philippinarum in response to high water temperature and high temperature air-exposure. This study provided a theoretical basis for the development of healthy aquacultural practices for these shellfish.

Alterations of oxygen consumption and gills morphology of Nile tilapia acclimatized to extreme warm ambient temperature

Elevation of water temperature due to global warming influences the physiological properties of fish by increasing their rate of metabolic function and demand for oxygen. It is important to know how fish respond to changing environments for indicating and predicting the impacts of climate change on fish populations, communities and for their sustainable management. Hence, the present study was aimed to investigate the effects of high water temperature on juvenile Nile tilapia, based on the oxygen consumption rate, blood physiology and gill morphology in different temperature (31 °C, 34 °C and 37 °C) in triplicates for a period of 28 days. Results showed that the oxygen consumption rate increased significantly at 37 °C, whereas no significant difference was observed at 31 °C and 34 °C. Hemoglobin (Hb) and red blood cell (RBC) were decreased significantly at 37 °C after 14 and 28 days of exposure, whereas blood glucose levels showed the opposite scenario. On the other hand, no significant changes were observed for white blood cell (WBC) on day 14, but a significant increase was observed on day 28 at 37 °C. Being the site of main gaseous exchange moderate to severe histopathological changes (epithelial lifting, epithelial necrosis, hypertrophy of chloride cell, lamella fusion, telangiectasia, vacuolation of epithelium and epithelial edema) were observed in the gill especially in the gill lamellae of the experimental fish at 37 °C. The findings of the study indicate the adaptive physiological strategy in changing climate despite being a thermal tolerant species, and the alteration in oxygen consumption rate, gill morphology and blood parameters could be used as an assessment strategy to know the condition of the fish and their surrounding environment.

How does elevated water temperature affect fish brain? (A neurophysiological and experimental study: Assessment of brain derived neurotrophic factor, cFOS, apoptotic genes, heat shock genes, ER-stress genes and oxidative stress genes)

Water temperature is one of the most important environmental factors affecting the growth and survival of fish. Increased water temperature became a global problem and it is estimated that there will be an increase in water temperature due to global climate change. The physiological mechanism for the effects of high water temperature on the fish brain is not fully known. In the present study, fish were exposed to different temperatures (10 °C/15 °C/20 °C/25°) and brain tissues were sampled 2 h-4h-6h–8h per hour respectively and then we investigated transcriptional changes of BDNF, cFOS, apoptotic genes (caspase 3, Bax, Bcl2), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1) and oxidative stress genes (CAT, SOD, and GPx) and also immunoflourescence changes of BDNF and cFOSin rainbow trout brain. The results indicated that high temperature stress lead to physiological changes in the fish brain by causing a decrease in mRNA expression levels of CAT, SOD, GPx and Bcl2 and by causing an increase in mRNA expression of BDNF, cFOS, apoptotic genes (caspase 3, Bax), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1). This study will provide important information to elucidate the physiological mechanisms related to the effects of high water temperature on the fish brain.

Evaluation of Nutrients Mass Balance on the Weirs in the Mid-lower Nakdong River Basin

The construction of artificial weirs as part of the Four Major Rivers Restoration Project is expected to result in the Nakdong River Basin having the characteristics of closed water bodies and properties of water quality that convert suspended components into soluble ones due to a long retention time, thereby leading to the continuous deterioration of water quality. In this regard, this study investigated the changes of water quality on four weirs in the mid-lower Nakdong River Basin. In addition, it examined the organic matters and nutrient salts affecting the water quality, established mass balance with respect to the nutrient salts, and analyzed the load accumulations of each weir to present the directions for water quality management. With regard to the water quality, the items of BOD and COD, T-N and NH4-N, and T-P and PO4-P showed similar tendencies, and most of the items exhibited high concentrations from July to September. Furthermore, it was confirmed that the concentrations of the water quality items were high in Dalseong Weir and Hapcheon-Changnyeong Weir. In July, most of the weirs showed the greatest difference of DO in the surface layer and deepwater layer, while the DO concentration of the deepwater layer dropped below 4.0 mg/L in all four weirs. The sediment survey showed that the SS, T-N, and T-P have a larger amount of sediment in the aphotic zone than in the photic zone, and the amount of sediment per unit area was greatest in Dalseong Weir. According to the sediment release survey results, the release concentration was high in July, which was due to the effects of high water temperature and low DO concentration. T-N was eluted mostly from Dalseong Weir and Gangjeong-Goryeong Weir, and T-P was eluted mostly from Dalseong Weir and Hapcheon-Changnyeong Weir. Among the mass balance, nitrogen balance showed the highest amount of accumulation in Gangjeong-Goryeong Weir (6109 kg/d), and phosphorus balance showed the highest amount of accumulation in Changnyeong-Haman Weir (447 kg/d). These results are expected to be utilized as important materials for setting the management directions for each weir.

Changes in Blood Cell Morphology and Number of Red Spotted Grouper, Epinephelus akaara in Response to Thermal Stress.

Rising of water temperature due to global warming is a great concern to aquaculturists and fishery biologists. Hence, the present study aimed to investigate the effects of high water temperature on juvenile red spotted grouper, Epinephelus akaara based on the evaluation of stress responses in blood. E. akaara juveniles were exposed to different thermal conditions (25℃, 28℃, 31℃, and 34℃) for 6 weeks following 2 weeks of acclimation at 25℃. Blood cell morphology and number were examined at three sampling points (2, 7, and 42 days) from a total of 180 fish. Major erythrocytic cellular abnormalities (ECA) observed in blood smears of thermally stressed groups (31℃ and 34℃) after 6 weeks were echinocytes, teardrop-like cells, swollen cells and vacuolated cells. Both red and white blood cell number (RBC and WBC) were significantly (p<0.05) elevated in 31℃ and 34℃ group after 6 weeks thermal exposure. Differential leucocytes number showed significant increases in neutrophil (N) and decreases in lymphocytes (L) in the highest temperature (34℃). Different N:L ratio was observed at different thermal conditions which can be used as a reliable alternative to measure stress response. Taken together, these results suggest that higher temperature (31℃ and 34℃) can interfere the immune system of red spotted grouper by altering the blood cell morphology and number.

Influence of Water Temperature Anomalies on the Growth of Zostera marina Plants Held Under High and Low Irradiance Levels

Coastal water temperature anomalies are expected to intensify during the current period of global climate change. Sudden water temperature elevation (e.g., heat waves) or decrease (e.g., summer upwelling) can have a far-reaching influence on seagrasses in temperate regions. We examined the influence of anomalously elevated and decreased water temperatures on the growth of Zostera marina plants held under two different levels of irradiance. Core samples of wild Z. marina shoots were cultured under either suddenly elevated (from the in situ level of 20 to 27 °C during the fall experiment) or decreased (from the in situ level of 27 to 20 °C during the summer experiment) temperature. We included light as an experimental factor because the light requirements of seagrasses increase when plants are under thermal stress. The growth of Z. marina shoots under anomalously elevated water temperature conditions, which simulated marine heat waves, was significantly declined, whereas the plant growth under suddenly decreased water temperature conditions, which simulated summer upwelling events, was maintained or slightly increased. In the fall 2014 experimental period, Z. marina shoots under the suddenly elevated water temperature condition (27 °C) showed significant decreases in shoot density, biomass, and leaf productivity by ca. 40–80%, whereas plants held under the ambient water temperature condition (20 °C) maintained or slightly increased their growths. In the summer 2015 experimental period, Z. marina under the sudden temperature reduction conditions (20 °C) maintained relatively high shoot density and leaf productivity, whereas plants under the in situ high water temperature condition (27 °C) showed significantly reduced growths. The growth of Z. marina shoots, which were cultured in the optimal temperature condition (20 °C), was enhanced by increasing underwater irradiance. However, the adverse effects of high water temperature on Z. marina growth could not be reversed by increasing irradiance levels at the end of the experiments. According to the results of this study, the intensified sea surface water temperature anomalies induced by global climate change will alter the growth and distribution of temperate seagrasses and, consequently, the structure and function of the coastal seagrass ecosystems in the temperate region.

Effect of High Water Temperature on the Growth and Lipid Compositions of the Sea Cucumber Apostichopus japonicus

Effect of High Water Temperature on the Growth and Lipid Compositions of the Sea Cucumber Apostichopus japonicus

Increased tolerance of Beauveria bassiana and Metarhizium anisopliae conidia to high temperature provided by oil-based formulations.

The influence of the temperature of aqueous conidial sprays on conidial viability and virulence against Diatraea saccharalis was evaluated for pure conidia, rice + fungus (technical concentrates) and oil-based formulations of Beauveria bassiana s.s. and Metarhizium anisopliae s.s. under laboratory conditions. The fungal preparations were suspended in water and maintained at 26 °C, 36 °C and 46 °C for one, four and six hours. Conidial viability was determined by plating aliquots of each suspension onto PDA medium followed by incubation for 20-22 h and observing for viable conidia (germ tubes longer than diameter of conidia). Fungal virulence was determined by spraying suspensions onto third-instar larvae of D. saccharalis. In general, germination and virulence, particularly for unformulated conidia, were negatively affected by increases in water temperature and exposure time in suspension. However, the decrease in conidial viability in the oil-in-water emulsion was less than 7% for both species after 6 h of exposure at 36 °C, in contrast to reductions of 7-21% and 28-60% for the oil-free suspensions of B. bassiana and M. anisopliae, respectively. For the sprays of conidia in an oil-in-water emulsion previously exposed to elevated water temperatures for longer periods, the levels of insect mortality were higher than those of pure conidia or technical concentrates under identical conditions. Our results indicate that emulsifiable oil-based formulations can protect the conidia of both species of fungi from the adverse effects of high water temperatures before spraying in the field.

Fine-tuning for the tropics: application of eDNA technology for invasive fish detection in tropical freshwater ecosystems.

Invasive species pose a major threat to aquatic ecosystems. Their impact can be particularly severe in tropical regions, like those in northern Australia, where >20 invasive fish species are recorded. In temperate regions, environmental DNA (eDNA) technology is gaining momentum as a tool to detect aquatic pests, but the technology's effectiveness has not been fully explored in tropical systems with their unique climatic challenges (i.e. high turbidity, temperatures and ultraviolet light). In this study, we modified conventional eDNA protocols for use in tropical environments using the invasive fish, Mozambique tilapia (Oreochromis mossambicus) as a detection model. We evaluated the effects of high water temperatures and fish density on the detection of tilapia eDNA, using filters with larger pores to facilitate filtration. Large-pore filters (20μm) were effective in filtering turbid waters and retaining sufficient eDNA, whilst achieving filtration times of 2-3min per 2-L sample. High water temperatures, often experienced in the tropics (23, 29, 35°C), did not affect eDNA degradation rates, although high temperatures (35°C) did significantly increase fish eDNA shedding rates. We established a minimum detection limit for tilapia (1 fish/0.4megalitres/after 4days) and found that low water flow (3.17L/s) into ponds with high fish density (>16fish/0.4megalitres) did not affect eDNA detection. These results demonstrate that eDNA technology can be effectively used in tropical ecosystems to detect invasive fish species.

Arachidonic Acid and Eicosapentaenoic Acid Metabolism in Juvenile Atlantic Salmon as Affected by Water Temperature.

Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal environmental conditions, such as high water temperatures during summer seasons. Aerobic scope increases and lipid metabolism changes are known plasticity responses of fish for a better acclimation to high water temperature. The present study aimed at investigating the effect of high water temperature on the regulation of fatty acid metabolism in juvenile Atlantic salmon fed different dietary ARA/EPA ratios (arachidonic acid, 20:4n-6/ eicosapentaenoic acid, 20:5n-3), with particular focus on apparent in vivo enzyme activities and gene expression of lipid metabolism pathways. Three experimental diets were formulated to be identical, except for the ratio EPA/ARA, and fed to triplicate groups of Atlantic salmon (Salmo salar) kept either at 10°C or 20°C. Results showed that fatty acid metabolic utilisation, and likely also their dietary requirements for optimal performance, can be affected by changes in their relative levels and by environmental temperature in Atlantic salmon. Thus, the increase in temperature, independently from dietary treatment, had a significant effect on the β-oxidation of a fatty acid including EPA, as observed by the apparent in vivo enzyme activity and mRNA expression of pparα -transcription factor in lipid metabolism, including β-oxidation genes- and cpt1 -key enzyme responsible for the movement of LC-PUFA from the cytosol into the mitochondria for β-oxidation-, were both increased at the higher water temperature. An interesting interaction was observed in the transcription and in vivo enzyme activity of Δ5fad–time-limiting enzyme in the biosynthesis pathway of EPA and ARA. Such, at lower temperature, the highest mRNA expression and enzyme activity was recorded in fish with limited supply of dietary EPA, whereas at higher temperature these were recorded in fish with limited ARA supply. In consideration that fish at higher water temperature recorded a significantly increased feed intake, these results clearly suggested that at high, sub-optimal water temperature, fish metabolism attempted to increment its overall ARA status -the most bioactive LC-PUFA participating in the inflammatory response- by modulating the metabolic fate of dietary ARA (expressed as % of net intake), reducing its β-oxidation and favouring synthesis and deposition. This correlates also with results from other recent studies showing that both immune- and stress- responses in fish are up regulated in fish held at high temperatures. This is a novel and fundamental information that warrants industry and scientific attention, in consideration of the imminent increase in water temperatures, continuous expansion of aquaculture operations, resources utilisation in aquafeed and much needed seasonal/adaptive nutritional strategies.

Activation of AMP-activated protein kinase in response to temperature elevation shows seasonal variation in the zebra mussel, Dreissena polymorpha

Global climate change is affecting ectothermic species, and a variety of studies are needed on thermal tolerances, especially from cellular and physiological perspectives. This study utilized AMP-activated protein kinase (AMPK), a key regulator of cellular energy levels, to examine the effects of high water temperatures on zebra mussel (Dreissena polymorpha) physiology. During heating, AMPK activity increased as water temperature increased to a point, and maximum AMPK activity was detected at high, but sublethal, water temperatures. This pattern varied with season, suggesting that cellular mechanisms of seasonal thermal acclimatization affect basic metabolic processes during sublethal heat stress. There was a greater seasonal variation in the water temperature at which maximum AMPK activity was measured than in lethal water temperature. Furthermore, baseline AMPK activity varied significantly across seasons, most likely reflecting altered metabolic states during times of growth and reproduction. In addition, when summer-collected mussels were lab-acclimated to winter and spring water temperatures, patterns of heat stress mirrored those of field-collected animals. These data suggest that water temperature is the main driver of the seasonal variation in physiology. This study concluded that AMPK activity, which reflects changes in energy supply and demand during heat stress, can serve as a sensitive and early indicator of temperature stress in mussels.

Growth and Survival of Apache Trout Under Static and Fluctuating Temperature Regimes

AbstractIncreasing stream temperatures have important implications for arid‐region fishes. Little is known about effects of high water temperatures that fluctuate over extended periods on Apache Trout Oncorhynchus gilae apache, a federally threatened species of southwestern USA streams. We compared survival and growth of juvenile Apache Trout held for 30 d in static temperatures (16, 19, 22, 25, and 28°C) and fluctuating diel temperatures (±3°C from 16, 19, 22 and 25°C midpoints and ±6°C from 19°C and 22°C midpoints). Lethal temperature for 50% (LT50) of the Apache Trout under static temperatures (mean [SD] = 22.8 [0.6]°C) was similar to that of ±3°C diel temperature fluctuations (23.1 [0.1]°C). Mean LT50 for the midpoint of the ±6°C fluctuations could not be calculated because survival in the two treatments (19 ± 6°C and 22 ± 6°C) was not below 50%; however, it probably was also between 22°C and 25°C because the upper limb of a ±6°C fluctuation on a 25°C midpoint is above critical thermal maximum for Apache Trout (28.5–30.4°C). Growth decreased as temperatures approached the LT50. Apache Trout can survive short‐term exposure to water temperatures with daily maxima that remain below 25°C and midpoint diel temperatures below 22°C. However, median summer stream temperatures must remain below 19°C for best growth and even lower if daily fluctuations are high (≥12°C).Received June 26, 2013; accepted May 19, 2014

Genotypic variation in the response to high water temperature during vegetative growth and the effects on rice productivity under a cool climate

We examined the effects of high water temperature (Tw) during early vegetative growth on dry matter production, grain yield, and grain quality in a 2-year field trial in northern Japan using two rice cultivars: ‘Hitomebore’, a standard cultivar for this region, and ‘Koshihikari’, a late-maturing cultivar. The heading date of ‘Koshihikari’ was 8–9 days later than that of ‘Hitomebore’. Heading date was significantly earlier for both cultivars (by 2–5 days) in the high Tw treatment, without a significant cultivar×Tw interaction. High Tw significantly increased dry matter production before heading, and there was a significant cultivar×Tw interaction: ‘Koshihikari’ responded more than ‘Hitomebore’ to high Tw. This genotypic difference was explained by the daily rate of dry matter increase rather than by the growth duration. After heading, leaf senescence measured as the reduction of the SPAD value was greater at high Tw for both cultivars. Radiation-use efficiency after heading was significantly reduced by high Tw for both cultivars. Consequently, the positive effect of high Tw on dry matter production was reduced for both cultivars at harvest. Grain yield was significantly increased by high Tw (by 1–20%), but without a significant Tw×cultivar interaction. These results suggest that to increase grain yield above that for the standard cultivar ‘Hitomebore’, manipulation of the accelerated leaf senescence caused by high Tw will be a key factor in efforts to adapt rice to future global warming.

High water temperature impairs ovarian activity and gene expression in the brain–pituitary–gonadal axis in female red seabream during the spawning season

Temperature plays a pivotal role in the control of seasonal reproduction in temperate fish species. It is well known that temperatures that exceed a certain threshold impair gonadal development, maturation, and spawning. However, the endocrine mechanisms that underlie these effects are poorly understood. We evaluated the effect of high water temperature on the brain–pituitary–gonadal (B–P–G) axis of a perciform fish, red seabream, Pagrus (Chrysophrys) major during its spawning season (April–May). Fish were reared at either high (24°C: H-group) or optimal/control (17°C: C-group) temperatures for 5 or 10d. After 5d, the transcript abundance of gonadotropin-releasing hormone-1 (GnRH1) in the brain and GnRH receptor (GnRH-R) and FSH-β in the pituitary were significantly lower in H-group than in C-group. Conversely, there was no difference in pituitary LH-β mRNA levels, serum concentrations of estradiol-17β (E2), or the gonadosomatic index (GSIs) between H- and C-groups on Day 5. After 10d, the ovaries of all H-group fish had completely regressed and were filled with only perinucleolar stage primary oocytes and atretic oocytes. The brain GnRH1 expression, pituitary GnRH-R and pituitary LH-β expression, serum E2 concentrations, and the GSI were significantly lower in the H-group on Day 10. Our results suggest that high water temperature is the proximate driver of the termination of the spawning season of female red seabream. The effect appears to be mediated by suppression of gene expression in the B–P–G axis.

瀬戸内海産イカナゴの死亡と再生産に及ぼす夏眠期における高水温飼育の影響

夏眠期の水温条件（24, 26 および 28℃）が瀬戸内海産イカナゴの死亡および再生産へ及ぼす影響を飼育試験により調べた。試験開始 3 ヵ月後の累積死亡率はそれぞれ 3.0, 13.7 および 29.7% で，水温が高いほど死亡率が高くなる傾向が認められた。12 月後半にはいずれの水温区においても概ね順調に成熟したが，28℃ 区ではよう卵数および精巣重量が低い傾向にあった。従って，天然海域においても夏眠期の高水温はイカナゴの死亡および再生産に悪影響を及ぼしている可能性が示唆された。

Effect of High Water Temperature During the Vegetative Growth Stage on Dry Matter Production and Yield of Two Rice Cultivars in Cool Climate

Effect of High Water Temperature During the Vegetative Growth Stage on Dry Matter Production and Yield of Two Rice Cultivars in Cool Climate

Extrahypophyseal expression of gonadotropin subunits in pejerrey Odontesthes bonariensis and effects of high water temperatures on their expression

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.

The effect of high water temperatures on the allometric scaling effects of energy and protein starvation losses in juvenile barramundi, Lates calcarifer

This study was undertaken to examine the effects of high water temperatures on the allometric scaling effects of energy and protein starvation losses by juvenile barramundi, Lates calcarifer. The somatic energy and protein loss was examined in fish of varying sizes when starved for 24 or 25 days at temperatures ranging from 23 °C to 38 °C. The amount of energy and protein lost varied according to both size and temperature and was consistent with the function of a ⁎ W b , where a is a temperature dependent coefficient, W the animal's weight and b an exponent relating energy loss to live-weight. The coefficient for energy or protein loss varied and was described by a polynomial function, with a general increase from 23 °C to 32 °C, before a dramatic decline after 35 °C. In contrast, the exponent for energy loss was relatively constant between 23 °C and 35 °C, but showed a rapid increase at 38 °C. Both the coefficients and exponents of protein loss mirrored that of energy loss. Analysis of the protein and lipid contributions to energy loss shows that typically lipid loss accounts for the greater part of energy loss (~ 67%), but also shows that above 35 °C protein energy loss increases (from ~ 33% to ~ 39%) while the losses seen from lipid catabolism remain the same. These results show that one of the main nutritional issues associated with heat stress in fish is a dramatic increase in endogenous loss of protein.

Effect of high water temperature during vegetative growth on rice growth and yield under a cool climate

Global warming is likely to increase spring temperatures in regions with a cool climate. To examine the effects of this change on rice productivity, we exposed rice plants to a higher (by +2.7 to +2.8 °C) water temperature ( T w) during the vegetative growth period (for 35–50 days) under three levels of N fertilization. High T w during vegetative growth made the heading stage occur 4–7 days earlier for all levels of N fertilization in both years. The crop growth rate during the treatment period was greatly enhanced by high T w: by 51–82% in 2008 and by 49–62% in 2009. There was no T w × N fertilizer interaction. This increased growth was associated with increased leaf expansion and increased canopy radiation capture rather than with increased radiation-use efficiency. However, the positive effect decreased during subsequent growth stages under all levels of N fertilization, leading to no significant differences in total biomass at maturity. High T w during vegetative growth greatly reduced SPAD values during the grain-filling stage compared with SPAD values in the control T w treatment, for all levels of N fertilization, and decreased leaf photosynthesis during the mid-grain filling stage. Grain yield was not significantly affected by high T w at any N fertilizer level or in either year.