Reduction In Specific Growth Rate Research Articles

Microplastics impair the reproductive behavior and life history traits of the amphipod Parhyale hawaiensis

We investigated the distribution and effects of waterborne microplastic (MP) (polyethylene microspheres, 53–63 um) on the emergent model for ecotoxicology, the amphipod Parhyale hawaiensis, during 30 days of exposure. The following life-history traits were measured: (1) survival, (2) specific growth rate (SGR), (3) reproductive performance (precopulatory pairing behavior, fecundity, and time to release neonates), (4) molting frequency, (5) F1 newborn offspring survival and (6) MP bioaccumulation. No significant mortality or molt was seen in any of the treatments. MP caused a reduction in SGR, being more pronounced in females. The time for precopulatory pairing was 3-fold longer in amphipods exposed to MP. Fecundity decreased by 50 %, and the time to release juveniles was 6.7 days longer for amphipods exposed to MP. Finally, neonate survival decreased by 80 % after ten days of release. MP disrupts the reproductive mechanisms and triggers adverse effects on life history traits in P. hawaiensis.

Monitoring welfare indicators of rainbow trout (Oncorhynchus mykiss) in a commercial organic farm: Effects of an innovative diet and accelerometer tag implantation

To meet the growing demand for aquatic products, the aquaculture sector is expanding, including organic aquaculture. One of the main challenges in this industry is the development of suitable fish feeds. EU regulations have made recommendations, including the incorporation of fishmeal from organic aquaculture trimmings. However, the use of such fish meal may pose issues due to lower protein content and elevated phosphorus concentrations that could conflict with national environmental regulations. Thus, there is a pressing need for innovative research to formulate environmentally friendly feeds for organic aquaculture. This study aims to evaluate the feasibility of utilizing an innovative organic feed derived from trimmings (substitution of 64.3% of dietary fish meal trimmings with fishmeal protein concentrate from trimmings) for rainbow trout (Oncorhynchus mykiss). This study assessed the impact of this innovative diet on rainbow trout welfare over a two-month period in real-farming conditions, using: (i) growth parameters, (ii) external morphological damages, (iii) swimming activity, used as a proxy for energy expenditure, and (iv) blood and liver health and welfare indicators. Given that fish swimming activity was evaluated using surgically implanted accelerometer tags, we also investigated the potential adverse effects of implanting these tags on fish welfare. Our findings indicate that accelerometer implantation did not significantly affect fish welfare, but a 18.6% reduction in specific growth rate was shown in tagged fish compared to their non-tagged counterparts. Importantly, the innovative diet did not impair health and welfare indicators of blood and liver or lead to external morphological abnormalities. An increased energy expenditure in fish fed the innovative diet compared to those on a control diet was, however, shown, but there was no observable impact on growth performance. The use of this innovative diet may offer a viable solution to reduce the release of soluble phosphorus into the environment while maintaining appropriate standards for fish growth and welfare in organic conditions. Nevertheless, long-term consequences should be explored.

Accumulated CO2 affects growth, acid-base regulation and ion balance of turbot (Scophthalmus maximus) in a recirculating aquaculture system

The major advantage of recirculating aquaculture systems (RAS) is the ability to manipulate and control environmental variables to optimize production efficiency. However, the characteristics of water recycling and high-density aquaculture in RAS may result in the rapid accumulation of carbon dioxide (CO2) when raising high-density marine fish. This study aimed to evaluate the effects of CO2 on growth-related parameters, tissue structure, acid-base homeostasis, and ion regulation in turbot (Scophthalmus maximus). Turbot were subjected to five different CO2 treatments (C, 8, 16, 24, and 32 mg/L) at a temperature of 14 °C for durations of 7, 15, 30, and 60 days. The results indicated a substantial reduction in specific growth rate with increasing duration of CO2 exposure, accompanied by a significant increase in feed conversion rate. Exposure to CO2 also triggered the deposition of lipids or glycogen in the turbot liver, inhibiting the expression of growth factors. Additionally, it caused dissolution of the intestinal lamina propria and vacuolation of the intestinal mucosa. Even exposure to low levels of CO2 (8 mg/L) caused damage to the turbot gill tissue. Plasma analysis of turbot showed significantly higher concentrations of plasma HCO3− and significantly lower concentrations of Na+ and Cl−. Plasma HCO3− concentrations reached a maximum of 33.35 ± 0.13 mmol/L in the 32 mg/L treatment, and genes related to osmoregulation and acid-base homeostasis in the gill (H+-ATPase, NBCI, CA, AE, NHE1, NHE2) were altered based on the duration of CO2 exposure. The kidney did not exhibit significant damage throughout the experiment, and genes related to renal osmoregulation and acid-base homeostasis (AE, NBCI, NHE3, CAII, CAIV) were significantly elevated with CO2 exposure compared to the control group. These findings indicate that prolonged exposure to CO2 has a severe impact on feeding, resulting in damage to the liver and intestinal tissues, stress within the fish body, and disrupted expression of key genes related to the growth hormone/insulin-like growth factor axis. The study highlights the significance of monitoring CO2 concentrations in RAS for optimal marine fish health, as even concentrations below the 8 mg/L threshold have an impact on turbot. The involvement of turbot kidneys strengthens their buffering capacity against CO2, but CO2 stress still affects the gut and growth axis due to ion exchange and the progression of the HCO3−buffering system, leading to growth inhibition. Overall, this study provides valuable insights into the effects of CO2 exposure on turbot aquaculture and underscores the importance of monitoring CO2 concentrations in RAS to ensure optimal health of marine fish.

Alkyl Benzene Sulfonate Induced Acute Toxicity and Potential Alteration of Growth, Hematological, Biochemical, Enzymological and Stress Biomarkers in Oreochromis mossambicus (Peters, 1852)

The present study was intended to determine the toxic effect of Alkyl benzene sulfonate (ABS) on Oreochromis mosambicus. Probit analysis was employed to determine the 96h LC50 of surfactants for O. mossambicus. Moreover, the survivability of surfactant exposed was calibrated and validated using general threshold survival models (GUTS) in terms of required data sets and fit performance. Subsequently, fish were assigned to experimental groups exposed to 10% and 20% of 96h LC50 of surfactants for the period of 45 d to assess the changes in growth, hematological, plasma biochemical, and enzymological as well as stress enzyme parameters in gills and liver by employing standard protocol. The 24h, 48h, 72h and 96h LC 50 values of ABS to O. mossambicus are 0.55mg/l, 0.28 mg/l, 0.09 mg/l and 0.06 mg/l respectively. Moreover, the GUTS- IT model better projected the survivability in O. mossambicus for ABS exposure. During sublethal exposure, a consequential reduction in specific growth rate (SGR), RBC, hemoglobin (Hb), hematocrit (Ht) value, plasma protein, albumin, and acetylcholinesterase (AChE) activities in gills and liver, as well as significant induction in gastrosomatic index (GSI), feed conversion ratio (FCR), plasma glucose, creatinine, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels and catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA) in gills and liver were observed in exposed fish. Moreover, in both gills and the liver, GST and glutathione peroxidase (GPx) exhibited a significant initial increase followed by a subsequent decrease in exposed fish. The effects of ABS on fish were identified using the correlation matrix, integrated biomarker response (IBR) and biomarker response index (BRI). These findings show that exposure to surfactant affects multiple biomarkers in O. mossambicus.

Cortisol regulates insulin-like growth-factor binding protein (igfbp) gene expression in Atlantic salmon parr

The growth hormone (Gh)/insulin-like growth-factor (Igf)/Igf binding protein (Igfbp) system regulates growth and osmoregulation in salmonid fishes, but how this system interacts with other endocrine systems is largely unknown. Given the well-documented consequences of mounting a glucocorticoid stress response on growth, we hypothesized that cortisol inhibits anabolic processes by modulating the expression of hepatic igfbp mRNAs. Atlantic salmon (Salmo salar) parr were implanted intraperitoneally with cortisol implants (0, 10, and 40 μg g−1 body weight) and sampled after 3 or 14 days. Cortisol elicited a dose-dependent reduction in specific growth rate (SGR) after 14 days. While plasma Gh and Igf1 levels were unchanged, hepatic igf1 mRNA was diminished and hepatic igfbp1b1 and -1b2 were stimulated by the high cortisol dose. Plasma Igf1 was positively correlated with SGR at 14 days. Hepatic gh receptor (ghr), igfbp1a, -2a, -2b1, and -2b2 levels were not impacted by cortisol. Muscle igf2, but not igf1 or ghr, levels were stimulated at 3 days by the high cortisol dose. As both cortisol and the Gh/Igf axis promote seawater (SW) tolerance, and particular igfbps respond to SW exposure, we also assessed whether cortisol coordinates the expression of branchial igfbps and genes associated with ion transport. Cortisol stimulated branchial igfbp5b2 levels in parallel with Na+/K+-ATPase (NKA) activity and nka-α1b, Na+/K+/2Cl--cotransporter 1 (nkcc1), and cystic fibrosis transmembrane regulator 1 (cftr1) mRNA levels. The collective results indicate that cortisol modulates the growth of juvenile salmon via the regulation of hepatic igfbp1s whereas no clear links between cortisol and branchial igfbps previously shown to be salinity-responsive could be established.

The effects of acute crude oil exposure on growth and competition in red drum, Sciaenops ocellatus

Crude oil is a well-known toxicant that reduces cardiorespiratory performance in acutely exposed fishes. While toxic effects can manifest in death in severe cases, the ecological consequences of sub-lethal exposure remain uncertain. This study investigated the impact of crude oil exposure on long-term social competition, growth, and metabolic performance in a coastal species, the red drum (Sciaenops ocellatus). Fish were acutely exposed to either control or one of two environmentally relevant oil concentrations and reared together in groups of 15 (5 from each exposure concentration) for eight weeks under resource-rich or resource-limited scenarios. Relative to controls, a 41.3% and 45.9% reduction in the specific growth rate was-observed following exposure to 25.3 and 53.4 μg l−1 ΣPAH respectively under resource-limited conditions. These fish were subsequently sampled for metabolic performance and common indicators of social subordination including reduced glucocorticoid receptors in the gill and caudal fin damage. The reduction in specific growth rate coincided with a 15.1% and 17.3% reduction in standard metabolic rate; however, maximum metabolic rate and aerobic scope were unaffected. Additionally, measures of social subordination showed no differences between oil-exposed and control fish. These results reinforce the hypothesis that acute oil exposure can have prolonged sub-lethal effects that compromise the ability of exposed individuals to perform effectively in their environment, including gathering and/or metabolizing food. Furthermore, this work highlights the premise that oil spills can be more detrimental in already at-risk ecosystems.

Toxicity of ten herbicides to the tropical marine microalgae Rhodomonas salina

Herbicide contamination of nearshore tropical marine ecosystems is widespread and persistent; however, risks posed by most ‘alternative’ herbicides to tropical marine microalgae remain poorly understood. Experimental exposures of the important but understudied microalgae Rhodomonas salina to seven individual Photosystem II (PSII) inhibitor herbicides (diuron, metribuzin, hexazinone, tebuthiuron, bromacil, simazine, propazine) led to inhibition of effective quantum yield (ΔF/Fm′) and subsequent reductions in specific growth rates (SGR). The concentrations which reduced ΔF/Fm′ by 50% (EC50) ranged from 1.71-59.2 µg L−1, while the EC50s for SGR were 4-times higher, ranging from 6.27-188 µg L−1. Inhibition of ΔF/Fm′ indicated reduced photosynthetic capacity, and this correlated linearly with reduced SGR (R2 = 0.89), supporting the application of ∆F/Fm’ inhibition as a robust and sensitive indicator of sub-lethal toxicity of PSII inhibitors for this microalga. The three non-PSII inhibitor herbicides (imazapic, haloxyfop and 2,4-Dichlorophenoxyacetic acid (2,4-D)) caused low or no toxic responses to the function of the PSII or growth at the highest concentrations tested suggesting these herbicides pose little risk to R. salina. This study highlights the suitability of including R. salina in future species sensitivity distributions (SSDs) to support water quality guideline development for the management of herbicide contamination in tropical marine ecosystems.

Low temperature and low salinity drive putatively adaptive growth differences in populations of threespine stickleback

Colonisation can expose organisms to novel combinations of abiotic and biotic factors and drive adaptive divergence. Yet, studies investigating the interactive effects of multiple abiotic factors on the evolution of physiological traits remain rare. Here we examine the effects of low salinity, low temperature, and their interaction on the growth of three North American populations of threespine stickleback (Gasterosteus aculeatus). In north-temperate freshwater habitats, stickleback populations experience a combination of low salinity and low winter temperatures that are not experienced by the ancestral marine and anadromous populations. Here we show that both salinity and temperature, and their interaction, have stronger negative effects on marine and anadromous populations than a freshwater population. Freshwater stickleback showed only a ~20% reduction in specific growth rate when exposed to 4 °C, while marine and anadromous stickleback showed sharp declines (82% and 74% respectively) under these conditions. The modest decreases in growth in freshwater stickleback in fresh water in the cold strongly suggest that this population has the capacity for physiological compensation to offset the negative thermodynamic effects of low temperature on growth. These results are suggestive of adaptive evolution in response to the interactive effects of low salinity and low temperature during freshwater colonisation.

Effects of iron limitation on silicon uptake kinetics and elemental stoichiometry in two Southern Ocean diatoms, Eucampia antarctica and Proboscia inermis, and the temperate diatom Thalassiosira pseudonana

AbstractWe investigated the effects of iron (Fe) limitation on the elemental stoichiometry, silicic acid (Si(OH)4) uptake kinetics and cell morphology in two Southern Ocean diatoms Eucampia antarctica and Proboscia inermis and the temperate diatom Thalassiosira pseudonana. An increase in Fe‐stress resulted in reductions in specific growth rate and decreases in cellular nitrogen (N) and carbon (C) content relative to cellular biogenic silica (BSi) in both Southern Ocean diatoms and a reduction in growth rate only for T. pseudonana. Both E. antarctica and P. inermis exhibited an increase in cell volume in response to Fe‐limitation resulting in a decrease in the cell surface to volume ratio, while normalization of BSi content to cell surface area suggests these diatoms do not become more heavily silicified under Fe limitation. Kinetic Si(OH)4 uptake experiments performed on all three diatom species show that Si(OH)4 uptake is reduced under Fe‐limited conditions. For Southern Ocean diatoms, this was manifested through a decrease in the maximum specific uptake rate of Si(OH)4 (VSi‐max), along with a decrease in the half‐saturation constant for Si(OH)4 uptake (KSi) under Fe stress for E. antarctica. Our data also show that when normalized to cell surface area, VSi‐max of the three diatoms species exhibited a linear relationship with cellular growth rate, and was independent of cell morphological variations. Our results suggest that the morphological adaptations of Southern Ocean diatoms in response to Fe‐stress have the potential to affect phytoplankton community dynamics and Si(OH)4 : NO3 uptake and export ratios in Southern Ocean waters.

The growth feasibility of Lomentaria sp. in Laboratory conditions.

The growth feasibility of Lomentaria sp. in ocean water (OW) and inland saline water (ISW) at salinity 30‰ was tested in a series of four experiments. To grow Lomentaria sp., potassium chloride (KCl) was used to fortify ISW to approximately 100%, 66%, and 33% (ISW100, ISW66, and ISW33 respectively) of [K+] in OW and compared to two controls of OW and ISW. The results showed that the ISW66 medium resulted in the highest (P<0.05) Lomentaria sp biomass from day 14-56. The Lomentaria sp. was then cultured in OW, ISW and ISW66 enriched weekly with ammonium (NH4) 100 μmol by NH4Cl. A significantly slower reduction of specific growth rate (SGR) of Lomentaria sp. was recorded in the NH4 enriched waters than non-enriched waters. The effect of three temperature levels of 18-19°C, 21-22°C, and 25-26°C were also tested on the growth of Lomentaria sp. The 18-19°C resulted in highest biomass loss, whereas the higher temperatures resulted in similar SGRs of Lomentaria sp in both OW and ISW66. Four levels of NH4:PO4 including 0:0, 75:7.5, 150:15, and 300:30 μmol L-1 NH4:PO4 by NH4Cl and Na2HPO4, were weekly added to OW and ISW66, and these combined nutrient supplementation showed no effect on the Lomentaria sp. SGR. This study identified the suitable conditions for Lomentaria sp. growth in captivity as a temperature of 21-26°C, a supply of [NH4] no greater than 100 μmol L-1 in K+ fortification ISW 33-66% of [K+] in OW for higher biomass gain.

Endoplasmic Reticulum-Associated rht-PA Processing in CHO Cells: Influence of Mild Hypothermia and Specific Growth Rates in Batch and Chemostat Cultures.

BackgroundChinese hamster ovary (CHO) cells are the main host for producing recombinant proteins with human therapeutic applications mainly because of their capability to perform proper folding and glycosylation processes. In addition, mild hypothermia is one of the main strategies for maximising the productivity of these systems. However, little information is available on the effect of culture temperature on the folding and degradation processes of recombinant proteins that takes place in the endoplasmic reticulum.MethodsIn order to evaluate the effect of the mild hypothermia on processing/endoplasmatic reticulum-associated degradation (ERAD) processes, batch cultures of CHO cells producing recombinant human tissue plasminogen activator (rht-PA) were carried out at two temperatures (37°C and 33°C) and treated with specific inhibitors of glycosylation and ERAD I (Ubiquitin/Proteasome system) or ERAD II (Autophagosoma/Lisosomal system) pathways. The effect of mild hypothermia was analysed separately from its indirect effect on specific cell growth rate. To do this, chemostat cultures were carried out at the same incubation conditions as the batch cultures, controlling cell growth at high (0.017 h-1) and low (0.012 h-1) dilution rates. For a better understanding of the investigated phenomenon, cell behaviour was also analysed using principal component analysis (PCA).Results and ConclusionResults suggest that rht-PA is susceptible to degradation by both ERAD pathways studied, revealing that processing and/or ERAD processes are sensitive to temperature cultivation in batch culture. Moreover, by isolating the effect of culture temperature from the effect of cell growth rate verifyed by using chemostat cultures, we have found that processing and/or ERAD processes are more sensitive to reduction in specific growth rate than low temperature, and that temperature reduction may have a positive effect on protein processing. Interestingly, PCA indicated that the integrated performance displayed by CHO cells is modulated predominantly by specific growth rate, indicating that the culture temperature has a lower weighted effect within the range of conditions evaluated in this work.

The inhibition effect of methanol, as a component of crude glycerol, on the growth rate of Cupriavidus necator and other micro-organisms

Methanol is known for its toxicity to a wide range of micro-organisms. The presence of methanol in a system can significantly suppress microbial growth. In this paper, the growth of Cupriavidus necator DSM4058 in mineral medium containing methanol in a range 0–125g/L is reported. It was found that methanol tested at any concentration had a negative influence on growth. However, the reduction in specific growth rate could be predicted by neither substrate nor product inhibition equations, and so a model, based on a saturation equation was developed and is presented here. The model is shown to fit particularly well, not only with the C. necator data but also with several sets of data extracted from publications based on other micro-organisms. It was found that the model successfully predicted the data with regression coefficients of over 96%, regardless of micro-organism or particular alcohol inhibitor.

GH, IGF-I and GH receptors mRNA expression in response to growth impairment following a food deprivation period in individually housed cichlid fish Cichlasoma dimerus.

Cichlasoma dimerus is a social cichlid fish capable of growing at high rates under laboratory conditions, but knowledge on somatic growth regulation is still unclear. Growth hormone (GH)/insulin-like growth factor I (IGF-I) axis is the key regulator of somatic growth in vertebrates. Two types of growth hormone receptors have been described in teleost fish, named GH receptor type 1 (GHR1) and type 2 (GHR2). In addition, isoforms of these receptors lacking part of the intracellular region have been described. The aim of this study was to evaluate the somatic growth, liver histology and changes in the GH/IGF-I axis after 4 weeks of food deprivation in C. dimerus. Four-week fasted fish showed reductions in specific growth rates in body weight (p < 0.001) and standard length (p < 0.001). Additionally, the hepatosomatic index (p < 0.001) and hepatocyte area (p < 0.001) decreased in fasted fish, while no changes in glucose levels were detected in plasma. The starvation protocol failed to induce changes in GH mRNA levels in the pituitary and IGF-I mRNA levels in liver. In contrast, IGF-I mRNA levels in muscle decreased in fasted fish (p = 0.002). On the other hand, GHR2 (detected with primer sets designed over the extracellular and intracellular region) was upregulated by starvation both in liver and muscle (p < 0.05), while GHR1 remained unchanged. These results show that a fasting period reduced somatic growth both in length and body weight concomitantly with alterations on liver and muscle GHR2 and muscle IGF-I mRNA expression.

Production performance of Atlantic salmon (Salmo salarL.) postsmolts in cyclic hypoxia, and following compensatory growth

This study investigated the production performance of the Atlantic salmon postsmolt (Salmo salar L.) subjected to cyclic oxygen reductions (hypoxia) of varying severity. Triplicate groups (N = 955) were kept at constant 80% O2 (control) or subjected to 1 h and 45 min of hypoxia (50, 60 or 70% O2, termed 80:70, 80:60 and 80:50 groups) every 6 h at 16°C for 69 days. Feed was provided in normoxia. One third of the fish were kept further for 30 days in normoxia to study possible compensatory growth. Cyclic hypoxia did not alter the oxygen uptake rates of fish, measured in night-time. Fish subjected to 50% and 60% O2 reduced feeding by 13% and 6% compared with the controls, respectively, with corresponding reductions in specific growth rates. Feed utilization was not reduced. Compensatory growth was observed in fish from the 80:50 group, but full compensation was not achieved. The main conclusions were that feeding in normoxia does not fully alleviate negative effects of cyclic hypoxia on feeding and growth, when oxygen is reduced to 60% or below in hypoxic periods, that feed utilization is maintained, and that compensatory growth may lessen negative effects.

Plasmid DNA production for pharmaceutical use: Role of specific growth rate and impact on process design

Application of plasmid DNA as pharmaceutical to be used in gene therapy and vaccination has been investigated intensively in recent years. To be able to provide sufficient material that is in accordance with quality of pharmaceutical grade it is mandatory to gain comprehensive process knowledge which is even requested by regulatory agencies. Regarding plasmid DNA production the specific growth rate has been identified as one of the key parameters. The reduction of specific growth rate results in an increase of plasmid DNA formation. However, quantitative explanations that allow for efficient process development and design are still missing. The presented study proposes a model that clearly demonstrates the relationship between specific growth rate and plasmid formation due to identification of the specific plasmid production rate as relevant key parameter. In addition the model is proved to serve as a useful tool in process development and design.

A semiempirical model to control the production of a recombinant aldolase in high cell density cultures of Escherichia coli

A semi-empirical mathematical model for recombinant rhamnulose 1-phosphate aldolase (RhuA) production in high cell density cultures of Escherichia coli has been developed. An unstructured and non-segregated approach allowed to identify the inducer–biomass ratio ( I/ X) as the key parameter influencing initial specific production rate and specific growth rate reduction after induction. Biomass, substrate and RhuA concentration profiles have been properly fitted in fed-batch cultures induced by an IPTG pulse at different I/ X ratio ranging from 0 to 3 μmol IPTG·g-1dry cell weight. The model has been validated firstly as able to predict recombinant aldolase and biomass production. In addition, since glucose accumulation in the induced period, which is an indicator of activity reduction by proteolysis, can be anticipated, the model has been used for control purposes with excellent results.

Effects of repeated crowding on the stress response and growth performance in Atlantic salmon (Salmo salar)

A 64-day growth experiment was conducted in which two groups of Atlantic salmon parr were grown under either control conditions or subjected to a weekly crowding stressor. Subjecting fish to the stressor resulted in a 7.7% reduction in wet weight after 29 days, which was maintained at 7.9% by day 64. This reduction in weight was reflected in a 44% reduction in specific growth rate and 38% increase in feed conversion ratio over the first 29 days of the experiment. Elevation in plasma cortisol was observed in crowded fish on days 1, 29 and 64. Similarly, on days 1 and 29 an increase in both plasma glucose and lactate was detected. On day 64, however, no differences in plasma glucose and lactate were observed, with the magnitude of the cortisol response also significantly reduced. Overall, the relatively moderate impact on growth performance and reduction in magnitude of measured stress parameters at the end of the experiment suggests possible habituation to the applied stressor.

Influence of Thiamine Deficiency on Lake Trout Larval Growth, Foraging, and Predator Avoidance

Diet-related thiamine deficiency increases the acute mortality, known as early mortality syndrome, of salmonines from some of the Great Lakes. The consequences of thiamine deficiency as measured at the egg stage for other important early life stage processes like growth, foraging efficiency, and predator avoidance that may also result in mortality, are unknown. Accordingly, we investigated the impacts of low thiamine on the specific growth rate (SGR) of first-feeding fry, the ability of first-feeding fry to capture Daphnia, fry emergence in the presence of a potential predator (round goby Apollina [formerly Neogobius] melanostomus), and predation by slimy sculpin Cottus cognatus. We used a combination of thiamine-deficient and thiamine-replete wild stocks of lake trout Salvelinus namaycush for this purpose. From these investigations we developed predictive relationships. Specific growth rate was related to egg thiamine concentration. From the exponential relationship, it was predicted that the threshold egg thiamine concentrations associated with 20% and 50% reductions in SGR are 8.1 and 5.1 nmol/g, respectively. The foraging rate on Daphnia was also related to egg thiamine concentration by an exponential relationship. It was predicted that the threshold concentrations associated with 20% and 50% reductions in this rate are 6.9 and 2.9 nmol/g, respectively. The presence of a round goby significantly reduced emergence success, but the level of goby predation was unrelated to egg thiamine concentration. Sculpin predation was related, although weakly, to the initial egg thiamine concentration. This research found that thiamine deficiency affected growth, foraging, and predator avoidance in lake trout fry. Growth effects resulting from thiamine deficiency may represent the most sensitive means of monitoring the impact of the secondary consequences of thiamine deficiency. Mortality associated with the combined effects of reduced growth and foraging has the potential to seriously impair lake trout recruitment.

Impacts of elevated water carbon dioxide partial pressure at two temperatures on Atlantic salmon ( Salmo salar L.) parr growth and haematology

Atlantic salmon ( Salmo salar L.) parr (10–13 g) were exposed to two levels of carbon dioxide partial pressure (0.3–0.5 mm Hg, control group and 12 mm Hg, high group) at two different temperatures (5 °C and 15 °C) for 47 days in an open flow system. Fish density was low in all groups (less than 7–8 kg m − 3 ) and the specific water flow was high (higher than 1 L kg − 1 min − 1 ) to avoid accumulation of other metabolites. Sodium bicarbonate was added to the water with high carbon dioxide concentration, stabilizing the pH in the range 6.4–6.9 for all four groups. Final mean weight, length and condition factor of the high carbon dioxide groups were significantly reduced compared to their respective control group ( p < 0.05). The reduction in specific growth rate was more pronounced at 5 °C than at 15 °C. At 5 °C there was almost no growth at elevated carbon dioxide concentrations, with mean reduction in weight of 80% relative to the control group. The weight reduction caused by high carbon dioxide concentration was much less at 15 °C (approx 30%) even though the oxygen saturation was lowest in this group. Significant gill lesions, mortality and nephrocalcinosis were not detected in any group. Red blood cell count did not differ between the groups. However, erythrocyte volume declined and erythrocyte haemoglobin content increased in fish exposed to high water carbon dioxide levels at low temperature. The present investigation showed that the impact of elevated carbon dioxide was lowest in the high temperature group.

Adaptation to UVA radiation of E. coli growing in continuous culture

Adaptive responses of bacteria to physical or chemical stresses in the laboratory or in the environment are of great interest. Here we investigated the ability of Escherichia coli growing in continuous culture to adapt to UVA radiation. It was shown that E. coli indeed expressed an adaptive response to UVA irradiation at an intensity of 50 W/m 2. Cells grown in continuous culture with complex medium (diluted Luria Bertani broth) at dilution rates of 0.7 h −1, 0.5 h −1 and 0.3 h −1 were able to maintain growth under UVA irradiation after a transient reduction of specific growth rate and recovery. In contrast, slow-growing cells ( D = 0.05 h −1) were unable to induce enough protection capacity to maintain growth under UVA irradiation. We propose that faster growing E. coli cells have a higher adaptive flexibility to UVA light-stress than slow-growing cells. Furthermore it was shown with flow cytometry and viability stains that at a dilution rate of 0.3 h −1 only a small fraction (⩽1%) of the initial cell population survived UVA light-stress. Adapted cells were significantly larger (30%) than unstressed cells and had a lower growth yield. Furthermore, efflux pump activity was diminished in adapted cells. In a second irradiation period (after omitting UVA irradiation for 70 h) adapted cells were able to trigger the adaptive response twice as fast. Additionally, this study shows that continuous cultivation with direct stress application allows reproducible investigation of the physiological and possibly also molecular mechanisms during adaptation of E. coli populations to UVA light.