Similar Specific Growth Rates Research Articles

Body size and population dynamics of annual fishes from temporary wetlands in Southern Brazil

Annual fishes live exclusively in temporary wetlands where several species coexist. Understanding how annual fishes cohabit in small and isolated pools is still a challenge. In this study, we aimed to examine the prediction that annual fish assemblages in temporary pools in Southern Brazil are structured by temporal differences in body size, specific growth rate and density. Two–three fish species coexisted in each pool. The most abundant and frequent species were Cynopoecilus melanotaenia and Austrolebias nigrofasciatus, while A. wolterstorffi was less abundant and rare. The species differed significantly in body size throughout the flooding phase and showed similar growth patterns, with higher specific growth rates in the first months of flooding and a reduction in growth rate thereafter. The monthly average densities of A. nigrofasciatus and C. melanotaenia did not differ over time, but they were higher than values observed for A. wolterstorffi. Our results provide evidence for hatching synchrony, similar specific growth rates and densities among the most abundant species and differences in body sizes among all species that are more evident after adulthood, suggesting that differences in body size mediate the coexistence of annual fishes in temporary pools.

Does graded substitution of soy protein concentrate by an insect meal respond on growth and N-utilization in Nile tilapia (Oreochromis niloticus)?

Besides fishmeal, soybean protein is the most common protein source in aquafeed. However, the sustainability of soybean production is criticized. Due to the rapid development of aquaculture, the increasing demand for high value feed proteins has initiated research into alternative and more sustainable proteins for aquafeeds. In order to evaluate one promising alternative protein source, a growth study (56 days) was conducted with juvenile Nile tilapia (Oreochromis niloticus, 35 g on average) with a partial substitution of soybean protein by a partly defatted insect meal from black soldier fly larvae (Hermetia illucens). Growth performance, feed utilization and dietary protein quality parameters were evaluated based on analysed body protein deposition.A control feed (8% fish meal, 37% soy protein concentrate (SPC)) and three iso-nitrogenous and iso-energetic experimental feeds with 25, 50 or 100% replacement of SPC by partly defatted Hermetia meal (HM) were formulated. All feeds supplied essential amino acids as recommended for Nile tilapia. Growth response and protein utilization were examined in a semi-closed in-door water recirculation system. A comparative slaughter technique was applied to generate N deposition data for protein quality evaluation based on the standardized net protein utilization (NPUstd) according to the “Goettingen approach”. All feeds were very well accepted. Replacement of SPC by HM up to 50% improved feed protein quality and result in similar specific growth rate and feed conversion ratio, respectively. However, a higher inclusion rate of HM tended to impair growth, but not the observed protein quality. In conclusion, the replacement of SPC by partly defatted HM up to a level of 50% had no negative effect on growth performance and improved the dietary protein quality of tilapia feeds under study. Insect protein from Hermetia illucens could be a promising option to make aquafeed formulation more flexible and sustainable.

LA POTENCIA VOLUMÉTRICA COMO UN PARÁMETRO CONFIABLE PARA EL ESCALAMIENTO DE MATRACES AGITADOS A BIORREACTOR DE TANQUE AGITADO: PRODUCCIÓN DE UNA GLICOPROTEINA RECOMBINANTE POR Streptomyces lividans

In Streptomyces lividans, filamentous morphology varies according to hydrodynamics/aeration culture conditions, playing important roles in the production, secretion, and post-translational modification of recombinant glycoproteins. Volumetric power input (P/V) is normally used to scale-up bioprocesses. Here, we analyzed the effect of P/V on S. lividans growth and morphology as well as the production and O-mannosylation of the recombinant glycoprotein APA from Mycobacterium tuberculosis. Previously, we measured the P/V in conventional normal (NF, 0.20 kW/m3) and coiled (CF, 0.44 kW/m3) shake flasks. Here, these P/V were matched in 1.0 L bioreactors by adjusting the stirring speed. Similar specific growth rates were observed between shake flask and bioreactor cultures. In addition, similar rAPA yields (~25%) were observed in both the bioreactor and NF cultures, but these were lower than the yield in the CF culture (~36%). Furthermore, up to seven mannose residues were attached to the C-terminal of rAPA in both bioreactor cultures, which was one more than in the NF and CF cultures. However, at similar P/V, the morphology and biomass kinetics of growth were not similar. Our data indicate that scaling-up the production of recombinant glycoproteins using S. lividans by matching the P/V can be successful in terms of some, but not all stequeometric parameters, suggesting that the cellular responses could be differently affected by hydrodynamics/aeration differences between shake flasks and bioreactors.

Induction by Bradyrhizobium diazoefficiens of Different Pathways for Growth in D-mannitol or L-arabinose Leading to Pronounced Differences in CO2 Fixation, O2 Consumption, and Lateral-Flagellum Production.

Bradyrhizobium diazoefficiens, a soybean N2-fixing symbiont, constitutes the basic input in one of the most prominent inoculant industries worldwide. This bacterium may be cultured with D-mannitol or L-arabinose as carbon-plus-energy source (C-source) with similar specific growth rates, but with higher biomass production with D-mannitol. To better understand the bacterium’s carbon metabolism, we analyzed, by liquid chromatography and tandem mass spectrometry (MS), the whole set of proteins obtained from cells grown on each C-source. Among 3,334 proteins identified, 266 were overproduced in D-mannitol and 237 in L-arabinose, but among these, only 22% from D-mannitol cultures and 35% from L-arabinose cultures were annotated with well defined functions. In the D-mannitol-differential pool we found 19 enzymes of the pentose-phosphate and Calvin–Benson–Bassham pathways and accordingly observed increased extracellular-polysaccharide production by D-mannitol grown bacteria in a CO2-enriched atmosphere. Moreover, poly-3-hydroxybutyrate biosynthesis was increased, suggesting a surplus of reducing power. In contrast, the L-arabinose-differential pool contained 11 enzymes of the L-2-keto-3-deoxyarabonate pathway, 4 enzymes for the synthesis of nicotinamide-adenine dinucleotide from aspartate, with those cultures having a threefold higher O2-consumption rate than the D-mannitol cultures. The stoichiometric balances deduced from the modeled pathways, however, resulted in similar O2 consumptions and ATP productions per C-mole of substrate. These results suggested higher maintenance-energy demands in L-arabinose, which energy may be used partly for flagella-driven motility. Since B. diazoefficiens produces the lateral-flagella system in only L-arabinose, we calculated the O2-consumption rates of a lafR::Km mutant devoid of lateral flagella cultured in L-arabinose or D-mannitol. Contrary to that of the wild-type, the O2-consumption rate of this mutant was similar on both C-sources, and accordingly outcompeted the wild-type in coculture, suggesting that the lateral flagella behaved as parasitic structures under these conditions. Proteomic data are available via ProteomeXchange with identifier PXD008263.

Effects of Dietary Protein and Lipid Levels with Different Protein‐to‐Energy Ratios on Growth, Feed Utilization, and Plasma Biochemical Parameters of Dianchi Golden‐line Barbell, Sinocyclocheilus grahami

AbstractAn 8‐wk feeding trial was conducted to evaluate the effects of varying dietary protein and lipid levels with different protein‐to‐energy (P/E) ratios on growth, feed utilization, and plasma biochemical parameters of Sinocyclocheilus graham. Nine experimental diets were formulated to contain three protein levels (35, 40, and 45%), and each with three lipid levels (4, 8, and 12%), to produce a range of P/E ratios from 71.31 to 98.64 mg protein/kcal. Each diet was randomly assigned to triplicate groups of 25 fish. Fish grew best when fed the diet containing 45% protein and 12% lipid. However, fish fed the diet with 40% protein and 8% lipid had similar weight gain and specific growth rate as those fed the above diet but showed relatively better feed conversion ratio, protein efficiency ratio, and protein and energy retentions. Additionally, plasma total amino acids and blood urea nitrogen contents and γ‐glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase activities in fish fed the diet containing 40% protein and 8% lipid were relatively low among the dietary treatments. These results may indicate that a diet containing 40% protein and 8% lipid with P/E ratio of 84.05 mg protein/kcal would be suitable for the optimal growth, feed utilization, and health of S. graham.

Effects of a Total Dietary Fish Oil Replacement with Vegetable Oils to the Survival, Growth and Development of the Blue Swimming Crab Portunus Pelagicus Early Juveniles

The feasibility of different vegetable based lipids as a complete replacement to dietary fish oil (FO) to blue swimmer crab Portunus pelagicus juveniles was assessed. A total of five iso-nitrogenous and iso-lipidic diets were formulated to contain FO, soybean oil (SBO), linseed oil (LSO), canola oil (CO), or palm oil (PO) as the main lipid source. The diets were fed to first staged juvenile crabs (total of 45 replicate crabs/treatment) over at least four molts. After 35 days, final sizes and weights were determined, and then measured for whole-body cholesterol. Crabs fed the FO, SBO, LSO, or CO-based diets showed similar specific growth rates (SGR) (p > 0.05) for carapace length and width, which was significantly higher (p < 0.05) compared to crabs in the dietary PO treatment. Whole-body cholesterol content was significantly lower for crabs fed the PO-based diets, which may have contributed to their poorer performance, compared to those fed the FO, LSO or CO-based diets. Results indicate SBO, LSO or CO can totally replace FO, which may improve cost-effective and sustainable diets for portunid crabs. Further research into the use of dietary PO blends with other vegetable oils should be conducted.

Effects of food availability on metabolism, behaviour, growth and their relationships in a triploid carp.

Metabolism, behaviour and growth are highly flexible in fish species, and inter-individual variation in these traits is evolutionarily and ecologically significant. It has long been suggested that these traits co-vary, although their relationships are debated. In the present study, we investigated whether metabolism, behaviour, growth and the potential relationships among them vary with food availability in sterile triploid carp. In this experimental animal model, we investigated the standard metabolic rate (SMR), growth performance and personality traits (i.e. activity, exploration and boldness) of juvenile individuals before and after 25 days of rearing in which fish were fed either once or twice a day to satiation. Inter-individual differences in SMR in each group showed high repeatability across the experimental period, and twice-fed fish showed higher SMRs than once-fed fish after 25 days of rearing. Compared with the once-fed group, the twice-fed group showed higher feeding rates (FRs) and lower feeding efficiencies (FEs) but similar specific growth rates (SGRs). None of the personality traits was affected by food availability. Furthermore, both boldness and exploration were highly repeatable throughout the experiment in the group fed twice a day, whereas only exploration showed repeatability in the group fed once a day. In the once-fed group, SMR and the personality traits were positively correlated with FR and negatively correlated with FE and/or SGR; however, these relationships did not exist in the twice-fed group due to the surplus of food. These results suggest that food availability significantly affects physiological, behavioural and ecological processes in these fish by altering the trade-off between metabolism and growth.

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.

The effect of sustained swimming exercise on the growth performance, muscle cellularity and flesh quality of juvenile qingbo (Spinibarbus sinensis)

This study was undertaken to investigate the effects of sustained swimming exercise on the growth performance, muscle cellularity and flesh quality of juvenile qingbo fish (Spinibarbus sinensis). Experimental fish were exercised under four water velocities, nearly still (control, 3cms−1) and 1, 2 and 4body lengths (bl)s−1, for eight weeks at 25°C. Then, growth performance indicated by the specific growth rate (SGR), white muscle cellularity suggested by the diameter and density of white muscle fiber, flesh quality evaluated by some textural mechanical properties (hardness, springiness, chewiness, cohesiveness) and physico-chemical parameters (pH, color, moisture, ash, protein, fat, amino acids, and fatty acids) were measured. Sustained swimming at moderate velocities (1 and 2bls−1) resulted in a significantly higher SGR and similar white fiber diameter and density compared with the controls. However, the fish trained at a water velocity of 4bls−1 displayed a similar SGR, smaller white fiber diameter and higher white fiber density compared with the controls. Sustained swimming resulted in significant increase in the values of pH and all textural traits but showed no significant effect on the color of the flesh for juvenile S. sinensis. Fish swimming under moderate water velocities exhibited higher levels of the protein content of the muscle, total essential amino acids (∑EAA) (at 2bls−1) and total amino acids (∑AA) (at 1 and 2bls−1) compared with control fish. However, the lowest levels of total amino acids (∑AA) and total n-6 poly-unsaturated fatty acids (∑n-6 PUFA) were observed in fish swimming at water velocity of 4bls−1. These data suggest that (1) moderate swimming exercise (1 or 2bls−1) improved growth performance, which could not be attributed to changes in white muscle cellularity; (2) sustained swimming showed a positive effect on texture characteristics, which was partly due to the higher white fiber density and flesh pH compared with controls; and (3) moderate swimming exercise (1 or 2bls−1) was beneficial for improving the nutritional quality of the flesh, whereas high-intensity swimming (4bls−1) resulted in an impairment of the nutritional quality of the flesh in juvenile S. sinensis. Statement of relevanceWe declare that the experiments complied with the current laws of the country in which the experiments were performed and that our paper complied with the laws of commercial aquaculture.

The effect of aerobic exercise and starvation on growth performance and postprandial metabolic response in juvenile southern catfish (Silurus meridionalis)

To investigate the effects of aerobic exercise and starvation on growth performance, postprandial metabolic response and their interaction in a sedentary fish species, either satiation-fed or starved juvenile southern catfish (Silurus meridionalis) were exercised at 25°C under three water velocities, i.e., nearly still water (control), 1 body length (bl) s−1 and 2 bl s−1, for eight weeks. Then, the feed intake (FI), food conversion efficiency (FCE), specific growth rate (SGR), morphological parameters, resting ṀO2 (ṀO2rest) and postprandial ṀO2 responses of the experimental fish were measured. Exercise at a low velocity (1 bl s−1) showed no effect on any growth performance parameter, whereas exercise at a high velocity (2 bl s−1) exhibited higher FI but similar SGR due to the extra energy expenditure from swimming and consequent decreased FCE. Starvation led to a significant body mass loss, whereas the effect intensified in both exercise groups. Exercise resulted in improved cardio-respiratory capacity, as indicated by increased gill and heart indexes, whereas it exhibited no effect on resting and postprandial metabolism in S. meridionalis. The starved fish displayed significantly larger heart, gill and digestive tract indexes compared with the feeding fish, suggesting selective maintenance of cardio-respiratory and digestive function in this fish species during starvation. However, starved fish still exhibited impaired digestive performance, as evidenced by the prolonged duration and low postprandial metabolic increase, and this effect was further exacerbated in both the 1 and 2 bl s−1 exercise groups. These data suggest the following: (1) aerobic exercise produced no improvement in growth performance but may have led to the impairment of growth under insufficient food conditions; (2) the mass of different organs and tissues responded differently to aerobic exercise and starvation due to the different physiological roles they play; and (3) aerobic exercise had no effect on the postprandial metabolic response under a “normal feeding” situation, whereas it may have resulted in the impairment of the digestive capacity when food availability was low due to the competition of energy and oxygen under unfavorable conditions in juvenile S. meridionalis.

Absorption of different macroalgae by sea cucumber Apostichopus japonicus (Selenka): Evidence from analyses of fatty acid profiles

Fatty acids (FAs) were used as trophic markers to examine the absorption of different algae species, including brown alga Sargassum muticum (S), red alga Gracilaria lemaneiformis (G) and green alga Ulva lactuca (U) by sea cucumber Apostichopus japonicus. A 56-day feeding experiment was carried out to investigate the FA profile of the A. japonicus feeding on 6 different types of diets with the ingredient of either pure powder of single algae species or mixtures of 3 algae species, i.e., the mixtures (1:1) of S. muticum and G. lemaneiformis (SG), S. muticum and U. lactuca (SU), and G. lemaneiformis and U. lactuca (GU). The FA profile of A. japonicus showed obvious changes over the experimental period and was remarkably affected by the different diets. Analyses of variations in the specific FAs and the multidimensional scaling (MDS) ordination of the overall FA profiles revealed that A. japonicus preferentially absorbed U. lactuca relative to S. muticum in the diet group SU while showed the discrimination against G. lemaneiformis in the diet groups SG and GU. Moreover, A. japonicus fed with U. lactuca displayed a similar or higher specific growth rate (SGR) than those fed on S. muticum or G. lemaneiformis, respectively. The results of the present study suggested that green alga U. lactuca might be used as a suitable substitute for replacing the traditional ingredient brown alga Sargassum thunbergii in the artificial feed for A. japonicus farming. Statement of relevanceThe results of the present study could be used to further optimize the ingredient of A. japonicus artificial feeds.

Influence of the growth morphology on the behavior of Salmonella Typhimurium and Listeria monocytogenes under osmotic stress

The microbial growth morphology, as a consequence of the food structure, has been acknowledged to play a key role on the growth behavior. While in liquid media planktonic growth is observed, in a solid(like) environment cells are immobilized and forced to grow as (surface) colonies. This immobilization could affect the cell physiology and metabolism. Apart from the growth morphology, other intrinsic factors influence microbial growth. Osmotic stress and acidic stress have an impact on microbial growth. Moreover, the combination of intrinsic factors could result in a synergetic inhibitory effect on the growth behavior (hurdle technology). In this paper, the growth dynamics of Salmonella Typhimurium and Listeria monocytogenes under stressing conditions are studied for two different growth morphologies, i.e., (i) planktonic cells and (ii) surface colonies. Microorganisms are grown in petri dishes, incubated at 20°C under static conditions. To create the solid(like) environment, 5% (w/v) gelatin is added. Stressing growth conditions are created by adding salt [0–8% (w/v)] and adapting the pH [5.5–7.0]. Cell density is determined via the viable plate count technique. While the studied pH-range has a negligible effect, the addition of salt significantly reduces growth. The growth morphology, resulting from the intrinsic food (model) structure, affects the microbial growth dynamics under static incubation conditions. In contrast to literature, surface colonies have higher or similar maximum specific growth rates than planktonic cells under most of the selected experimental conditions. For example, for S. Typhimurium at pH6.5 and 2% (w/v) NaCl, planktonic cells have a maximum specific growth rate of 0.4351/h while μmax for surface colonies has a value of 0.4641/h. For L. monocytogenes at pH6.0 and 0% (w/v) NaCl, μmax, planktonic cells is 0.3751/h and μmax, surface colonies is 0.4241/h. This is due to limited oxygen availability as a result of the experimental protocol implemented, leading to lower μmax values for planktonic cells as opposed to μmax values for shaken cultures in other studies appearing in literature. This indicates that under static incubation, the effect of the microstructure is often negligible as compared to the oxygen availability. However, for the most stressing experimental conditions, the combination of high salt concentrations and a solid(like) growth environment inhibits growth, and the order μmax, planktonic cells≥μmax, surface colonies is respected. This is for instance illustrated in the case of S. Typhimurium at pH5.5 and 6% (w/v) NaCl: μmax, planktonic cells reaches a value of 0.1831/h while μmax, surface colonies is only 0.1421/h. Also for L. monocytogenes at pH6.0 and 8% (w/v) NaCl, μmax, planktonic cells (0.1451/h) is higher than μmax, surface colonies (0.1131/h). This study indicates the relevance of intrinsic factors on the growth dynamics and addresses the importance to include growth morphology, determined by the intrinsic food structure, in predictive models.

Carotenoid deposition, flesh quality and immunological response of Nile tilapia fed increasing levels of IMTA-cultivated Ulva spp.

Increasing levels of a mixture of Ulva spp. (Ulva rigida and Ulva lactuca) produced in an integrated multi-trophic aquaculture (IMTA) system were evaluated in Nile tilapia. A control diet (CTRL) was compared with two experimental isonitrogenous (36 %) and isoenergetic (20 kJ g−1) diets containing 5 % (U5) and 10 % (U10) of Ulva spp. meal. Duplicate groups of 18 fish (255 g initial body weight) were reared at 25 °C and fed each diet for 68 days to evaluate carotenoid deposition, flesh organoleptic properties and immunological response. By the end of the trial, all groups of fish showed similar final body weight and specific growth rate. Whole body composition was also similar among treatments. The dietary incorporation of Ulva spp. meal increased total carotenoid content in the skin, with fish fed U5 displaying significantly higher levels (6.5 μg g−1) than the CRTL (1.4 μg g−1). No carotenoids could be found in tilapia muscle. Muscle colour determined using a spectrocolorimeter indicated that tilapia fillets from fish fed U10 showed the highest lightness (highest L* value) and yellowness (less negative b* value), but the lowest redness (lowest a* value). Furthermore, sensory attributes of flesh showed no significant effects of dietary treatments on visual, olfactory, texture and flavour parameters, with the exception of sour parameter that was lowest in U10-fed tilapia. The dietary inclusion of Ulva spp. meal had no beneficial effect on lysozyme or peroxidase activity, but the complement activity (ACH50), an important component of innate immune system in fish, increased concomitantly with the dietary inclusion level of Ulva spp. meal. The inclusion of Ulva spp. meal in diets for Nile tilapia seems to be possible up to 10 % without major effects on growth performance or flesh organoleptic properties but enhancing the innate immune response of the fish.

Effect of physico-chemical and operating conditions on the growth and activity of Acidithiobacillus ferrooxidans in a simulated heap bioleaching environment

Recent understanding of microbial retention within heap bioleaching systems has highlighted the importance of quantifying microbial growth and activity in both the bulk flowing solution and in the ore-associated phases. Typically, industrial heap bioleaching operations report variations in process conditions such as inoculum preparation and concentration and elevated copper concentrations in the recycled irrigation solution. In this paper, a mini-column reactor system containing pre-constructed and agglomerated, low-grade ore samples representing grab samples from a larger heap, were used to investigate the effect of a selection of physico-chemical and operating conditions on microbial growth, colonisation and substrate utilisation kinetics, considering both the planktonic and sessile populations of Acidithiobacillus ferrooxidans. The factors studied included inoculum size, inoculum cultivation conditions, availability of ferrous iron in the bulk flowing solution and copper concentration in the bulk flowing solution. The microbial population in the interstitial phase, i.e. associated with, but not bound to, the ore, remained the most abundant within the heap under all physico-chemical conditions considered. A comparison of the tests with different inoculum sizes found that a smaller inoculum size resulted in an increased delay in microbial growth and ferrous iron oxidation, but similar apparent maximum specific growth rates and iron oxidation rates. In contrast to the microbial culture grown on pyrite, a delay in microbial activity was observed for the culture grown on ferrous iron. However, greater microbial cell densities were reached, in the interstitial and attached phases compared with the pyrite-grown culture. The introduction of 6gL−1 cupric ions into the feed solution containing 0.2gL−1 ferric iron resulted in decreased microbial growth rate in the interstitial phase but not in the attached phase. Where the pyrite culture was pre-exposed to cupric ion, the microbial growth rate in the interstitial and attached phases was significantly enhanced. Nevertheless, the presence of cupric ion in the irrigation solution resulted in a decrease in microbial ferrous iron oxidation rate, irrespective of pre-culture conditioning. This study emphasises the important role played by the stagnant interstitial phase during the colonisation of a low-grade heap, particularly under adverse conditions for microbial growth and activity. It also highlights the role of inoculum culture conditions on the potential trade-off between increased heap colonisation and increased lag periods in microbial activity during heap start-up.

Comparison of biomass detachment from biofilms of two different Pseudomonas spp. under constant shear conditions

In the context of biofilm development, detachment is of practical importance when placed in a biofilm management perspective. The objective of the present study was to examine biofilm structure and biofilm detachment under controlled conditions for two distinct microorganisms grown under constant shear conditions. Detached biofilm biomass was regularly collected and analysed over the course of 72 h biofilm growth by Pseudomonas putida and Pseudomonas fluorescens cells, and biofilm structural development assessed using confocal microscopy. The two Pseudomonas spp., which had very similar specific growth rates in planktonic culture, presented notably different characteristics in terms of biofilm morphology but their detachment behaviours over time were very similar. These findings underline the intrinsic complexity of the detachment phenomenon.

Production of glycolipid biosurfactants, mannosylerythritol lipids, from pentoses and d-glucose/d-xylose mixtures by Pseudozyma yeast strains

The pentose-assimilating capacity of yeasts from the genus Pseudozyma, P. antarctica PYCC 5048T, P. aphidis PYCC 5535T and P. rugulosa PYCC 5537T, was exploited towards the production of mannosylerythritol lipids (MEL), a glycolipid with biosurfactant properties. The three strains tested were able to grow on d-xylose and l-arabinose with similar maximum specific growth rates to those estimated on d-glucose (around 0.2h−1). The highest MEL titres (4.8–5.4g/l) and yields (0.11–0.14g/g) from d-xylose were found in P. antarctica PYCC 5048T, which presented similar values to those estimated on d-glucose and on d-xylose/d-glucose mixtures. P. rugulosa PYCC 5537T showed a pattern of sugar conversion into MEL similar to P. antarctica, but at 40% lower titres. P. aphidis PYCC 5535T presented lower MEL titres from d-xylose (1.2g/l) than from d-glucose (3.4g/l). Nitrate supply increased sugar consumption rate and, when accompanied by d-glucose or d-xylose feeding, additional biomass production. In this case, sugar was completely consumed before sugar feeding at day 7, but not when feeding is performed at day 4. Higher MEL titres where obtained for the later condition reaching 7.3g/l and 5.8g/l, in fed-batch cultures with glucose and xylose, respectively.

The effects of constant and diel-fluctuating temperature acclimation on the thermal tolerance, swimming capacity, specific dynamic action and growth performance of juvenile Chinese bream

We investigated the effects of constant and diel-fluctuating temperature acclimation on the thermal tolerance, swimming capacity, specific dynamic action (SDA) and growth performance of juvenile Chinese bream (Parabramis pekinensis). The critical thermal maxima (CTmax), critical thermal minima (CTmin), lethal thermal maxima (LTmax), lethal thermal minima (LTmin), critical swimming speed (Ucrit) and fast-start escape response after 30d acclimation to three constant temperatures (15, 20 and 25°C) and one diel-fluctuating temperature (20±5°C) were measured. In addition, feeding rate (FR), feeding efficiency (FE) and specific growth rate (SGR) were measured. The diel-fluctuating temperature group showed lower CTmin than the 20°C group but a similar CTmax, indicating a wider thermal scope. SDA linearly increased with the temperature. Temperature variation between 20 and 25°C had little effect on either swimming or growth performance. However, fish in the 15°C group exhibited much poorer swimming and growth performance than those in the 20°C group. Ucrit decreased slightly under low acclimation temperature due to the pronounced improvement in swimming efficiency under cold temperature. Fish in the diel-fluctuating temperature group fed more but exhibited similar SGR compared to 20°C group, possibly due in part to an increase in energy expenditure to cope with the temperature fluctuation. The narrower thermal scope and lower CTmax of Chinese bream together with the conservation of CTmax with temperature acclimation, suggests that local water temperature elevations may have more profound effects on Chinese bream than on other fish species in the Three Gorges Reservoir.

Effects of feeding frequency and dietary protein levels on juvenile allogynogenetic gibel carp (Carassius auratus gibelio) var. CAS III: growth, feed utilization and serum free essential amino acids dynamics

A 8 week growth trial of three feeding frequencies (2, 4 and 6 meals day(-1)) and three dietary protein levels (30%, 34% and 38%) was conducted to investigate the influence of feeding frequency and dietary protein level on growth, feed utilization, serum free essential amino acids (EAA) dynamics and nitrogen (N), phosphorus (P), carbon (C) retention in juvenile allogynogenetic gibel carp (Carassius auratus gibelio) 'CAS III'. The results showed that feeding frequency and dietary protein level increased feed intake (FI), specific growth rate (SGR) and feed efficiency (FE). SGR increased significantly with the increase in feeding frequency and dietary protein level. But, the increase in dietary protein level from 30% to 38% in group 6 meals day(-1) did not result in better growth. Compared with the group of 4 meals day(-1) 9 38%, the fish fed the diet containing 30% crude protein at 6 meals day(-1) obtained similar SGR but showed lower FIp (protein intake). Compared with 2 meals day(-1), NREs (nitrogen retention efficiency) of 4 and 6 meals day(-1) were relatively higher. PRE (phosphorus retention efficiency) and CRE (carbon retention efficiency) increased significantly with feeding frequency while TNW (total nitrogen waste output), TPW (total phosphorus waste output) and TCW (total carbon waste output) decreased significantly. Feeding frequency and dietary protein level increased trypsin activity. Serum free EAA concentrations varied more synchronously at 6 meals day(-1) than 2 meals day(-1). It could be concluded that increasing feeding frequency could improve growth by increasing feed intake and feed efficiency for juvenile gibel carp. The increase in feeding frequency showed protein-sparing effect.

Effect of dynamic oxygen concentrations on the growth of Neochloris oleoabundans at sub-saturating light conditions

In tubular photobioreactors micro-algae continuously experience dynamically changing oxygen and light conditions when circulating from the solar receiver to the dark degasser. These changes in oxygen concentration and light were simulated in a CSTR using sub-saturating light intensity. Elongation of the residence time in the solar receiver from 30 to 300 min was also investigated. Specific growth rates measured at constant low oxygen concentration PO2=0.21 bar were; 1.14 ± 0.06 day(-1) using continuous light 0.80 ± 0.16 day(-1) with 30 min light and 1.09 ± 0.05 day(-1) with 300 min light. The effect of dynamically changing oxygen concentrations from PO2=0.21 to 0.63 bar followed by degassing resulted in similar specific growth rates. The exposure of the algae cells to dark periods in the degasser has a bigger negative impact than the temporary exposure to accumulating oxygen concentrations in the solar receiver. This shows that considerable energy savings for degassing are possible.

Effects of including shrimp protein hydrolysate in practical diets on the growth and survival of redclaw crayfish hatchlingsCherax quadricarinatus(Von Martens, 1868)

An experiment was carried out to analyse the effects of substituting fish-meal (FM) with soya bean meal and shrimp protein hydrolysate (SPH) on the percent survival, growth rate, feed efficiency and molt frequency of redclaw crayfish hatchlings, Cherax quadricarinatus. The experiment was performed in a closed recirculating-water system over a 56-day period. Five diets were tested: a control diet (SPH0) comprising 100% FM without SPH, and four diets with 2.5%, 5.0%, 10.0% and 15.0% SPH substitution (diets SPH2.5, SPH5, SPH10 and SPH15 respectively). Analysis of water quality indicated that it was adequate to maintain a good growth and survival of hatchlings. The results showed that 100% survival was obtained for hatchlings fed with SPH5, SPH10 and SPH15 diets. Higher mean values of final weight were obtained for the SPH5 diet. The highest weight gain was observed in SPH2.5 and SPH5 diets. Hatchlings showed similar specific growth rates for all diets. The efficiency rate of the SPH15 diet was lower compared to the other diets. Overall, individual feed consumption was higher in hatchlings fed diets of SPH5 and SPH15. It is recommended that 5.0% of SPH could be included in diets of hatchling redclaw crayfish to improve their growth efficiency.