Growth Of Juvenile Rainbow Trout Research Articles

Zinc nutrition at first feeding imprints a programming effect on growth and hepatic lipid metabolism in juvenile rainbow trout

The objective of this study was to determine whether supplementation with deficient zinc (Zn) or/and excess copper (Cu) in the first-feeding diet of rainbow trout fry influenced the growth and physiological regulation of juvenile fish subjected to similar challenge feeds again. The feeding trial lasted for 24 weeks and had three phases. In phase I, rainbow trout fry was treated with one of four different plant-based feeds containing or exempting Zn or Cu supplementation (coded Zn-Cu-, Zn+Cu-, Zn-Cu+, Zn+Cu+) for 6 weeks. Thereafter, all groups were fed a common commercial feed for the next 12 weeks (phase II). In phase III, all groups were fed with the “challenge diet” for another 6 weeks which was the basal diet (Zn-Cu-) except that the vegetable oils were replaced by fish oil. The results demonstrated that fish fed a Zn+ diet at first feeding increased larval growth (phase-I), but it had no effect on growth at the end of phase II when fed commercial feeds. In phase III, when re-introduced to a Zn- challenge diet, the feed intake and growth of juveniles with Zn+ history significantly increased, with reduced feed efficiency. Fish growth was neither influenced by dietary Cu levels or by the dietary Cu history in any of the growth phases, but dietary Cu excess (Cu+) reduced body lipid and energy content in fry. In phase I, lower whole-body Zn concentration was observed in the fry of Zn- group compared to Zn+, while the contrary was observed in the juvenile fish as affected by dietary Zn history (phase III). In addition, Zn- dietary history showed increased levels of PUFA and higher mRNA expression of fatty acid biosynthesis genes in the liver. To conclude, early-stage dietary Zn+ history improved growth of juvenile rainbow trout, while dietary Zn- history exhibited signs of improved fatty acid biosynthesis capacity in the liver.

Partially replacing plant protein sources with torula yeast in rainbow trout (Oncorhynchus mykiss) feed increases growth and factors related to immune status

AbstractIn this study, the impact of adding 10% or 20% torula yeast (PB TY10 and PB TY20) to a fishmeal‐free diet on digestibility and growth of juvenile rainbow trout was assessed. The yeast diets were compared with a plant‐only diet (PB) and a diet containing 20% fishmeal (FM). The apparent digestibility of dry matter, protein, energy, and ash of yeast in trout (~120 g) were 78.6%, 93.8%, 84.8%, and 48.7%, respectively. All PB diets had higher protein digestibility and PB TY20 had higher ash digestibility than the FM diet. To assess growth, trout (~44 g) were divided into triplicate tanks (30 per tank) and fed one of the four experimental diets for 12 weeks. The PB diet resulted in lower growth and daily feed intake (p < 0.05), but adding yeast significantly improved them. Final weight of PB TY10 did not differ significantly from that of FM. Expression of oclna and cldn15 in the proximal intestine increased in trout fed yeast (p < 0.05). Expression of tlr2, mcsfr, and tnfa, as well as the plasma lysozyme concentration, increased with PB TY20 (p < 0.05). In conclusion, torula yeast has the potential to improve the robustness and growth of rainbow trout in the context of fishmeal‐free diets.

Fish feeds supplemented with calcium-based buffering minerals decrease stomach acidity, increase the blood alkaline tide and cost more to digest

Predatory fish in the wild consume whole prey including hard skeletal parts like shell and bone. Shell and bone are made up of the buffering minerals calcium carbonate (CaCO3) and calcium phosphate (Ca3(PO4)2). These minerals resist changes in pH, meaning they could have physiological consequences for gastric acidity, digestion and metabolism in fish. Using isocaloric diets supplemented with either CaCO3, Ca3(PO4)2 or CaCl2 as non-buffering control, we investigated the impacts of dietary buffering on the energetic cost of digestion (i.e. specific dynamic action or SDA), gastric pH, the postprandial blood alkalosis (the “alkaline tide”) and growth in juvenile rainbow trout (Oncorhynchus mykiss). Increases in dietary buffering were significantly associated with increased stomach chyme pH, postprandial blood HCO3−, net base excretion, the total SDA and peak SDA but did not influence growth efficiency in a 21 day trial. This result shows that aspects of a meal that have no nutritional value can influence the physiological and energetic costs associated with digestion in fish, but that a reduction in the SDA will not always lead to improvements in growth efficiency. We discuss the broader implications of these findings for the gastrointestinal physiology of fishes, trade-offs in prey choice in the wild, anthropogenic warming and feed formulation in aquaculture.

Effects of different photoperiod regimes on the smoltification and seawater adaptation of seawater-farmed rainbow trout (Oncorhynchus mykiss): Insights from Na+, K+–ATPase activity and transcription of osmoregulation and growth regulation genes

Photoperiod is thought to be the main zeitgeber that induces smoltification in salmonids. However, its effects on the smoltification of rainbow trout (Oncorhynchus mykiss) are not fully understood and no published data documents the effects of the photoperiod regime currently used commercially, continuous light (LL). The present study compared the effect of four different photoperiod regimes (i.e. advanced phase photoperiod (APP), delayed phase photoperiod (DPP), LL and simulated natural photoperiod (SNP)) on the smoltification and growth of juvenile rainbow trout during their freshwater phase of winter-spring and the following summer post smolt phase. Smoltification was evaluated by monitoring gill Na+,K+–ATPase (NKA) activity and transcription of NKA α-subunit isoforms 1a and 1b, and Na+,K+,2Cl‐cotransporter 1a. Growth was measured as specific growth rate of both length and weight, and through molecular growth proxies such as the levels of circulating insulin-like growth factor 1 (IGF-I) in plasma and transcription of igf-I, igf binding protein 1b (igfbp1b), growth hormone receptor 1 (ghr1) and cathepsin L (ctsl) in the liver. Results indicate that APP induces a longer smolt window and higher levels of plasma IGF-I in both freshwater and seawater (two months post transfer), while DPP led to a shorter smolt window, lower plasma IGF-I levels in freshwater and seawater, an earlier decrease in liver igf-I and ctsl transcription in freshwater (as seen by modelling over time) and lower specific growth rate in freshwater. The transcription analysis of osmoregulatory genes complemented NKA activity and allowed for the detection of a transient response to light and of differences between the osmoregulatory capacity of parr and desmolted fish. Furthermore, an upregulation of the liver transcription of igf-I, ghr1 and ctsl was found in all treatments during the smolt window, which corresponded to the periods with highest growth. Finally, both plasma IGF-I and liver igf-I in seawater were found to be significantly correlated to fish growth in seawater. However, our data did not show that plasma IGF-I prior to seawater transfer could be used as a reliable predictor of growth in seawater. Overall, and especially when compared with other salmonid species, photoperiod seems to be a weaker inducer of smoltification in rainbow trout, according to the parameters that were tested, suggesting that other environmental cues might be more important drivers of this process.

Effects of dietary supplementation with red seaweed, Gracilaria pygmaea, on growth, carcass composition and hematology of juvenile rainbow trout, Oncorhynchus mykiss

A feeding trial was carried out to evaluate the effects of inclusion of 3 (GL3), 6 (GL6), 9 (GL9), and 12 (GL12) % red seaweed, Gracilaria pygmaea, in rainbow trout, Oncorhynchus mykiss, feeds. A feed without seaweed was used as the control. All feeds were formulated to be iso-nitrogenous (48% protein), iso-lipidic (16%), and iso-energetic (20 kJ g−1), and they were fed to triplicate groups of 30 rainbow trout (initial average body weight 0.26 g) for 7 weeks. At the end of the trial, the final weight (FW) was significantly higher in fish fed the GL6 feed (3.49 ± 0.03 g) than that in fish fed the control (3.23 ± 0.03 g) and GL12 (2.85 ± 0.02 g) feeds (P 0.05). In conclusion, the findings suggest that a dietary supplement of circa 6% G. pygmaea may be useful to promote the growth of juvenile rainbow trout.

The Effect of a Mycotoxin Deactivation Product on Growth of Juvenile Rainbow Trout Fed Distillers Dried Grains

AbstractDistillers dried grains (DDG) with solubles (DDGS) is a product that has shown potential as a protein source for some fish species, but high inclusion rates of DDGS have not always been successfully achieved for Rainbow Trout Oncorhynchus mykiss. Our objective was to determine whether inclusion of a mycotoxin deactivation product (Biofix Plus) could improve the ability of high‐protein DDG (HPDDG) to replace a portion of the fish meal in diets for Rainbow Trout. The 2 × 2 factorial feeding trial examined protein source (menhaden fish meal [MFM] or HPDDG) with or without Biofix Plus. A control diet (42% digestible protein, 20% crude lipid, 25% MFM) was compared to a test diet in which HPDDG replaced 12% of the total MFM on a digestible‐protein basis (24% HPDDG inclusion). Diets were fed to juvenile Rainbow Trout (initial weight: mean ± SE = 30.5 ± 1.6 g) in four replicate tanks per treatment for 9 weeks in a 15°C recirculating system. At the conclusion of the feeding trial, we observed no negative effects of fish meal replacement on growth or feed conversion ratio; no benefit of Biofix Plus supplementation was observed. These data indicate that when Rainbow Trout diets containing a high‐quality DDGS product are balanced for digestible protein, lysine, methionine, and threonine, dietary fish meal levels can be successfully reduced to 13% without compromising growth and without the need for mycotoxin deactivator inclusion.

Dietary probiotic supplementation modulated gut microbiota and improved growth of juvenile rainbow trout (Oncorhynchus mykiss)

In aquaculture, infectious diseases are the major cause of economic losses. Probiotic supplementation may change the microbiota of the digestive tract and modulate the immune defences and nutritional performance. This study was conducted to evaluate the dietary supplementation of multi-species (A: Bacillus sp., Pediococcus sp., Enterococcus sp., Lactobacillus sp.) and single-species probiotics (B: Pediococcus acidilactici) on growth performance and gut microbiota of rainbow trout (Oncorhynchus mykiss). A basal diet was supplemented with probiotic A or B, at two concentrations each (A1, A2, B1 and B2) or not supplemented (control treatment). Diets were distributed to 30 groups of 20 fish, 3 times a day. The gut microbiota was analysed at the end of the feeding trial (96days) with 16S rDNA denaturing gradient gel electrophoresis (16S-DGGE). Changes in gut microbial community were assessed by Shannon index (H´) and number of operational taxonomic units (OTUs). After 56days of feeding, weight gain was significantly improved in fish fed diet A1 when compared to the control group. Dietary probiotic supplementation changed the gut microbial composition. Number of OTUs (R) was higher in fish fed A1 (multi-species at lower concentration) than in control group, while H´ was higher in fish fed A1, B1 and B2.

The chronic aquatic toxicity of a microbicide dibromonitrilopropionamide

The chronic aquatic toxicities of a microbicide dibromonitrilopropionamide (DBNPA) in Daphnia magna and rainbow trout were evaluated. DBNPA can significantly affect the reproduction and survival of D. magna. The lowest observed effective concentration (LOEC) and the no observed effective concentration (NOEC) of DBNPA to D. magna were 0.053 and 0.072 mg L(-1), respectively, and the intrinsic rate of natural increase (r) was significantly decreased (p < 0.05) at a concentration of 0.01 mg L(-1). Meanwhile, DBNPA affected the growth of juvenile rainbow trout at a concentration of 0.01875 mg L(-1) after 28-day exposure. The results showed that DBNPA has chronic deleterious effects on aquatic organisms.

The relative importance of waterborne and dietborne arsenic exposure on survival and growth of juvenile rainbow trout

Previous work demonstrated reduced growth of rainbow trout receiving diets containing environmentally relevant concentrations of arsenic, but did not address the relative and combined potency of waterborne and dietborne exposures. In the current study, juvenile rainbow trout were exposed for 28 d to a range of arsenic concentrations in water and in a live oligochaete diet, separately and in combination. In clean water, fish fed worms previously exposed to arsenate at 4 or 8 mg As/L showed pronounced reductions in growth, but fish exposed to these same water concentrations and a clean diet experienced less or no effect. Increasing waterborne arsenate to 16 or 32 mg As/L had substantial effects on both growth and survival, and simultaneous exposure via both routes intensified growth effects, but not mortality. Growth reduction was strongly correlated to total arsenic accumulation in the fish tissue, regardless of the route of exposure, but mortality was better correlated to waterborne arsenic concentration. The relative concentration of total arsenic in fish viscera and in the remaining carcass was not a useful indicator of exposure route. Speciation analysis showed that most arsenate was converted to arsenite within the worms, but organoarsenic species were not found. The greater toxicity of dietborne exposure when fish and prey were exposed to the same waterborne arsenate concentration emphasizes the need to address dietborne exposure when assessing the aquatic risks of arsenic contamination. This is of particular concern because risk from dietary exposure may occur at even lower water concentrations than used here when prey organisms are exposed for longer periods and via multiple routes.

Dietary administration of beta-mercapto-ethanol treated Saccharomyces cerevisiae enhanced the growth, innate immune response and disease resistance of the rainbow trout, Oncorhynchus mykiss

The effects of dietary whole cell yeast ( Saccharomyces cerevisiae), n-3 HUFA-enriched yeast and treated yeast cells with beta-mercapto-ethanol (2ME) on immunity, growth performance and disease resistance to Yersinia ruckeri were investigated in Oncorhynchus mykiss. During 30 days, juvenile rainbow trout were fed diets supplemented with different forms of yeast at 5 × 10 7 CFU g −1 or a control diet. After the feeding trial, remaining fish of each treatment were challenged by pathogenic Yersinia ruckeri and kept under observation for 14 days to record clinical signs and daily mortality rate. Yeast supplementation in all treatment groups significantly promoted the growth performance compared to control group. A significantly increase was also observed in immune responses in juvenile fish fed 2ME-treated yeast diet. More ever, the lowest fish mortality was obtained in this treatment group. The present results show that a diet supplemented with 2ME-treated yeast stimulates the immune system and growth of juvenile rainbow trout thus enhancing their resistance against Y. ruckeri.

An Ecological Risk Assessment of the Exposure and Effects of 2,4-D Acid to Rainbow Trout (Onchorhyncus mykiss)

Numerous state and federal agencies are increasingly concerned with the rapid expansion of invasive, noxious weeds across the United States. Herbicides are frequently applied as weed control measures in forest and rangeland ecosystems that frequently overlap with critical habitats of threatened and endangered fish species. However, there is little published chronic toxicity data for herbicides and fish that can be used to assess ecological risk of herbicides in aquatic environments. We conducted 96-h flowthrough acute and 30-day chronic toxicity studies with swim-up larvae and juvenile rainbow trout (Onchorhyncus mykiss) exposed to the free acid form of 2,4-D. Juvenile rainbow trout were acutely sensitive to 2,4-D acid equivalent at 494 mg/L (95% confidence interval [CI] 334-668 mg/L; 96-h ALC(50)). Accelerated life-testing procedures, used to estimate chronic mortality from acute data, predicted that a 30-day exposure of juvenile rainbow trout to 2,4-D would result in 1% and 10% mortality at 260 and 343 mg/L, respectively. Swim-up larvae were chronically more sensitive than juveniles using growth as the measurement end point. The 30-day lowest observable effect concentration (LOEC) of 2,4-D on growth of swim-up larvae was 108 mg/L, whereas the 30-day no observable effect concentration (NOEC) was 54 mg/L. The 30-day maximum acceptable toxicant concentration (MATC) of 2,4-D for rainbow trout, determined as the geometric mean of the NOEC and the LOEC, was 76 mg/L. The acute:chronic ratio was 6.5 (i.e., 494/76). We observed no chronic effects on growth of juvenile rainbow trout at the highest concentration tested (108 mg/L). Worst-case aquatic exposures to 2,4-D (4 mg/L) occur when the herbicide is directly applied to aquatic ecosystems for aquatic weed control and resulted in a 30-day safety factor of 19 based on the MATC for growth (i.e., 76/4). Highest nontarget aquatic exposures to 2,4-D applied following terrestrial use is calculated at 0.136 mg/L and resulted in a 30-day safety factor of 559 (e.g., 76/0.163). Assessment of the exposure and response data presented herein indicates that use of 2,4-D acid for invasive weed control in aquatic and terrestrial habitats poses no substantial risk to growth or survival of rainbow trout or other salmonids, including the threatened bull trout (Salvelinus confluentus).

Effects of ambient colour on colour preference and growth of juvenile rainbow trout Oncorhynchus mykiss (Walbaum)

Colour preference of individual juvenile rainbow trout Oncorhynchus mykiss was tested at 1 and 12° C, and also at 12° C after a 42 day growth experiment under white, blue, green, yellow or red ambient colour. All experiments were carried out under controlled laboratory conditions and the preference was assessed by the location of the fish in a preference tank with four chambers. Rainbow trout showed a preference for blue and green at 1° C and for green at 12° C. After the growth experiment the fish reared in blue tanks preferred blue and green but green was the most preferred colour for the fish reared in green, yellow and red tanks. Yellow and especially red chambers were avoided, irrespective of the ambient colour during the growth trial. The final mass of fish reared in the red aquaria was significantly smaller than that of the fish in green tanks. In addition, when the data of the preference tests were correlated with the data of the growth experiment using mean values of the four tested colours, a very good linear relationship was observed between the preference (i.e. visit frequency in coloured compartments) and growth rate as well as food intake. When considering the results both from the preference and growth trials it is suggested that green is the best environmental colour for rearing juvenile rainbow trout while rearing in a red environment cannot be recommended.

Relationships among Feed Intake, Feed Efficiency, and Growth in Juvenile Rainbow Trout

AbstractImproving the efficiency of aquaculture production is important for both economic and environmental sustainability. The purpose of this work was to define the relationships between feed intake, weight gain, and feed efficiency (measured as residual feed intake) in rainbow trout Oncorhynchus mykiss fed either to apparent satiation or a limited ration. The results indicated that under an apparent satiation feeding regime, a weak but significant correlation existed between weight gain and residual feed intake (RFI; r = −0.31, P &lt; 0.04). When fed a limited ration, the correlation between weight gain and RFI was stronger (r = −0.57, P &lt; 0.001). Genetic differences between family groups were detected only under the apparent satiation feeding regime and not under limited feeding. Although these experiments were conducted on different groups of fish, it appears that the variation in RFI was greater in satiation‐fed fish than in fish fed a limited ration (coefficient of variation = 174% versus 33%). Estimates of residual feed intake measured on individuals from full‐sib families and on groups of individuals from the same families were correlated (r = 0.66, P = 0.03), suggesting that the feed efficiency measured on individually reared fish captures a trait expressed in social groups as well.

Effects of repeated handling, with or without anaesthesia, on feed intake and growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum)

The effects of weekly anaesthetization with clove oil and tricaine methanesulphonate (MS-222) on feed intake and growth were examined in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually. Repeated handling without anaesthetics significantly reduced feed intake and weight gain compared with an unhandled control group during an 8-week experiment. When anaesthetics were used during handling the feed consumption and weight gain were significantly (MS-222) or not significantly (clove oil) higher than in fish handled without anaesthesia. When compared with the unhandled control group, neither of these two anaesthetics had significant effects on feed intake but, in contrast to MS-222, repeated anaesthesia with clove oil had a significant negative effect on growth. However, the effects of MS-222 and clove oil on the growth were not significantly different from each other. Feed conversion ratio (feed/gain) of MS-222-anaesthetized fish was significantly higher compared with unhandled control and handled control fish but was not significantly different from fish anaesthetized with clove oil. These results suggest that both MS-222 and clove oil alleviate handling stress in juvenile rainbow trout, and that these two anaesthetics are rather similar with respect to their effects during repeated exposures.

Dietary l-tryptophan and tank colour effects on growth performance of rainbow trout ( Oncorhynchus mykiss) juveniles reared in a recirculating water system

The aim of the present study was to evaluate the possible anti-stressful effect of dietary tryptophan supplementation on growth of juvenile rainbow trout ( Oncorhynchus mykiss) reared in different background colour using recirculating water system. Therefore, rainbow trout (4.7 g ± 0.02) were reared for 11 weeks in black, light blue and white tanks and fed either a commercial diet (CD) or the same diet supplemented with tryptophan (2 g 100 g −1 diet). Rearing in black tanks led to reduced final weight and total length, lower food consumption, food conversion ratio and body protein, while no differences were observed between fish reared in light blue or white tanks. Feeding the fish tryptophan supplemented diet resulted in depressed growth, increased food consumption and food conversion ratio, decreased body protein and increased body lipid, reduced liver total lipids and a marked increase in hepatosomatic index (least in fish reared in white tanks). It is concluded that rearing on a black background was stressful for rainbow trout juveniles, while the dietary level of tryptophan used failed as a stress-releasing factor and probably evoked an amino acid imbalance.

Compensatory growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually

The effect of feed cycling on compensatory growth was examined in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually at 15 °C. Fish were fasted for 2, 4, 8, or 14 days and then refed until either their relative feed intake differed by less than 10% of fed controls, or the duration of the refeeding period was four times the fasting period. After 80 days, fish fasted for 8 days at a time were smaller than controls, or fish experiencing 2 or 4 days of fasting, while fish fasted for 14 days did not differ from other groups. There were no differences in visceral fat or hepatosomatic indices, but within-treatment variation was high. Fish subjected to fasting displayed compensatory growth, and high growth rate during the recovery phase was achieved by hyperphagia, rather than improved feed conversion. There was a highly significant relationship ( R 2=0.951) between feed intake and weight gain, and feed conversion did not differ between fish subjected to the different treatments. The results indicate that rainbow trout can be subjected to short periods of fasting without significant effects on growth, but no improvement in feed utilization was obtained during the refeeding period.

Interaction between diet and genetic aptitude for weight and growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum)

Samples of rainbow trout, Oncorhynchus mykiss (Walbaum) alevins from 17 independent families (full-sib-groups) were raised from the start of feeding until the age of 18 weeks post-hatching with three diets (C, G and S) differing in protein content (fish soluble protein concentrate: 84% in C, 54% in G and 44% in S) and carbohydrates (none in C, 30% glucose in G and 40% crude corn starch in S). Fish were fed to near satiation, and their body weight and growth were measured. Diet effect was highly significant (G< C < S), as well as the familial effect. The major part of the familial variance (80–90%) was common to the three diets. However, a minor part of the familial variance was observed to be diet dependent (family × diet interaction), and was found to result mainly from relative performances with carbohydrates (G and S diets) vs. pure protein (C diet). These results indicate that genetic improvement of growth should suffer little impairment from possible changes in future feed formulations.

The effect of dietary flumequine on food consumption and growth in rainbow trout

Antibiotics are important chemotherapeutants and under intensive farmingconditions, drug administration via the diet seems to be the only practicalroute. Medicated diets often suffer the problems of reduced palatability andfrequently affect growth by reducing the nutritional value of feeds and/ornutrient digestibility (Cravedi et al., 1987; Schreck and Moffitt, 1987; Ahmadand Matty, 1989; Poe and Wilson, 1989; Choubert et al., 1991; Hustvedt etal., 1991; Robinson and Tucker, 1992; Toften et al., 1995).Flumequine is a synthetic antimicrobial compound and, although it is notlicenced for use in aquaculture throughout Europe, it has been widely used totreat furunculosis (Barnes et al., 1991; O’Grady and Smith, 1992; Scallan andSmith, 1995). However, there is evidence that administration of flumequineto rainbow trout in combination with gentamycin may affect nutrient absorp-tion and thereby the nutritional quality of the diet (Choubert et al., 1991). Inthe present study the effect of flumequine on individual consumption ratesand growth of juvenile rainbow trout (

Effects of Pure and Atmospheric Oxygen to the Growth of Juvenile Rainbow Trout (Oncorhynchus mykiss) on the Light and Dark Conditions

In this study the effect of pure and atmospheric oxygen on the growth rate of juvenile rainbow trout (Oncorhynchus mykiss) at constant temperature were investigated. In the investigation experiments were realized as two stages. The firs stage has continued fourteen weeks. The difference between pure and atmospheric oxygen was not significant as statistically (P>0.05). Even if, on the groups are maintenance at light and dark conditions were found difference total length and weight data between pure and atmospheric oxygen groups were significant as statistically (P0.05) at the end of the seventh week. Thus, effects of the pure oxygen of the growth rate juvenile trout were found significant as evidence in the fish cultures.

Effects of elevated summer temperatures and reduced pH on metabolism and growth of juvenile rainbow trout (Oncorhynchus mykiss) on unlimited ration

Des truites juveniles (Oncorhynchus mykiss) ont ete exposees a une simulation de rechauffement global et d'acidification de l'eau pendant une periode de 90 jours en ete (plage de temperature temoin de 13-24°C). Le relevement de 2°C du cycle fluctuant de la temperature estivale des eaux cotieres du lac Ontario et l'ajout de H 2 SO 4 a de l'eau douce de synthese ont servi a pratiquer quatre traitements : temoin, acidification du temoin, simulation de rechauffement global seulement, et rechauffement plus acidification. Le regime d'alimentation biquotidien a fait monter le metabolisme a 75% de Mo 2 (max). De fortes augmentations (de 4,5 a 11,5%) des lipides du corps entier, des augmentations plus faibles (de 12,0 a 15,5%) des proteines et des baisses compensatoires de la teneur en eau ont ete observees dans tous les traitements (de 77 a 71%) au fil du temps. Le relevement de 2°C a cause une diminution de l'appetit et de la croissance, particulierement apres le pic de temperature jours 60 a 90; 26°C). Le metabolisme et l'excretion de dechets azotes ont egalement baisse. Globalement, l'exposition a un pH faible a occasionne une augmentation de l'appetit et de la croissance. Le relevement de 2°C a reduit l'absorption d'energie brute et accru les pertes d'energie par les feces, tandis que l'exposition a un faible pH a cause une augmentation de l'absorption et du gain d'energie, et une meilleure efficacite de conversion. L'absence de perturbation de la regulation ionique chez les truites chroniquement exposees a un pH de 5,2 permet de penser que le Nacl contenu dans l'aliment peut avoir compense les pertes ioniques au niveau branchial.