Probiotic bacteria <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> influences the blood profile in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> (Walbaum)

This paper reports the effect of feeding probiotic diets on blood profiles in rainbow trout. Two experiments were performed: in the first, fish of average weight 75 g were offered either a commercial feed or the same incorporated with 10⁹ CFU g⁻¹ of lactic acid bacteria Lactobacillus rhamnosus for 30 days; in the second study performed for a similar duration, fish of average weight 126 g were offered formulated diets that either contained the same bacteria in heat-killed or freeze-dried form (nearly 10¹¹ CFU g⁻¹), or the basal diet without the bacteria. Blood samples were collected at different times after commencement of probiotic feeding to determine the total cholesterol, triglyceride contents, the plasma alkaline phosphatase activity, plasma protein and hematocrit value. The plasma cholesterol significantly increased upon probiotic feeding in the first experiment. A significant elevation (P < 0.05) of plasma cholesterol and triglyceride and alkaline phosphatase activity level was found in the freeze-dried probiotic fed groups at 20 and 30 days postfeeding. This was concomitant with the increased plasma protein and hematocrit values in FD group at 20 and 30 days. Likewise, the heat-killed probiotic fed group registered significantly high values of triglycerides, alkaline phosphatase activity, and plasma protein compared to the control diet fed groups after 20 days of feeding. Thus, alterations in the blood profiles could serve as supplementary information when examining the benefits of probiotics for fish.     

Wheat grains fermented by fungal mycelia (<Emphasis Type="Italic">Pleurotus ostreatus</Emphasis> or <Emphasis Type="Italic">Lentinus edodes</Emphasis>) as alternative feed ingredients for juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

We investigated the effects of replacing non-fermented wheat grains with wheat grains fermented by fungal mycelia in the diet of juvenile rainbow trout (Oncorhynchus mykiss). We assessed growth performance, feeding parameters, and body composition in three experimental groups (0.33?±?0.01 g, in triplicates of 50 individuals each). The diets for all the groups contained ca. 43% protein and 19% lipids. Experimental diets were made by replacing the 100 g kg^?1 of wheat grains present in the basal diet (CTRL) with the same proportion of wheat grains fermented by Pleurotus ostreatus (PWD) or Lentinus edodes (LWD) mycelium. Fish were fed to apparent satiation twice a day for 56 days. Both, PWD and LWD, significantly increased fish body weight from day 28 onwards. Final body weight was 2.37?±?0.04 g (CTRL), 4.29?±?0.02 g (PWD), and 3.50?±?0.05 g (LWD), and feeding efficiency (%) was increased from 64.5?±?0.7 (CTRL) to 92.5?±?0.5 (PWD) and 84.8?±?1.5 (LWD). The experimental diets also improved nutrient retention efficiency (%): 30.0?±?0.5 (PWD), 27.7?±?1.1 (LWD), and 21.0?±?0.1 (CTRL), for crude protein; 40.3?±?0.6 (PWD), 31.0?±?1.8 (LWD), and 16.1?±?0.7 (CTRL), for ether extract; and 16.1?±?0.1 (PWD), 14.0?±?0.3 (LWD), and 11.6?±?0.6 (CTRL), for phosphorus. Body lipid content was highest for PWD followed by LWD and CTRL (81.4?±?1.4, 63.2?±?2.5, 42.3?±?2.6 g kg^?1, respectively), while viscerosomatic index was lowest for PWD (p?<?0.05). Liver glycogen in LWD and PWD fish (0.62?±?0.10 and 0.21?±?0.08% liver weight) was significantly higher than in CTRL fish (0.05?±?0.01% liver weight). Wheat-mycelium meals appear to be suitable dietary ingredients for improving juvenile rainbow trout growth and nutritional performance. These benefits vary according to the mushroom species used.     

Tissue-specific daily variation in the oxidative status of sturgeon (<Emphasis Type="Italic">Acipenser naccarii</Emphasis>) and rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>): a comparative study

The oxidative status is associated with animal lifespan, metabolism, activity and circadian rhythms. The objective of this work is to study the time course of the oxidative status over a daily cycle in the plasma, liver and brain, and the changes in the plasma cortisol levels of sturgeon and trout. The knowledge of daily oxidative status will provide a better understanding of the trout and sturgeon physiology and adequate maintenance and food supply of farmed fish in relation to photoperiod. Superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione transferase, DT-diaphorase activities, lipid peroxidation and cortisol were measured. Our results showed that the antioxidative enzyme activities and lipid peroxidation in the liver of trout and sturgeon changed through the day, with increased levels in lipid peroxidation of liver in the dark period for sturgeon. This could be related to the different activity time in both species, an issue to be taken into account when designing the guidelines of the maintenance of these species in fish farms. On the contrary, there was not clear influence of the daily rhythms on brain oxidative status. The higher efficiency of the antioxidant defences in the brain of sturgeon, which displays less lipid peroxidation and higher antioxidative activity, could be related to its longer life expectancy. The absence of any apparent daily rhythm in the plasma cortisol levels in sturgeon could indicate a lower susceptibility to stress, and that mechanisms involved in cortisol secretion in chondrosteans could be different from that described for teleosteans.     

Thermal tolerance of a rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> strain selected by high-temperature breeding

ABSTRACT:   Thermal tolerance was studied in a rainbow trout strain successively selected through high temperature breeding at 20–27°C since 1966 in Miyazaki Prefecture, Japan. The hatching rate and fry mortality at high temperatures were examined in the selected strain along with normal strains cultured at water temperature of 9–17°C. The hatching rate of embryos fertilized at either 10 or 14°C and subsequently subjected to high temperatures in the blastula or neurula stage of the selected strain, was marginally higher than that of the normal strain counterparts. The upper 50% lethal temperatures (LT₅₀) for embryos in the early segmentation, blastula and neurula stages of the selected strain were also higher than those of the normal strain counterparts. Death temperatures and LT₅₀ of fries acclimated to 20°C of the selected strain were significantly higher than those of the normal strains. However, no difference in the critical thermal maximum was detected between the different strains. These results suggest that the selected strain of rainbow trout established by selecting successively for many generations at high temperatures acquired a degree of thermal tolerance.     

Effects of organic acids on growth and phosphorus utilization in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

ABSTRACT:   An experiment was conducted to investigate the effect of various organic acid (OA) supplementation on phosphorus (P) and nitrogen (N) retention by rainbow trout fed low fishmeal-based diets. Six experimental diets were formulated, and diet 0.5P was arranged as a positive control diet with 0.5% calcium phosphate and 0P as a negative control without additional P. Diets CA and LA were supplemented with 1% citric (CA), and lactic (LA) acids, respectively, and diets MHA and LTE were supplemented with 1% methionine hydroxy analog (MHA) and 1% liquid trace elements (LTE), respectively. Fish fed CA and LTE showed similar growth to that of the positive control diet. P retention was lowest in the 0.5P group and was elevated with CA and LTE diets. Therefore, in this study it is suggested that it might not be necessary to supplement the low fishmeal-based diet of rainbow trout with P if certain organic acids such as CA are added.     

Molecular characterization of PRR13 and its tissue-specific expression in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The proline-rich protein 13 (PRR13) is reported to be a key regulator of the resistance to cytostatica by decreasing the copy number of the proapoptotic gene thrombospondin-1. We isolated and characterized the complete PRR13 gene sequence of rainbow trout (Oncorhynchus mykiss). The gene comprises four exons and three introns, the latter of comparatively short lengths (100–811 bp). The full-length PRR13 cDNA consists of 1,101 nucleotides, including an open reading frame of 563 bp, which is predicted to encode a 187 amino acid protein with a molecular mass of 18.8 kDa. A continuous stretch of ten serine residues at the C-terminus is highly conserved and characteristic for vertebrate PRR13, but not for other known proline-rich proteins. Phylogenetic analyses suggest a clear separation of teleostean PRR13 proteins and those from mammalian and reptilian species. Comparison of the tissue-specific PRR13 mRNA abundance in two strains of the rainbow trout coastal form (TCO Steelhead II-WA vs. BORN Steelhead II-Germany) revealed an increased expression in the BORN trout in nearly all examined tissues. The major expression differences were detected in gill (2.29-fold) and in liver tissue (2.16-fold). Hence, the increased PRR13 expression in BORN trout might cause improved protection from natural cytostatica and therefore support our assumption that PRR13 is a candidate gene possibly involved in the varying ability of the two rainbow trout strains to handle environmental stress under local conditions of the Southern Baltic.     

Effects of chronic high stocking density on liver proteome of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

The main aim of the present study was to assess the effects of chronic high stocking density on liver proteome of rainbow trout. Rainbow trout juveniles (42.6 ± 2.3 g average body weight) were randomly distributed into six tanks at two stocking densities (low stocking density (LD) = 20 kg m^?3 and high stocking density (HD) = 80 kg m^?3). Both treatments were performed in triplicate tanks for a period of 60 days. High stocking density caused a reduction in the growth performance compared with LD fish. Lysozyme activity increased with stocking density, while serum complement activity presented the opposite pattern. Serum cortisol and total protein levels did not show significant differences (P > 0.05) between experimental groups. The fish reared at high stocking density showed significantly lower osmolality and globulin values but higher albumin level. The HD group had significantly higher activities of catalase, glutathione peroxidase and superoxide dismutase, and malondialdehyde content in the liver when compared to the LD group. Comparative proteomics was used to determine the proteomic responses in livers of rainbow trout reared at high stocking density for 60 days. Out of nine protein spots showing altered abundance (>1.5-folds, P < 0.05), eight spots were successfully identified. Two proteins including apolipoprotein A-I-2 precursor and mitochondrial stress-70 protein were found to increase in HD group. The spots found to decrease in the HD group were identified as follows: 2-peptidylprolyl isomerase A, two isoforms of glyceraldehydes-3-phosphate dehydrogenase, an unnamed protein product similar to fructose-bisphosphate aldolase, 78 kDa glucose-regulated protein, and serum albumin 1 protein.     

Adverse and beneficial effects of long-term high-concentration ascorbic acid supplementation in rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The present study examined the effects of high-concentration ascorbic acid (AsA) supplementation over a long period on growth, plasma components, nonspecific immune responses, and thermal tolerance in rainbow trout Oncorhynchus mykiss. Four commercial diets supplemented with 0, 100, 1000, and 5000 mg AsA per kg of diet (designated AsA0, AsA100, AsA1000, and AsA5000, respectively) were fed to rainbow trout (initial weight 1.85 g) for 100 days. AsA contents in liver increased with increasing dietary AsA levels. Feeding period, growth performance, and plasma components did not differ significantly between the AsA groups. On the other hand, the phagocytic assay [nitro-blue tetrazolium (NBT) assay] was significantly higher in fish fed AsA1000 and AsA5000 than those fed a diet without AsA (AsA0) at the end of feeding trial. Superoxide dismutase (SOD) activity in the intestines of fish fed AsA5000 was also significantly higher than that of fish fed AsA0. In the thermal tolerance test, fish fed AsA5000 only showed significantly lower cumulative mortality compared with the AsA0 group. In conclusion, high-concentration AsA supplementation such as AsA5000 over a long period does not induce any adverse effects and can enhance disease and stress resistance in rainbow trout.     

Stress response of juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)to chemical cues released from stressed conspecifics

The objective of this study was to determine whether exposure of rainbow trout (Oncorhynchus mykiss) to water containing a stressed trout or skin extract from stressed and non-stressed trout would elicit a stress response in conspecifics. Juvenile rainbow trout were exposed for 1 hour to water containing a stressed fish, homogenized skin extracts from a non-stressed fish, skin extract from a stressed fish and water with none of these factors. The stress response was measured over a 24-h period (1, 6, 12, 24 h after exposure). Plasma cortisol levels increased at 12 h in fish exposed to water from a stressed fish and skin extract from a stressed fish. Plasma glucose and hepatic hsp70 levels were not affected by treatments. The results suggest that rainbow trout elicit a stress response when exposed to stress-related alarm cues released from conspecifics.     

Anti-oxidative functions of <Emphasis Type="Italic">mt2</Emphasis> and <Emphasis Type="Italic">smtB</Emphasis> mRNA expression in the gills and brain of zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) upon cadmium exposure

There were not any past studies about metallothionein isoforms (smtB and mt2) having anti-oxidative functions on zebrafish after Cd²⁺ exposure. On the other hand, the anti-oxidative enzymatic factors such as superoxide dismutase (sod), glutathione peroxidase (gpx1a), and catalase (cat) are used as references to investigate whether the smtB and mt2 have anti-oxidative responses on the gills and brain of zebrafish after 1–6 h of 0 and 1.78 μM Cd²⁺ exposure. The anti-oxidative system such as sod, cat, and gpx1a mRNA expressions demonstrated a cascade response upon Cd²⁺-induced oxidative stress in the present study. Interestingly, the smtB mRNA expression levels increased by 3.2- to 6.1-fold, and mt2 raised by 4.1- to 11.3-fold in gills at 1 and 3 h after exposure to Cd²⁺, respectively. On the other hand, the smtB mRNA levels increased by 10.6- to 58.6-fold, but mt2 mRNA levels increased by 2.3- to 11.1-fold in brain at 1 and 3 h after exposure to Cd²⁺, respectively. In addition, both tissues showed increased apoptosis levels at 3 h, and recovery after 6 h of Cd²⁺ exposure. From the results, we suggest that both mt2 and smtB play a role in anti-oxidation responses within 6 h after exposure to Cd²⁺. In conclusion, the smtB mRNA levels have a higher response than mt2 in the brain, but both mRNA expressions appear to have a similar pattern in the gill. We suggest that smtB plays an important role to defend oxidative stress in the brain of adult zebrafish upon acute Cd²⁺ exposure.     

Medicinal plant extracts modulate respiratory burst and proliferation activity of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) leukocytes

The present study was designed to investigate the immunomodulatory effects of Aloe vera, Curcuma longa, Echinacea purpurea, Lavandula officinalis, Origanum vulgare, Panax ginseng, and Rheum officinale extracts on leukocytes purified from rainbow trout (Oncorhynchus mykiss) head kidney. The cells were cultured in a medium containing increasing doses of extracts; afterwards, they were tested for reactive oxygen species production after stimulation with phorbol myristate acetate (PMA) and proliferation in the presence or absence of phytohemagglutinin from Phaseolus vulgaris (PHA-P). After a 2-h exposure, the extracts of L. officinalis, O. vulgare, and R. officinale strongly reduced the oxidative burst activity of PMA-stimulated leukocytes, in a dose-dependent manner (P ≤ 0.05). A. vera, C. longa, E. purpurea, and P. ginseng extracts reduced this response with lower efficacy and especially at lower concentrations. On the contrary, the highest concentration of ginseng extract stimulated the respiratory burst of leukocytes compared to untreated control cells. After a 72-h exposure, the extracts of L. officinalis, R. officinale, C. longa, E. purpurea, and P. ginseng had a clear dose-dependent stimulatory effect on leukocyte proliferation (P ≤ 0.05). The results suggest that these medicinal plants can be considered as reliable sources of new antioxidants or immunostimulants to be used in aquaculture.     

Effect of follicle cell autophagy on gonadal development of triploid female rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Autophagy is a cellular process which occurs in eukaryotic cells. To study the mechanism regulating polyploid fish growth and development is of significance in genetic, because of its growth advantages and economic values. This study focused on triploid female rainbow trout (RBT) which discusses the effects of autophagy on gonadal development of polyploid fish. Autophagy-related genes of RBT lc3b, atg12, atg4b, gabarap1, and bcl2 were cloned, and autophagy gene expressions in gonads were analyzed at different developmental period. Gonadal ultrastructures were observed under transmission electron microscopy. To detect autophagy protein expression and localization, antibodies of RBT-LC3B and RBT-ATG12 were produced. Results showed clear evidence that autophagy-related genes were highly expressed during 200–300 days post fertilization (dpf), in which autophagosome structures were identified. In this stage, the conversion of LC3B-I to LC3B-II was greater than those in other stages. Immunolabeling-manifested autophagy occurred intensively in the cytoplasm of follicular cells. The morphology of follicular cells was gradually changed, leading to gonadal fibrosis and regression. This autophagic research is a new study area on gonadal development of polyploid fish.     

Farming evaluation of the brownbow triploid hybrid (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis><Emphasis Type="Italic">Salmo trutta</Emphasis>)

Triploid hybrids between female rainbow trout (Oncorhynchus mykiss Walbaum) and male brown trout (Salmo trutta L.) were tested for farming performances, with reference to parental species. The main drawback of hybrids lay in embryonic and larval mortalities, amounting to 60% on average, and displaying a large variability between spawns. Further survival was inferior to that of diploid, but similar to that of triploid rainbow trout. Hybrid body weight was intermediate between weights of rainbow and brown trout of the same age, mainly as a consequence of differences in precocious growth. Analysis of relative growth rates from 6 to 18 months showed that hybrids were surpassed by rainbow controls in common rearing, but not in separate rearing. Hybrid behaviour was similar to that of rainbow trout. These results are discussed in the scope of providing fisheries managers with original and sterile game fishes. An erratum to this article can be found at .     

Effect of dietary macronutrient proportion on intermediate metabolism and oxidative status in sturgeon (<Emphasis Type="Italic">Acipenser naccarii</Emphasis>) and trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>): comparative study

Three isoenergetic diets varying the proportion of dietary energy supplied by each of the macronutrients (carbohydrate, lipid, or protein) were delivered, to farmed sturgeon (Acipenser naccarii) and trout (Oncorhynchus mykiss), to test the possible effects on the intermediate metabolism and oxidative status in liver, white muscle, and heart. In trout, there is an adaptive metabolic response to an increase in lipids and carbohydrates in the diet. However, this does not happen in the sturgeon. These differences may be due to different dietary habits of both species. In terms of oxidative status, only the liver displayed oxidative stress in both species, showing an increase in the lipid peroxidation and antioxidant enzyme activities after feeding with the high-lipid and high-protein diet.     

Impact of microwave-assisted enzymatic hydrolysis on functional and antioxidant properties of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> by-products

Fishery by-products can be better utilized following enzymatic hydrolysis treatment to produce fish protein hydrolysates (FPH) with potentially enhanced interface-stabilizing properties (e.g. functionality). The production of FPH could be accelerated through the application of rapid heating methods [e.g. microwave-assisted heating (MW)] rather than slower conventional heating (CH) treatments. The objective of this study was to investigate the effects of microwave heating during enzymatic hydrolysis on the functionality and antioxidant properties of FPH. Trout by-products were hydrolyzed with Alcalase at an enzyme substrate ratio (E:S) of 0.5, 1.7, and 3.0% (w/v), respectively, for 3, 5 and 15 min using a microwave system (1200 W, 20% power with 50% duty cycle at 50–55 °C) and a conventional heating method (water bath at 50 °C). The degree of hydrolysis and protein solubility was higher (P < 0.05) for the MW-FPH than for the CH-FPH. MW-FPH at 5 min (0.5% E:S) demonstrated higher (P < 0.05) emulsifying activity and emulsion stability than CH-FPH with the same treatment. Foam capacity and stability were also greater (P < 0.05) for MW-FPH samples that were treated 15 min by microwave-assisted heating (0.5% E:S) when compared to CH. Overall, MW-FPH exhibited higher (P < 0.05) 2,2-diphenyl-1-picryhydrazyl and ferric ion reducing capacity than CH-FPH. We therefore conclude that microwave-assisted hydrolysis is an alternative method to produce FPH with improved solubility, emulsifying activity, foaming properties and antioxidant activity.     

Immunomodulatory effects of <Emphasis Type="Italic">Rhodomyrtus tomentosa</Emphasis> leaf extract and its derivative compound,rhodomyrtone, on head kidney macrophages of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Rhodomyrtus tomentosa is a medicinal plant that shows biological effects including immunomodulatory activity on human and other mammals but not in fish. In this study, we evaluated the in vitro immunomodulatory effects of R. tomentosa leaf extract and its active compound, rhodomyrtone, on the immune responses, using rainbow trout (Oncorhynchus mykiss) head kidney (HK) macrophages as a model. The tested immune functions included the expression of genes involved in innate immune and inflammatory responses and the production of reactive oxygen species (ROS). Gene expression was evaluated after exposure to 10 μg mL^?1 of R. tomentosa and 1 μg mL^?1 of rhodomyrtone for 4 and 24 h. R. tomentosa and rhodomyrtone induced changes in the expression of pro-inflammatory cytokines (il1β, il8, and tnfα), anti-inflammatory cytokines (il10 and tgfβ), inducible enzymes (inos, cox2, and arginase), and an antioxidant enzyme (gpx1). Co-exposure of R. tomentosa with LPS resulted in a prominent reduction in the expression of genes related to an inflammatory process (il1β, il8, tnfα, inos, saa, hepcidin, and gpx1), suggesting anti-inflammatory effects. Similarly, co-exposure of rhodomyrtone with LPS led to a downregulation of inflammation-related genes (il1β, inos, saa, and hepcidin). In addition, exposure to both natural plant products caused a reduction in cellular ROS levels by HK macrophages. The present results indicate that R. tomentosa and rhodomyrtone exerted immunostimulatory and anti-inflammatory effects on fish macrophages, thus opening up the possibility of using these natural products to further develop immunostimulants for health management in aquaculture.     

Effects of long-term silymarin oral supplementation on the blood biochemical profile of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Silymarin, an extract from “milk thistle” (Silybum marianum) plant is traditionally used as herbal medicine. The present study was conducted to investigate the clinical effects and possible side effects of silymarin on biochemical blood parameters of rainbow trout (Oncorhynchus mykiss). Fishes were treated with 0 (control), 100, 400, and 800 mg of silymarin per kg of food during 4 weeks. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), creatine kinase (CK), glucose, total protein, creatinine, triglyceride, cholesterol, urea, uric acid and liver cellular total antioxidant, and protein content were measured after 7, 14, and 28 days of silymarin treatment. The results showed that oral administration of silymarin in fish significantly reduced plasma glucose and cholesterol levels and relatively increased plasma total protein and globulin concentrations (P < 0.05). Increasing plasma albumin levels indicate the important role of albumin in drug transportation in circulatory system of fish. Silymarin also stabilized cellular membrane structure and regulated the levels of AST, ALT, ALP, CK, and LDH activity. In conclusion, on the basis of these results, oral administration of silymarin up to 400 mg per 1 kg of food has no side effect on blood biochemical and clinical parameters of fishes. However, oral administration of 800 mg/kg- of silymarin caused cytotoxicity and modifications in blood biochemical parameters of fish.     

Effects of dietary <Emphasis Type="SmallCaps">l</Emphasis>-carnitine and chromium picolinate supplementations on performance and some serum parameters in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

An experiment was conducted to determine the effects of supplemental dietary l-carnitine, chromium picolinate (Cr-Pic) and their combination on growth performance and serum total protein, cholesterol, triglyceride and glucose of rainbow trout (Oncorhynchus mykiss). A total of 276 rainbow trout were randomly allocated to four groups. Fish (average initial body weight = 151 ± 1.69 g) were fed a basal diet without supplemental l-carnitine and chromium picolinate in the control group. The basal diet was supplemented with either 500 mg/kg l-carnitine, 1.6 mg/kg chromium picolinate or 500 mg/kg l-carnitine plus 1.6 mg/kg chromium picolinate for experimental groups 1 (C), 2 (Cr-Pic) and 3 (C + Cr-Pic), respectively. Fish were fed twice a day to apparent satiation for 58 days. Weight gain, growth rate, feed consumption and feed conversion ratio (feed/gain) were calculated for the whole period. At the end of the study, six fish were chosen randomly from each tank to represent the experiment and frozen at −20°C for subsequent dorsal muscle analysis. The results showed no significant differences in final body weight, weight gain or feed conversion ratio among groups. There were also no significant differences in serum total protein, cholesterol, triglyceride or glucose concentrations among groups. Significantly higher lipid concentration of dorsal muscle was observed in experimental groups 1 and 3. In conclusion, supplemental dietary l-carnitine, chromium picolinate and their combination have no beneficial effects on improving growth performance and feed conversion ratio in rainbow trout. However, dietary l-carnitine slightly increased lipid concentration in dorsal muscle of rainbow trout.