Gastrointestinal Tract Of Rainbow Trout Research Articles

Dietary lipid sensing through fatty acid oxidation and chylomicron formation in the gastrointestinal tract of rainbow trout

In mammals, physiological processes related to lipid metabolism, such as chylomicron synthesis or fatty acid oxidation (FAO), modulate eating, highlighting the importance of energostatic mechanisms in feeding control. This study, using rainbow trout (Oncorhynchus mykiss) as model, aimed to characterize the role of FAO and chylomicron formation as peripheral lipid sensors potentially able to modulate feeding in fish. Fish fed with either a normal- (24%) or high- (32%) fat diet were intraperitoneally injected with water alone or containing etomoxir (inhibitor of FAO rate-limiting enzyme carnitine palmitoyl-transferase 1). First, feed intake levels were recorded. We observed an etomoxir-derived decrease in feeding at short times, but a significant increase at 48 h after treatment in fish fed normal-fat diet. Then, we evaluated putative etomoxir effects on the mRNA abundance of genes related to lipid metabolism, chylomicron synthesis and appetite-regulating peptides. Etomoxir treatment upregulated mRNA levels of genes related to chylomicron assembly in proximal intestine, while opposite effects occurred in distal intestine, indicating a clear regionalization in response. Etomoxir also modulated gastrointestinal hormone mRNAs in proximal intestine, upregulating ghrl in fish fed normal-fat diet and pyy and gcg in fish fed high-fat diet. These results provide evidence for an energostatic control of feeding related to FAO and chylomicron formation at the peripheral level in fish.

Fatty Acid Sensing in the Gastrointestinal Tract of Rainbow Trout: Different to Mammalian Model?

It is well established in mammals that the gastrointestinal tract (GIT) senses the luminal presence of nutrients and responds to such information by releasing signaling molecules that ultimately regulate feeding. However, gut nutrient sensing mechanisms are poorly known in fish. This research characterized fatty acid (FA) sensing mechanisms in the GIT of a fish species with great interest in aquaculture: the rainbow trout (Oncorhynchus mykiss). Main results showed that: (i) the trout GIT has mRNAs encoding numerous key FA transporters characterized in mammals (FA transporter CD36 -FAT/CD36-, FA transport protein 4 -FATP4-, and monocarboxylate transporter isoform-1 -MCT-1-) and receptors (several free FA receptor -Ffar- isoforms, and G protein-coupled receptors 84 and 119 -Gpr84 and Gpr119-), and (ii) intragastrically-administered FAs differing in their length and degree of unsaturation (i.e., medium-chain (octanoate), long-chain (oleate), long-chain polyunsaturated (α-linolenate), and short-chain (butyrate) FAs) exert a differential modulation of the gastrointestinal abundance of mRNAs encoding the identified transporters and receptors and intracellular signaling elements, as well as gastrointestinal appetite-regulatory hormone mRNAs and proteins. Together, results from this study offer the first set of evidence supporting the existence of FA sensing mechanisms n the fish GIT. Additionally, we detected several differences in FA sensing mechanisms of rainbow trout vs. mammals, which may suggest evolutionary divergence between fish and mammals.

Ammonia transport is independent of PNH3 gradients across the gastrointestinal epithelia of the rainbow trout: A role for the stomach.

Although the gastrointestinal tract (GIT) is an important site for nitrogen metabolism in teleosts, the mechanisms of ammonia absorption and transport remain to be elucidated. Both protein catabolism in the lumen and the metabolism of the GIT tissues produce ammonia which, in part, enters the portal blood through the anterior region of the GIT. The present study examined the possible roles of different GIT sections of rainbow trout (Oncorhynchus mykiss) in transporting ammonia in its unionized gas form-NH3 -by changing the PNH3 gradient across GIT epithelia using in vitro gut sac preparations. We also surveyed messengerRNA expression patterns of three of the identified Rh proteins (Rhbg, Rhcg1, and Rhcg2) as potential NH3 transporters and NKCC as a potential ammonium ion (NH4 + ) transporter along the GIT of rainbow trout. We found that ammonia absorption is not dependent on the PNH3 gradient despite expression of Rhbg and Rhcg2 in the intestinal tissues, and Rhcg2 in the stomach. We detected no expression of Rhbg in the stomach and no expression of Rhcg1 in any GIT tissues. There was also a lack of correlation between ammonia transport and [NH4 + ] gradient despite NKCC expression in all GIT tissues. Regardless of PNH3 gradients, the stomach showed the greatest absorption and net tissue consumption of ammonia. Overall, our findings suggest nitrogen metabolism zonation of GIT, with stomach serving as an important site for the absorption, handling and transport of ammonia that is independent of the PNH3 gradient.

Fatty acids of different nature differentially modulate feed intake in rainbow trout

Feed intake is subjected to a complex regulation involving a plethora of signals, among which nutrients stand as one of the most important. In mammals, the gastrointestinal tract is able to sense nutrients in the lumen, and respond with the release of signaling molecules that ultimately modulate brain circuits governing appetite, resulting in decreased/increased feeding. Whether equivalent mechanisms operate in fish remains unknown. In a recent study, we described that the gastrointestinal tract of rainbow trout contains several sensors for free fatty acids (FAs), and that the luminal presence of FAs of different length and degree of unsaturation modulates the levels of key gastrointestinal hormones involved in feed intake regulation. In this study, our aim was to characterize the impact of such a luminal presence of FAs on brain appetite-regulatory centers, as well as its effects on rainbow trout feed intake. Major results from this study demonstrated that: (i) FAs of different length and degree of unsaturation [medium-chain (MCFAs, octanoate), long-chain (LCFAs, oleate), long-chain polyunsaturated (PUFA, α-linolenate), and short-chain (SCFA, butyrate) FAs] differentially modulate feed intake levels when administered intragastrically, (ii) intragastrically-administered FAs modulate the phosphorylation status of appetite-related transcription factors, as well as mRNA levels of key appetite-regulating neuropeptides, in the hypothalamus and/or telencephalon, (iii) luminal presence of FAs results in changes in the central abundance of mRNAs encoding gastrointestinal hormone receptors, and (vi) luminal FA-derived central changes in neuropeptide mRNAs are not observed (or are lessened) in vagotomized fish. Together, these results provide comprehensive evidence in favor of a gut-brain axis in fish. In addition, we observed different responses in terms of feed intake regulation depending on the type of fatty acid administered into the lumen, which is very relevant for aquaculture considering differences in fatty acid composition in aquafeeds.

Characterization of two novel lactic acid bacteria isolated from the intestine of rainbow trout (Oncorhynchus mykiss, Walbaum) in Slovakia

An effective probiotic must comply with criteria, which determines its effect. The aim of this work was to isolate lactic acid bacteria (LAB) from the intestinal content of rainbow trout (Oncorhynchus mykiss), subsequently potentially used as probiotics in order to improve health status of fish during fish farming. Selection criteria were used to obtain suitable probiotic candidates for aquaculture of salmonid. A total of 6 lactic acid bacteria isolated from intestines of rainbow trout belonging to the genus Lactobacillus were included in this study, and encompassed the following species: L. plantarum (n = 3), L. fermentum (n = 2), and L. brevis (n = 1). Antimicrobial susceptibility test has been performed on the basis of Guidance on the assessment of bacterial susceptibility to antimicrobials of human and veterinary importance by the EFSA. Sensitivity or intrinsic resistance of the isolated LAB to a recommended set of antibiotics make them safe for use as probiotics in aquaculture. All six autochthonous isolates showed the antagonistic activity against both salmonid pathogens Aeromonas salmonicida subsp. salmonicida CCM 1307 and Yersinia ruckeri CCM 6093. Determined in vitro survival conditions in the gastrointestinal tract of rainbow trout, and taking into account the previous results, two isolates - Lactobacillus plantarum (R2) and Lactobacillus fermentum (R3), which showed the highest level of tolerance to different pH values, bile, temperature, and the best growth properties, were selected as candidates for probiotics. These two strains have been sent to the Czech Collection of Microorganisms (CCM) of Masaryk University in Brno for purposes of Patent Procedure under the Budapest Treaty.

Characterization of melatonin synthesis in the gastrointestinal tract of rainbow trout (Oncorhynchus mykiss): distribution, relation with serotonin, daily rhythms and photoperiod regulation.

Melatonin is synthesized in peripheral locations of vertebrates, including the gastrointestinal tract (GIT). In teleost, information regarding this topic is scarce. Here we studied the presence and synthesis of melatonin at the rainbow trout GIT. Different sections of trout GIT (from esophagus to hindgut) were dissected out and assayed for contents of melatonin, serotonin (5-HT) and its metabolite, 5-hydroxyindole acetic acid, as well as for aanat1, aanat2 and hiomt mRNA abundance. A trout group was pinealectomized to evaluate changes in plasma and gut melatonin content. Finally, the daily profile of melatonin and 5-HT content, and aanat1, aanat2 and hiomt mRNA abundance were analyzed in gut of trout kept under normal lighting, and then under constant darkness. Melatonin was detected in all GIT regions with higher concentrations in the muscular wall than in the mucosa, a similar trend to that of 5-HT. In contrast, transcripts of melatonin synthesis enzymes were more abundant in the mucosa. Pinealectomy did not affect melatonin levels in midgut and hindgut either at day or at night. Additionally, no daily rhythms could be defined for melatonin content in gut tissues but increases during late light phase and at midnight occurred. However, aanat1, aanat2 and hiomt mRNA abundance showed clear daily rhythms with peaks at night. These rhythms remained with a 3-h phase advanced peak in fish exposed to constant darkness. Our results provide clear evidence for a local synthesis of melatonin in trout GIT that might be influenced by the content of 5-HT in the tissue. The process is affected by environmental light cycle and is likely to be under circadian regulation.

Effects of Enzyme-Producing Probiotic Bacteria Isolated from the Gastrointestinal Tract of Trout on the Growth Performance, Survival, and Digestive Enzyme Activity of Rainbow Trout Fry (Oncorhynchus mykiss)

In this study, we investigated the effects of enzyme-producing probiotic bacteria isolated from the gastrointestinal tract of rainbow trout on the growth performance, feed conversion ratio, and digestive enzyme activity, of fry (Oncorhynchus mykiss). Three isolates (G8/2013, T7/2013 and U5/2013) of candidate bacteria elicited the highest protease, lipase, and amylase activities, respectively. Isolates were identified as Aeromonas sp., Bacillus sp. and Citrobacter braakii by morphological, physiological, biochemical characterizations as well as 16S rRNA gene sequence analysis. The fry basal diet was supplemented with probiotics at varying concentrations; G8 group, Aeromonas sp. 1.72 x 108 CFU/g; U5 group, Bacillus sp. 3.01 x 108 CFU/g; T7 group, C. braakii 2.96 x 108 CFU/g and a mixed group (same bacterial concentrations), and control group (no bacteria). The rainbow trout fry were fed ad libitum in triplicate treatments with supplemented and non-supplemented probiotic diets for 70-days. The total bacterial count in the intestine was significantly higher in the mixed group (30th and 50th days) and U5 group (50th and 70th days) compared with the control group. However, there was no significant difference in weight gain, specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility, or digestive enzyme activity among the groups.a

In situ analysis of cadmium uptake in four sections of the gastro-intestinal tract of rainbow trout (Oncorhynchus mykiss)

This study links results from past in vitro and in vivo experiments, by implementing an in situ experiment in order to determine the relative importance for cadmium (Cd) uptake of different sections of the gastro-intestinal tract (GIT) of rainbow trout. Transport of Cd from four sections of the GIT of adult rainbow trout (∼220g) was individually examined by infusing ligated sections of the GIT in live, free-swimming fish with 50μM Cd spiked with radiolabelled 109Cd (0.5μCiml−1). Fish were exposed for an 8-h period. The percentage of the total injected 109Cd which was internalized from the different segments was only between ∼0.1 and ∼7%, indicating low uptake efficiency. The stomach is the most important GIT segment for Cd transport into the internal compartment of the animal, while the posterior intestine also plays a significant role. The majority of 109Cd recovered at the end of the flux period was detected within gut material (ranging from 28 to 95%); the portion of Cd which was internalized was largely found in the carcass (32 to 60%). Distribution between the measured organs varied with uptake from the various GIT sections. Our results also confirm that the GIT acts as a protective barrier against Cd uptake from dietary exposure.

Isolation of bacterial probiotic candidates from the gastrointestinal tract of rainbow trout, Oncorhynchus mykiss (Walbaum), and screening for inhibitory activity against Flavobacterium psychrophilum

In this study, 318 bacterial strains were isolated from the gastrointestinal (GI) tracts of 29 rainbow trout, Oncorhynchus mykiss (Walbaum). These bacteria were screened in vitro for their ability to inhibit growth of Flavobacterium psychrophilum, the causative agent of coldwater disease. Bacteria observed to inhibit F.psychrophilum growth were further screened against rainbow trout bile, as an indicator of their ability to survive in the GI tract. This screening resulted in narrowing the pool to 24 bacterial isolates. Those 24 isolates were then tested for pathogenicity in rainbow trout by intraperitoneal injection. Following a 28-day challenge, eight isolates were shown to cause direct mortality and were eliminated from further study. As a result, 16 bacterial isolates were identified as probiotic candidates with the potential to control or reduce disease caused by F.psychrophilum.

In vitro characterization of cadmium transport along the gastro-intestinal tract of freshwater rainbow trout ( Oncorhynchus mykiss)

An in vitro gut sac technique was used to examine the mechanism(s) of cadmium (Cd) uptake along the gastro-intestinal tract (GIT) of rainbow trout ( Oncorhynchus mykiss). The spatial distribution of Cd between three compartments (mucus-binding, mucosal epithelium, and transport into blood space) was determined using a modified Cortland saline containing 50 μM Cd (as CdCl 2) labeled with 109Cd radiotracer. Taking into account total surface areas, the order of relative importance for total Cd uptake rate was: posterior intestine > anterior intestine > stomach > mid intestine. Cd transport was not inhibited by experimentally reducing fluid transport rates by manipulation of osmotic gradients using mannitol, but was sensitive to internal luminal pressure changes, suggesting a mechanosensitive pathway. Q 10 values (1, 11, and 19 °C) indicated a facilitated transport of Cd in the anterior- and mid-intestine. The effects of 10 mM Ca on the kinetics of Cd uptake suggest the presence of a common uptake pathway for Cd and Ca in the stomach, anterior-, and mid-intestine. Further evidence of a shared route of entry was found using three Ca channel blockers, lanthanum, verapamil, and nifedipine: both voltage-insensitive and voltage-sensitive Ca channels appear to be present in either some, or all portions of the GIT. Elevated Fe (500 μM), Mg (50 mM), and Zn (500 μM) showed varying degrees of inhibition of Cd transport depending on the compartment and segment of the GIT. Overall it appears that there are multiple sites, and mechanisms, of Cd uptake along the GIT of rainbow trout.

Drying and Storage Stability of a Probiotic Strain Incorporated into a Fish Feed Formulation

A Lactobacillus brevis strain was isolated from the gastrointestinal tract of rainbow trout (Oncorhynchus mykiss) fished from the BioBio Region (Chile) and dried in order to obtain a stable dehydrated product during storage. Fish feed pellets featuring Lactobacillus strain concentrations within the range 108–109 CFU/g and 5% moisture were obtained. Fluidized bed (air at 40°C) and rotary vacuum (49.21 kPa, 60°C) dryers were used to prepare those feedstock formulations that were able to maintain viability at 4 and 20°C. Fluidized bed convective heat transfer coefficients were estimated as 17.1 and 21.9 W/m2 K for feed pellets of 2 and 4 mm diameter, respectively. Decreasing drying rate period diffusion coefficients were calculated as 9.4 × 10−10 and 20.8 × 10−10 m2/s for feed pellets of 2 and 4 mm diameter, respectively.

Characterization of dietary Ni uptake in the rainbow trout, Oncorhynchus mykiss

We characterized dietary Ni uptake in the gastrointestinal tract of rainbow trout using both in vivo and in vitro techniques. Adult trout were fed a meal (3% of body mass) of uncontaminated commercial trout chow, labeled with an inert marker (ballotini beads). In vivo dietary Ni concentrations in the supernatant (fluid phase) of the gut contents averaged from 2 μmol l −1 to 24 μmol l −1, and net overall absorption efficiency of dietary Ni was approximately 50% from the single meal, similar to that for the essential metal Cu, adding to the growing evidence of Ni essentiality. The stomach and mid-intestine emerged as important sites of Ni uptake in vivo, accounting for 78.5% and 18.9% of net absorption respectively, while the anterior intestine was a site of net secretion. Most of the stomach uptake occurred in the first 4 h. In vitro gut sac studies using radiolabeled Ni (at 30 μmol l −1) demonstrated that unidirectional uptake occurred in all segments, with area-weighted rates being highest in the anterior intestine. Differences between in vivo and in vitro results likely reflect the favourable uptake conditions in the stomach, and biliary secretion of Ni in the anterior intestine in vivo. The concentration-dependent kinetics of unidirectional Ni uptake in vitro were biphasic in nature, with a saturable Michaelis–Menten relationship observed at 1–30 μmol l −1 Ni ( K m = 11 μmol l −1, J max = 53 pmol cm −2 h −1 in the stomach and K m = 42 μmol l −1, J max = 215 pmol cm −2 h −1 in the mid-intestine), suggesting mediation by a channel or carrier process. A linear uptake relationship was seen at higher concentrations, indicative of simple diffusion. Ni uptake (at 30 μmol l −1) into the blood compartment was significantly reduced in the stomach by high Mg (50 mmol l −1), and in the mid-intestine by both Mg (50 mmol l −1) and Ca (50 mmol l −1). In both regions, kinetic analysis demonstrated reductions in J max with unchanged K m , suggesting non-competitive interactions. Therefore the Mg and Ca content of the food will be an important consideration affecting the availability of Ni.

Phylogenetic analysis and in situ identification of the intestinal microbial community of rainbow trout (Oncorhynchus mykiss, Walbaum).

To identify the dominant culturable and nonculturable microbiota of rainbow trout intestine. Microbial density of rainbow trout intestine was estimated by direct microscopic counts (4',6-diamidino-2-phenylindole, DAPI) and by culturing on tryptone soya agar (TSA). Differential gradient gel electrophoresis analysis of bacterial DNA from intestinal samples, re-amplification of bands and sequence analysis was used to identify the bacteria that dominated samples where aerobic counts were < or =2% of the DAPI counts. 16S rDNA gene sequences of 146 bacterial isolates and three sequences of uncultured bacteria were identified. A set of oligonucleotide probes was constructed and used to detect and enumerate the bacterial community structure of the gastrointestinal tract of rainbow trout by fluorescence in situ hybridization (FISH). Members of the gamma subclass of Proteobacteria (mainly Aeromonas and Enterobacteriaceae) dominated the bacterial population structure. Acinetobacter, Pseudomonas, Shewanella, Plesiomonas and Proteus were also identified together with isolates belonging to the beta subclass of Proteobacteria and Gram-positive bacteria with high and low DNA G + C content. In most samples, the aerobic count (on TSA) was 50-90% of the direct (DAPI) count. A bacterium representing a previously unknown phylogenetic lineage with only 89% 16S rRNA gene sequence similarity to Anaerofilum pentosovorans was detected in intestinal samples where aerobic counts were < or =2% of direct (DAPI) counts. Ten to 75% of the microbial population in samples with low aerobic counts hybridized (FISH) with a probe constructed against this not-yet cultured bacterium. Proteobacteria belonging to the gamma subclass dominated the intestinal microbiota of rainbow trout. However, in some samples the microflora was dominated by uncultivated, presumed anaerobic, micro-organisms. The bacterial population structure of rainbow trout intestine, as well as total bacterial counts, varied from fish to fish. Good correlation was seen between cultivation results and in situ analysis, however, a molecular approach was crucial for the identification of organisms uncultivated on TSA.

Immunohistochemical Localization and Differential Expression of Cytochrome P450 3A27 in the Gastrointestinal Tract of Rainbow Trout

In mammals the cytochrome P450 3A (CYP3A) subfamily isoforms are primarily expressed in liver and intestines with lesser amounts found in other tissues. The aim of this study was to examine the cellular localization and the expression pattern of CYP3A27 in the gastrointestinal tract (GI tract) of a freshwater teleost species, the rainbow trout (Oncorhynchus mykiss), a fish model used extensively for toxicological and carcinogenesis research. Using an avidin biotinylated enzyme complex and 3,3′-diaminobenzidine staining, strong cytoplasmic immunohistochemical staining was observed for CYP3A27 protein in hepatocytes and in enterocytes of the intestinal ceca and the proximal descending intestine when probed with a polyclonal antibody raised against rainbow trout P450 LMC5, a CYP3A protein. The intensity of epithelial staining decreased distally along the GI tract with faint staining observed in the epithelial cells examined near the vent. Western blot analysis was supportive of the immunohistochemistry results. Northern blot analysis also demonstrated that CYP3A27 mRNA was expressed along the entire GI tract. The major area of CYP3A27 mRNA expression was in the intestinal ceca, followed by the proximal descending intestine, at levels that were about three- to five-fold and two- to four-fold, respectively, greater than seen in the liver of the fish studied. Monooxygenase activities of intestinal ceca microsomes against testosterone and progesterone confirmed the presence of active CYP3A enzyme in this tissue. These results suggest that the intestine of rainbow trout may possesses substantial capacity for first-pass metabolism of xenobiotics by CYP3A27, which makes it an excellent model in which to study the consequence of such metabolism.

Does Carnobacterium divergens isolated from Atlantic salmon, Salmo salar L., colonize the gut of early developing turbot, Scophthalmus maximus L., larvae?

It is well established from endothermic animals that the adhesion of lactic acid bacteria involves host speci®city (Fuller 1986). In juvenile ®sh, JoEborn, Olsson, Westerdahl, Conway & Kjellberg (1997) reported by in vitro tests that a Carnobacterium sp. isolated from Atlantic salmon, Salmo salar L., colonized the gastrointestinal tract of rainbow trout, Onchorynchus mykiss (Walbaum). However, no information from ®sh larvae is available on whether the adhesion of lactic acid bacteria involves host speci®city. This is relevant in the context of whether or not it is possible to colonize the gastrointestinal tract of larvae at early stages with probiotics, notably Gram-positive bacteria, such as lactic acid bacteria, or by a resident micro ora, which may contribute to nutrition. The following bacteria were used in the present study: Vibrio pelagius isolated from copepod-fed turbot, Scophthalmus maximus L., larvae (Munro, Barbour & Birkbeck 1994), which is unusual in that it contains the polyunsaturated fatty acid eicosapentaenoic acid (20:5 n-3) (Ringu, Sinclair, Birkbeck & Barbour 1992), and a lactic acid bacterium, Carnobacterium divergens, isolated from Atlantic salmon. The main reason for using this species was that it produced a substance that inhibited the growth of both Vibrio anguillarum and Proteus vulgaris (Strum 1988), and Aeromonas salmonicida (Ringu 1999). Recently, colonization of different bacterial strains in larval turbot was determined using an enzyme-linked immunosorbent assay (ELISA) (Ringu, Birkbeck, Munro, Vadstein & Hjelmeland 1996; Ringu & Vadstein 1998). The purpose of the current study, was to evaluate whether a C. divergens, orginally isolated from Atlantic salmon, was able to colonize the gut of turbot larvae by adding this bacterial species to the rearing water and to compare these results with those for larvae exposed to V. pelagius, by using the ELISA method. Furthermore, a previous study (Ringu et al. 1996) demonstrated that antisera used in ELISA showed high sensitivity against homologous bacterial antigens and very little crossreaction with heterologous bacteria. Turbot eggs were obtained from Tinfos Aqua, Norway, and 1000 eggs were incubated in 80-L circular tanks with at bottoms in static water. A detailed description of larval rearing conditions and cultivation of live feed (Brachionus plicatilis SINTEFstrain) is given by Ringu et al. (1996). The following bacterial strains were used: C. divergens, originally isolated from young Atlantic salmon juveniles (Strum 1988); and Vibrio pelagius, isolated from copepod-fed turbot larvae (Munro et al. 1994). Vibrio pelagius was identi®ed as described by Munro et al. (1994) using the `Bacterial Identi®er' program (Bryant, Lee, West & Colwell 1986). Carnobacterium divergens was identi®ed using carboR

Binders in fish feeds: I. Effect of alginate and guar gum on growth, digestibility, feed intake and passage through the gastrointestinal tract of rainbow trout

Alginate and guar gum were fed in different concentrations in dry, moist and wet diets to rainbow trout ( Salmo gairdneri, Richardson). Both binders reduced the apparent digestibility of protein and fat. They also reduced the feed intake and increased the moisture content of the faeces. Guar gum caused a delayed rate of passage through the gastro-intestinal tract. High levels of guar gum reduced the growth and the dry matter and fat contents of the fish. The protein content, Ca P -ratio of the bones, condition factor, viscera and liver weights, and mortality were not influenced by the binders.

Influence of environmental temperature on flow rate of foodstuffs through the gastrointestinal tract of rainbow trout

Experiments were carried out with rainbow trout ( Salmo gairdneri) to determine the rate of passage of foodstuffs through the digestive tract, before and after a rise in environmental temperature from 9–10°C to 18°C in 1 day. Transit rate was analyzed from the rate of fecal excretion of a marker (Cr 2O 3) incorporated in the diet. In a first experiment on trout weighing about 80 g, mean retention time (MRT) (Castle, 1956) and mean transit time (MTT) (Zierlier, 1958) of the marker, starting from the 9°C acclimated values (34 h for MRT and MTT), decreased as early as the first day after the temperature change (24 and 26 h respectively) and reached the 18°C acclimated values (19 and 21 h respectively) in 4–7 days. In a second experiment on trout weighing about 140 g the pattern of response of MRT and MTT to the temperature increase was similar to that observed in the first experiment: they were 27 and 29 h at 10°C, 16 and 19 h on the second day after the temperature change, and 13 h and 15 h after acclimation at 18°C, respectively. These changes related to environmental temperature were independent of any increase in food consumption. The differences in transit rate of marker between the two experiments could be attributed to the higher body weight and food consumption in the second experiment. Excretion of Cr 2O 3 in the feces was analyzed in the second experiment through a four-compartment model involving the stomach, anterior and posterior intestine, and feces. Fractional evacuation rate of marker in each digestive tract compartment was calculated according to the model. All compartments were affected by the temperature increase. There was a transitory acceleration of transit rate, observed principally in the stomach. These alterations were achieved by the eighth day after the temperature change and it was concluded that acclimation to the new temperature was accomplished in 1 week.