Effect of feeding and fasting on plasma tryptophan and tryptophan to large neutral amino acid ratio,and on brain serotonin turnover in rainbow trout,Oncorhynchus mykiss

Two time-course experiments were conducted to determine the effect of feeding and fasting on the plasma ratio of tryptophan (trp) to the large neutral amino acids (LNAA), (trp/LNAA ratio) and brain serotonin (5-HT) turnover in rainbow trout,Oncorhynchus mykiss. Trout were fasted overnight or for 3 days and were then either fed or continued to be fasted for up to a further 3 days. Changes in plasma trp, plasma trp/LNAA ratio, brain trp, brain 5-HT, brain 5-hydroxyindoleacetic acid (5-HIAA) and brain 5-HIAA/5-HT ratio were determined over time. Feeding decreased the plasma trp/LNAA ratio, brain trp and the brain 5-HIAA/5-HT ratio. In addition, in fish sampled over 3 days, there appeared to be a rhythm in plasma trp and the brain 5-HIAA/5-HT ratio which was independent of feeding. These results indicate that in rainbow trout, feeding is a sufficient physiological event to decrease brain 5-HT turnover. Furthermore, feeding-independent changes in the brain 5-HIAA/5-HT ratio, which were evident in fasted fish sampled over 3 days, also suggest an additional, non-feeding-related modulator(s) of brain 5-HT turnover in rainbow trout.     

Effects of vasoactive intestinal polypeptide,substance P, 5-hydroxytryptamine,met-enkephalin and neurotensin on the swimbladder smooth muscle of two teleost species,Gadus morhua andAnguilla anguilla

The effects of vasoactive intestinal polypeptide (VIP), substance P (SP), 5-hydroxytryptamine (5-HT), neurotensin (NT) and met-enkephalin (mEnk) on the smooth muscles of the teleost swimbladder were studied in two teleost species, the Atlantic cod (Gadus morhua) and the eel (Anguilla anguilla). The study was made on isolated strip preparations of the muscularis mucosae, using putative transmitters corresponding to the immunoreactive materials that have previously been localized by immunohistochemical methods in nerves or endocrine/paracrine cells of the teleost swimbladder and/or the gastrointestinal canal. VIP was relaxatory on both cod and eel swimbladder smooth muscle, SP and 5-HT were constrictory in both species, and mEnk was excitatory on the eel swimbladder smooth muscle. Clear effects of these agents were usually seen at a concentration ofca. 10 nM in cumulative concentration/effect experiments. NT had no effect in either species. In the eel, the effects on the pneumatic duct were generally greater than on the swimbladder proper. The study indicates that the 5-HT and peptides previously observed by immunohistochemistry have physiological functions in the swimbladder.     

Distribution of 5-hydroxytryptamine and related compounds in various brain regions of rainbow trout (Oncorhynchus mykiss)

The levels of tryptophan (Try), 5-hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the brain regions of rainbow trout (Oncorhynchus mykiss) by high performance liquid chromatography with electrochemical detection (HPLC-EC). Brain tryptophan concentrations varied from 3.972 ± 357 ng/g cerebellum) to 8.841 ± 772 ng/g (hypothalamus). The 5-HT concentrations varied from 69 ± 7 ng/g (optic tectum) to 573 ± 34 ng/g (hypothalamus). The concentrations of 5-HIAA varied from 29 ± 3 ng/g (medulla oblongata) to 68 ± 7 ng/g (hypothalamus). Total and free serum tryptophan levels were also determined; in adult rainbow trout 92% of the serum tryptophan was observed to be free i.e., not protein-bound.     

Changes in smooth muscle contractility of rainbow trout (Oncorhynchus mykiss Walbaum) intestine during acclimation to altered temperature

The effects of altered water temperature in vivo on in vitro smooth muscle contractility of rainbow trout intestine were investigated. Temperature has a significant effect on receptor-mediated intestinal smooth muscle contractility in the rainbow trout. The efficacy of 5-HT, carbachol, and transmural stimulation increased with temperatures above 10°C, with an optimal increase at 15°C. There was also a modest increase in the potency of 5-HT and carbachol within 2 days of establishing trout at 20°C. By day 8, most of these changes had either stabilized or were returning to control values, suggesting that acclimation changes in membranes and enzyme activities were taking effect. However, the contractile responses to carbachol and transmural stimulation were still increasing at this time. This may imply that the muscarinic receptors are more resistant to membrane acclimation changes and may take longer to adapt. Because these experiments were controlled for handling stress and seasonal changes that affect contractility, we have been able to demonstrate some early changes in smooth muscle contractility that occur during acclimation to altered temperature.     

Influence of dietary soy protein and peptide products on bile acid status and distal intestinal morphology of rainbow trout Oncorhynchus mykiss

To investigate the influence of dietary soy protein size on the bile acid status and the distal intestinal morphology in rainbow trout Oncorhynchus mykiss, diets based on soybean meal (SBM), soy protein isolate (SPI) and 4 soy peptide products having different molecular sizes were fed to trout (initial BW, 19?g) for 10?weeks. A diet based on fish meal (Cont) and a diet including the smallest-peptide and low-saponin product (Hi-Nute AM) and supplemented with soya saponin (AMS) were also fed. In fish fed diets SBM and SPI, the gallbladder was atrophied, the proportion of biliary cholyltaurine decreased, and highly vacuolated epithelial cells of mucosal folds and proliferation of connective tissues in the submucosa of the distal intestine were observed. These parameters tended to improve in fish fed soy peptide diets and especially those of fish fed diet AM were similar to fish fed diet Cont. Although the gallbladder of fish fed diet AMS was smaller than fish fed the unsupplemented diet AM, no morphological abnormalities were observed in the distal intestine. These results suggest that soy proteins/peptides with relatively large sizes and with soya saponin affect the bile acid status and distal intestinal morphology of rainbow trout.     

Effect of dietary bile extracts on serum response of astaxanthin in rainbow trout (Oncorhynchus mykiss): a preliminary study

Effects of porcine bile extracts added at three different dietary concentrations 0, 10 and 20 g kg^?1 were studied on astaxanthin serum concentration in rainbow trout (mean weight 200 ± 7 g). Astaxanthin from micro‐algae Haematococcus pluvialis and synthetic astaxanthin (CAROPHYLL® pink) were incorporated in diets of rainbow trout at a rate of 100 mg astaxanthin kg^?1 of feed. Fish were hand fed twice a day. After 5 days of feeding there was a significant effect of the pigment source on the ratio (total blood astaxanthin per unit body weight to cumulative astaxanthin intake per unit body weight). Trout receiving synthetic astaxanthin showed a significantly (P < 0.05) higher ratio than trout fed algal astaxanthin. Increasing dietary bile extract did not lead to produce any effect on this ratio. The power of the statistical analysis is discussed. Therefore, the interaction (pigment source × dietary bile concentration) showed no more effect.     

Triacylglycerol-, wax ester- and sterol ester-hydrolases in midgut of Atlantic salmon (Salmo salar)

Bile salt‐dependent lipase (BSDL) is assumed to be the predominant lipid hydrolase in fish digestive tracts where it hydrolyses dietary triacylglycerols (TAG), sterol esters (SE) and wax esters (WE). BSDL is known to hydrolyse TAG at much faster rates than SE and WE in both fish and mammals. An assay for BSDL has previously been developed for rainbow trout (Oncorhynchus mykiss). However, this setup may not be valid in other fish species. Accordingly, the present study aimed at optimizing previous assays in rainbow trout for use on intestinal luminal contents of Atlantic salmon (Salmo salar L.). Crude intestinal extracts from midgut were desalted before the assay and concentrated bile salts supplemented. In general, the rank order for the degree of hydrolysis in Atlantic salmon was TAG > WE > SE. The optimal assay conditions were determined as being 100 μg protein, 125 μm lipid substrate and 20 mM bile salt (taurocholate) during the 4 h of incubation. Atlantic salmon and rainbow trout of 1500 g showed similar lipolytic activity, while salmon smolts of 300 g showed a significantly lower activity. Furthermore, the inhibition of intestinal lipase activities, especially triacylglycerol hydrolase and sterol ester hydrolase, observed in trout intestinal extracts at bile salt concentrations around 10 mm , was not observed in salmon. This could indicate that the activities in these two salmonids may display different enzyme biochemistry.     

Supplemental effect of bile salts to soybean meal-based diet on growth and feed utilization of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

A feeding experiment was conducted to evaluate the supplemental effect of bile salts to a defatted soybean meal-based non-fish meal diet for rainbow trout Oncorhynchus mykiss. A fish meal-based diet (FM) and two non-fish meal diets with and without bovine bile salts (SC+B and SC, respectively) were fed to fish (13 g initial weight) for 10 weeks. Fish fed diet SC showed inferior growth and feed efficiency, while bile salt supplementation improved the parameters to the same levels as fish fed diet FM. Crude fat and starch digestibility of diet SC-fed fish decreased after the 10-week feeding trial compared to the data obtained with fish that had no experience of the diet. Total biliary bile salt content and intestinal maltase activity of fish fed diet SC were the lowest among treatments, while these parameters were improved by bile salt supplementation. Morphological changes occurred in the distal intestine and liver of the diet SC group, although the histological features of fish fed diet SC+B were similar to those of fish fed diet FM. These results suggest that bile salt supplementation to a soybean meal-based diet improves the nutrient utilization by normalizing digestive processes in rainbow trout.     

Withdrawal times of freshwater rainbow trout,Salmo gairdneri Richardson,after treatment with oxolinic acid,oxytetracycline and trimetoprim

Abstract. Oxolinic acid (OA), oxytetracyline (OTC) and trimetoprim (TMP) were investigated in whole gutted rainbow trout, Salmo gairdneri Richardson, and in their skin, muscle and blood, at 6, 12 and 18°C. Concentrations of drugs were measured by high-pressure liquid chromatography. It is recommended that withdrawal times for rainbow trout be based on whole gutted rainbow trout and not, as in earlier investigations, from residual concentrations in muscle. Any concentrations in rainbow trout feed were found to be stable during the pelleting process used and up to 81 days after pelleting. The absorption of the drugs in rainbow trout show different temperature dependencies. A quantitative comparison of our overall data from this work with individual results from earlier investigations was undertaken. Suggested withdrawal times for freshwater rainbow trout treated with these drugs are: for OTC, 90 days below 6°C, 70 days between 6 and 12°C and 60 days above 12°C; for TMP, 60 days below 8°C and 40 days above 8°C; for OA, 20 days at approximately 18°C.     

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.     

A comparative tissue distribution study of oxytetracycline in rainbow trout, Oncorhynchus mykiss (Walbaum), and chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Oxytetracycline (OTC), a broad-spectrum antibiotic, is used widely to treat bacterial diseases in farmed fish. In the present study, the time course of OTC concentrations in freshwater rainbow trout, Oncorhynchus mykiss (Walbaum), and seawater chinook salmon, Oncorhynchus tshawytscha (Walbaum), were compared, tissue by tissue, after receiving a bolus dose of the antibiotic (5 mg kg^–1 or 50 mg kg^–1) intra-arterially (i.a.). The OTC concentration–time profiles of rainbow trout tissues were found to be very similar to those of the corresponding tissues in chinook salmon. Therefore, neither water salinity nor fish species seemed to play an important role in the disposition and elimination of OTC in these salmonids. In a separate experiment, rainbow trout were implanted surgically with a urinary cannula and received a single dose of OTC (50 mg kg^–1) i.a. Urine was collected from the cannula daily for 13 days. The amount of OTC excreted into the bile was found to be larger than that eliminated by the urine. These results show the similarity of OTC pharmacokinetics in freshwater rainbow trout and seawater chinook salmon and render support in using a single fish species to study the pharmacokinetics of a drug for other species in the same taxon.     

Identification and characterization of lactic acid bacteria isolated from rainbow trout, Oncorhynchus mykiss (Walbaum), with inhibitory activity against Lactococcus garvieae

A study was conducted to evaluate the probiotic properties of endogenous rainbow trout microbiota against pathogenic Lactococcus garvieae. A total of 335 bacterial strains were isolated from rainbow trout and screened for antagonistic activity against L. garvieae using an agar spot assay. Antagonistic strains were grouped by PCR amplification of repetitive bacterial DNA elements (rep‐PCR) and identified by 16S rRNA gene sequence analysis. The results revealed that the antagonistic strains belonged to the genera Lactobacillus, Lactococcus and Leuconostoc. Further probiotic characteristics, such as specific growth rate, doubling time, resistance to biological barriers, antibiotic resistance, hydrophobicity and production of antimicrobial substances, were also studied. These strains were able to survive low pH and high bile concentrations, showed good adherence characteristics and a broad spectrum of antibiotic resistance. The antagonistic efficacy was maintained after sterile filtration and was sensitive to proteinase K, indicating that proteinaceous extracellular inhibitory compounds were at least partially responsible for pathogen antagonism. Based on these results, these strains should be further studied to explore their probiotic effects in challenge experiments in vivo. This study shows clear evidence that the indigenous trout‐associated microbiota may provide a defensive barrier against L. garvieae.     

Influence of soya saponin, soya lectin, and cholyltaurine supplemented to a casein-based semipurified diet on intestinal morphology and biliary bile status in fingerling rainbow trout Oncorhynchus mykiss

To investigate the cause of the changes in intestinal morphology and biliary bile status of rainbow trout Oncorhynchus mykiss fed defatted soybean meal (SBM)-based diets, casein-based semipurified diets supplemented with soya saponin, soya lectin, and cholyltaurine were fed to rainbow trout for 6 weeks. An unsupplemented control diet and a SBM-based diet were also tested as references. Poor development of microvilli and pinocytotic vacuoles, and accumulation of large vacuoles in the epithelial cells were observed in the distal intestine of fish fed diets containing saponin but not cholyltaurine. Hyperplastic connective tissue in the mucosal folds of the distal intestine was observed in fish fed a diet containing both saponin and lectin but not cholyltaurine. However, intestinal histological features in fish fed diet supplemented with cholyltaurine and lectin and/or saponin were similar to those in the control diet group. Liver morphology and biliary bile status were not affected by saponin and lectin. These results suggest that the abnormal features of the distal intestine of rainbow trout fed SBM-based diets are caused by the combination of soya saponin and soya lectin, and that supplemental cholyltaurine plays certain roles in normalizing the intestinal abnormalities caused by the saponin and lectin.     

Effect of musical stimuli and white noise on rainbow trout (Oncorhynchus mykiss) growth and physiology in recirculating water conditions

Two musical stimuli transmissions (Mozart and Romanza) as compared with white noise treatment or control, both resulted in significantly higher growth performance in juvenile (6.7 ± 0.12 g) rainbow trout (Oncorhynchus mykiss) reared for 14 weeks. Carcass chemical composition and fatty acid composition (% of total fatty acids and mg/g carcass wet weight) did not differ among experimental treatments. The same was observed with regard to liver composition. Brain serotonin (5-HT) and its metabolite (5-HIAA) levels were increased in Mozart fish groups compared to all other treatments. However, serotonergic activity (as defined by the 5-HIAA: 5-HT ratio) for the Mozart groups was similar to control groups and was increased in Romanza and white noise fish groups. Brain dopaminergic activity (as defined by the DOPAC: DA ratio, i.e. dopamine metabolite to dopamine levels) was lower in Mozart compared to control fish groups. Differences were also observed as regards total carbohydrase and protease activity in several parts of the digestive tract.In conclusion, the results of the present data indicate that the musical stimuli transmitted were beneficial for the growth performance of rainbow trout. The fact that white noise treatment presented no major differences from control fish groups suggests that this specific stimulus was neither beneficially nor negatively perceived by rainbow trout, while it further supports the hypothesis that it is the musical stimuli per se that make all the difference.     

Effects on Lipid Oxidation and Bioactive Properties of Rainbow Trout Fillets Fed with Barley

Barley concentrations ranging from 0% to 32% were incorporated into rainbow trout (Oncorhynchus mykiss) diets. The effect of barley concentration on lipid peroxidation and antioxidant activity of fish fillets were analyzed. Results showed that the inclusion of barley in rainbow trout diets had an inhibitory effect on lipid oxidation, probably associated with certain bioactive compounds in barley that could interact with scavenging and reducing metabolites involved in lipid oxidation. Concentrations up to 8% of barley produced fish fillets with high antioxidant activity and higher levels of alpha-tocopherol.     

Effect of dietary phospholipid sources and levels on growth performance,enzymes activity,cholecystokinin and lipoprotein fractions of rainbow trout (Oncorhynchus mykiss) fry

This study was conducted to evaluate the effect of soybean lecithin (SBL) and chicken egg lecithin (EGL) on growth performance; pancreatic and intestine enzymes, cholecystokinin (CCK) and lipoprotein fractions of rainbow trout, Oncorhynchus mykiss (Walbaum) fry. Seven isonitrogenic and isolipidic diets were prepared by replacing 0 (as a control), 2%, 4% and 6% soybean and chicken egg lecithin instead of soybean oil in diets. Trout fry with initial average weight of 120 ± 4.08 mg, were randomly distributed in 21 90 L tanks. Triplicate groups (165 fish for each tank) of fry were fed each diet to visual satiation at six meals per day for 40 days. Dietary supplements of 2% and 4% chicken egg lecithin led to increase in fry final weight, weight gain and specific growth rate suggesting that moderate PL levels are needed during this stage of rainbow trout. Also 2% chicken egg lecithin caused significantly higher activity of amylase, lipase, phospholipase A₂, alkaline phosphatase (AP), aminopeptidase‐N (AN) and lower activity of leucine alanine peptidase (leu‐ala) in the digestive tract of fry than those in control group. Furthermore, fry fed 2% chicken egg lecithin had a higher ratio of AN/leu‐ala and AP/leu‐ala than that in the control group. Chicken egg lecithin increased significantly cholecystokinin (CCK) and chylomicron fractions of fry compared to control group. It is noteworthy that soybean lecithin had moderate effect on final growth, weight gain and specific growth rate of fry and induced significantly higher activity of amylase, lipase, phospholipase A₂ and secretion of CCK compared to control group. The results of this study indicate that dietary supplementation 2% chicken egg lecithin indirectly through some biochemical parameters improves growth performance of rainbow trout fry.     

The effect of competition among three salmonids on dominance and growth during the juvenile life stage

Although non‐native species can sometimes threaten the value of ecosystem services, their presence can contribute to the benefits derived from the environment. In the Great Lakes, non‐native brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) support substantial recreational fisheries. With current efforts underway to restore once‐native Atlantic salmon (Salmo salar) to Lake Ontario, there is some concern that Atlantic salmon will impede non‐native contributions to the recreational fishery because Atlantic salmon exhibit niche overlap with brown trout and rainbow trout, particularly during the juvenile life stage. We therefore examined competition and growth of juvenile Atlantic salmon, brown trout and rainbow trout in semi‐natural streams. We found that brown trout were the most dominant and had the greatest growth rate regardless of what other species were present. Rainbow trout were more dominant than Atlantic salmon and consumed the most food of the three species. However, in the presence of brown trout, rainbow trout fed less frequently and exhibited negative growth as compared to when the rainbow trout were present with only Atlantic salmon. These data suggest that, outside of density‐dependent effects, Atlantic salmon will not impact stream production of brown trout and rainbow trout.     

Annual variations in brain serotonin and related compounds of domesticated rainbow trout (Oncorhynchus mykiss)

The levels of tryptophan (Trp), 5-hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in two brain regions (hypothalamus and medulla oblongata) of rainbow trout (Oncorhynchus mykiss) were measured throughout the year using a sensitive high performance liquid chromatographic method with electrochemical detection. Trp was also quantified in serum, liver and brain regions. Trp concentrations were higher in sera than in tissues (brain and liver) throughout the year. Hypothalamic and medullary Trp offered similar annual patterns showing two peaks, the first on 10 May and the second on 15 June. 5-HT levels were always higher in the hypothalamus than in the medulla and much higher than the 5-HIAA levels in both regions. Moreover hypothalamic and medullar serotonin patterns were very different, in the latter region few variations were observed. In addition, the 5-HIAA/5-HT ratio was different in the brain regions, the hypothalamus showed two peaks (April 8 and June 15) whereas the equivalent was not observed in the medulla. All measured compounds showed significant variations during the year.     

Distribution and prevalence of T. bryosalmonae in Austria: A first survey of trout from rivers with a shrinking population

The first evidence of proliferative kidney disease (PKD) in an Austrian river (the River Kamp) was documented in 2016, and no information on the PKD infection status of trout in other rivers was available. Since then, brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) have been collected from rivers in Upper and Lower Austria for different diagnostic purposes. In this study, we summarize the recent findings of a first survey concerning the distribution of Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), from these samples. Between September 2015 and October 2017, a total of 280 brown trout and 39 rainbow trout were collected from 21 rivers in the provinces of Upper and Lower Austria. T. bryosalmonae was detected by PCR of kidney tissue in 17 of 21 sampled rivers and in 138 of 280 brown trout as well as in 11 of 39 rainbow trout. Pathological signs of PKD (e.g., hypertrophy of the kidney) were observed in 33 analysed brown trout and six rainbow trout samples. No correlations between fish infected by T. bryosalmonae and the parameters size and age class, condition factor, geological origin of the streams and distribution within the river course were found, while positively tested fish are significantly increased at sampling sites exceeding water temperatures of 15°C for median periods of 115 days. The prevalence within the affected streams or stream sections is highly variable, and in single rivers, infection rates of up to 90% are confirmed.     

Effects of modulatory agents on neurally-mediated responses of trout intestinal smooth musclein vitro

Mediators and mechanisms responsible for the inhibitory modulation of trout intestinal smooth muscle were examined using a series of putative mediators and substances known to modulate neurotransmission in mammalian systems. Frequency response relationships to transmural stimulation and concentration response relationships to 5-hydroxytryptamine, carbachol, and substance P were established on paired segments of rainbow trout intestinein vitro in the presence and absence of putative modulatory agents. Modulation of neurally-mediated contractions of trout intestine was achieved with dibutyryl cyclic AMP and forskolin, agents that increase intracellular levels of cyclic AMP. The effect appears to be at the level of the smooth muscle, since the adenylate cyclase activator, forskolin, inhibited muscarinic and serotoninergic contractions as well as transmurally stimulated contractions. Substance P-induced contractions were unaffected by forskolin. The endogenous agonists/neurotransmitters which would increase cyclic AMP levels in rainbow trout intestinal smooth muscle are as yet unknown. The effects do not appear to be modulated by vasoactive intestinal peptide (VIP), calcitonin, calcitonin gene-related peptide (CGRP), or agents that activate -adrenoceptors. Prostaglandin E₂ (PGE₂) and ₂-adrenergenic agonists are possible agents which will decrease contractility of the smooth muscle. They were only active in the proximal intestine and on transmurally stimulated contractions. The effects of both PGE₂ and ₂-agonists appear to be prejunctional, decreasing release of contractile neurotransmitters in the enteric nervous system.