Trout Stomach Research Articles

Trophic Linkages in the Lower Colorado River: Multiple Stable Isotope Evidence

Trophic linkages in Glen and Grand Canyons of the lower Colorado River downstream from Glen Canyon Dam were examined using multiple stable isotope analysis. The δ ¹³C values of dissolved inorganic carbon (DIC), and the δ ¹³C, δ ¹⁵N, and δ ³⁴S values of seston, aquatic and terrestrial plants, and aquatic animals were determined. The δ ¹³C value of DIC varied among sites. DIC from the epilimnion of the reservoir (Lake Powell) and from a tributary was more ¹³C-enriched than DIC in the Colorado River, probably as a result of variation in aquatic primary production and dissolution of carbonate among sites. Four potential bases of aquatic secondary production: upland vegetation, riparian vegetation, reservoir plankton, and benthic algae were isotopically (δ ¹³C and δ ¹⁵N) distinct from each other. Analysis of δ ¹³C, δ ¹⁵N, and δ ³⁴S showed that seston from the dam tailwater (Glen Canyon) consisted of lotic algae and zooplankton from Lake Powell, except for the ultra fine fraction (<0.053 mm) which was derived from Lake Powell particulate organic matter. Longitudinal variation in the composition of Glen Canyon seston was generally small. Seston from a tributary (the Paria River) was derived from a mixture of upland and riparian vegetation and was isotopically distinct from Colorado River seston. Isotope analysis revealed three trophic levels in Glen Canyon: algae (Cladophora glomerata and diatoms), macroinvertebrates (e.g., Gammarus lacustris and chironomids), and fish (primarily rainbow trout, Oncorhynchus mykiss). Trout also consumed zooplankton exported from Lake Powell. Direct assimilation of algal N by trout was not indicated despite the high incidence of algae in trout stomachs. Isotope values of fishes (trout and speckled dace, Rhinichthys osculus) from Grand Canyon tributaries reflected variation in the trophic basis of fish production; one tributary fish population appeared to be supported by tributary autochthonous production or mainstem organic matter sources, and others were linked to riparian or upland organic matter inputs.

Characterization of trout galanin and its distribution in trout brain and pituitary.

Galanin was purified from an extract of the stomach of the rainbow trout, Oncorhynchus mykiss, and its primary structure was established as Gly-Trp-Thr-Leu-Asn-Ser- Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Gly-Ile-Asp-Gly-His-Arg20- Thr-Leu-Ser-Asp- Lys-His-Gly-Leu-Ala. Trout galanin shows six amino acid substitutions compared with pig galanin, but the N-terminal region (residues 1-14) has been fully conserved. The distribution of galanin-immunoreactive (GAL-IR) structures in the trout brain and pituitary was studied via immunohistochemistry. GAL-IR cell bodies were observed only in the caudal telencephalon, the preoptic region, and the mediobasal hypothalamus. GAL-IR fibers, however, are widely distributed throughout the brain, with a much lower density in the midbrain and posterior brain than in the tel- and diencephalon. Particularly dense innervation of the mediobasal hypothalamus, the ventral and supracommissuralis parts of the caudal telencephalon, and the region above and below the anterior commissure was observed. A heavy innervation of the pituitary was consistently detected. GAL-IR fibers were present in neurohypophyseal digitations of both the anterior and intermediate lobes with highest density in the region of the proximal pars distalis, where growth hormone and gonadotropic cells are located. Fibers were also seen in digitations of the rostral pars distalis, in particular between the prolactin follicles. The distribution of GAL-IR neurons in the central nervous system and pituitary of the trout suggests that the peptide may exercise an important role in the regulation of neuroendocrine functions, particularly those related to reproduction.

Regulatory peptides in gastric endocrine cells of the rainbow trout Oncorhynchus mykiss: General distribution and colocalizations

The endocrine cells of the rainbow trout ( Oncorhynchus mykiss) stomach have been investigated using the immunocytochemical techniques of peroxidase-anti-peroxidase and avidin-biotin-peroxidase complexes on paraffin sections. 33 antisera were tested and eight immunoreactivities were detected: somatostatin-, glucagon-, bombesin-, substance P-, serotonin-, met-enkephalin-, CCK/gastrin-, and chromogranin-like containing cells. All of them were present throughout the gastric mucosa except CCK/gastrin-like containing cells that were restricted to the pyloric epithelium. Somatostatin 25 and chromogranin immunoreactive cells are described for the first time in fish stomach. Serotonin immunoreactive cells were also positive for the Grimelius technique and some of them were immunoreactive to anti substance P or anti CCK/gastrin. Immunoreactivities for gastrin 17, gastrin 34 and CCK appeared in the same cells and the absorption controls showed that a molecule containing the carboxi-terminal pentapeptide of this family was present in trout stomach.

Effects of stocking of piscivorous brown trout, Salmo trutta L., on stunted Arctic charr, Salvelinus alpinus (L.)

AbstractTo study the effects on a stunted freshwater population of Arctic charr, Salvelinus alpinus (L.), two groups of large (26–45 cm) individually tagged brown trout, Salmo trutta L., were released and recaptured with gillnets after 1, 7, 11 and 63 weeks. One group of trout was trained on a fish diet before release, and the other, reared on commercial dry pellets, served as a control. Specific growth rates in both groups were negative 1 week after release and approached zero after 63 weeks. Condition factor and internal fat content decreased during the experiment. Although only 11% of the trout stomachs examined contained fish prey, charr represented 79% of the total stomach weight content. Gillnet samples of charr before and 63 weeks after the release of trout indicated a decreasing population size of charr. Individual growth and mean length of charr increased after release of trout, especially for charr at age 4 years. After the release of trout, 35% of the charr were longer than 20 cm as compared with 6% before the release.

A technique using sequential feedings of different coloured foods to determine food intake by individual rainbow trout, Oncorhynchus mykiss: effect of feeding level

Sequential meals do not mix to any extent in the stomach of rainbow trout. This observation was used to develop a technique to measure food intake by individual fish based on the consumption of sequential meals consisting of different coloured foods [brown (natural coloured food), red (carmine added) or green (chromic oxide added)]. The method was evaluated by examining the effect of underfeeding, feeding to satiety or overfeeding on food intake by individual rainbow trout, Oncorhynchus mykiss, raised in groups. Fish were fasted overnight and fed the test meal at 50, 75, 100 or 133% of predicted satiety for the group as a whole. Following feeding, fish were killed and stomach contents were separated by colour and quantitated by weighing. In fish fasted for 16 h prior to consuming the test meal, almost 1 3 of the total stomach contents were residual contents. Increasing the amount of food provided in the test meal increased the level of consumption, but did not alter the variability between fish within the tank. There was no apparent relationship between body weight and food consumption. This method provides an easy and objective means to quantitate intake of several sequential meals by individual fish.

Changes in Habitat Use and Feeding Chronology of Juvenile Rainbow Trout (Oncorhynchus mykiss) in Fall and the Onset of Winter in Silver Creek, Idaho

We assessed changes in density, distribution, and microhabitat of age-0 rainbow trout (Oncorhynchus mykiss) in Silver Creek, a partially spring-fed stream, by periodic snorkeling in August 1987 through January 1988. We examined trout stomach contents and invertebrate drift samples in diel collections in August, September, October, and January to test if the period of feeding shifted from daytime to nighttime, concurrent with a transition to day concealment. In late September, fish aggregated briefly during the day and then began to conceal themselves in macrophyte beds, undercut banks, and submerged sedges and grasses along streambanks as temperature dropped below 8 °C in early October. Fish emerged from concealment at night, and numbers of trout visible were greatest 30–60 min after sunset and about 30 min before sunrise. Periods of peak feeding changed from afternoon and evening in August and September, when fish were day active, to mainly at night in October after the initiation of day concealment. Trout did not feed upon abundant chironomids in the daytime drift in October. In January, fish fed at 1–4 °C on mayflies, and stomachs were fullest in the early morning. Observations suggest that Silver Creek trout experienced a metabolic deficit that began in September.

Primary structures and effects on gastrointestinal motility of tachykinins from the rainbow trout.

Purification and structural characterization of tachykinins from rainbow trout (Oncorhynchus mykiss) intestine has demonstrated the presence of three different peptides related to the mammalian tachykinins: substance P, neurokinin A, and neuropeptide-gamma. The substance P- and the neurokinin A-related peptides present in the intestine are identical to the tachykinins previously isolated from the trout brain. The neuropeptide-gamma-related peptide (Ser-Ser-Ala-Asn-Pro-Gln-Ile-Thr-Arg-Lys-Arg-His-Lys-Ile-Asn-Ser-Phe- Val-Gly-Leu-Met-NH2), not previously identified in brain tissue, has the sequence of the neurokinin A-related tachykinin at its COOH-terminus. Both trout substance P and neurokinin A stimulated the motility of isolated trout intestinal muscle [pD2(-log of EC50) values 8.5 +/- 0.15 and 7.35 +/- 0.08, respectively] and the vascularly perfused trout stomach (pD2 values 9.63 +/- 0.23 and 8.18 +/- 0.23, respectively). Trout substance P was 14 times more potent than trout neurokinin A in the intestine and 28 times more potent in the stomach. The data suggest that receptors interacting with tachykinins in the trout gastrointestinal tract have a similar selectivity as the mammalian NK-1 receptor.

Isolation and primary structure of gastrin-releasing peptide from a teleost fish, the trout ( Oncorhynchus mykiss)

Immunohistochemical studies have established that fish gastrointestinal tissues contain peptides with gastrin-releasing peptide (GRP)/bombesin-like immunoreactivity, but the molecular nature of this material is unclear. In this study, the most abundant peptide that was immunoreactive towards an antiserum raised against pig GRP was isolated in pure form from an extract of the stomach of the rainbow trout ( Oncorhynchus mykiss). The primary structure of the peptide was established as: Ser-Glu-Asn-Thr-Gly-Ala-Ile-Gly-Lys-Val 10-Phe-Pro-Arg-Gly-Asn-His-Trp-Ala-Val-Gly 20-His-Leu-Met-NH 2. Although this amino acid sequence is shorter than those of mammalian GRPs by four residues, the COOH-terminal dodecapeptide is identical to the corresponding region in pig GRP. The data indicate, therefore, that the predominant molecular form of GRP in the stomach of a teleost fish is structurally more similar to mammalian GRP than to the amphibian skin peptide, bombesin.

Release of substance P-like immunoreactive material from the stomach of the rainbow trout.

The release of substance P-like immunoreactive material (SPLI) from the vascularly perfused stomach of the rainbow trout, Oncorhynchus mykiss, was studied. In most cases, SPLI was detected in the collected vascular perfusate during experimental resting conditions. Distensions of the stomach, accomplished by a water-filled intragastric balloon, produced an initial rapid relaxation of the stomach, followed by a slow further relaxation and a stimulation of contractile activity. The amount of SPLI in the vascular perfusate was significantly elevated during the distension period. Tetrodotoxin had no effect on the response to distension or on the release of SPLI during distension, indicating release from tetrodotoxin-insensitive neurons or endocrine cells. The results suggest that a substance P-like peptide may be involved in the contractile response and/or in the maintenance of muscular tone during gastric distensions in the rainbow trout. Infusion of capsaicin had no effect on the release of SPLI. However, capsaicin caused an increase in vascular flow, an effect that could be repeated on a second infusion of capsaicin, indicating that the action may not be specific to sensory neurons.

Intrinsic Mechanisms Controlling Cardiac Stomach Volume of the Rainbow Trout (Oncorhynchus Mykiss) Following Gastric Distension

ABSTRACT Inflation of the cardiac stomach of the rainbow trout induced reflex muscular contractions. The stomach then slowly relaxed asymptotically towards its maximum volume. Continued distension caused the stomach to become compliant and this was irreversible within the time course of each experiment (8h). Repeated periods of rest and distension revealed a short-term inhibition of reflex contractions which recovered as resting periods were extended. Sectioning the vagosympathetic trunk did not influence the response to distension. Similar responses occurred in isolated, perfused stomachs. Both tetrodotoxin and atropine plus methysergide induced immediate compliance, suggesting that it was caused by the blockade of enteric excitatory neurones. Atropine alone primarily reduced reflex contractions whilst methysergide completed this suppression and induced profound gastric relaxation. Somatostatin reversibly suppressed reflex contractions whilst vasoactive intestinal polypeptide (VIP) induced gastric relaxation. A model is proposed in which distension initially causes reflex activity via cholinergic and serotonergic nerves, whilst gastric tone remains high. Somatostatin then suppresses rhythmic contractions, whilst VIP suppresses the tryptamin-ergic mechanisms that maintain gastric tone. The rainbow trout stomach possesses intrinsic mechanisms that mimic the extrinsic, nerve-controlled ‘receptive relaxation’ or ‘accommodation’ that follows feeding in higher vertebrates.

Rates of gastric evacuation in piscivorous brown trout, Salmo trutta

SUMMARY. 1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.

Influence of digestive processes on the absorption and fate of quinoline ingested by rainbow trout (Oncorhynchus mykiss)

AbstractRainbow trout were fed pelleted food containing [14C]‐quinoline to assess the relationship of digestive processes to xenobiotic pharmacokinetics. The pH of material in the stomach of rainbow trout ranged from 2.7 to 5.2 and was highly correlated (r = 0.89) with the size of the food bolus remaining. At 2 h after feeding, 67% of the quinoline was estimated to be un‐ionized and available for absorption across gastric epithelium. Quinoline was &gt;99% un‐ionized in the alkaline environment of the intestine; however, relative concentrations in the intestine were about 8% of those measured in the stomach. Gastric absorption was consistent with known serum profiles and excretion patterns of dietary quinoline. Rates of gallbladder emptying appeared to exceed rates of hepatic bile secretion until about 8 h after a single feeding. Time since feeding influenced both the amount and concentration of quinoline‐derived radioactivity in the bile. Consecutive feedings enhanced the movement of the food bolus and associated radioactivity from the upper and midgut regions, but had no effect on disposition of quinoline.

Diel Feeding Chronology and Diet Selection of Rainbow Trout (Oncorhynchus mykiss) in the Henry's Fork of the Snake River, Idaho

Concurrent rainbow trout (Oncorhynchus mykiss) stomach contents and invertebrate drift samples were collected during three 24-h periods in summer 1987. Feeding was discontinuous through the day on all dates. Mean stomach content weight was minimal after 0400 MST and sharply increased between 1000 and 1200 MST on all three dates. Feeding apparently did not occur after twilight. Mean stomach content weight was correlated with water temperature on two dates and was never correlated with invertebrate drift density for non-age-0 trout. Daily ration (wet weight) was 7% of live weight for non-age-0 trout and 21% for age-0 trout. Trichoptera, Ephemeroptera, and Diptera were most important in the diet; terrestrial insects and aquatic vertebrates were rare. The degree of selectivity varied through 24 h and the interpretation depended on the method of analysis used. Occurrence of low-drift cased Trichoptera larvae in stomachs was correlated with amount of filamentous algae ingested, indicating a degree of epibenthic foraging, although no diel pattern could be reliably discerned. Mean length of prey items in stomachs was larger that the drift in 83% of the samples. Our findings support experimentally derived decision rules-of-thumb for foraging trout: select larger prey items, select vulnerable prey, and relax selectivity when hungry.

5-Hydroxytryptamine is a possible neurotransmitter of the non-cholinergic excitatory nerves in the longitudinal muscle of rainbow trout stomach (Salmo gairdneri).

1. The neurotransmitter of the non-cholinergic excitatory nerves in the rainbow trout stomach was identified on the basis of the pharmacological properties of the contractile responses to transmural stimulation (TMS) and nicotine. 2. TMS caused tetrodotoxin-sensitive contractions of rainbow trout stomach strips in a frequency-dependent manner (0.5-50 Hz). Atropine (1 microM) significantly decreased the contractile response to low-frequency stimulation (0.5-2 Hz), but did not affect that to high-frequency stimulation (3-20 Hz). 3. The atropine-resistant contractile response to TMS (20 Hz) was unaffected by hexamethonium (100 microM), phentolamine (5.4 microM), pyrilamine (1 microM), naloxone (1 microM) or substance P-induced desensitization. 4. 5-Hydroxytryptamine (5-HT, 3 nM-3 microM) caused atropine-resistant contractions in a concentration-dependent manner. In the presence of atropine, methysergide (1 microM) decreased the contractile responses to TMS and 5-HT. 5. Nicotine (3 microM-500 microM) induced atropine-resistant contractions that were completely abolished by tetrodotoxin or hexamethonium. Also methysergide inhibited the contractile responses to nicotine. 6. An acid extract of rainbow trout stomach exhibited atropine-resistant contractions that were decreased by methysergide, in both rainbow trout stomach and guinea-pig ileum longitudinal smooth muscle preparations. 7. The present results indicate that, in longitudinal muscle strips of the rainbow trout stomach, 5-HT is one of the mediators (neurotransmitters) of the non-cholinergic excitatory contractions induced by TMS and nicotine.

Feeding by hatchery-reared brown trout, Salmo trutta L. released in lakes

. Shortly after their release in two Norwegian lakes (3 hours to 3 weeks), hatchery-reared brown trout, Salamo trutta L., yearlings were recaptured, and their feeding was compared with that of wild brown trout. Investigations were conducted during three different periods (June, August and September). In all three periods most of the hatchery-reared fish started feeding immediately after their release. The amounts of exuviae from Ephemeroptera larvae and Chironomidae pupae found in the stomachs of hatchery-reared trout decreased with time, indicating that their feeding habits were influenced by a learning process. However, within one week of their release, hatchery trout appeared to be feeding on wild prey as well as did wild fish.

Antagonist like action of synthetic α2-adrenoceptor agonists on contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach ( Salmo gairdneri)

1. 1. The effects of some synthetic α 2-adrenoceptor agonists on the mechanical activity and on contractile responses to catecholamines were examined in smooth muscle strips isolated from rainbow trout stomach. 2. 2. Contractile responses to noradrenaline and adrenaline in the rainbow trout stomach strips were due to α 2-adrenoceptor activation. 3. 3. Clonidine, p-aminoclonidine, naphazoline and guanabenz caused no mechanical response but concentration-dependently inhibited the contractile responses to noradrenaline and adrenaline without affecting the responses to acetylcholine, carbachol, 5-hydroxytryptamine and methionine-enkephalin. The order of potency was naphazoline > p-aminoclonidine > clonidine > guanabenz. 4. 4. It is suggested that in the smooth muscle preparation of the trout stomach, some synthetic compounds (clonidine, p-aminoclonidine, naphazoline and guanabenz), which act on mammalian preparations as α 2-adrenoceptor agonists, show an antinoradrenaline (-adrenaline) effect; those compounds can be classified as α 2-adrenoceptor antagonists.

Apomorphine-induced vomiting in rainbow trout ( Salmo gairdneri)

1. 1. The ld 50 for a 7-day period following intraperitoneal injection of apomorphine-HCl was calculated to be 158 mg/kg in rainbow trout. 2. 2. Intraperitoneal injection of apomorphine at doses of 60 mg/kg or greater caused vomiting of plastic balls which had been placed in the stomachs of rainbow trout. 3. 3. Apomorphine-induced effects included vomiting, vomiting behavior, toxicity, increased respiration, impaired motor control and equilibrium, and increased aggression. 4. 4. The vomiting control mechanism of trout may be similar to that described in mammals.

Evidence of Food Limitation of Rainbow and Brown Trout in Southern Appalachian Soft-Water Streams

Abstract Seasonal patterns of age-specific growth rates and condition factors of rainbow trout Salmo gairdneri and brown trout S. trutta were studied in relation to the available food resources in five streams of the southern Appalachian mountains. Standing crops of benthic invertebrates were low relative to streams of similar size in other geographic areas. Although terrestrial organisms contributed substantially to the invertebrate drift, total drift rates were also relatively low. Numbers of prey items per trout stomach were small and were directly related to drift rate. These results reflected the limited food base. Condition factors (weight˙length-3) of age- 1 trout declined during summer, and growth rates among age-1 and older trout were generally lower in summer than in winter, despite favorable summer water temperatures. This “inverted” seasonal pattern of growth was likely due to an inadequate food base. We believe that growth rates were relatively low in summer because much of the limited energy...

Effect of dietary histidine or histamine on growth and development of stomach erosion in rainbow trout.

Five experiments, four for rainbow trout and one for chicks, were conducted to examine effect of dietary histamine or its related compounds on growth and stomach of rainbow trout by feeding them diets containing different levels of histidine or histamine, or diets containing whole meal which caused gizzard erosion and ulceration (GE) in chicks after heat treatment (HT). Effect of of dietary α-tocopherol (VE) levels on appearance of GE-like abnormality in rainbow trout was also examined. The results indicated that abnormality of stomach in both rainbow trout and chicks was induced by HT of whole meal with histidine or histamine. In rainbow trout, thickness of stomach walls tended to decrease in proportion to dietary histamine levels. In histological observation, pycanosis and necrosis of gastric gland cells were found in fish fed diets containing high levels of histamine, HT-histidine and HT-histamine. Moreover, body color of fish was darkened by addition of histamine to white fish meal. Feeding the histamine diet without supplement of VE resulted in lower growth and higher GE score than the diet with VE.

Alpha 2-adrenoceptor-mediated contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach (Salmo gairdneri).

The type of adrenoceptor involved in the contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach was determined. Noradrenaline (10 nM-10 microM) and adrenaline (10 nM-3 microM) caused non-sustained contractions which were markedly decreased by phentolamine (5.4 microM) but not by carteolol (5 microM). Phenylephrine (1 microM-1 mM) was less effective in causing muscle contraction and methoxamine produced no contraction. Clonidine (100 nM-300 microM) caused no mechanical response but inhibited the contraction to noradrenaline or adrenaline but not acetylcholine or 5-hydroxytryptamine. Yohimbine (10 nM-1 microM) decreased the contraction induced by noradrenaline or adrenaline but prazosin (1 microM) did not. Tetrodotoxin (780 nM) partially reduced the contraction induced by noradrenaline or adrenaline but atropine (500 nM) did not. In the presence of atropine (1 microM), electrical transmural stimulation caused frequency-dependent, tetrodotoxin-sensitive contractions. These results suggest that the contractile response induced by noradrenaline or adrenaline is mediated by alpha 2-adrenoceptors. It is also suggested that noradrenaline and adrenaline contract the smooth muscle by direct action and by indirect action through the non-cholinergic excitatory nerve.