The effect of pre-fasting diet and water temperature on liver glycogen and liver weight in rainbow trout, Salmo gairdneri Richardson, during fasting

The effect of feeding an isocaloric and isonitrogenous trout diet that contained different levels of digestible carbohydrate (cerelose) to rainbow trout at either 10 or 15° C on liver glycogen and liver weight was determined in two fasting studies of 12 and 41 days duration. Trout fed diets with increased levels of digestible carbohydrate (HC) had significantly higher liver-body weight ratios (LW) and liver glycogen (LG) than trout reared on low digestible carbohydrate diets (HF). Both LW and LG declined in fasting trout previously fed HC diets but declined little in fasting trout previously fed HF diets. Trout reared at 10° C had higher LW and LG than trout reared at 15° C on either the HC or HF diets. During fasting, the trout reared on HC diets at 10° C required a longer period of time for the LG and LW to decline to the levels of trout reared on the low carbohydrate diets, than did trout reared on the HC diets at 15° C. The results indicate that both pre-fasting diet and water temperature can affect liver glycogen utilization and liver weight in fasting trout. Prolonged elevation of LW and LG in fasting trout could jeopardize the survival rate of stocked trout, particularly at low water temperatures.     

Food partitioning between coexisting Atlantic salmon and brook trout in the Sainte‐Marguerite River ecosystem, Quebec

Food resource partitioning between similar‐sized, sympatric Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis was examined as a possible mechanism enabling their coexistence in a stream (Allaire) of the Sainte‐Marguerite River ecosystem, Quebec, Canada. Fish stomach contents and invertebrate drift were collected concurrently during three diel cycles in August to September 1996. The food and feeding habits of an allopatric brook trout population in a nearby stream (Epinette) were studied for comparison. The diel feeding rhythms of the two coexisting fish species were similar. The composition of their diet, however, showed significant differences. Atlantic salmon predominantly (60–90%) fed on aquatic insects, mainly Ephemeroptera (35–60% of the diet). The brook trout mostly (50–80%) fed upon the allochthonous terrestrial insects (mainly adults of Coleoptera, Hymenoptera and Diptera) which comprised 5–40% of the stream drift. The allopatric brook trout fed opportunistically on the more abundant aquatic insects and terrestrial insects rarely formed 25% of its diet. The allopatric trout fed nearly twice as much as the sympatric brook trout during a day. The results suggest that the differences in feeding by brook trout in the two streams (with and without Atlantic salmon) are the result of inter‐specific interaction with Atlantic salmon and are not related to the differences in food availability between the two streams. Food resource partitioning between Atlantic salmon and brook trout may be viewed as an adaptive response resulting in a greater exploitation of available resources and coexistence.     

A comparative study of trout and chicks regarding dietary effects on glycogen concentration in liver and muscle during feeding and subsequent to feed withdrawal

1. Glycogen concentrations in liver and skeletal muscle were compared in rainbow trout and in chicks of two genetic sources. 2. Tissue glycogen concentrations were determined during feeding and after feed withdrawal in response to diets high in carbohydrate and oil, respectively. 3. Livers of trout and chicks were heavier and glycogen concentrations were higher in both liver and muscle of trout and chicks fed high-carbohydrate diets. 4. Feed withdrawal resulted in gradual but steady declines in trout glycogen over a 16-day period but caused sharp declines in liver glycogen in chicks followed by a rebound and a more gradual decline within a 5-day period. 5. Feed withdrawal from trout caused declines in muscle glycogen followed by rebounds which occurred more rapidly when the high-carbohydrate diet had been fed. 6. Feed withdrawal had little effect on muscle glycogen in broiler-type chicks. In White Leghorn chicks there was a general decline in muscle glycogen which showed marked fluctuations when the high-fat diet had been fed.     

Carbohydrate energy reserves and effects of food deprivation in male and female rainbow trout

We investigated the effects of nutritional state on carbohydrate, lipid, and protein stores in the heart, liver, and white skeletal muscle of male and female rainbow trout. For fed animals we also partitioned glycogen into fractions based on acid solubility. Fish (10-14 months-old, ~400-500 g) were held at 14 °C and either fed (1% of body weight, every other day) or deprived of food for 14 days. Under fed conditions, glycogen was increased 54% in ventricles from males compared with females, and elevated in the liver (87%) and white muscle (70%) in sexually-maturing versus immature males. Acid soluble glycogen predominated over the acid insoluble fraction in all tissues and was similar between sexes. Food deprivation 1) selectively reduced glycogen and free glucose in male ventricles by ~30%, and 2) did not change glycogen in the liver or white muscle, or triglyceride, protein or water levels in any tissues for both sexes. These data highlight sex differences in teleost cardiac stores and the metabolism of carbohydrates, and contrast with mammals where cardiac glycogen increases during fasting and acid insoluble glycogen is a significant fraction. Increased glycogen in the hearts of male rainbow trout appears to pre-empt sex-specific cardiac growth while storage of acid soluble glycogen may reflect a novel strategy for efficient synthesis and mobilization of glycogen in fishes.     

Influence of dietary composition on gluconeogenesis from L-(U-14C)glutamate in rainbow trout (Salmo gairdneri)

The effect of dietary composition (high-protein, high-carbohydrate and high-fat diets) and starvation on in totum gluconeogenesis from L-(U-14C)glutamate was studied in the rainbow trout. High-fat and high-carbohydrate diets produced a significant hyperglycaemia. Lower blood glucose values were obtained in trout fed on a high-protein diet. Liver glycogen levels were significantly lower in trout fed on carbohydrate-free diets (high-protein and high-fat diets) and in starved fish. Gluconeogenesis from L-(U-14C)glutamate was markedly reduced in fish given the high-carbohydrate diet and significantly enhanced in starved fish. Radioactive liver glycogen was higher in starved fish, although the amount of radioactivity incorporated into glycogen was very low.     

The feeding response of diploid and triploid Atlantic salmon and brook trout

Pair and group experiments were conducted to determine whether differences exist in feeding success between juvenile diploid and triploid salmonids in a competitive situation. In the pair experiments, 22 pairs (one diploid and one triploid) of size-matched Quebec-strain brook trout Salvelinus fontinalis (7·2–46·3 g) were fed an unlimited number of pellets three times a day for 5 days. Dominance was assigned to the fish which ate the most pellets within each pair. In the group experiments, groups of three diploid and three triploid size-matched fish were fed a restricted ration three times a day for 5 days. Hierarchical rank within the group was assigned based on the number of pellets consumed by each fish. The group experiment was repeated 10 times with Atlantic salmon Salmo salar (5·1–62·7 g), Quebec-strain brook trout (11·8-110·8 g), and large UNB-strain brook trout (18·2–33·0 g), and 12 times with smaller UNB-strain brook trout (0·6–2·0 g). A statistically significant difference in rank between ploidies was found only for the smaller UNB-strain brook trout in the group experiments, with diploids dominant over triploids. This suggests that there may be a difference in competitive feeding success between diploid and triploid brook trout early in development, but that this difference diminishes as the fish grow.     

Carbohydrate metabolism in several tissues of rainbow trout,Oncorhynchus mykiss,is modified during ovarian recrudescence

• 1.1. Several pathways of carbohydrate metabolism were evaluated in three different tissues—liver, gonad and kidney—of a hatchery-reared population of rainbow trout (Oncorhynchus mykiss) which characterised two different stages of their gonadal maturation, i.e. previtellogenesis and established exogenous vitellogenesis.
• 2.2. A fall in liver glycogen levels was observed during exogenous vitellogenesis. A decrease in activity of the enzymes involved in glycolysis and in the pentose phosphate shunt was also observed, suggesting that at the end of exogenous vitellogenesis the necessity of energy and reducing power has decreased compared to the situation at the onset of this period.
• 3.3. The main changes observed in gonad during vitellogenesis were the decreased activity of glycolysis and the pentose phosphate shunt as well as increased glycogen levels. The stored glycogen should be used later in association with the embryo development.
• 4.4. No major changes were observed in kidney metabolism throughout the vitellogenic process.
• 5.5. Exogenous vitellogenesis in rainbow trout is mainly associated with increased glycogen levels in the gonad and decreased metabolic activity in the liver.

     

Metallo-protease activity increases prior to ovulation in brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) follicle walls

Proteolytic activity was measured in the follicle wall surrounding oocytes from brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) by use of two different protease assays: sodium dodecyl sulfate-polyacrylamide gel electrophoresis (substrate-SDS-PAGE) and a chromogenic synthetic peptide for type I collagen. In brook trout follicle walls, substrate-SDS-PAGE studies demonstrated that the activity of two proteolytic enzymes (80 kDa and 66 kDa) increased significantly before ovulation. The 80 kDa enzyme decreased significantly after ovulation whereas the 66 kDa enzyme remained elevated following ovulation. In yellow perch follicle walls, substrate-SDS-PAGE studies demonstrated that the activity of the major protease (66 kDa) increased before ovulation and remained elevated after ovulation. A chromogenic synthetic peptide was used to assay collagenolytic activity in follicle walls of brook trout and yellow perch. This assay revealed that collagenolytic activity increased significantly in both species before ovulation and remained elevated after ovulation. These findings suggest that metallo-proteases are involved in digesting the follicle wall in teleosts before and after ovulation.     

Effects of food deprivation on 24 h-changes in brain and liver carbohydrate and ketone body metabolism of rainbow trout

Plasma glucose, lactate and acetoacetate, brain glycogen and acetoacetate, and liver acetoacetate, glycogen and lactate in fed rainbow trout exhibited daily changes. However, no daily changes were observed in the activities of the brain enzymes glycogen synthetase, 6-phosphofructo 1-kinase, and lactate dehydrogenase. Depending on the length of the previous fasting period most daily changes observed in the metabolic parameters of fed fish disappeared, except for liver acetoacetate levels, which displayed daily changes in both fed and fasted fish. These results suggest that feeding is an important factor regulating most daily changes in the brain and liver carbohydrate and ketone body metabolism of rainbow trout.     

Alien invasions in aquatic ecosystems: Toward an understanding of brook trout invasions and potential impacts on inland cutthroat trout in western North America

Experience from case studies of biologicalinvasions in aquatic ecosystems has motivated aset of proposed empirical rules forunderstanding patterns of invasion and impactson native species. Further evidence is neededto better understand these patterns, andperhaps contribute to a useful predictivetheory of invasions. We reviewed the case ofbrook trout (Salvelinus fontinalis)invasions in the western United States andtheir impacts on native cutthroat trout (Oncorhynchus clarki). Unlike many biologicalinvasions, a considerable body of empiricalresearch on brook trout and cutthroat trout isavailable. We reviewed life histories of eachspecies, brook trout invasions, their impactson cutthroat trout, and patterns and causes ofsegregation between brook trout and cutthroattrout. We considered four stages of theinvasion process: transport, establishment,spread, and impacts to native species. Most ofthe research we found focused on impacts. Interspecific interactions, especiallycompetition, were commonly investigated andcited as impacts of brook trout. In many casesit is not clear if brook trout invasions have ameasurable impact. Studies of speciesdistributions in the field and a variety ofexperiments suggest invasion success of brooktrout is associated with environmental factors,including temperature, landscape structure,habitat size, stream flow, and humaninfluences. Research on earlier stages ofbrook trout invasions (transport,establishment, and spread) is relativelylimited, but has provided promising insights. Management alternatives for controllingbrook trout invasions are limited, and actions tocontrol brook trout focus on direct removal,which is variably successful and can haveadverse effects on native species. Themanagement applicability of research has beenconfounded by the complexity of the problem andby a focus on understanding processes atsmaller scales, but not on predicting patternsat larger scales. In the short-term, animproved predictive understanding of brooktrout invasions could prove to be most useful,even if processes are incompletely understood. A stronger connection between research andmanagement is needed to identify more effectivealternatives for controlling brook troutinvasions and for identifying managementpriorities.     

Species-specific probe,based on 18S rDNA sequence,could be used for identification of the mucilage producer microalga <Emphasis Type="Italic">Gonyaulax fragilis</Emphasis> (Dinophyta)

Brook trout (Salvelinus fontinalis) in Appalachia experience prolonged periods of poor feeding conditions, particularly during summer and fall. To determine which prey organisms are important in sustaining brook trout populations, we monitored the feeding patterns of a population of brook trout over the course of 2 years with an emphasis on seasonal change. We employed a bioenergetics model to estimate whether or not each fish had obtained enough energy to meet daily metabolic demand. As a result, qualitative comparisons between fish feeding above maintenance ration (successfully feeding fish) and fish feeding below maintenance ration (unsuccessfully feeding fish) were possible. With the exception of winter, brook trout derived significantly more energy from terrestrial organisms than aquatic organisms. During each season, successfully feeding brook trout fed on greater proportions of specific prey types. Terrestrial Coleoptera and Lepidoptera consistently proved to be important prey during warmer seasons, while large organisms such as vertebrates and crayfish appeared to be important during winter. Our findings suggest that terrestrial organisms are more important than aquatic organisms in sustaining brook trout populations. Further, certain large and abundant terrestrial taxa are critical in providing energy to brook trout.     

Role of pectin from cucumber (Cucumis sativus) in modulation of protein kinase C activity and regulation of glycogen metabolism in rats

The regulatory role of protein kinase C (PKC) in glycogen metabolism in pectin fed rats was investigated. Administration of pectin (5 g/kg body wt/day) from cucumber (Cucumis sativius L.) led to inhibitory effects on PKC activity in the liver of rats. In the brain and pancreas, PKC activity was significantly higher in pectin-treated rats as compared to the control group. Level of blood glucose was significantly lowered and the level of glycogen in the liver was significantly increased in pectin-administered rats. Glycogen synthase activity was enhanced, while glycogen phosphorylase enzyme showed inhibition in pectin-treated rats. Results indicated that pectin administration might have caused an increase in the secretion of the insulin, which, in turn, had a stimulatory effect on the PKC activity in the pancreas. The decreased PKC activity in the liver and increased PKC activity in the brain and pancreas on pectin administration indicated enhanced glycogenesis and reduced glycogenolysis.     

The effect of antioxidants on the quality of cryopreserved semen in two salmonid fish, the brook trout (Salvelinus fontinalis) and the rainbow trout (Oncorhynchus mykiss)

Until now the supplementation of cryopreservation extenders with antioxidants has not been examined in teleost fish. Therefore, the present study investigated whether addition of antioxidants (catalase, superoxide dismutase, peroxidase, reduced glutathione, reduced methione, mixtures of reduced and oxidized glutathione or methionine) to the cryopreservation extenders could increase the quality of frozen-thawed semen of brook trout, Salvelinus fontinalis, and rainbow trout, Oncorhynchus mykiss. In brook trout and rainbow trout semen post-thaw fertility and motility were evaluated and in brook trout additionally the membrane integrity, DNA integrity, and sperm lipid peroxidation were evaluated. The tested antioxidants affected the motility parameters, DNA integrity, and fertility of cryopreserved semen, but not the membrane integrity. Most of the observed effects were negative and only minor positive effects were found. In brook trout 1.5 mmol/l reduced methionine and a mixture of 1.5 mmol/l oxidized and reduced glutathione increased the swimming velocity of frozen-thawed semen. One hundred U/l catalase, 1.5 mmol/l reduced glutathione, and 1.5 mmol/l reduced methionine slightly, but not statistically significantly increased the semen post-thaw fertility. However, these effects were not detectable in rainbow trout. Antioxidative stress or damage seems to play no role during cryopreservation, as also in the lipid peroxidation test no differences were obtained between fresh and cryopreserved semen. Therefore, for routine cryopreservation extender supplementation with antioxidants is not recommended in brook trout and rainbow trout.     

Daily changes in parameters of energy metabolism in liver, white muscle, and gills of rainbow trout: dependence on feeding

We assessed the daily patterns of parameters involved in energy metabolism in liver, white muscle, and gills of rainbow trout. Where daily rhythms were found, we analyzed the potential influence of feeding. Immature rainbow trout were randomly distributed in 3 groups: fish fed for 7 days, fish fasted for 7 days, and fish fasted for 7 days and refed for 4 days. On sampling day, fish of fed and refed groups were fed at 11.00 h, and all fish were sampled from each treatment group using the following time schedule: 14.00, 18.00, 21.00, 00.00, 04.00, 07.00, 10.00 and 14.00 h. The results obtained from metabolic parameters can be grouped into four different categories, such as i) those displaying no daily changes in any group assessed in liver (acetoacetate and lactate levels), white muscle (protein levels, and low Km (glucose) hexokinase (HK) and HK-IV activities) and gills (protein levels), ii) those displaying no 24 h changes in fed fish but in refed or fasted fish in liver (glucose, glycogen, amino acid and protein levels, and HK-IV activity), white muscle (glycogen and amino acid levels) and gills (glucose levels), iii) those displaying 24 h changes that were apparently dependent on feeding since they disappear in fasted fish in liver (Low Km (glucose) HK, lactate dehydrogenase (LDH-O), glucose 6-phosphatase (G6Pase), fructose 1,6-bisphosphatase (FBPase) , alpha-glycerophosphate dehydrogenase (G3PDH), glutamate dehydrogenase (GDH) and aspartate aminotransferase (Asp-AT) activities), white muscle (glucose levels, and pyruvate kinase (PK), LDH-O, G3PDH and Asp-AT activities) and gills (glycogen and lactate levels, and Low Km (glucose) HK, HK-IV, LDH-O and Asp-AT activities), and iv) those parameters displaying 24 h changes apparently not dependent on feeding in liver (lactate levels and PK activity) and gills (amino acid levels, and PK and GDH activities). In general, most 24 h changes observed were dependent on feeding and can be also related to daily changes in activity.     

Comparison of antimicrobial activity in the epidermal mucus extracts of fish

The mucus layer on the surface of fish consists of several antimicrobial agents that provide a first line of defense against invading pathogens. To date, little is known about the antimicrobial properties of the mucus of Arctic char (Salvelinus alpinus), brook trout (S. fontinalis), koi carp (Cyprinus carpio sub sp. koi), striped bass (Morone saxatilis), haddock (Melanogrammus aeglefinus) and hagfish (Myxine glutinosa). The epidermal mucus samples from these fish were extracted with acidic, organic and aqueous solvents to identify potential antimicrobial agents including basic peptides, secondary metabolites, aqueous and acid soluble compounds. Initial screening of the mucus extracts against a susceptible strain of Salmonella enterica C610, showed a significant variation in antimicrobial activity among the fish species examined. The acidic mucus extracts of brook trout, haddock and hagfish exhibited bactericidal activity. The organic mucus extracts of brook trout, striped bass and koi carp showed bacteriostatic activity. There was no detectable activity in the aqueous mucus extracts. Further investigations of the activity of the acidic mucus extracts of brook trout, haddock and hagfish showed that these fish species had specific activity for fish and human pathogens, demonstrating the role of fish mucus in antimicrobial protection. In comparison to brook trout and haddock, the minimum bactericidal concentrations of hagfish acidic mucus extracts were found to be approximately 1.5 to 3.0 times lower against fish pathogens and approximately 1.6 to 6.6 folds lower for human pathogens. This preliminary information suggests that the mucus from these fish species may be a source of novel antimicrobial agents for fish and human health related applications.     

Long-term population demographics of native brook trout following manipulative reduction of an invader

Although laboratory studies have provided evidence for negative interactions between brook trout and brown trout, it is unknown how these interactions affect larger scale demographics in a natural setting. We tested the effects of invasive brown trout on brook trout demographics by removing brown trout from a sympatric population using a before–after control-impact study design. The study was conducted across a large stream network for a period of 6 years. Abundance of brook trout increased after brown trout removal primarily as a result of increased recruitment and immigration. Size structure also shifted towards larger individuals as a result of increased growth rates and a decrease in emigration of larger trout. Size at maturity and body condition did not change after brown trout removal. Adult brook trout survival increased during the post-treatment period in both the treatment and control reach. A decrease in flood intensity during the post-treatment time period may have led to increased survival. Adult survival may not be the best metric to use when assessing interactions between trout species, especially when the subordinate species has suitable areas to emigrate.     

Dietary carotenoid pigment supplementation influences hepatic lipid and mucopolysaccharide levels in rainbow trout (Oncorhynchus mykiss)

We assessed the effects of dietary carotenoid pigment supplementation on liver histochemistry in the rainbow trout. One hundred and eight rainbow trout (mean mass 266 ± 10 g) were assigned to each of three replicate tanks for each of three dietary treatments; astaxanthin, canthaxanthin, or control at a target dietary inclusion of 100 mg/kg, by top-coating a pigment-free commercially extruded basal diet (Trouw Aquaculture, U.K.). Fish were fed for 3 weeks at a ration of 1.2% body mass/day, in a recirculating freshwater system maintained at 16 °C. Frozen liver sections were stained for total lipids, unsaturated lipids, glycogen, mucopolysaccharides, glycogen phosphorylase and aspartate aminotransferase. Relative amounts were measured quantitatively by image analysis. Carotenoid treatment significantly (P < 0.05) altered the total lipid profile and hepatic mucopolysaccharide contents of livers of rainbow trout. Results are discussed in relation to the catabolic potential of the liver in carotenoid pigment metabolism.