Genetic variability in residual feed intake in rainbow trout clones and testing of indirect selection criteria (Open Access publication)

Little is known about the genetic basis of residual feed intake (RFI) variation in fish, since this trait is highly sensitive to environmental influences, and feed intake of individuals is difficult to measure accurately. The purpose of this work was (i) to assess the genetic variability of RFI estimated by an X-ray technique and (ii) to develop predictive criteria for RFI. Two predictive criteria were tested: loss of body weight during feed deprivation and compensatory growth during re-feeding. Ten heterozygous rainbow trout clones were used. Individual intake and body weight were measured three times at threeweek intervals. Then, individual body weight was recorded after two cycles of a three-week feed deprivation followed by a three-week re-feeding. The ratio of the genetic variance to the phenotypic variance was found high to moderate for growth, feed intake, and RFI (VG/VP = 0.63 ± 0.11, 0.29 ± 0.11, 0.29 ± 0.09, respectively). The index that integrates performances achieved during deprivation and re-feeding periods explained 59% of RFI variations. These results provide a basis for further studies on the origin of RFI differences and show that indirect criteria are good candidates for future selective breeding programs.     

Interindividual variations in feeding and growth in rainbow trout during restricted feeding and in a subsequent period of compensatory growth

Compensatory growth responses of rainbow trout Oncorhynchus mykiss were studied by examining food intake and growth of individual fish held within groups that were switched between regimes that involved full and restricted feeding. Restricted feeding led to marked interindividual variability in food intake, probably as a result of the establishment of feeding hierarchies. This disparity in food acquisition was reflected in highly heterogeneous growth amongst the fish fed low rations. When fish were transferred from restricted to full rations, they became hyperphagic and displayed high rates of growth. Growth compensation was most marked amongst those fish which had shown the poorest growth during the period of feed restriction. These results suggest that the feeding hierarchies established under feed restriction did not persist, but were rapidly broken down when food became increasingly available, enabling the previously suppressed fish to gain access to food and to display rapid growth.     

Rhythmic pattern of growth and nutrient retention in response to feeding time in the rainbow trout

The effect of six different feeding times was tested on feed intake, growth performance, proximate body composition and nutrient retention in the rainbow trout Oncorhynchus mykiss . Using a non‐linear regression model, a significant rhythmic pattern over a 24 h period was observed for feed gain ratio and nutrient retention responses to feeding time. Specific growth rate and protein growth rate responses were also rhythmic but the trends were not significant. There was no clear effect of feeding time on feed intake and proximate body composition. The study suggested that feed intake, at least under the experimental conditions encountered, was synchronized to feeding time while some physiological rhythms involved in nutrient metabolism were probably synchronized to photoperiod.     

Natural reproduction of anadromous rainbow trout in Norway

Six naturally reproduced 0+ rainbow trout were caught in a Norwegian river in 1994. This is the second report and first recorded sample of descendants from anadromous parents found in a Norwegian river. If this is not a unique event, the finding bodes ill for future conservation of native anadromous Salmonids.     

The effect of vagotomy on the increase in food intake induced by the cholecystokinin antagonist, proglumide

Cholecystokinin, secreted when ingested food enters the duodenum, may act as a satiety factor. Injection of proglumide, a specific antagonist of cholecystokinin, induced an increase in food intake. The satiety effect of administered cholecystokinin is abolished by bilateral subdiaphragmatic vagotomy. If endogenous and exogenous cholecystokinin act via the same mechanism, then vagotomy should abolish the proglumide-induced increase in food intake. Proglumide was used to block the satiety effect of a food preload in sham-operated and vagotomized rats. Proglumide induced an increase in food intake in sham-operated rats confirming earlier results. No change in meal size was observed in vagotomized rats following proglumide injection. These results suggest that vagotomy abolishes the effect of endogenous cholecystokinin on food intake. However, evidence of dumping in vagotomized rats prevents the interpretation of the data as a direct vagal involvement in endogenous CCK-induced satiety.     

Glucose 6-phosphate dehydrogenase in rainbow trout

Electrophoretic analysis of glucose 6-phosphate dehydrogenase from liver and blood of rainbow trout revealed a complex series of bands, which could differ between fish. The partial interconvertible nature of these bands was demonstrated with enzyme that had been incompletely inactivated at pH 8.4. In a single population of 40 fish, a homozygote and a heterozygote for an electrophoretic variant allele were found. We suggest that G6PD in rainbow trout liver and blood is determined by two alleles at a single locus, with posttranslational modification responsible for the complex electrophoretic patterns seen. The basis for this variation appears to be NADH binding to the protein molecule. Another variant and other properties of the enzyme are described.Supported in part by the State of California Department of Mental Hygiene and by USPHS Grants GM-15253, HD-04612, HD-00315, HD-05615, and HL-15125. One of us (S.D.C.) was a Special Postdoctoral Fellow of NIAMD (No. 1F03AM-40, 329-01) during part of this work.     

Successful shoreline spawning of rainbow trout in two Canadian alpine lakes

Successful shoreline spawning of rainbow trout Oncorhynchus mykiss has occurred for several decadal periods without hatchery stocking in Joe and Harry Lakes, two small (5–6 ha) alpine waters at >2000 m elevation in south-central British Columbia. Redds are most concentrated near groundwater inflows, in Joe Lake mainly on sand and gravel, in Harry Lake mainly over rocks and boulders.     

Brain distribution of myosin Va in rainbow trout Oncorhynchus mykiss

This study presents data on myosin Va localization in the central nervous system of rainbow trout. We demonstrate, via immunoblots and immunocytochemistry, the expression of myosin Va in several neuronal populations of forebrain, midbrain, hindbrain and spinal cord. The neuronal populations that express myosin Va in trout constitute a very diverse group that do not seem to have many specific similarities such as neurotransmitters used, cellular size or length of their processes. The intensity of the immunoreactivity and the number of immunoreactive cells differ from region to region. Although there is a broad distribution of myosin Va, it is not present in all neuronal populations. This result is in agreement with a previous report, which indicated that myosin Va is approximately as abundant as conventional myosin II and kinesin, and it is broadly involved in neuronal motility events such as axoplasmatic transport. Furthermore, this distribution pattern is in accordance with what was shown in rats and mice; it indicates phylogenetic maintenance of the myosin Va main functions.     

Absence of developmental incompatibility in hybrids between rainbow trout and two subspecies of cutthroat trout

We examined the developmental rate of hybrids between rainbow trout (Salmo gairdneri) and two subspecies of cutthroat trout: westslope cutthroat trout (Salmo clarki lewisi) and Yellowstone cutthroat trout (Salmo clarki bouvieri). These taxa show considerable genetic divergence at 42 structural loci encoding enzymes; the mean Nei's d between the rainbow trout and the two species of cutthroat trout is 0.22. We used four measures of developmental rate: time of hatching and yolk resorption, rate of increase in activity of four enzymes, and time of initial detection of seven isozyme loci. The two cutthroat trout subspecies reached hatching and yolk resorption earlier than rainbow trout. Cutthroat trout had higher relative enzyme activities than rainbow trout from deposition of eye pigment to hatching. There was no difference in the rate of increase in enzyme activity or time of initial expression of these loci between these species. Hybrids showed developmental rates intermediate or similar to that of the parental species using all measures. Our results indicate an absence of regulatory and developmental incompatibility between these taxa.This research was supported by NSF Grants ISP-8011449 and BSR-8300039. M.M.F. was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.     

Primary cell culture from gill explants of rainbow trout

Primary cultures of gill cells were initiated from gill filament explants of rainbow trout, Oncorhynchus mykiss . The explants were cultured in Leibovitz l -15 medium with 5, 10 or 20% foetal calf serum (FCS) and l -glutamine. The attachment efficiency was serum-dependent though increased FCS concentration did not stimulate further outgrowth of cells. The explants produced cell outgrowth 24 h after attachment as a sheet of cells which exhibited characteristics of gill pavement epithelial cells as indicated by surface microridges revealed by scanning electron micrographs. There was high proliferation for the first 14 days then a stable plateau for 30 days followed by a decline phase from 45 days. Following removal of cells, the explants produced further cell outgrowth which was especially active at the proliferation phase (14 days). Removal of these cells caused the explants to produce a further proliferation of cells reaching confluence in 10–14 days. After the third cell removal cell outgrowth from explants showed migratory activity but did not develop to resemble gill epithelial cells. The use of gill explants to establish primary cultures of fish gill cells has advantages which include longevity of the culture and successive proliferations from explants which could provide a useful tool for the investigation of long-term processes in cellular biology and reduce the number of culture preparations.     

Diel variation in branchial calcium uptake by the rainbow trout

Branchial Ca uptake varied dielly with a nadir at 1000 hours and two peaks at 1600 and 0400 hours in rainbow trout. This variation profile essentially reflected Ca uptake through the arterio-arterial circulation.     

Antibody response to VHS virus proteins in rainbow trout

The antibody response to viral haemorrhagic septicaemia virus proteins in rainbow trout surviving a disease outbreak under field conditions as well as animals immunised under laboratory conditions was analysed by immunoblotting, immunofluorescence and plaque neutralisation. No direct correlation between the serum reactivity in immunoblotting and the other serological tests was observed. Among sera from survivors from a disease outbreak in a farm, virus specific antibodies could be detected in most of the sera by immunofluorescence but only in a minority by immunoblotting. In fish injected with the individual viral proteins G, N, M1, or M2 under aquarium conditions, only the glycoprotein induced antibodies detectable by immunoblotting. Challenge of the fish with virulent virus indicated that only minor degrees of protective immunity had been induced. In sera from fish surviving the challenge, the neutralising activity was high. In immunoblotting however, a significant antibody reactivity was observed only in sera from fish primed with the glycoprotein. The results are discussed with respect to the immunogenicity of VHSV proteins in rainbow trout as well as the character of the epitopes recognised by antibodies induced in infected or immunised fish.     

The bold and the shy: individual differences in rainbow trout

Boldness and shyness were investigated as 'personality' traits in hatchery-reared rainbow trout Oncorhynchus mykiss . Bold fish spent more time in an open area and were more active than shy fish and these behaviours could be used as indicators of boldness and shyness. These differences were related to learning ability in a simple conditioning task. Bold fish learned the task more quickly than shy fish.     

Recombination is suppressed over a large region of the rainbow trout Y chromosome

The previous genetic mapping data have suggested that most of the rainbow trout sex chromosome pair is pseudoautosomal, with very small X-specific and Y-specific regions. We have prepared an updated genetic and cytogenetic map of the male rainbow trout sex linkage group. Selected sex-linked markers spanning the X chromosome of the female genetic map have been mapped cytogenetically in normal males and genetically in crosses between the OSU female clonal line and four different male clonal lines as well as in outcrosses involving outbred OSU and hybrids between the OSU line and the male clonal lines. The cytogenetic maps of the X and Y chromosomes were very similar to the female genetic map for the X chromosome. Five markers on the male maps are genetically very close to the sex determination locus ( SEX ), but more widely spaced on the female genetic map and on the cytogenetic map, indicating a large region of suppressed recombination on the Y chromosome surrounding the SEX locus. The male map is greatly extended at the telomere. A BAC clone containing the SCAR (sequence characterized amplified region) Omy - 163 marker, which maps close to SEX , was subjected to shotgun sequencing. Two carbonyl reductase genes and a gene homologous to the vertebrate skeletal ryanodine receptor were identified. Carbonyl reductase is a key enzyme involved in production of trout ovarian maturation hormone. This brings the number of type I genes mapped to the sex chromosome to six and has allowed us to identify a region on zebrafish chromosome 10 and medaka chromosome 13 which may be homologous to the distal portion of the long arm of the rainbow trout Y chromosome.     

The effect of acidification on oogenesis of rainbow trout during sex differentiation

Rainbow trout larvae were kept in acid water from 16 to 55 days after hatching. Initially, the acid environment stimulated a significant increase of gametes in the gonads of females at all developmental stages, but after longer exposure the stimulation was replaced by inhibition of gonadal development in the treated fish. In some fish, gamete reserves increased, while in others there was increased growth and maturation of late-generation oocytes.     

Gastrointestinal responses of rainbow trout to dry pellet and low-fat herring diets

Long-term voluntary-feeding experiments were carried out on farmed, 2-year-old rainbow trout offered a commercial dry feed, or chopped low-fat Baltic herring. Despite large differences in dietary water, protein and lipid content, the trout adjusted their intake to consume similar amounts of dry matter. After an 18-week trial, the stomach volumes of the herring-fed trout were significantly larger (30–35%) than those fed on the dry diet. Greatest differences were observed when fish were fed one meal per day; increasing the number of daily feeding opportunities reduced these expected stomach volumes on each diet by 15–20%. The relative increase in stomach volume was shown to be due to growth of the cardiac stomach region (corpus) rather than the pyloric region, and not to muscle relaxation; the change was completed within 10 weeks. Data were collected in a separate study to investigate stomach size in fish (age 0+, 1+, 2+) of similar genetic backgrounds which had been grown using dry pelleted diets. Despite considerable variation between populations, stomach volume to body weight relationship was allometric ( S = a W ^b) with the exponent in the range of 0.3–0.4.     

Identification of polymorphisms influencing feed intake and efficiency in beef cattle

Feed efficiency is an economically important trait in beef cattle. Net feed efficiency, measured as residual feed intake (RFI), is the difference between actual feed intake and the predicted feed intake required for maintenance and gain of the animal. SNPs that show associations with RFI may be useful quantitative trait nucleotides for marker-assisted selection. This study identified associations between SNPs underlying five RFI QTL on five bovine chromosomes (BTA2, 5, 10, 20 and 29) with measures of dry matter intake (DMI), RFI and feed conversion ratio (FCR) in beef cattle. Six SNPs were found to have effects on RFI (P < 0.05). The largest single SNP allele substitution effect for RFI was -0.25 kg/day located on BTA2. The combined effects of the SNPs found significant in this experiment explained 6.9% of the phenotypic variation of RFI. Not all the RFI SNPs showed associations with DMI and FCR even though these traits are highly correlated with RFI (r = 0.77 and r = 0.62 respectively). This shows that these SNPs may be affecting the underlying biological mechanisms of feed efficiency beyond feed intake control and weight gain efficiency. These SNPs can be used in marker-assisted selection but first it will be important to verify these effects in independent populations of cattle.     

Brain glucose and insulin: effects on food intake and brain biogenic amines of rainbow trout

The effects of central (intracerebroventricular, 9 g fish^–1) and peripheral (intraperitoneal, 4 mg kg^–1) administration of bovine insulin, as well as the effect of hyperglycemia (oral administration of 1 g glucose fish^–1) and brain glucodeprivation (intracerebroventricular administration of 2-deoxy-D-glucose) on food intake and levels of brain (telencephalon, preoptic area, and hypothalamus) biogenic amines (serotonin, dopamine, noradrenaline and their metabolites 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid) were assessed on rainbow trout (Oncorhynchus mykiss). Treatment with insulin inhibited food intake after 26 or 52 h of administration, central or peripheral, respectively. This effect was still apparent after 74 h of central treatment. When assessing changes in the levels of biogenic amines after 26 h of central insulin administration, there was a significant increase in the levels of 5-hydroxyindoleacetic acid, and in the ratio of dihydroxyphenylacetic acid/dopamine of insulin-treated fish, in telencephalon and hypothalamus, respectively. These results suggest that peripherally administered insulin is involved in a feedback regulatory loop with food intake and body weight. Moreover, at least part of the effects of insulin could be mediated by hypothalamic dopaminergic activity. The strong hyperglycemia induced by oral administration of glucose did not induce significant changes either on food intake (control versus treated), or in brain levels of biogenic amines. The intracerebroventricular administration of 2-deoxy-D-glucose induced an increase in food intake without altering plasma glucose levels, suggesting that fish brain possesses a control system for detecting hypoglycemia in plasma and therefore keep brain glucose levels high enough for brain function.Abbreviations 2-DG 2 Deoxy-D-glucose - 5-HIAA 5-Hydroxyindoleacetic acid - 5-HT 5-Hydroxytryptamine or serotonin - DA Dopamine - DOPAC Dihydroxyphenylacetic acid - EDTA Ethylenediaminetetraacetic acid - FI Food intake - HPLC High pressure liquid chromatography - icv Intracerebroventricular - i.p. Intraperitoneal - MS 222 3-Aminobenzoic acid ethyl esther methanesulfonate salt - NA Noradrenaline     

The cholecystokinin type A receptor g.179A>G polymorphism affects feeding rate

A polymorphism within the 5' untranslated region of the cholecystokinin type A receptor ( CCKAR ) gene has been shown to affect feed intake and growth in commercial pig lines. To further investigate the phenotype of animals carrying alternative alleles at this polymorphism, we genotyped animals from a distinct segregating commercial line and an experimental cross F₂ population, both with electronically recorded feeding pattern data. The data indicate that the daily feed intake increasing effect of the DQ496228:g.179G allele is mediated through a faster rate of feed intake, without evidence for an effect on other feeding behaviour traits.