Dietary vitamin E and the response of rainbow trout, Oncorhynchus mykiss (Walbaum), to infection with Yersinia ruckeri

Rainbow trout fed diets containing 7, 86 or 806 mg vitamin E kg⁻¹ for 22 weeks were exposed to virulent Yersinia ruckeri by bath or injection. Mortalities were always least among those fed the highest concentration of vitamin E but serum antibody production was not affected by vitamin E levels.     

Cortisol and immune characteristics in rainbow trout (Oncorhynchus mykiss) selected for high or low tolerance to stress

The influence of exposure to stressors on cortisol and the non-specific immune traits lysozyme and serum haemolytic activity were examined in second generation rainbow trout ( Oncorhynchus mykiss ) selected for either high or low serum cortisol level following a confinement stress. Lysozyme and serum haemolytic activity were also assessed, together with levels of specific antibodies against Aeromonas salmonicida A-layer, Vibrio salmonicida O-antigen and Vibrio anguillarum O-antigen, following injection of vaccines against these pathogens.
Significant differences in mean cortisol levels between the two selection lines were observed, but in only one of two stress experiments was the 'high-stress' line found to have the higher cortisol level; in the other experiment the 'high-stress' line had significantly lower cortisol levels than the 'low-stress' line. Lysozyme levels were in four of four assessments higher in the high-stress line than in the low-stress line, whereas components of serum haemolytic activity tended to be lower in the high-stress line than in the low-stress line. Levels of specific antibodies against all three bacterial pathogens were elevated following the injection of the vaccines. Only antibody production against A. salmonicida A-layer was significantly different between the two lines, the higher production of antibody being in the high-stress line.     

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.     

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.     

Relationships between boron concentrations and trout in the Firehole River, Wyoming: historical information and preliminary results of a field study

The Firehole River (FHR) in Yellowstone National Park (YNP) is a world-renowned recreational fishery that predominantly includes rainbow trout (RBT,Oncorhynchus mykiss) and brown trout (BNT,Salmo trutta). The trout populations apparently are closed to immigration and have been self-sustaining since 1955. Inputs from hot springs and geysers increase the temperature and mineral content of the water, including elevating the boron (B) concentrations to a maximum of 1 mg B/L. Both RBT and BNT reside in warm-water reaches, except when the water is extremely warm (≥25°C) during midsummer. They spawn in late fall and early winter, with documented spawning of BNT in the cold-water reach upstream from the Upper Geyser Basin and of RBT in the Lower Geyser Basin reach, where water temperatures presumably are the warmest; however, successful recruitment of RBT in waters containing 1 mg B/L has not been demonstrated conclusively. Thus, we began investigating the relationships among temperature, B concentrations, other waterquality parameters, and the distribution and reproduction of trout in the FHR in spring 1997. However, atypical high water flows and concomitant lower than historical temperatures and B concentrations during summer 1997 preclude conclusions about avoidance of high B concentrations.     

Primary and secondary indices of stress in the progeny of rainbow trout (Oncorhynchus mykiss) selected for high and low responsiveness to stress

A series of pooled gamete matings was carried out employing eggs and milt from mature male and female rainbow trout selected for a consistently high- or low-responsiveness to stress, as indicated by post-stress plasma cortisol elevation. Development of the progeny was closely monitored and the responsiveness to stress of the progeny of high-responding parents and the progeny of low-responding parents was assessed by two methods. For a period of 14 months, at approximately monthly intervals, the plasma cortisol elevation evoked by a standardized confinement stress was determined in fish from each group, and secondly, on one occasion, the time-course of the plasma cortisol response to a 24-h period of confinement was monitored. Progeny of high-responding parents snowed a significantly greater cortisol response to stress than the progeny of low-responding parents during both testing procedures. However, when the effect of a 14-day confinement stress was examined, high-responding progeny showed a more rapid recovery of plasma cortisol levels, while levels in the low-responding progeny, although initially lower, showed a more sustained elevation. To assess the possible functional implications of these observations, circulating lymphocyte numbers, an immunologically important cortisol-sensitive component of the blood cell complement, were determined. The duration of the lymphocytopenia observed following the onset of confinement was found to be related to the initial, not the sustained, cortisol response. These data suggest that manipulation of the sensitivity to stress of fish is feasible by selective breeding, but that careful.choice of the indices employed to identify traits considered desirable is necessary.     

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.     

Influence of growth rate on white muscle dynamics in rainbow trout and brook trout

In trout, fast growth stimulated white muscle fibre hypertrophy ( P 0·001) and hyperplasia ( P <0·01) in outer fibres but not in deep fibres. Glycogen was most prevalent in outer fibres ( P <0·01) and in brook trout ( P <0·01) that on average had three to four times larger fibres than rainbow trout.     

Competitive ability is related to metabolic asymmetry in juvenile rainbow trout

Of 55 size–matched pairs of juvenile rainbow trout Oncorhynchus mykiss , each consisting of one high and one low relative metabolic rate fish (relative size difference <5%), the high relative metabolic rate fish was dominant in 36 pairs (65·5%), significantly more often than expected by chance. The probability of a fish winning was related to its relative metabolic rate (measured prior to introduction into the test arena); the higher the relative metabolic rate of a fish compared to its opponent, the greater its probability of being dominant. In the 36 pairs of fish where the low relative metabolic rate fish was the subordinate, its competitive ability was significantly correlated with how closely the two fish were matched in terms of their relative metabolic rates. The smaller the difference between the relative metabolic rates of the dominant high relative metabolic rate fish and subordinate low metabolic rate fish, the greater the competitive ability and feeding success of the low relative metabolic rate subordinate. However, no such relation was found in the 19 pairs of fish where the high relative metabolic rate fish was the subordinate. In these pairs, the competitive ability of the subordinate high relative metabolic rate fish was correlated with its size relative to its dyad partner. The larger the dominant low relative metabolic rate fish, the lower the competitive ability of the subordinate high relative metabolic rate fish.     

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.     

维生素A缺乏致斑马鱼胚胎体节不对称及后脑图式形成异常

视黄酸(RA)在脊椎动物胚胎发生过程中发挥着关键作用。但是脊椎动物不能从头合成RA, 而必须以维生素A为前体通过视黄醇脱氢酶和视黄醛脱氢酶(Aldh1A)先将其氧化为视黄醛再氧化成RA。已知维生素A缺乏(VAD)会导致多种动物出现维生素A缺乏综合征, 但有关VAD对斑马鱼胚胎发育的影响尚未见报道。文章通过用不含维生素A及其他视黄类前体的饲料饲喂斑马鱼获得斑马鱼VAD胚胎。分析表明, 缺乏维生素A可导致斑马鱼胚胎体节出现不对称发育、胚胎的后脑图式形成异常。这些表型虽与aldh1a2基因敲落的及经醛脱氢酶抑制剂处理的斑马鱼胚胎表型类似, 但远不及后二者的严重, 提示VAD胚胎可能只是缺少而不是完全没有维生素A, 且可能存在不依赖视黄醛脱氢酶的RA合成途径。     

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.     

Use of trout serum to prepare primary attached monolayer cultures of hepatocytes from rainbow trout (Salmo gairdneri)

Summary The influence of trout serum on the attachment and spreading of isolated trout hepatocytes maintained in primary culture at different temperatures was evaluated. Hepatocytes were obtained from young rainbow trout (Salmo gairdneri) by collagenase dissociation and maintained in modified Leibowitz L15 medium at 10° or 27° C for 24 h in plastic dishes previously coated with type I bovine collagen. In the absence of serum, fewer than 10% of hepatocytes attached and none of them spread on the collagen substrate. Trout serum at concentrations as low as 1.25% in the medium resulted in a pronounced concentration-dependent increase in hepatocyte attachment, as determined by direct counts by phase contrast microscopy, or by percentage of lactate dehydrogenase activity attached to the dishes after washing away unattached cells. Attachment rates were greater at the lower temperature (10° C). Trout serum also substantially increased the proportion of attached hepatocytes that spread as monolayers on the collagen substrate, especially at 10° C. By comparison, fetal bovine serum had little influence on the attachment or spreading of trout hepatocytes. These studies demonstrate a simple inexpensive method for preparing attached monolayer trout hepatocyte cultures. This procedure may be useful in toxicologic or functional studies in which fish hepatocyte attachment is an operational requirement.     

Gill carbohydrate metabolism of rainbow trout is modified during gradual adaptation to sea water

The levels of glycogen and glucose, and the activities of several key enzymes of glycogenolysis, glycolysis and the pentose phosphate shunt were assessed in gills of rainbow trout of two sizes (97.03 ± 3.03 g and 165.69 ± 5.01 g) during gradual transfer to sea water (0, 9, 18 and 28 ppt). The results indicated changes, mainly size-independent, in carbohydrate metabolism of gills during gradual adaptation to sea water. Glucose availability in gills increased as a result of both higher glycogenolysis and greater supply of exogeneous glucose. This glucose was mainly used for increased glycolysis, providing the ATP needed to perform the hypo-osmoregulatory work occurring in gills during adaptation to sea water.     

Influence of temperature on silver accumulation and depuration in rainbow trout

To assess the influence of water temperature on silver uptake, rainbow trout Oncorhynchus mykiss ( c . 50 g; held at 13° C) were exposed to 0·1 μM AgNO₃ in ion‐poor water for 1 week at 4 and 16° C without previous temperature acclimation. To assess the influence of temperature on elimination of previously accumulated Ag, rainbow trout were exposed to 0·1 μM AgNO₃ in ion‐poor water for 1 week at 12° C, then were randomly divided amongst two Ag‐free water containers, differing only in temperature (3 and 16° C), for 2 months. In the uptake study greater accumulation of Ag was seen in the gills, plasma and especially the livers and bile of 'warm' rainbow trout (16° C) compared to 'cold' rainbow trout (4° C), which can be explained by the higher metabolic rates of the warmer fish. In the depuration study there was no net elimination of Ag from the livers and bile but there was biphasic elimination of Ag from the gills and plasma of 'warm' and 'cold' fish, but with few differences between them. This indicated that temperature‐dependent processes were less important in Ag elimination than in Ag uptake. Toxicokinetic modelling of Ag uptake by livers indicated four‐fold greater uptake of Ag by 'warm' rainbow trout compared to 'cold' rainbow trout (one compartment uptake model). Elimination of previously accumulated Ag from the plasma was best fitted by a two compartment rate‐constant based model, with approximately half the plasma Ag load eliminated within 24 h, followed by slower elimination of Ag over 2 months.     

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.     

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.     

Contrasting seasonal modulation of the stress response in male and female rainbow trout

Between June and September the magnitude of the plasma cortisol response of maturing male and female rainbow trout to confinement was indistinguishable. A progressive increase in confinement-induced cortisol levels in both sexes occurred during May to September, associated with the seasonal rise in water temperature. Between September and January a reduction of >50% in the magnitude of the cortisol response to confinement in male fish (but no decline in females) coincided with declining water temperature and significant increases in plasma 11-ketotestosterone and elevated plasma testosterone levels. Plasma oestradiol-17β levels were significantly greater in females than males throughout the study period and this difference was maximal between September and January. However, plasma testosterone was also elevated in females during this period and levels overall were higher than those in male fish. Previous studies have shown oestradiol-17β and testosterone to have diametrically opposed effects on stress responsiveness in trout, with the former enhancing, and the latter suppressing, the cortisol response to a stressor. The relative roles of androgens, estrogen and water temperature in modulating the stress responsiveness of rainbow trout are discussed.