Gut size in GH‐transgenic coho salmon is enhanced by both the GHtransgene and increased food intake

Growth hormone transgenic coho salmon Oncorhynchus kisutch fed at the same ration level as non‐transgenic controls (Tc) had the same growth rate as non‐transgenic controls (Nt). In contrast, growth hormone transgenic coho salmon (Tf) fed ad libitum ate about twice as much and had much higher growth rates than the other two groups. The most obvious result was the significantly larger caeca in the Tf group relative to both Nt or pair‐fed Tc. The Tf fish had more caeca that were longer. The results suggested that the effect was indirect and the enlarged caeca required both the GHtransgene and hyperphagia to cause enlarged caecal capacity. A small part of the results, however, also suggested that there was a direct effect of the GHtransgene on some gut tissues, particularly the intestine.     

Disease resistance and health parameters of growth-hormone transgenic and wild-type coho salmon,Oncorhynchus kisutch

To extend previous findings regarding fish health and disease susceptibility of growth-enhanced fish, hematological and immunological parameters have been compared between growth hormone (GH) transgenic and wild-type non-transgenic coho salmon (Oncorhynchus kisutch). Compared to non-transgenic coho salmon, transgenic fish had significantly higher hematocrit (Hct), hemoglobin (Hb), mean cellular hemoglobin (MCH), mean cellular volume (MCV), and erythrocyte numbers, and lower white cell numbers. In addition, resistance to the bacterial pathogen Aeromonas salmonicida (causal agent of furunculosis) has been assessed between the strains. Higher susceptibility of transgenic fish to this disease challenge was observed in two separate year classes of fish. The present findings provide fundamental knowledge of the disease resistance on GH enhanced transgenic coho salmon, which is of importance for assessing the fitness of transgenic strains for environmental risk assessments, and for improving our understanding effects of growth modification on basic immune functions.     

Short‐term freshwater exposure benefits sea lice‐infected Atlantic salmon

Atlantic salmon Salmo salar were infected with sea lice Lepeophtheirus salmonis (0·08 ± 0·007 sea lice g⁻¹) over a period of 4 h. Both infected and non‐infected fish were swim tested in sea water (SW) and fresh water (FW). The ventral aorta of each fish was fitted with a Doppler cuff in order to measure cardiac output, stroke volume and heart rate during swim testing. Blood samples were taken at rest and after exercise. Critical swimming speed of infected fish in SW (2·14 ± 0·08 body lengths, bl s⁻¹) was significantly lower ( P  < 0·05) than infected fish switched to FW (2·81 ± 0·08 bl s⁻¹) and non‐infected fish in SW (2·42 ± 0·04 bl s⁻¹) and FW (2·61 ± 0·08 bl s⁻¹). Cardiac and blood results indicated infected fish exposed to FW did experience stress, but relief from osmotic and ionic distress probably reduces energy expenditure, allowing the increase in performance. As the performance of sea lice‐infected fish improved upon transfer to FW, it is likely that heavily infected salmonids do return to FW to restore compromised osmotic and ionic balance, and remove sea lice in the process.     

Oxygen uptake of growth hormone transgenic coho salmon during starvation and feeding

Oxygen uptake of growth hormone transgenic coho salmon Oncorhynchus kisutch was measured in individual fish with a closed-system respirometer and was compared with that of similar-sized non-transgenic control coho salmon during starvation and when fed a fixed ration or to satiation. Transgenic and control fish did not differ in their standard oxygen uptake after 4 days of starvation, although control fish had a higher routine oxygen uptake, scope for spontaneous activity and initial acclimation oxygen uptake. During feeding, transgenic fish ate significantly more than control fish, and had an overall oxygen uptake that was 1·7 times greater than control fish. When fish that had eaten the same per cent body mass were compared, transgenic fish had an oxygen uptake that was 1·4 times greater than control fish. Differences in oxygen uptake in growth hormone transgenic coho salmon and non-transgenic fish appear to be due to the effects of feeding, acclimation and activity level, and not to a difference in basal metabolism.     

Determination of body shape variation in Irish hatchery‐reared and wild Atlantic salmon

Discriminant function analysis was used to distinguish morphologically between samples of parr, smolts and adult Atlantic salmon Salmo salar from several hatchery and river systems in Ireland. The effect of habitat shift was investigated in Atlantic salmon parr. Parr grown from the eyed‐egg stage with a non‐sibling group in a hatchery environment, came to resemble the mean body shape of their host hatchery Atlantic salmon stock more closely than that of a full sibling group grown at their natal hatchery. Wild Atlantic salmon smolts differed in shape from hatchery‐reared smolts. This difference was less pronounced, but still statistically significant when wild adults were compared with hatchery‐reared adults captured in the coastal drift‐net fishery after a year spent at sea. Rearing conditions had a significant impact on the production and growth of fish body shape. This in turn may have affected adaptability and survivorship of ranched Atlantic salmon in the marine environment.     

Rearing in Seawater Mesocosms Improves the Spawning Performance of Growth Hormone Transgenic and Wild-Type Coho Salmon

Growth hormone (GH) transgenes can significantly accelerate growth rates in fish and cause associated alterations to their physiology and behaviour. Concern exists regarding potential environmental risks of GH transgenic fish, should they enter natural ecosystems. In particular, whether they can reproduce and generate viable offspring under natural conditions is poorly understood. In previous studies, GH transgenic salmon grown under contained culture conditions had lower spawning behaviour and reproductive success relative to wild-type fish reared in nature. However, wild-type salmon cultured in equal conditions also had limited reproductive success. As such, whether decreased reproductive success of GH transgenic salmon is due to the action of the transgene or to secondary effects of culture (or a combination) has not been fully ascertained. Hence, salmon were reared in large (350,000 L), semi-natural, seawater tanks (termed mesocosms) designed to minimize effects of standard laboratory culture conditions, and the reproductive success of wild-type and GH transgenic coho salmon from mesocosms were compared with that of wild-type fish from nature. Mesocosm rearing partially restored spawning behaviour and success of wild-type fish relative to culture rearing, but remained lower overall than those reared in nature. GH transgenic salmon reared in the mesocosm had similar spawning behaviour and success as wild-type fish reared in the mesocosm when in full competition and without competition, but had lower success in male-only competition experiments. There was evidence of genotype×environmental interactions on spawning success, so that spawning success of transgenic fish, should they escape to natural systems in early life, cannot be predicted with low uncertainty. Under the present conditions, we found no evidence to support enhanced mating capabilities of GH transgenic coho salmon compared to wild-type salmon. However, it is clear that GH transgenic salmon are capable of successful spawning, and can reproduce with wild-type fish from natural systems.     

Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions

The lifetime success and performance characteristics of communally reared offspring of wild native Burrishoole (native), ranched native (ranched) and non‐native (non‐native) Atlantic salmon Salmo salar from the adjacent Owenmore River were compared. Non‐native 0+ year parr showed a substantial downstream migration, which was not shown by native and ranched parr. This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic conditions within the Owenmore River catchment where the main nursery habitat is downstream of the spawning area. There were no differences between native and ranched in smolt output or adult return. Both of these measures, however, were significantly lower for the non‐native group. A greater proportion of the non‐native Atlantic salmon was taken in the coastal drift nets compared to the return to the Burrishoole system, probably as a result of the greater size of the non‐native fish. The overall lifetime success of the non‐native group, from fertilized egg to returning adult, was some 35% of native and ranched. The ranched group showed a significantly greater male parr maturity, a greater proportion of 1+ year smolts, and differences in sex ratio and timing of freshwater entry of returning adults compared to native, which may have fitness implications under specific conditions.     

Oxidative stress in growth hormone transgenic coho salmon with compressed lifespan - a model for addressing aging

Abstract Growth hormone (GH) transgenic fish have dramatically enhanced growth rates, increased oxygen demands and reactive oxygen species production. GH-transgenic coho salmon provide an opportunity to address effects of increased metabolism on physiological aging. The objective of this study was to compare oxidative stress in wild-type (WT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch) of different ages (1 and 2 years). Antioxidant enzyme activity, protein carbonyls (PC) and glutathione (GSH, GSSG) were measured. PC correlated to growth rates in individual fish. T fish exhibited lower antioxidant enzyme activities and GSH levels compared to the WT, while levels of PC and GSSG were higher. Age affects were observed in both WT and T fish; enzyme activities and GSH decreased while PC and GSSG increased. Our results support the metabolic rate theory of aging. This study aims to be a platform for continued studies of the theories of aging using fish as model organisms.     

The effect of exercise and captivity on energy partitioning, reproductive maturation and fertilization success in adult sockeye salmon

Releasing a population of adult Fraser River sockeye salmon Oncorhynchus nerka from an energetically more expensive non‐feeding natural migration (1089 km, natal groups) and allowing them to sexually mature in either a moderate flow (captive exercise group) or a no flow (captive non‐exercise group) environment resulted in significant differences in body energy densities (MJ kg⁻¹) among groups (ranked: initial natural migrator > non‐exercise > exercise > natal arrivals). Similarly, per cent body lipids were significantly lower in exercise females compared with non‐exercise females, experimentally confirming the central role lipid catabolism has in powering swimming. Although restricting exercise did result in greater body energy reserves at spawning, this did not result in a reallocation of energy to reproduction, as fecundity, egg size and gonad composition were unchanged among the groups. Furthermore, non‐exercise females had delayed maturity, lower egg deposition rates, and were more likely to die prior to egg ovulation than exercise females and natal spawners. Eggs from captive exercise adult females were more likely to survive to the eyed stage than eggs from captive non‐exercise females, but both captive groups had significantly lower egg fertilization success than natal spawners suggesting that confinement stress played a role in some of results presented. There were no significant differences in plasma levels of glucose, lactate, cortisol and reproductive hormones among the groups, but correlations among acute and chronic indicators of stress were significant among individuals. These results indicate that exercise during the late stages of maturation, as might occur normally, may be required for optimizing reproductive maturation and maximizing reproductive success.     

Oxidative stress in growth hormone transgenic coho salmon with compressed lifespan – a model for addressing aging

Abstract

Growth hormone (GH) transgenic fish have dramatically enhanced growth rates, increased oxygen demands and reactive oxygen species production. GH-transgenic coho salmon provide an opportunity to address effects of increased metabolism on physiological aging. The objective of this study was to compare oxidative stress in wild-type (WT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch) of different ages (1 and 2 years). Antioxidant enzyme activity, protein carbonyls (PC) and glutathione (GSH, GSSG) were measured. PC correlated to growth rates in individual fish. T fish exhibited lower antioxidant enzyme activities and GSH levels compared to the WT, while levels of PC and GSSG were higher. Age affects were observed in both WT and T fish; enzyme activities and GSH decreased while PC and GSSG increased. Our results support the metabolic rate theory of aging. This study aims to be a platform for continued studies of the theories of aging using fish as model organisms.     

Susceptibility of turbot (Scophthalmus maximus), coho salmon (Oncorhynchus kisutch, and rainbow trout of. my kiss) to strains of Vibrio anguillarum and their exotoxins

The susceptibility of turbot, coho salmon, and rainbow trout to strains of Vibrio anguillarum of serotypes 01 and 02 and their extracellular products (ECP) was investigated in order to clarify the role of exotoxins in the mechanism of virulence of both serotypes. All V. anguillarum isolates were virulent for trout, salmon, and turbot. Despite the origin of the strains tested, rainbow trout was the most susceptible fish species to experimentally induced vibriosis. Coho salmon and turbot did not differ significantly in their susceptibility to V. anguillarum live cells. In contrast, the ECP from Vibrio strains of serotypes 01 and 02 exhibited similar lethal dose for turbot, salmon, and trout (ranging from 4.52 to 7.32 μg protein/g fish). Therefore, differences in susceptibility to vibriosis are not completely due to a differential sensitivity of fish to the extracellular products of Vibrio strains. The ECP from 7 of 10 V. anguillarum strains possessed vascular permeability factors, and all the extracts displayed proteolytic, hemolytic and cytotoxic activities. All the biological activities of ECP were lost after heat treatment at 80° C/10 min.     

Genetic evidence for lacustrine spawning of the non‐anadromous Atlantic salmon population of Little Gull Lake, Newfoundland

Allozyme markers were used to investigate the spatial boundaries of the non‐anadromous Atlantic salmon population of Little Gull Lake, Eastern Canada. Mixed year class samples of juvenile salmon were analysed from inlet streams, upstream lakes, the outlet river and sites downstream. No evidence was found that individuals from the Lake's non‐anadromous population were present in these samples, strongly suggesting that the non‐anadromous population is confined to the lake and has a lacustrine spawning habit.     

Swimming performance, oxygen consumption and excess post-exercise oxygen consumption in adult transgenic and ocean-ranched coho salmon

Routine oxygen consumption ( M o ₂) was 35% higher in 1 day starved and 21% higher in 4 day starved adult transgenic coho salmon Oncorhynchus kisutch relative to end of migration ocean-ranched coho salmon. Critical swimming speed ( U _crit) and M o ₂ at U _crit ( M o _2max) were significantly lower in 4 day starved transgenic coho salmon (1·25 BL s⁻¹; 8·79 mg O₂ kg⁻¹ min⁻¹) compared to ocean-ranched coho salmon (1·60 BL s⁻¹; 9·87 mg O₂ kg⁻¹ min⁻¹). Transgenic fish swam energetically less efficiently than ocean-ranched fish, as indicated by a poorer swimming economy at U _crit ( M o _2max     ). Although M o _2max was lower in transgenic coho salmon, the excess post-exercise oxygen consumption (EPOC) measured during the first 20 min of recovery was significantly larger in transgenic coho salmon (44·1 mg O₂ kg⁻¹) compared with ocean-ranched coho salmon (34·2 mg O₂ kg⁻¹), which had a faster rate of recovery.     

Embryo survival and smolt to adult survival in second‐generation outbred coho salmon

Outbreeding depression was not detectable in observations of embryonic survival and of survival of smolts to adulthood relative to controls in coho salmon Oncorhynchus kisutch experimentally outbred over two generations by crossing fish from three widely separated populations. Survival in outbred coho salmon was not detectably less than that in second‐generation hybrid controls or second‐generation parental controls. Variation of embryonic survival was affected by the maternal source population and by individual females but not by the paternal source population or by individual males. Survival of smolts to adulthood at sea was greater in one second‐generation control group than in two others, but survival in second‐generation outbred groups was no less than in parental controls or hybrid controls.     

Antimicrobial peptides protect coho salmon from Vibrio anguillarum infections

Fish losses from infectious diseases are a significant problem in aquaculture worldwide. Therefore, we investigated the ability of cationic antimicrobial peptides to protect against infection caused by the fish pathogen Vibrio anguillarum. To identify effective peptides for fish, the MICs of certain antimicrobial peptides against fish pathogens were determined in vitro. Two of the most effective antimicrobial peptides, CEME, a cecropin-melittin hybrid peptide, and pleurocidin amide, a C-terminally amidated form of the natural flounder peptide, were selected for in vivo studies. A single intraperitoneal injection of CEME did not affect mortality rates in juvenile coho salmon infected with V. anguillarum, the causative agent of vibriosis. Therefore, the peptides were delivered continuously using miniosmotic pumps placed in the peritoneal cavity. Twelve days after pump implantation, the fish received intraperitoneal injections of V. anguillarum at a dose that would kill 50 to 90% of the population. Fish receiving 200 microg of CEME per day survived longer and had significantly lower accumulated mortalities (13%) than the control groups (50 to 58%). Fish receiving pleurocidin amide at 250 microg per day also survived longer and had significantly lower accumulated mortalities (5%) than the control groups (67 to 75%). This clearly shows the potential for antimicrobial peptides to protect fish against infections and indicates that the strategy of overexpressing the peptides in transgenic fish may provide a method of decreasing bacterial disease problems.     

Antimicrobial Peptides Protect Coho Salmon from Vibrio anguillarum Infections

Fish losses from infectious diseases are a significant problem in aquaculture worldwide. Therefore, we investigated the ability of cationic antimicrobial peptides to protect against infection caused by the fish pathogen Vibrio anguillarum. To identify effective peptides for fish, the MICs of certain antimicrobial peptides against fish pathogens were determined in vitro. Two of the most effective antimicrobial peptides, CEME, a cecropin-melittin hybrid peptide, and pleurocidin amide, a C-terminally amidated form of the natural flounder peptide, were selected for in vivo studies. A single intraperitoneal injection of CEME did not affect mortality rates in juvenile coho salmon infected with V. anguillarum, the causative agent of vibriosis. Therefore, the peptides were delivered continuously using miniosmotic pumps placed in the peritoneal cavity. Twelve days after pump implantation, the fish received intraperitoneal injections of V. anguillarum at a dose that would kill 50 to 90% of the population. Fish receiving 200 μg of CEME per day survived longer and had significantly lower accumulated mortalities (13%) than the control groups (50 to 58%). Fish receiving pleurocidin amide at 250 μg per day also survived longer and had significantly lower accumulated mortalities (5%) than the control groups (67 to 75%). This clearly shows the potential for antimicrobial peptides to protect fish against infections and indicates that the strategy of overexpressing the peptides in transgenic fish may provide a method of decreasing bacterial disease problems.     

Transgenesis changes body and head shape in Pacific salmon

Insertion of a pOnMTGH1 gene construct into coho salmon altered centroid size significantly (P<0·05). The dorsal caudal peduncle and abdominal regions were also distinctly enhanced in transgenic fish when compared to controls. Shape change patterns of both whole body and syncranium were prominent.     

Gill Morphometry in Growth Hormone Transgenic Pacific Coho Salmon,Onchorhynchus kisutch,Differs Markedly from that in GH Transgenic Atlantic Salmon

In a previous study we showed that many of the morphological features of the respiratory system of GH (growth hormone) transgenic Atlantic salmon are greater than similarly sized control salmon. Here we show that the manifestation of GH transgene is similar in two different lines of GH transgenic Pacific coho salmon, but that it is very different from that in the GH transgenic Atlantic salmon. The GH transgenic Pacific coho salmon do not have a larger gill surface area than similarly sized control fish.     

Coho salmon haematological, metabolic and acid‐base changes during exercise and recovery in sea water

Cannulated, seawater‐acclimated coho salmon Oncorhynchus kisutch were swum to exhaustion in a seawater tunnel (10° C, mean U _crit 50 cm s⁻¹), resulting in metabolic acidosis and increased plasma electrolyte and cortisol concentrations, which were corrected during a 4 h recovery. Because the swimming and physiological performance data were similar to those of other salmonids, it was concluded that life‐history limitations, besides their exercise capabilities in upwelling zones, probably explain declining coho salmon populations.     

Increased intrinsic growth rate is advantageous even under ecologically stressful conditions in coho salmon (<Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis>)

Growth rate is an ecologically important trait, affecting the energy acquisition from, and provisioning to, the surrounding community. One of many costs suggested to counteract the evolution of increased intrinsic growth rate is an associated reduction in tolerance to conditions of nutrient stress. Here we test this concept with individuals possessing experimentally increased intrinsic growth rates (growth hormone transgenic coho salmon, Oncorhynchus kisutch) relative to wild genotypes. Using a series of three experiments, survival and growth of both genotypes were assessed on a physiological and behavioral level while varying food abundance, social interactions, and predation risk. Only in complete absence of exogenous food in newly emerged fry did the high intrinsic growth rate appear costly with a shorter average survival time compared to wild-type (Exp. 1). In experiment 2, genotypes with elevated intrinsic growth showed equal or higher survival and growth than wild-type genotypes In a third experiment, adding very limited amounts of food and allowing for social interactions in a simulated natural environment benefited transgenic individuals relative to wild-types, but at similar magnitudes in both the absence and presence of predators. Populations with transgenic individuals present did not crash under these competitive conditions as previously reported when studied in simple environments where hiding and attack escape were not possible. Our data suggest that transgenic fish have a greater scope for growth under most conditions, but are not obligated to use this capability. Physiological (e.g. appetite and conversion efficiency) and behavioral traits (e.g. competitive ability and risk-taking) found previously to correlate positively with intrinsic growth rate in the transgenic strain likely aided in their survival and growth, even under food limited conditions. Hence, at least in coho salmon, intrinsic growth rate does not appear to strongly affect survival under nutrient stress.