Muscle growth and development in normal-sex-ratio and all-female diploid and triploid Atlantic salmon

Determining patterns of motor recruitment during locomotion

Motor units are the functional units of muscle contraction in vertebrates. Each motor unit comprises muscle fibres of a particular fibre type and can be considered as fast or slow depending on its fibre-type composition. Motor units are typically recruited in a set order, from slow to fast, in response to the force requirements from the muscle. The anatomical separation of fast and slow muscle in fish permits direct recordings from these two fibre types. The frequency spectra from different slow and fast myotomal muscles were measured in the rainbow trout Oncorhynchus mykiss. These two muscle fibre types generated distinct low and high myoelectric frequency bands. The cat paw-shake is an activity that recruits mainly fast muscle. This study showed that the myoelectric signal from the medial gastrocnemius of the cat was concentrated in a high frequency band during paw-shake behaviour. During slow walking, the slow motor units of the medial gastrocnemius are also recruited, and this appeared as increased muscle activity within a low frequency band. Therefore, high and low frequency bands could be distinguished in the myoelectric signals from the cat medial gastrocnemius and probably corresponded, respectively, to fast and slow motor unit recruitment. Myoelectric signals are resolved into time/frequency space using wavelets to demonstrate how patterns of motor unit recruitment can be determined for a range of locomotor activities.

Sensitivity of muscle satellite cells to pollutants: an in vitro and in vivo comparative approach

Muscle satellite cells from rainbow trout were exposed in vitro to increasing concentrations of different xenobiotics: copper, dichloroaniline, prochloraz, nonyl-phenol polyethexylate. Mortality and proliferation rate were measured by Hoechst binding and BrdU incorporation. Dose dependent effect of copper on survival and proliferation was observed with an EC50 at 100 microM. A dose dependent effect of nonyl-phenol diethoxylate was observed on survival with an EC50 at 100 microM. This was associated with a biphasic effect on proliferation rate observed both for nonyl-phenol di and poly-ethoxylate: a stimulation of proliferation at low concentration and an inhibition proliferation at large concentration. These effects were related to the inhibition of cells adhesion through the detergent capacity of nonyl-phenol polyethoxylate. The effects of prochloraze and dichloroaniline on cells mortality (EC 50 > 500 microM) and proliferation rate (LOEC: 100 microM) were limited. Whole fish growth, muscle fibre size distribution and satellite cells survival and proliferation were measured on rainbow trout (60-80 g BW) exposed to two concentrations of prochloraze (10 and 100 microg/ml) or nonyl phenol diethoxylate IGEPAL 210 (100 and 400 microg/ml) during 14 and 10 days exposure, respectively. Muscle fibre size distribution and satellite cells proliferation were affected by prochloraz exposure in vivo and this could be related to the alteration in fish feeding status. The exposure to IGEPAL 210 affected the number of satellite cells extracted and induce a biphasic effect on satellite cells proliferation similar to that observed in vivo. The combined exposure to IGEPAL 210 and prochloraze revealed additive effects of these two compounds. The in vivo and in vitro comparison demonstrated that in vitro satellite cells system could be used as a valuable tool to test the effects of pollutants.

Early thermal experience has different effects on growth and muscle fibre recruitment in spring- and autumn-running Atlantic salmon populations

The consequence of early thermal experience for subsequent growth patterns was investigated in Atlantic salmon (Salmo salar L.). Spring- and autumn-running salmon were caught in upland (Baddoch) and lowland (Sheeoch) tributaries of the River Dee, Aberdeenshire, Scotland, respectively, on the final stages of their spawning migrations. The eggs were incubated at the simulated natural temperature regime of each stream, which was on average 2.8 degrees C lower for the Baddoch. The offspring, representing 11 families per population, were transferred at first feeding to constant environmental conditions (12–14 degrees C; 16h:8h light:dark photoperiod) and reared in replicate tanks. Salmon of both populations were longer and heavier at 6 and 12 weeks in fish initially reared under the cooler Baddoch regime. Length frequency distributions became bimodal after 18 weeks, and only the upper growth mode was studied. Modelling of length distributions at 40 weeks revealed significantly different patterns of muscle growth according to initial temperature regime, but only for the Sheeoch salmon. In fish of Sheeoch origin, significantly more white muscle fibres were recruited per mm(2) increase in myotomal cross-sectional area at Sheeoch than at Baddoch temperatures (P<0.01). After 40 weeks, the density of white fibres was 10.4 % higher in fish initially reared at the Sheeoch (533+/−6 mm(−2)) than at the Baddoch (483+/−5 mm(−2)) thermal regimes (means +/− s.e.m., 16 fish per group; P<0.001). Muscle satellite cells were identified using an antibody to c-met. At 24 weeks, the density of muscle satellite cells was 29 % higher in Sheeoch salmon reared to first feeding at the temperature of their natal stream than at cooler Baddoch temperatures (P<0.01). In contrast, the number and size distributions of white muscle fibres in the myotomes of Baddoch salmon were independent of early thermal experience.

Phenotypic plasticity of early myogenesis and satellite cell numbers in atlantic salmon spawning in upland and lowland tributaries of a river system

Early myogenesis was studied in the offspring of Atlantic salmon (Salmo salar L.) spawning in a lowland (Sheeoch) and an upland (Baddoch) tributary of the River Dee System, Aberdeenshire, Scotland. Eggs from each population were incubated at the simulated natural thermal regimes of each stream, which was on average 2.8 degrees C cooler for the Baddoch than for the Sheeoch. Relationships between muscle cellularity variables, the density of myonuclei and responses to temperature were investigated using multivariate statistical techniques. These revealed highly significant temperature effects (P<0.001) at hatch (H) and first feeding (FF) and significant interactions between population and temperature (P<0.001), indicating that Baddoch and Sheeoch salmon responded differently to the two temperature regimes. The total cross-sectional area of white muscle (WF.ta) at the adipose fin was relatively independent of temperature at hatch and first feeding in the Sheeoch population. In contrast, for alevins of Baddoch origin, WF.ta was 18.9% (H) and 30.5% (FF) higher in fish incubated at Baddoch than at Sheeoch temperatures. At hatch, there were 15.6% more white muscle fibres (WF.no) at the cooler incubation temperature in fish of Sheeoch origin and 6.0% more in fish of Baddoch origin. However, by first feeding, the difference in WF.no between temperatures had narrowed to 7.2% in the Sheeoch fish and increased to 17.4% in the Baddoch population. In contrast, at hatch, the density of myonuclei was 59.8% higher at the warmer incubation temperature in the Sheeoch population and 23.5% higher in the Baddoch population, but differences were less evident at first feeding. In Baddoch fish, 22.5% of the total muscle nuclei were actively dividing at first feeding, as assessed by staining for proliferating cell nuclear antigen (PCNA). Of the PCNA-positive nuclei, 78% were present in cells that stained for the c-met tyrosine kinase receptor, a marker of satellite cells and their division products. The proportion of c-met-positive cells staining for individual myogenic regulatory factors was 72.4% for the myogenic transcription factor MyoD, 76.3% for the myogenic transcription factor Myf-5, 62.1% for myogenin and 48.7% for the myogenic transcription factor Myf-6. For the Sheeoch population, there were 26.5% more c-met-expressing (P<0.01) and 23.2% more myogenic-regulatory-factor-expressing (P<0.05) cells at Sheeoch than at Baddoch temperatures. In contrast, incubation temperature had no significant effects on satellite cell density in the Baddoch population.

A novel rod-like opsin isolated from the extra-retinal photoreceptors of teleost fish

We have isolated a novel opsin from the pineal complex of Atlantic salmon (Salmo salar) and from the brain of the puffer fish (Fugu rubripes). These extra-retinal opsins share approximately 74% identity at the nucleotide and amino acid level with rod-opsins from the retina of these species. By PCR, we have determined that the novel rod-like opsin is not expressed in the salmon retina, and the retinal rod-opsin is not expressed in the salmon pineal. Phylogenetic analysis suggests that the rod-like opsins arose from a gene duplication event approximately 205 million years ago, a time of considerable adaptive radiation of the bony fish. In view of the large differences in the coding sequences of the pineal/brain rod-like opsins, their extra-retinal sites of expression, and phylogenetic position we have termed these novel opsins 'extra-retinal rod-like opsins' (ERrod-like opsins). We speculate that the differences between retinal rod-opsins and ERrod-like opsins have arisen from their differing photosensory roles and/or genetic drift after the gene duplication event in the Triassic.