Effects of temperature and body weight on growth rate and feed conversion ratio in turbot (Scophthalmus maximus)

Six size groups of hatchery produced turbot (2–499 g) were reared at six constant temperatures (10–25 °C). The results were used to develop a mathematical model for growth rate and feed conversion in turbot. At each temperature there were linear relationships between logarithms of (a) specific growth rate (G%/day) and body weight (W g), and (b) feed conversion ratio (FCR) and W. The slopes of the regressions were linearly related to temperature and the intercepts of the regression changed with temperature according to a second order polynomial. The optimal temperature for growth (T_opt.G) is predicted to decline with increasing body weight: T_opt.G = 22.45 − 0.713lnW, i.e. 22.5, 20.8, 19.1 and 17.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the growth rates of these fish sizes at their optimal temperature (G_max) were predicted to be 7.63, 2.73, 1.03 and 0.40%/day, respectively. The optimal temperature for feed conversion (T_opt.FCR) is also predicted to decline with increasing fish size: T_opt.FCR = 18.80 − 0.625lnW, i.e. 18.8, 17.4, 15.9 and 14.5 °C for 1, 10, 100 and 1000 g fish, respectively, and the predicted feed conversions of these fish sizes (FCR_min) were 0.44, 0.56, 0.68 and 0.82 for the present feed types. The growth model predicts that 2 g turbot can reach 743 and 619 g in 1 year when reared at T_opt.G and T_opt.FCR, respectively.     

Physiological response of temperature shocks in turbot and sole

In the present study, selected temperature drops were examined to investigate the effects of live chilling on stress and welfare in turbot and sole. This study demonstrated that rapid temperature drops from 11°C–12°C and 18°C–18.7°C to 4°C–0°C in turbot resulted in higher blood sodium and potassium at 0°C (164 mmol l^?1, 4.4 mmol ^?1) compared to 4°C (153 mmol l^?1, 3.1 mmol ^?1), indicating osmoregulatory disturbance. A rapid temperature drop from 18°C to 0°C in Senegal sole also resulted in higher blood sodium and potassium at 0°C (164 mmol l^?1, 4.8 mmol ^?1) compared to the control group at 18°C (157 mmol l^?1, 3.2 mmol ^?1). Based on present findings, we conclude that immersion in ice water will have a negative effect on the animal osmoregulatory capacity, and we recommend that turbot and sole are stunned before slaughter.     

Estradiol-17β-induced calcium uptake and resorption in juvenile rainbow trout,Oncorhynchus mykiss

Juvenile rainbow trout, Oncorhynchus mykiss, were injected with estradiol-17β (E₂) in order to study the source of extra calcium needed during vitellogenesis. E₂-treatment increased the calcium uptake from the external medium as well as calcium mobilization from muscle and scale. Judged by the increase in plasma protein-bound calcium levels, the E₂-induced increase in calcium uptake is an apparent over-mobilization of calcium, i.e., the calcium uptake of the fish is in excess of what is found bound to plasma proteins. As the calcium excretion and calcium space (calculated from free plasma calcium levels) were unaffected, the excess calcium is suggested to be incorporated into internal calcium stores. This implies that the systems regulating vitellogenesis and calcium balance are integrated on the mechanistic or endocrine level, and that E₂ causes calcium mobilization of a magnitude geared to the needs of the sexually maturing female.     

Tracking escaped Atlantic cod (Gadus morhua L.) aggregated around Norwegian farms: Considerations for management strategies

To examine site fidelity and potential for ecosystem impacts, 20 escapee cod (Gadus morhua L.) from fjord‐based cod farms were tagged with acoustic transmitters, released in the vicinity of the same farm, and their subsequent behaviour and survival monitored using a fixed array of acoustic receivers. Most individuals demonstrated high fidelity to their farm where tagged, and this increased during the polar night. Only five individuals (25%) were occasionally detected at another farm (4 km distance), and only three cod (15%) migrated out of the fjord during the 6‐month study period. Vertical movements were consistently greater in the hours around noon than at night, a behaviour inconsistent with that observed for wild fish. A high mortality rate (40%) was observed during the first 4 months post‐release, and actual mortality may have been even higher, limiting the potential for negative ecosystem effects from cod escapees. Findings from this study are used to discuss the development of recapture strategies for minimising potential impacts from cod escapees to ensure sustainable farming activity.     

The effect of water-borne magnesium on the dietary magnesium requirement of the rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) (mean initial weight 0.84 g) were fed diets containing graded levels of magnesium (Mg) (78 to 725µg/g) while being exposed to one of several levels in the rearing water (1.4 to 1000 mg/l). Uptake of Mg from the water, in Mg-deficient fish, was linearly related to the water Mg concentrated. It appears that the fish's Mg requirement can be met from either or both the diet or water. Under the experimental conditions, a water-borne concentration of 46 mg/l was calculated to be sufficient to meet the Mg requirement of the fish fed a Mg-free diet.     

Compensatory growth in Atlantic halibut: Effect of starvation and subsequent feeding on growth, maturation, feed utilization and flesh quality

A group of juvenile Atlantic halibut (mean, SD, 199.5 g, 44.7) was split into two experimental groups: one group was fed in excess twice a day and later five days a week (i.e. Control group), and the other group was starved for 5 weeks and then subsequently re-fed for 10 weeks (i.e. 5/10 starvation/re-fed group). This treatment was repeated for three years until the fish were harvested (mean final weight, 4.4 kg). A size +specific compensatory response was seen; partial compensation was observed in halibut weighing less than 500 g whereas full recovery growth was seen in halibut over 2 kg. Food consumption and feed conversion efficiency was measured during two full 5/10 starvation/re-fed cycles. The Control group consumed 86% more food in the measurement period, whereas the FCE 40% higher in the 5/10 starvation/re-fed group (FCE = 0.95) compared to the Control group (FCE = 0.68). In males lower gonadosomatic index (2.2 vs. 3.0) and plasma 11-ketotestosterone (0.22 vs. 1.26 ng ml^− 1) levels in the 5/10 starvation/re-fed group were observed during late winter and spring of 2006 (age 3 years) indicating higher age at 1st maturity. Starvation had a significant effect for improving the quality as starved fish had higher muscle pH (6.4 vs. 6.2), less gaping (0.1 vs. 0.3) and harder texture (61.4 vs. 57.6 N). Overall, the rearing on a repeated 5/10 starvation/re-fed regime for 3 years led to full growth compensation, higher feed conversion efficiency, lower male maturation and improved flesh quality.     

Predicting the temperature of the Barents Sea

Knowledge of the influence of the physical environment on commercially important fish stocks in the North Atlantic has increased during the last decade. To allow this information to be used in fisheries management, some forecast of the environment is important. Predictions of temperature in the Arcto-boreal Barents Sea have been given for many years, both as subjective opinions of scientists and implicitly in stock assessment assumptions of, e.g., mortality rates. To evaluate an objective statistical forecasting system, we have analysed time series representing mechanisms previously proposed as influencing the temperature of the Barents Sea. These include components of suggested periodic nature, large-scale advective effects, regional processes, and atmospheric teleconnections. The predictability of Barents Sea temperature based on the above mechanisms was evaluated through calculations of auto- and cross-correlations, linear regression, spectral analysis and autoregressive modelling. Forecasts based on periodic fluctuations in temperature performed poorly. Advection alone did not explain a major part of the variability. The precision of predictions six months ahead varied with season; forecasts from spring to autumn had least uncertainty. A first-order autoregressive model, including modelled atmospherically driven volume flux to the western Barents Sea during the preceding year and the position of the Gulf Stream off the eastern coast of the USA two years earlier, explained 50% of the total historical temperature variability.     

Growth performance,nutrient digestibility and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.     

Performance and welfare of Atlantic salmon,Salmo salar L. post-smolts in recirculating aquaculture systems: Importance of salinity and water velocity

Producing a larger post-smolt in recirculating aquaculture systems (RAS) could shorten the production time in sea cages and potentially reduce mortality. Knowledge of the biological requirements of post-smolts in closed-containment systems is however lacking. In the present study, the effects of salinity and water velocity on growth, survival, health, and welfare of Atlantic salmon reared in RAS were examined. Salmon smolts were stocked in three separate RAS with salinities of 12, 22, and 32‰ and subjected to high (1.0 body lengths per s⁻¹) or low (0.3 body lengths second⁻¹) water velocity. Growth performance, survival, welfare, and physiological stress responses were monitored until the fish reached a bodyweight of around 450 g. Growth rate was higher at lower salinity and higher water velocity generally had a positive effect on growth in all salinities. Feed conversion ratio was lower at 12‰ compared to the 22 and 32‰ when the fish were between 250 and 450 g. Higher mortality, elevated plasma cortisol levels, higher incidence of cataract, and a higher expression of stress-induced genes in the skin (iNOS, Muc5ac-like) indicated a negative effect of higher salinity on fish welfare. Male maturation was low (<1%), and not affected by salinity or water velocity.     

Selecting the hologenome to breed for an improved feed efficiency in pigs—A novel selection index

Most traits in animal breeding, including feed efficiency traits in pigs, are affected by many genes with small effect and have a moderately high heritability between 0.1 and 0.5, which enables efficient selection. Since the microbiota composition in the gastrointestinal tract is also partly heritable and was shown to have a substantial effect on feed efficiency, the host genes affect the phenotype not only directly by altering metabolic pathways, but also indirectly by changing the microbiota composition. The effect of the microbiota composition on the breeding value of an animal is the conditional expectation of its breeding value, given the vector with microbiota frequencies, that is The breeding value of an animal can therefore be decomposed into a heritable contribution that arises from an altered microbiota composition and a heritable contribution that arises from altered metabolic pathways within the animal, so Instead of selecting for breeding value , an index comprising the two components and with appropriate weights, that is , can be used. The present study shows how this breeding strategy can be applied in pig genomic selection breeding scheme for two feed efficiency traits and daily gain.