Effects of short‐term starvation periods on flesh quality in Arctic charr (Salvelinus alpinus) in different seasons

Possible effects of short‐term starvation on flesh quality in Arctic charr were studied in spring (March) and summer (August). Groups of juvenile Arctic charr (mean weight March 536 g ± 24; August 461 g ± 15 SEM) were starved for 1, 2 and 4 weeks (March) and 1, 2 and 3 (August). After each starvation period, the fish were slaughtered, and flesh samples collected in order to investigate quality and textural properties in the different experimental groups. Starvation had a positive effect on flesh quality giving firmer texture and lower gaping scores. Starved fish had lower cathepsin activity at slaughter, and a similar difference was seen one‐week post mortem. The results showed that the effect of starvation period was seasonally dependent. Starvation had a larger effect in summer, where a three‐week starvation resulted in firmer texture, whereas this was not seen during spring.     

Effects of restricted feeding regimes on growth and feed conversion on juvenile green sea urchin,Strongylocentrotus droebachiensis

Groups of juvenile green sea urchin, Strongylocentrotus droebachiensis (average wet weight = 3.3 g), were fed five different dry feed rations (0.2%, 0.4%, 0.8%, 1.2% and 2.4% of their body weight per week) under constant light and temperature conditions for 160 days (Experiment I) in groups to examine growth effects, and for 40 days as individual treatments (Experiment II) to examine feeding efficiency. There was 100% survival of the sea urchins during both experiments. In Experiment I, the lowest ration group (0.2%) had significantly lower growth than the rest of the groups. There was no significant differences in growth between the sea urchin fed ration over 0.4% dry feed of the body wet weight per week. In Experiment II, the lowest feed ration groups (0.2%) had significant lowest growth but had the best feed conversion ratio (FCR), using 0.5 g of feed of dry feed per gram of sea urchin wet weight body growth. The FCR increased with increasing feed ration and the 2.4% group had the poorest FCR, using 1.3 g of feed per gram weight gain. Results from Experiments I and II illustrate that juvenile green sea urchin can grow at a restricted feed ration that is under maximum feed intake, without reduction in growth.     

Ultrasound as potential inhibitor of salmon louse infestation—A small‐scale study

The effect of ultrasound exposure during controlled infection with salmon lice, Lepeophtheirus salmonis, has been studied. Salmon were placed in tanks with salmon lice copepodids for 1 hr, while simultaneously being exposed to sound frequencies of 9.3, 21 or 54 kHz. The sound transducers were operated at maximum power levels, and the 9.3 kHz transducer generated the highest sound level (220.6 dB). Only the group exposed to 9.3 kHz displayed a significant reduction in louse infestation. However, the observed effect of ultrasound was relatively small, and in a practical implementation in sea cages, the sound intensity will be lower than that used in the experiments. It is also possible that the observed reduction in infestation is due to ultrasonic cavitation effects, which are only present at a very short range from the ultrasound source. We therefore do not consider ultrasound a feasible method for preventing attachment of salmon lice copepodids on salmon in cage farms.     

Change in flesh quality associated with early maturation of Atlantic halibut (Hippoglossus hippoglossus)

To determine the effect of maturation on flesh quality, 20 Atlantic halibut (Hippoglossus hippoglossus) consisting of mature and immature fish of both sexes were killed on site, exsanguinated and stored on ice. After 6 days of storage, the fish was gutted and filleted before colour, texture hardness and shear force were evaluated to determine the effect of maturation. Results show that mature males excreted black mucus from the skin during ice storage, while a greyish mucus was observed from immature fish. Mature fish had approximately 2% lower slaughter yield and 6% lower fillet yield compared with immature fish. The fillets from mature males were significantly harder compared with fillets from immature fish and the muscle structure proved to be stronger as an increased fracturability was observed in mature fish. In colour, fillets from mature fish proved to have a whiter appearance (L^*) than immature fish, while no difference was seen in a^* and b^* values. We conclude that the physiological changes associated with maturation affects the end quality, and may be related to slower growth.     

Growth, feed conversion efficiency and growth heterogeneity in Atlantic halibut (Hippoglossus hippoglossus) reared at three different photoperiods

Juvenile Atlantic halibut, Hippoglossus hippoglossus (initial weight (SD) 191.3 (±44.7)) g, were reared for 99 days at a constant temperature of 11°C and subjected to three different light regimes from 13 September to 21 December: continuous light (LD24:0), simulated natural photoperiod of Bergen (60°25′N, LDN) and constant 20 h light:4 h dark (LD20:4). The fish reared on the different photoperiod regimes differed in their growth patterns as juveniles exposed to long days, i.e. LD20:4 and LD24:0, exhibited faster growth than those experiencing a natural photoperiod. The LD20:4 group showed the highest average specific growth rate (0.72% body weight day^?1), whereas fish on LDN displayed the lowest average specific growth rate (0.60% body weight day^?1). The final mean weights of the LD20:4 and the LD24:0 groups were 15% and 12% higher than those of the LDN group. Dividing the duration of the experiment into three time periods shows that the LD20:4 and LD24:0 had a higher feed conversion efficiency (FCE) as compared with the LDN group during the first and the last period, while a reversed situation was observed in the second period. Our data indicate a larger variation in growth rates among individuals in the best‐performing groups (here LD20:4 and LD24:0). This may indicate that formation of size hierarchies is more pronounced in groups with more homogenous growth (here LDN). Overall, our findings indicate that extended light regimes result in faster growth and better feed conversion in juvenile Atlantic halibut. In line with findings on other flatfish species, this supports the concept that constant long day:short night or continuous light regimes should be used by the farmer in order to maximize growth and improve feed conversion in Atlantic halibut.     

Comparisons of RNA/DNA Ratios, Growth, and Metabolism in Different Populations of Juvenile Turbot Scophthalmus maximus Reared at Four Temperatures

We compared RNA/DNA ratios, growth and routine oxygen consumption in populations of juvenile turbot from Norway, Scotland, and France reared at low (10 C), medium (14 C, 18 C) and high (22 C) temperatures. The relationships between growth and RNA/DNA ratios differed between temperatures, although they were always positive. Growth and RNA/DNA of the Norwegian fish were higher than those of the other populations especially at the two highest temperatures (18 C and 22 Q. Minor differences were found between the Scottish and French populations. Fish from the Norwegian population displayed the lowest oxygen consumption at these temperatures (146 and 270, 182 and 310, 192 and 328 mg O₂/kg per d, for 18 and 22 C, and Norwegian, French, and Scottish populations, respectively). Growth differences did not conform to a simple thermal adaptation model, but might represent an example of countergradient variation in growth. The findings have implications for turbot culture, particularly in selection focusing on growth performance.     

Worm control practice against gastro-intestinal parasites in Norwegian sheep and goat flocks

Background

Anthelmintic treatment is the most common way of controlling nematode infections in ruminants. However, several countries have reported anthelmintic resistance (AR), representing a limitation for sustainable small ruminant production. The knowledge regarding worm control management represents a baseline to develop a guideline for preventing AR. The aim of the present study was therefore to improve our knowledge about the worm control practices in small ruminant flocks in Norway.

Methods

A questionnaire survey regarding worm control practices was performed in small ruminant flocks in Norway. Flocks were selected from the three main areas of small ruminant farming, i.e. the coastal, inland and northern areas. A total of 825 questionnaires, comprising 587 sheep flocks (return rate of 51.3%) and 238 goat flocks (52.6%) were included.

Results

The results indicated that visual appraisal of individual weight was the most common means of estimating the anthelmintic dose used in sheep (78.6%) and goat (85.1%) flocks. The mean yearly drenching rate in lambs and ewes were 2.5 ± 1.7 and 1.9 ± 1.1, respectively, whereas it was 1.0 (once a year) in goats. However, these figures were higher in sheep in the coastal area with a rate of 3.4 and 2.2 in lambs and ewes, respectively. Benzimidazoles were the predominant anthelmintic class used in sheep flocks (64.9% in 2007), whereas benzimidazoles and macrocyclic lactones were both equally used in dairy goat flocks. In the period of 2005-2007, 46.3% of the sheep flocks never changed the anthelmintic class. The dose and move strategy was practiced in 33.2% of the sheep flocks.

Conclusions

The present study showed that inaccurate weight calculation gives a risk of under-dosing in over 90% of the sheep and goat flocks in Norway. Taken together with a high treatment frequency in lambs, a lack of anthelmintic class rotation and the common use of a dose-and-move strategy, a real danger for development of anthelmintic resistance (AR) seems to exist in Norwegian sheep and goat flocks. This risk seems particularly high in coastal areas where high treatment frequencies in lambs were recorded.     

Environmental problems,productivity and innovations in Norwegian salmon aquaculture

Abstract

Environmental issues have been of central importance throughout the history of salmon aquacuiture in Norway. In this paper we will examine some of the issues, and show that while there are still problems, many have also been resolved. A major reason for this is the fact that salmon farmers have internalized many of the environmental effects into their decision‐making due to the relationship between environmental impact and productivity. Another reason, particularly when it comes to treatment of diseases, is that lack of private innovative activity due to different market failures has been compensated for by government‐sponsored research and development.     

Forecasting weekly salmon prices: Risk management in fish farming

Abstract

Production of farmed salmon has increased substantially during the last decade. Most of the salmon production is sold spot, resulting in large price fluctuations both for the producer and for the exporter. No derivative markets exist; consequently, no one can hedge prices. If prices could be forecasted within reasonable confidence bounds, risk would be reduced. This study used six easily applicable procedures to forecast weekly producer prices for salmon. The procedures tested were Classical Additive Decomposition (CAD), Holt Winters Exponential Smoothing (HW), Auto Regressive Moving Average (ARMA), Vector Auto Regression (VAR) and two different naïve models: post‐sample predictive accuracy was evaluated. Results indicated that the CAD model forecasted the direction of price movements best, whereas the VAR model performed best according to accuracy measures.