Stepwise temperature regulation and its effect on growth,feeding and muscle growth patterns of juvenile Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis> L.)

To investigate the possible direct effect of a stepwise reduction in temperature with increasing size on growth, feeding parameters and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.), 804 juvenile halibut (mean initial weight individuals: 14.2 g ± 0.2 SEM) were reared at constant 9, 12 and 15°C or shifted (T-step, i.e. 15–12°C after 36 days) for 99 days. Despite indications of lower optimal temperature for growth with increasing size, equal end weights were obtained between the constant 12°C, constant 15°C and T-step groups. Best overall growth was observed for the group kept at constant 12°C. The limited effect of the T-step group may relate to the size at movement (too big), the temperatures investigated (close to optimum) and the time and size interval investigated (too narrow). Differences in growth were reflected more by alterations in feed intake (C _T and F%) than by differences in feed conversion efficiencies (FCE). Differences were found with respect to the density of muscle cells, whereas no differences were found between the average muscle cell diameters. The mean diameter of muscle cells tended to increase only slightly with increasing fish weight, while the mean density of muscle cells tended to decrease. Using an optimum temperature of 12°C, an indication of a possible increased rate of hyperplasia in relation to higher growth was seen.     

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.     

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.     

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.