We combined genetic selection and dietary treatment to produce a model to study metabolic pathways involved in genetic and nutritional control of fat deposition in fish muscle. Two experimental lines of rainbow trout, selected for a lean (L) or fat (F) muscle, were fed with diets containing either 10 or 23% lipids from the first feeding, up to 6 mo. At the end of the feeding trial, trout were distinguished by very different muscle fat content (from 4.2 to 10% wet weight), and line x diet interactions were observed for parameters related to fat storage. We analyzed the activity and gene expression of key enzymes involved in lipid metabolism (fatty acid synthase, hydroxyacyl-CoA dehydrogenase, carnitine palmitoyltransferase 1 isoforms, and peroxisome proliferator-activated receptor alpha) and glycolysis (hexokinase 1 and pyruvate kinase) as well as energy production (isocitrate dehydrogenase, citrate synthase, and cytochrome oxidase) in the liver and the white muscle of rainbow trout. The lipid-rich diet repressed the activity of the lipogenic enzymes and stimulated enzymes involved in fatty acid oxidation and glycolysis in liver but had little effect on muscle enzymes assessed in this study. Regarding the selection effect, enzyme activity and expression suggest that compared with the L line, the F line presented reduced hepatic fatty acid oxidation as well as reduced mitochondrial oxidative capacities and enhanced glucose utilization in both liver and muscle. Very few line x diet interactions were found, suggesting that the two factors (i.e., dietary energy content and selection) used in this study to modify muscle lipid content exerted some additive but mostly independent effects on these metabolic actors.

The present paper describes the main procedures used to slaughter fowl, pigs, calves and adult cattle, sheep, and farmed fish, starting on the farm and ending with the death of the animal at the abattoir. It reviews the currently known causes of stress, indicated by behavioural and physiological measurements on the animal level, and by post-mortem muscle metabolism. During the pre-slaughter period, psychological stress is due to changes of environment, social disturbances and handling, and physical stress is due to food deprivation, climatic conditions, fatigue, and sometimes pain. The exact causes of stress depend, however, on the characteristics of each species, including the rearing system. For fowl, bird catching and crating, duration and climatic conditions of transport and of lairage and shackling are the main known pre-slaughter stress factors. For pigs, stress is caused by fighting during mixing of pens, loading and unloading conditions, and introduction in the restrainer. Handling and novelty of the situation contribute to the stress reactions. For veal calves and adult cattle, disruption of the social group, handling, loading and sometimes unloading conditions, fatigue, novelty of the situation and for calves mixing with unfamiliar animals are known stress factors. Gathering and yarding of extensively reared lambs and sheep causes stress, particularly when shepherd dogs are used. Subsequent transport may induce fatigue, especially if sheep are commercialised through auctions or markets. In farmed fish, stress is predominantly related to environmental aspects such as temperature, oxygen, cleanliness of the water and, to a certain extent, stocking density and removal of the fish from the water. If transport and lairage conditions are good and their durations not too long, they may allow pigs, calves and adult cattle, sheep, and fish to rest. For certain species, it was shown that genetic origin and earlier experience influence reactions to the slaughter procedure. Stunning techniques used depend on the species. Pigs and fowl are mostly electrically or gas-stunned, while most adult cattle are stunned with a captive bolt pistol. Calves and sheep may be electrically stunned or with a captive bolt pistol. Various stunning methods exist for the different farmed fish species. Potential causes of stress associated with the different stunning procedures are discussed. The paper addresses further consequences for meat quality and possible itineraries for future research. For all species, and most urgently for fish, more knowledge is needed on stunning and killing techniques, including gas-stunning techniques, to protect welfare.

Lipids are the predominant source of energy for fish and are stored in fat depots in different parts of the body regions. This review focuses on visceral, subcutaneous and intramuscular adipose tissues that interfere with carcass and fillet yields and with flesh quality. The morphological, cellular and biochemical characteristics of these tissues are discussed as well as the different mechanisms involved in the regulation of their lipid metabolism. Particular emphasis is given to the modulation of these characteristics and mechanisms by different extrinsic (food composition, water parameters) and intrinsic (selective breeding, life cycle status) factors. This review focuses on recent studies that take into account the present challenges of fin-fish aquaculture, which are principally (1) the replacement of fish oil and meal by vegetable oil and meal due to the need for sustainability and the limited availability of fish to prepare food pellets, and (2) selective breeding programs to improve fish growth and flesh quality. These studies apply various modern technologies to different fish species, including the development of cell culture systems and transcriptomic and proteomic techniques. This review highlights that fish adipose tissues differ in their localization and their morphological characteristics and that they show a large plasticity in their responses to variations of both extrinsic and intrinsic factors. These different responses reinforce the idea of their differential participation in fish lipid homeostasis

Brown trout (Salmo trutta) (2.7 g initial mean weight) were reared in freshwater for 8 months at water velocities of <0.1 (control group), 1 or 2 body lengths per second (BL s−1) (exercise groups). Growth (body weight, body length and body width), muscle structure (muscle fibre diameter and width of myosepta) and flesh quality parameters (dry matter, muscle pH, collagen content and solubility, instrumental evaluation of texture) were measured at the end of the experiment. The body weight of fish at 1 BL s−1 was 22% higher than the control group. Muscle development was stimulated at 1 and 2 BL s−1, leading to a higher condition factor, greater body height and width, and muscle fibre hypertrophy (55 vs. 59.5 μm fibre diameter in the control and 2 BL s−1 groups respectively). Connective tissue and collagen were only slightly affected by exercise (no difference in collagen solubility, but a greater proportion of γ trimer and fewer α chains in the control compared with the exercised group). Flesh quality was affected, with greater dry matter content and lower post‐mortem pH in the 1 BL s−1 group compared with the control and 2 BL s−1 groups. The mechanical resistance of the raw fillets was slightly but significantly increased by exercise. The exercise‐related changes in muscle structure and texture are discussed.

Background: Growing interest is turned to fat storage levels and allocation within body compartments, due to their impact on human health and quality properties of farm animals. Energy intake and genetic background are major determinants of fattening in most animals, including humans. Previous studies have evidenced that fat deposition depends upon balance between various metabolic pathways. Using divergent selection, we obtained rainbow trout with differences in fat allocation between visceral adipose tissue and muscle, and no change in overall body fat content. Transcriptome and proteome analysis were applied to characterize the molecular changes occurring between these two lines when fed a low or a high energy diet. We focused on the liver, center of intermediary metabolism and the main site for lipogenesis in fish, as in humans and most avian species.