Skeletal muscle consists of several tissues, such as muscle fibers and connective and adipose tissues. This review aims to describe the features of these various muscle components and their relationships with the technological, nutritional, and sensory properties of meat/flesh from different livestock and fish species. Thus, the contractile and metabolic types, size and number of muscle fibers, the content, composition and distribution of the connective tissue, and the content and lipid composition of intramuscular fat play a role in the determination of meat/flesh appearance, color, tenderness, juiciness, flavor, and technological value. Interestingly, the biochemical and structural characteristics of muscle fibers, intramuscular connective tissue, and intramuscular fat appear to play independent role, which suggests that the properties of these various muscle components can be independently modulated by genetics or environmental factors to achieve production efficiency and improve meat/flesh quality.

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

Female gamete production relies on coordinated molecular and cellular processes that occur in the ovary throughout oogenesis. In fish, as in other vertebrates, these processes have been extensively studied both in terms of endocrine/paracrine regulation and protein expression and activity. The role of small non-coding RNAs in the regulation of animal reproduction remains however largely unknown and poorly investigated, despite a growing interest for the importance of miRNAs in a wide variety of biological processes. Here, we analyzed the role of miR-202, a miRNA predominantly expressed in male and female gonads in several vertebrate species. We studied its expression in the medaka ovary and generated a mutant line (using CRISPR/Cas9 genome editing) to determine its importance for reproductive success with special interest for egg production. Our results show that miR-202-5p is the most abundant mature form of the miRNA and that it is expressed in granulosa cells and in the unfertilized egg. The knock out (KO) of mir-202 gene resulted in a strong phenotype both in terms of number and quality of eggs produced. Mutant females exhibited either no egg production or produced a dramatically reduced number of eggs that could not be fertilized, ultimately leading to no reproductive success. We quantified the size distribution of the oocytes in the ovary of KO females and performed a large-scale transcriptomic analysis approach to identified dysregulated molecular pathways. Together, cellular and molecular analyses indicate that the lack of miR-202 impairs the early steps of oogenesis/folliculogenesis and decreases the number of large (i.e. vitellogenic) follicles, ultimately leading to dramatically reduced female fecundity. This study sheds new light on the regulatory mechanisms that control the early steps of follicular development, including possible targets of miR-202-5p, and provides the first in vivo functional evidence that a gonad-predominant microRNA may have a major role in female reproduction.

Archimer http://archimer.ifremer.fr Highlights ► Application of ultrasound and 2D imagery to predict processing yields in rainbow trout. ► Estimation of genetic parameters and genetic correlations with yields to predict. ► Comparison of different strategy of selection.