Ž . Aquaculture 177 1999 99–115 Muscle development and growth: potential implications for flesh quality in fish Ian A. Johnston ) Gatty Marine Laboratory, School of EnÕironmental and EÕolutionary Biology, UniÕersity of St. Andrews, St. Andrews, Fife, Scotland, KY16 8LB, UK Accepted 1 October 1998 Abstract Growth in fish involves the recruitment and hypertrophy of muscle fibres. Muscle recruitment is particularly important in species that reach a large ultimate body size. The number of muscle fibres recruited to reach a particular girth varies between families and strains and is influenced by environmental factors including diet, exercise, light and temperature regimes. The resulting variation in muscle cellularity and associated changes in connective tissue matrix are thought to be important determinants of texture and other flesh quality characteristics. The state of knowledge about muscle development and growth is reviewed and potential practical applications of the research to flesh quality issues are discussed. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Muscle; Growth; Myosatellite cells; Flesh quality; Atlantic salmon 1. Introduction The main edible part of the fish myotome is composed of white twitch muscle fibres that power high speed swimming using anaerobic metabolic pathways. Red twitch muscle fibres utilise aerobic metabolism and are recruited for routine activity such as foraging and migration. They are most numerous at the horizontal septum and increase in proportion towards the caudal fin, rarely exceeding 10% of the total cross-sectional area. Although a variety of other minor muscle fibre types have been described they are of little direct importance from an aquaculture perspective. Information on the physiol- ogy and biochemistry of fish muscle has been summarised in several recent reviews Ž . Bone, 1978; Johnston, 1981, 1994 . ) Fax: q44-1334-463443; E-mail: iaj@st-and.ac.uk 0044-8486r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00072-1