The locomotor roles of the myotomal muscles of fish are dependent on swimming speed. The mean maximum sustained swimming speed for coalfish (Gadus virens L.) during a 6-h period in an experimental exercise chamber was determined using a fixedvelocity technique and found to be 4 bodylengths/s. Biochemical measurements were made on the concentration of glycogen and lactate in the red muscle and white muscle at a series of known swimming speeds. Evidence is provided that red muscle alone is used at speeds below 2 bodylengths/s. The fall in concentration of red muscle glycogen was directly proportional to increased swimming speed. At speeds in excess of 2 bodylengths/s a statistically significant increase in lactate concentration occurred in the white muscle fibres. A reduction in glycogen content of the white muscle was also noted at speeds at and above the estimated mean sustained swimming speed. These results are discussed in the light of the current ideas pertaining to the division of labour between myotomal muscles in fish.

The growing interest in farming rainbow trout in the sea (MacLeod, 1977) or in brackish water (Tatum, 1973, 1976) is economically important because it involves the use of readily available sites and resources, and provides solutions to problems related to fresh water scarcity or its increased salinity (Al-Hamed, 1971; Al-Daham & Bhatti, 1977) in certain parts of the world.

There is evidence that selection for small body size in mice results in a decrease in the total number of muscle fibres in a given muscle (Luff & Goldspink, 1967; Hanrahan, Hooper & McCarthy, 1973). It has also been shown that small chickens have fewer muscle fibres in certain muscles than larger chickens (Smith, 1963). This type of work has not, however, been extended to a study of the larger domestic animals. At Göttingen in Germany, Haring et al. (1966) have developed a breed of miniature pig which, at 6 months of age, was about a third of the body weight of commercial pigs. We therefore decided to investigate the muscles of these miniature pigs and compare them with commercial pig muscles, paying particular attention to the number of muscle fibres.

Mammalian cardiomyocytes have limited regenerative capacity, such that cell death can result in a net loss of viable contractile elements and a decrease in cardiac functional reserve, both during normal ageing and after insults to the myocardium leading to heart failure. At least four types of cell death have been described, with apoptosis and necrosis being the most extreme phenotypes and most extensively studied. Many of the classical morphological and biochemical features associated with these forms of cell death have been derived from studies conducted in vitro and these may not always faithfully reflect events occurring in vivo. Before therapeutic interventions can be realistically developed, more studies need to be undertaken in vivo to simultaneously investigate these different death pathways, their control mechanisms and their relative contributions in depleting the pool of viable cardiomyocytes. We recently demonstrated immunohistochemically that a single injection of either a natural or synthetic catecholamine induces both cardiomyocyte apoptosis (identified by an anti-caspase 3 antibody) and necrosis (identified by an anti-myosin antibody) in the rat heart in vivo. After optimising the experimental conditions for hormone dose and temporal and spatial peaks of damage, the incidence of necrosis was 4-10 times greater than the incidence of apoptosis. Myocytes in the soleus muscle were also severely (7-10 %) damaged, involving both apoptosis and necrosis. In both striated muscles high levels of myocyte co-localisation for apoptosis and necrosis were observed, suggesting that secondary necrosis had occurred in most of the apoptotic myocytes in vivo. The ability of the catecholamines to cause myocyte death suggests that they might play an aetiological role in the progression of heart failure where over-activation of the sympathetic system results in sustained pathophysiological levels of these catecholamines. Experimental Physiology (2003) 88.3, 447-458.

1. Measurements have been made of the size and number of muscle fibres and number of nuclei in a small indicator muscle (m. flexor digiti V brevis) in the fore-foot of the pig. Wellnourished, 10-d-old and 1-year-old animals were studied, as well as 1- and 2-year-old animals that were severely energy-deficient and protein-deficient.

2. The normal 1-year-old animals had much larger muscle fibres, with more nuclei, than the pigs in any of the other groups.

3. There were no significant differences between the numbers of fibres in the muscles of pigs in any of the four groups.

4. There was a significant difference between the number of fibres in the muscles of pigs coming from different litters, irrespective of their dietary history after birth. This suggests that the number of fibres is determined genetically before birth, and all that can take place after birth is an alteration in size.

An ‘indicator muscle’ (m. flexor digiti V brevis) was removed in its entirety from several Large White and Landrace pigs of varying fat depth (measured over the eye-muscle area). The total muscle fibre number was measured in transverse sections for each muscle. Significant inverse relationships were found between this fibre number and fat depth measurements. These and other results suggest that fibre number is related to lean meat content. Fibre number was also shown to be highly correlated with fibre density and as thinner fibres (i.e. higher fibre density) are associated with more tender meat, fibre number may be associated with quality as well as quantity of meat.

Fibre number and fibre size were measured in the flexor digiti V brevis muscle and other muscles in pigs of different breeds. A large variation in fibre number (200%) was found among the breeds. However, the fibre number in the flexor digiti V brevis was closely correlated with fibre number of other muscles in the same animal. Fibre number and size measurements were also carried out on animals at different ages taken from a relatively pure breed of pig. Fibre size was found to increase to differing extents in different muscles, although the increase in the flexor digiti V brevis was almost the same as in the longissimus dorsi. Fibre number did not change during growth. On the basis of these findings it is suggested that the flexor digiti V brevis is a suitable indicator muscle for genetic experiments.