On the function of the two types of myotomal muscle fibre in elasmobranch fish

Abstract

There are two main types of muscle fibre in the dogfish myotome. Slow fibres make upabout 18 % of the mass of the myotome, the remainder consisting of fastfibres. The slow and fast fibres have a different pattern of innervation, and differ in such respects as their fat and glycogen contents, and in abundance of mitochondria. The two typesof fibre show different responses to depolarizing agents.Extracellular recordings from the myotomal muscle taken during the swimming of spinal fish show that only slow muscle fibres are active when the fish swims slowly, whereas during vigorous movements, the fast fibres are active. Although both types of fibre contain glycogen, the fast fibres contain only about 50–60 % ofthe amount found in the slow fibres. After a period of vigorous movement, the glycogen levels in the fast fibres fall markedly, whilst those in the slow fibres donot change. The slow fibres contain around 4–5 times the amount of fat found in thefast fibres; after long periods of sustained slow swimming, the fat levels inthe slow fibres fall, and there also may be a slight decrease in the glycogen levels in the slow fibres. Long periods of slow swimming do not alter the glycogen levels found in the fast fibres.

Activation of Embryonic Red and White Muscle Fibers During Fictive Swimming in the Developing Zebrafish

“…The neural basis for this muscle recruitment is unknown. However, the present findings and those of Bone (1966), Lauder (1994), andMos et al (1990) indicate that two unique populations of motoneurons, that can be activated or inactivated independently of each other, innervate ER and EW muscle fibers.…”

Does condition of Atlantic cod (Gadus morhua) have a greater impact upon swimming performance atUcrit or sprint speeds?

“…In white muscle, contractile activity during burst swimming primarily depends on ATP generation from phosphocreatine and from anaerobic glycolysis (Bone, 1966;Bone et al, 1978;Dobson et al, 1987;Altringham and Ellerby, 1999). During the first few seconds of intense muscular activity, such as sprint swimming, ATP is maintained at a relatively constant level, but the PCr level declines steadily as the CK reaction replenishes the depleted ATP.…”

Is there a synergistic effect between steady‐state exercise and water acidification in carp?

“…The absence of any such increase is a strong indication that our exercise regimen did not include burst-type exercise. As is generally accepted, red muscle fibres are specialized for long term, low-intensity exercise whereas white muscle fibres are involved in burst-type or high-intensity exercise (Bone, 1966). Steady state exercise by red muscle is fuelled by mitochondrial oxidation of pyruvate (derived from lactate, glucose or glycogen), fatty acids and ketone bodies.…”